The Cost of a Solar PV System


How much do solar panels cost?

Solar PV panels have reduced in price by approximately 40% as a result of falling manufacturing costs and increased competition in the market. This means you can now get a decent sized solar PV system installed on your roof for between £4,000 and £6,000.

We would always recommend trying to maximise the number of solar panels that you go for – but this is often limited by the size of the roof space.

A 250w solar panel will typically cost between £300 and £500 and each panel is approximately 1.7m2. Therefore for a 3.5kW system, you are looking at a price of between £4,200 and £7,000, and this would take up approximately 23.8m2.

For a smaller 2.0kW system, you are looking at paying between £2,400 and £4,000 and this size system would take up approximately 13.6m2.

Obviously, the more solar panels you have on the roof, the more electricity you can produce. This therefore means you need to buy less electricity from the grid (as you can use the electricity you produce).

You can also get payment from your energy supplier, provided they are signed up to the Smart Export Guarantee (SEG).

The SEG is a legal obligation for any electricity supplier that supplies at least 150,000 customers to offer an export tariff to those with solar panels for each kWh produced.

The actual export tariffs these energy companies offer can be flat, variable or smart rate (adjusting based on wholesale prices), however the tariff must always be greater than zero (even when wholesale prices of electricity are negative).

There is quite a large discrepancy between the different SEG rates from the different providers – for example in August 2020, Utility Warehouse offer £0.02 / kWh, while Octopus are offering £0.055 / kWh.

SEG versus FIT

The SEG was introduced in January 2020 to replace the older Feed in Tariff (FIT) scheme, which closed to new customers on 31st March 2019.

The main difference between SEG and the FIT scheme was that the FIT scheme paid the owner of the solar panels for both producing the electricity and also for exporting it, while the SEG only pays for exporting it – therefore the SEG is far less generous.

Eligibility for the SEG

To be eligible for the SEG, the solar system being installed needs to be under 5MW (or approximately 20,000 solar panels – so most homes should be okay!). The solar system must also be installed by an MSC certified installer. Finally you need to have a smart export meter installed to measure how much of the electricity is being exported back to the grid.

SEG Tariff vs. using the electricity at home

To maximise the return from the solar PV installation, you will want to use as much of the electricity you produce in your home as possible. In the most basic terms, if you use the electricity you produce in the home, then you don’t need to buy it from your energy provider (a saving of around 15p/kWh). If you export it, you only get paid a fraction of this (£0.05 at most!) – so if you can use it in the home, then it is strongly recommended to use it!

By incorporating battery storage technology into your solar system setup – it allows you to store the electricity you produce to use as and when you need it. You can learn more about battery technology by clicking here.

Solar PV worked examples

So, to start with, we will look at a typical 3kWh system (installed on a new build with a ‘higher’ energy efficiency requirement rating) and see the annual return, based on the percentage you use in the home versus how much you export. Over a year, a 3kW system would expect to be around 90% efficient and generate about 2700 kWh of electricity (an average home used 4,800 kWh per year).

Worked Examples – % of Electricity used in the Home : % of Electricity Exported to the Grid

100% : 0% 75% : 25% 50% : 50% 25% : 75%
Total kWh/year 2700kWh 2700kWh 2700kWh 2700kWh
SEG (@£0.05/kWh) £0 £33.75 £67.5 £101.25
Used by household (£0.15/kWh) £405 £303.75 £202.5 £101.25
TOTAL RETURN £405 £337.50 £270 £202.5

These numbers are correct as of 18th August 2020.

What impacts the initial cost of your solar PV installation?

The cost of your solar PV system is dependent on two things:

1. The size of the installation

Obviously the larger the system you install, the more electricity it has the potential to produce. The average solar PV system installed in the UK now is 3.5KW, which – working at 90% efficiency – will produce approximately 3150kWh of electricity (depending how much sun you get in your part of the country). As reference, an average house uses approximately 4,800kWh. The number of panels you can install will probably be limited by either the amount you can afford or the size of your roof. Suppliers will also charge different prices for their installation services and it’s important to ensure they are MCS-accredited to qualify for the SEG

2. The quality of the solar panels used

Not all solar panels are the same!

See our guide to the different types of solar panels for more details, but in a nutshell there are three types:

How are the efficiency figures calculated? Well it is determined by how many watts of power are produced in a square meter. 100% efficiency means that a square meter of panel would create 1,000 watts. Therefore a panel rated at 18% would create 180 watts from every m2; it follows that panels with higher efficiency ratings create more electricity (per meter squared) and this is reflected in the price.

>>> How solar return changes based on pitch and shading <<<

As you can see in the table above, the actual price of your installation varies depending on the types of panel you get installed, so a 4kW system could cost as little as £4,800, or as much as £8,000. In the table below we have assumed we are exporting 50% (so this is eligible for the SEG) and 50% is used within the home (so a saving on the electricity bill).

System A

System B

System C





Type of Panel




Efficiency of Panel




Output (kWh)




SEG (£)




Savings on electricity bill (£)




Annual Return (£)




Payback of your Solar System

So looking at ‘System A’ in the table above, the system costs £4,800 and the annual return is £320 per year, so it will take approximately 15 years to pay back. In addition, electricity prices are expected to go up over time, so the £0.15 you save for every kWh of electricity you use in your home will actually increase – and could be nearer 20 pence in just 5 years – therefore the absolute return could actually become bigger.

Once you have ‘made your money back’, then any money you make is paid directly to you as profit – so you will be in line to receive the SEG indefinitely while you are exporting electricity.

There are a few other costs to think about with solar PV


There are maintenance costs associated with your solar PV installation, including cleaning them at least twice a year to ensure they are working as efficiently as they can.

Replacing Inverters

In addition, despite the solar panels being good for 20 years plus, the inverters have a lifespan of about 10 years, and replacing these will cost just shy of £1,000 – so factor this in to your calculations when your solar installers give you a quote.

>>> Microinverters can also increase Solar PV return – click to find out more <<<


You will need to insure you solar PV array as part of your home insurance, so your insurance premium payments will slightly increase.

Planning Permission

Installing solar panels on your roof does normally not require planning permission. However if you live in a conservation area or world heritage site, you will need to speak to your planning authority to get the necessary permission. Note: there will also be legal fees associated with this.

Installing Solar PV

Are you thinking about installing a solar PV system at home? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

If you would like us to find you a local installer to help install a solar PV system in your home, just fill in the form below and we will be in touch shortly!

    Introduction to Solar Thermal


What is solar thermal?

Solar thermal (also known as solar heating) harnesses the energy provided by the sun to provide thermal energy to heat water. The hot water produced by the solar heating can be used to supplement your domestic hot water (although the temperature might need to be topped up by a boiler), larger stores of water (like swimming pools), underfloor heating, and for space heating/cooling.

Unlike a solar photovoltaic cell array, which is designed to produce electricity, a solar heating system is designed simply to produce heat. A well-designed solar heating system will provide approximately 55% of your annual domestic hot water requirement. However, as it is reliant on the sun, your solar heating system will produce more heat in the summer months.

Types of solar thermal system

Solar heating systems all have a few components in common: a solar collector, insulated heat transport piping and heat storage. More complex systems also have electronic controls and freeze-prevention mechanisms (when situated in colder climates). There are three main types of solar collectors:

1. Flat panel solar collectors

These are the most common type of solar heating technology and consist of a box with a piece of glass on the top and a dark absorber plate on the bottom. Sunlight passes through the glazing on the top of the box, heating up the absorber plate and converting the solar energy into thermal energy. Copper pipes are attached on the top of the absorber plates, and the liquid flowing through these pipes absorbs the heat, which is then pumped away and stored until it is needed in the house.

2. Evacuated tube solar collectors

The evacuated tube systems tend to be more efficient, especially in cold or cloudy climates; however their advanced design makes them more expensive. These solar collectors consist of rows of parallel, transparent glass tubes. Each tube contains an absorber assembly and the entire tube is evacuated of any air (so it operates within a vacuum). The sunlight enters the glass tubes and hits the absorber assembly where it is absorbed. As this is operating within a vacuum, heat does not travel back from the absorber to the glass, so these are more efficient. A fluid transfers the heat from the absorber assembly through to the storage tank, where it can be used.

The two major advantages of evacuated tube collectors are that they can produce warmer water (so you will not need to supplement the temperature with a boiler) and they can also produce more hot water than flat-panelled solar collectors.

3. Plastic collectors

These are the cheapest type of solar collector and consist of black plastic pipe treated to withstand UV degradation. Hot water is simply pumped through the black plastic pipes, where it warms up (as the plastic absorbs the suns energy). Plastic collectors are most susceptible to ambient temperatures as there is no insulation in place, so if the outside temperature is cold, very little heat will be produced.

These are an ideal solution for swimming pools though, as they amplify the effects of the weather and its seasons. For example, most swimming pools are used in the summer, so installing plastic collectors will allow you to use the pool sooner in the year, and it will keep the temperature consistently higher.

Things to consider before installing a solar thermal heating system

As with solar photovoltaic cells, solar heating technologies require sunlight, so ideally you would install the technology on a south-facing roof that receives sunlight for most of the day to maximise the benefits. Likewise, the amount of heat you can produce is directly proportional to the amount of installed surface area you have; therefore if you only have a small roof, then this technology may not be appropriate.

In addition, you will produce more hot water in the summer, as the energy from the sun is more intense at this time, therefore you may well have to supplement the temperature of the water in the winter using a boiler. To boost the system, your boiler must be compatible with your solar heating system, but currently most combi or CHP boilers are not compatible. It is therefore very important that you check with your installer before undergoing any works.

If you live in much colder climates you may need to have some sort of antifreeze within your system (when water freezes it turns to ice it expands, potentially causing cracks in the pipes).

If you live in a listed building please note the restrictions. Like with many green technologies, it is worth contacting the local planning office to get permission to place the panels, to save yourself problems further down the line.

Installing solar thermal normally requires a new hot water tank

For many of us with old heat-only boilers, we have a hot water tank hidden away in the airing cupboard. Typically these hot water tanks are heated by a boiler and were purpose-built.

Since the introduction of the RHI, there has been a huge increase in the number of people installing solar thermal in their homes.

If you decide to install solar thermal in your home you will need a hot water tank to store the hot water produced from your collector – the problem though, is that you can’t plumb one of these systems into the older hot water tanks that are historically found with boilers.

Twin coil cylinders

The reason for this is that inside the hot water tank there needs to be a separate coil for each ‘hot water source’. In this case you would need a coil for the solar thermal and one for the hot water. Normally in a residential solar store (i.e. a hot water tank with a solar coil), the solar is connected to the lower coil and the boiler (or main heating source) is connected to the top coil.

Solar coils are much larger than traditional boiler coils because they need a far bigger surface area to transfer their heat into the water compared to a boiler. The reason is that the hot water travelling through the solar thermal coil is at a much lower temperature than the water travelling through a boiler coil.

As a guide, the surface area of a solar thermal coil needs to be in excess of 1.5m2, while a boiler coil can be as little as 0.6m2 – this increased surface area maximises the opportunity for heat transfer and is a must based on the lower water temperature flowing through the coil.

If you cast your mind back to your GCSE science, you will know that heat rises and therefore within a hot water tank, the water at the top of the tank is far warmer than the bottom of the tank.

In a solar thermal store, it is important that this temperature differential is maximised and this is achieved by making the hot water tank rather large and tall. So while the top of the tank could achieve temperatures of 600C plus, the water at the bottom of the tank might be as low as 150C degrees. What this means is that even if the solar thermal is only producing water to 200C degrees, it will still contribute to the hot water demand of the property.

Storing the hot water you produce on sunny days

Since the hot water tanks used for solar thermal systems tend to be big, they tend to be able to store far more hot water than is actually required by most families that install one of them. Since solar thermal is intermittent, (i.e. it produces much more hot water when the sun is shining), this oversized heat tank allows you to store the hot water; thereby taking advantage of favourable conditions a day or two later to help minimise the need to use the boiler.

Maximising return on your investment

The Renewable Heat Incentive (RHI) is now up and running, which works in a similar way to the Feed-in Tariff, rewarding you for any hot water you produce from renewable sources. You can find all the information you need about the RHI on our page here.




Installing Solar Thermal

Interested in installing a solar thermal system at home? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

If you would like us to find you a local installer to help install a solar thermal system in your home, just fill in the form below and we will be in touch shortly!

    Interested in solar thermal?

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    I would like to receive occasional news from TheGreenAge

      Domestic Renewable Heat Incentive (RHI)

      Financial Incentives

    The Domestic Renewable Heat Incentive – what is it?

    The Renewable Heat Incentive (RHI) is a government scheme that pays people that produce their own heating and hot water using renewable energy sources such as heat pumps or solar thermal panels.

    The scheme has been launched in an effort to help the UK government meet its legal commitment to ensure 15% of the UK’s energy comes from renewable energy sources by 2020.

    Air source heat pump

    This scheme has been up and running in the commercial sector since November 2011, however the domestic RHI scheme kicked off in April 2014 for households in the UK. The Renewable Heat Incentive works in a similar way to the Feed-in Tariff (which is for domestic renewable electricity production); households in this case being paid based on the amount of renewable heat they produce.

    There are currently 4 technologies that are eligible for the domestic renewable heat incentive

    The payments will be made quarterly for seven years and should cover a significant proportion, if not all of the initial installation costs.

    Domestic Renewable Heat Incentive tariffs

    Each of the renewable technologies eligible for the renewable heat incentive have different RHI rates associated with them, mainly because the cost of installing the different technologies varies considerably and the RHI payments are designed to help cover some or all of the initial install cost.

    On the whole, the RHI rates have increased very slightly in line with inflation except for biomass boilers and wood pellet stoves with back boilers which have dropped considerably – the rates below are correct as of September 2018. These can change from quarter to quarter, depending on how many people claim the payments. This is known as ‘digression’. You can find current rates here.

    The payments are made on a quarterly basis and last for a total of 7 years. In addition, the tariff amounts are RPI index linked, so as inflation increases over time, the tariff rates above will increase with it. The RPI increases will be applied to the rates on 1st April each year.

    RHI Payments will last a total of 7 years

    Much like with the feed-in tariff, once you sign up to the RHI you will be locked in at the tariff rate that you initially get – so if you installed a Ground Source Heat Pump today you would get a payment of 20.46p per kWh of renewable heat you produced for the next 7 years (although it will increase with the the RPI each year).

    Since there is a finite pot of money available for the RHI payments, it is likely the current tariffs will get smaller over time (again much like the solar feed-in tariff) therefore if you are considering installing a renewable heating technology it is worth moving quickly to ensure you get the highest payment rate!

    The government do a quarterly review of the RHI scheme and adjust the tariff amounts in line with the total RHI budget so as to control the costs. Therefore if you install a renewable heating system you will get (and lock in) a better rate potentially than someone who installs a renewable heating measure 2 years down the line.

    RHI payments are estimated based on heat demand rather than Metered

    Tariff payments will be deemed rather than metered, which means they will estimate the heat demand of the property and base the RHI payment on that. This means that it is paramount to install a heating system that is correctly sized; because if you install a more expensive, oversized biomass boiler (that creates more than you require), you will be paid the same through the RHI and potentially won’t recoup the additional unnecessary investment.

    Likewise, there are ways to maximise your RHI payments!

    >>> Maximise you RHI payments <<<

    Click on the titles below to see exactly how the RHI is calculated for biomass, heat pumps and solar heating.

    For biomass boilers and wood pellet stoves, the RHI payment can be fairly easily calculated based on the heat demand of the property. This heat demand figure can be found right at the bottom of the Energy Performance Certificate (EPC) expressed in kWhs – so it is simply a case of multiplying £0.0674 x this number, which will give you the total annual payment.

    >>> The cost of heating your home with gas vs electricity <<<

    Example calculation for biomass:

    For a home with a heat demand of 18,000kWh installing a biomass boiler would provide you with an RHI payment each year of:

    18,000 x £0.0674 = £1213.20

    For solar thermal, the MCS approved installer calculates the RHI payment. They will deem a figure that is the estimated contribution of the solar thermal to the home’s hot water demand, but the calculation is based on occupancy – the more people that reside in the property, the higher the payment – worth bearing in mind when you are speaking to your installer / green deal assessor.

    For heat pumps (both ASHP and GSHP) the heat demand figure from the EPC is combined with the heat pumps estimated efficiency to calculate the RHI. Remember not all the heat produced by heat pumps is renewable, therefore only the part that is will receive RHI support.

    The technical term for the estimated efficiency is known as the Seasonal Performance Factor (SPF) – and this tends to be somewhere between 2.5 and 4 (this is also sometimes referred to as the Coefficient of Performance or CoP). So an SPF of 3 for example, means that for every one unit (kWh) of electricity used, 3 units (kWh) of useful heat will be produced.

    Therefore the RHI for heat pumps is calculated using the 2 formulas below:

    1. Eligible Heat Demand = Total Annual Energy Demand x (1 – 1 / SPF)

    2. Annual RHI = Eligible Heat Demand x RHI Tariff

    Example calculation for Air Source Heat Pumps:

    For a home with a heat demand of 25,000kWh installing an air source heat pump with a SPF of 3.5 the annual RHI payment would be:

    Eligible Heat Demand = 25,000 x (1 – 1 / 3.5) = 17,857 kWh

    Then multiply by RHI tariff (10.49p / kWh) = £1,873.20 per year

    Only heat pumps with an SPF of 2.5 or more are considered renewable under the EU Renewable Energy Directive and only those that are considered renewable will be eligible for the RHI.

    How long will my renewable heating investment take to pay back?

    This is a difficult one to answer to be honest because it is so dependent on your home’s individual heat demand.

    In terms of investment, you can expect to pay about £8,000 for an air source heat pump, £20,000 for a ground source heat pump, £8,000 for a biomass boiler and £4,500 for solar thermal.

    If you can get an accurate view of the heat demand (from the EPC) then you should be able to calculate the annual payment from the domestic RHI, which multiplied by 7, will give you to the total payments to expect over this period.

    With the investment figure and the total lifetime RHI return (comparing renewable heating to the next best alternative), you should be able to get a rough feel of the payback.

    Eligibility requirements for the Domestic Renewable Heat Incentive

    Renewable heating systems don’t come cheap – the domestic RHI makes these systems more affordable by offering a financial incentive based on the amount of heat they produce. However, there are quite strict eligibility criteria, so it is worth ensuring that you adhere to the rules to make sure you are entitled to the payments. 

    Which technologies are eligible for the domestic RHI? 

    As previously mentioned, the renewable heat incentive is available on installations of any of the following technologies:

    Download the full list of eligible installations here.

    Who is eligible for the domestic RHI?

    The scheme covers single domestic dwellings (as soon as the heating system is providing heat to more than one property, you would need to look at the non-domestic RHI). It is open to owner-occupiers, private landlords, registered providers of social housing, third party owners of heating system and self-builders.

    Note to private and social landlords: you will need to agree with the tenants that an annual servicing visit will be required to ensure the system complies with the detail set of requirements and continues to be eligible for domestic RHI payments.

    New builds are not eligible for the RHI – this means the renewable heating system was installed in the home before it was inhabited for the first time.

    You heating system needs to be on the Government approved list

    In order to ensure eligibility for the RHI, you must make sure the renewable heating system you get installed is listed on the Governments product eligibility list (PEL) – you can download this here.

    MCS accreditation is a must!

    To be eligible for the scheme, the installers must adhere to the European Standard EN 45011. The Microgeneration Certification Scheme (MCS) adheres to this standard, therefore as a rule of thumb you need to ensure that the team installing your renewable heating system are MCS accredited and the kit being installed is also MCS accredited.

    Equivalent schemes to MCS do exist, but don’t simply take your installers word for it that they adhere to EN 45011 – check all the relevant paperwork before getting any work done.

    Getting a Green Deal Assessment is no longer required! 

    In early 2016, the Government changed the elegibility requirements for the RHI and one of those changes involved scrapping the need for the Green Deal Report. The EPC is still a requirement though – this needs to be dated within the last 48 months – and will be used to calculate your RHI payments.

    If your EPC recommends loft and cavity wall insulation it must be installed before you apply and you’ll then need to get a new EPC that no longer recommends these measures. The reason for this is that heat pumps and solar thermal tend to produce hot water at lower temperatures than traditional gas central heating systems. This means that radiators and underfloor heating will be operating at cooler temperatures compared to regular central heating systems, therefore it is very important the house is really well insulated prior to having them installed. The insulation process should bring the heating requirements of your home right down.

    Need to get a new EPC for your home?

    Click to organise an EPC

     I have received other grants to pay for the technology. Do I still get the domestic RHI?

    DECC confirmed in 2013 that any public funding paying for the domestic renewable heating installation would be deducted from RHI payments made. In addition, where an installation was not at least in part paid for by the owner, even where the installation was funded from a private source, that installation will not be eligible for the domestic RHI. An installation which has been part-funded by the owner will be eligible.

    I have already installed my renewable heating system – Can I still claim the RHI?

    You must apply to join the Domestic RHI within 12 months of the commissioning date of the renewable heating system. This can be found on the MCS certificate. The team that run the admin side of the RHI at DECC offer very little wriggle room here (99 times out of 100 – zero wiggle room!) so make sure you apply within the stipulated timeframes.

    Technology Specific Eligibility Requirements

    Heat pumps

    Biomass boilers/wood pellet stove with back boiler

    How do I apply for the domestic RHI?

    The application process for the domestic Renewable heat Incentive is fairly simple, however numerous pieces of evidence (installation certificates, EPC, and photos for example) are required for the submission.

    Since the RHI is funded out of a public kitty (through tax payers), it is important that the money being spent to subsidise the scheme is under the right level of scrutiny, hence the volume of evidence required.

    Applying for the domestic RHI

    Applications for the domestic RHI are made through the OFGEM website through the My RHI portal

    >>> Log in to the ‘My RHI’ Portal’ <<<

    However if you find the thought of carrying out this process a little too onerous, there are third party companies offering to complete this on your behalf, although obviously there is a charge for this service. The process genuinely is pretty easy though, so in our opinion certainly worth giving it a try yourself before getting this kind of company in!

    The RHI is now closed to legacy applicants

    If you are a new applicant (so the installation took place after the scheme launched), then you will be able to claim the RHI straight away.

    Unfortunately the scheme has now closed to legacy applicants (i.e. those who installed their renewable heating system prior to the scheme going live in April 2014).

    Can the set RHI levels be changed once I have applied?

    The headline RHI tariff figures do change, like we have already seen for the biomass renewable heat payments, and as time goes on and the RHI budget gets used up, we expect further drops in the tariff to take place. The Government will look at the tariff levels every 3 months and adjust them accordingly – however if you are receiving the RHI – you have locked in to whichever rate was agreed at the beginning – this is the rate that you will receive for 7 years (although it will increase with RPI each year).

    Is there anything else I need to know?

    The government will run a “Metering and Monitoring Service Package”, which consumers can volunteer for. Data collected under this scheme will be shared by the Department of Energy & Climate Change (DECC) with the installer and consumer. Domestic RHI recipients who volunteer will receive £230 per year to have their heat pump installation monitored and £200 per year to have their biomass installation monitored.

    Hybrid systems installed with a gas boiler or oil boiler will need to be metered, except solar thermal systems.

    The system will need to be serviced annually in accordance with manufacturer’s instructions to ensure efficient running of the system.

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        Solar Power Plants


      Introduction to solar power plants

      The majority of our power comes indirectly from the sun, but the challenge is to make use of solar energy directly and in a non-polluting fashion.  This is not a new idea; development of solar energy dates back more than 100 years, to the middle of the industrial revolution. In this section, we discuss solar PV and solar heating for the home, but there is also a lot of capital investment directed at producing electricity from solar on a commercial scale.

      Types of solar power plant

      There are two types of large scale solar power plants: the first type are photovoltaic power plants, the largest of which is situated in Canada and is the 97MW Sarnia PV power plant. There are currently eight PV plants, located mainly in Europe, that have a power outage of over 50MW, however there are eight plants planned for the USA that have received funding guarantees that are in excess of 150MW, and these are all due to be completed between 2013 and 2015. The largest planned installation is in China, and this will produce 2000MW at peak (as a reference point the largest nuclear power plant is rated at more than 7900MW)

      The other type is the commercial concentrated solar power plants (CSP); these were first developed in the 1980s. The largest CSP is located in the Mojave Desert in California, known as SEGS CSP and has an output of 354MW. The majority of CSP plants are parabolic troughs (see below), and are located in Spain and the USA. Solar power plants provided Spain with 3% of its electricity in 2010, and with many more CSP plants in the pipeline this is sure to increase over the coming years.

      How solar photovoltaic power plants work

      The process of converting light (photons) to electricity (voltage) is called the solar photovoltaic (PV) effect. Photovoltaic solar power cells convert sunlight directly into solar power (electricity). They use a thin layer of semi-conducting material, usually silicone, encased between a sheet of glass and a polymer resin. When exposed to daylight electrons in the semi-conducting material become energised. These electrons are then able to flow through the material generating a direct current (DC). These are also used for residential needs on a smaller scale, and are discussed in more detail here.

      How concentrated solar power plants work

      CSP power plants do not convert sunlight directly into electricity, instead they use lenses and mirrors and tracking systems to focus a large area of sunlight into a small beam, which is then used as the heat source much like in a conventional power station. There are a few types of CSP power station but all use the same principal of heating the working fluid by direct sunlight.

      Parabolic trough solar power system

      In the case of the parabolic trough system, the sun’s energy is concentrated by parabolically curved, trough-shaped reflectors onto a receiver pipe running along the inside of the curved surface. This energy heats working fluid flowing through the pipe, and the heat energy is then used to generate electricity in a conventional steam generator.A collector field comprises many troughs in parallel rows aligned on a north-south axis.

      Power tower solar power system

      A power tower converts sunshine into clean electricity for the world’s electricity grids. The technology utilises many large, sun-tracking mirrors (heliostats) to focus sunlight on a receiver at the top of a tower. A heat transfer fluid heated in the receiver is used to generate steam, which in turn is used in a conventional turbine-generator to produce electricity.

      Early power towers (such as the Solar One plant) utilise steam as the heat transfer fluid; current US designs (including Solar Two, pictured) utilise molten nitrate salt because of its superior heat transfer and energy storage capabilities. Current European designs use air as the heat transfer medium because of its high temperature and its ease of use.

      Parabolic dish solar power system

      Parabolic dish systems consist of a parabolic-shaped point focus concentrator in the form of a dish that reflects solar radiation onto a receiver mounted at the focal point. These concentrators are mounted on a structure with a two-axis tracking system to follow the sun. The collected heat is typically utilized directly by a heat engine mounted on the receiver moving with the dish structure.

      Solar power and the UK industry

      Producing electricity on a mass scale in the UK does is not currently as commercially viable as wind power or hydroelectricity, although small scale community projects do exist. For example the Westmill Solar Plant, built in 2011, has one of the largest number of arrays, situated between Oxford and Swindon. Although the level of Feed-in Tariff support was cut for small scale producers, twice this year, ROC support still remains at two certificates per mWh of electricity produced for generators of over 5MW. In addition, the UK remains one of the leading nations in terms of providing solar power engineering expertise and solar energy services round the world and will continue to do so over the next few years.

        Introduction to Solar PV


      What is solar PV?

      The process of converting light (photons) to electricity (voltage) is called the solar photovoltaic (PV) effect. Photovoltaic solar cells convert sunlight directly into solar power (electricity). They use thin layers of semi-conducting material that is charged differently between the top and bottom layers. The semi-conducting material can be encased between a sheet of glass and/or a polymer resin.

      When exposed to daylight, electrons in the semi-conducting material absorb the photons, causing them to become highly energised. These move between the top and bottom surfaces of the semi-conducting material. This movement of electrons generates a current known as a direct current (DC). This is then fed through an inverter, which converts the power to alternating current (AC) for use in your home.

      Types of solar panel

      Different types of solar PV installations require slightly different components. However in the next two sections we have explained in detail all the main components that will make up your solar PV array and provide you with 100% renewable, free electricity.

      The solar panel is the key component of any solar photovoltaic system, which takes the sun’s energy and converts it into an electrical current. There are three main types of solar panel (as well as the hybrid version) currently in commercial production, all of which are based on silicon semiconductors:

      Monocrystalline solar cells

      This type of solar cell is made from thin wafers of silicon cut from artificially-grown crystals. These cells are created from single crystals grown in isolation, making them the most expensive of the three varieties (approximately 35% more expensive than equivalent polycrystalline cells), but they have the highest efficiency rating – between 15-24%.

      Polycrystalline solar cells

      This type of solar cell is also made from thin wafers of silicon cut from artificially grown crystals, but instead of single crystals, these cells are made from multiple interlocking silicon crystals grown together. This makes them cheaper to produce, but their efficiency is lower than the monocrystalline solar cells, currently at 13-18%

      Amorphous solar cells

      These are the cheapest type of solar cell to produce, are relatively new to the market and are produced very differently to the two other types. Instead of using crystals, silicon is deposited very thinly on a backing substrate.

      There are two real benefits of the amorphous solar cell; firstly the layer of silicon is so thin it allows the solar cells to be flexible, and secondly they are more efficient in low light levels (like during winter).

      This, however, comes at a price; they have the lowest efficiency rating of all three types – approximately 7% – 9%, requiring approximately double the panel area to produce the same output. In addition, as this is a relatively new science, there is no agreed industry-wide production technique, so they are not as robust as the other two types.

      Hybrid solar cells

      This is not a type of solar cell in its own right; instead it is a combination of both amorphous solar cells and monocrystalline solar cells. These are known as HIT solar cells (Heterojunction with Intrinsic Thin Layer – a bit of a mouthful!), and have higher efficiency ratings than any of the other three types of solar cell alone. In addition, they are also better suited in sunnier climes, where temperatures often exceed 250C, creating up to 10% more electricity.

      We think in many cases polycrystalline cells are the most suitable option, as they provide value for money while still also being relatively efficient.

      Future solar technologies

      Solar PV inverters

      All the electricity produced by the solar panels is produced as direct current (DC), which differs from the electricity that is distributed through the grid and we use in our homes, which is alternating current (AC). For this reason most solar photovoltaic systems are now connected up with some type of inverter, which changes the DC to AC, allowing the individual to sell the electricity back to the grid (in grid-tied systems) or to be used easily in homes.

      There are 2 major types of inverter that can be installed in your solar photovoltaic system:

      1. String inverters (also known as central inverters)

      These are used in grid-tied systems where the solar panels are wired together in series, which is known as a string of panels. Each string of panels is connected to a string inverter, which converts the DC current to AC for use in the home and selling back to the grid. You can imagine each string as a mini power station, producing electricity.

      The main issue with string inverters is that if one of the panels in the string fails or produces less electricity (from things like shading), this impacts the output of all the panels. They will all operate at the output of the worst panel, so a small amount of shading or debris on your solar array can disproportionally reduce the total output of your entire solar photovoltaic system.

      They also have relatively short lifespans when compared to micro inverters.

      The benefits include simple wiring and that you can use thinner wires within your solar PV system, so less copper is used which makes the system cheaper. Buying one string inverter (which is normally the case of most home solar PV systems) is also considerably cheaper than buying multiple micro inverters.

      2. Micro inverters

      These are a newer technology and service each solar panel individually, so each panel requires its own micro inverter and acts as an individual power station.  As a result, micro inverters do not suffer the same performance reduction as a result of shading because any power reduction in a particular solar panel is handled by one micro inverter, having little effect on the combined power output from the entire solar photovoltaic system.

      Micro inverters are much more expensive than the string inverters. However much of this cost is offset by the increased performance (25% more power produced using micro inverters) and the fact that they are more reliable than string inverters (warranties for micro inverters are up to 25 years).

      Buying inverters for your solar PV system

      When looking for which inverters to buy, ideally you want your alternating current (AC) to match that provided by the utility companies. Waveform relates to the quality of the AC signal that an inverter produces. Cheaper inverters will provide modified sine wave signal, while the more expensive versions will produce the pure sine wave signal. Some appliances (such as computers) simply don’t work unless they are powered by a pure sine wave signal, so we recommend strongly that you spend a little more to get this type of inverter.

      Grid tie inverters differ slightly from your regular inverters in that the AC pure sine wave signal has to be perfectly coordinated with the waveform from the grid. As such, these tend to be more expensive than the typical inverters that you buy. They also have a built-in safety feature to cut off power from the solar array if the electricity grid goes down for any reason.

      It is also worth noting that most inverters now also have ‘Maximum Power Point Tracking’ (known as MPPT) installed within them, which helps to maximise the electrical output of your solar photovoltaic array system.

      The principle of MPPT is to extract the maximum available power from the photovoltaic module by making them operate at the most efficient voltage (known as the maximum power point voltage). The algorithm included in the MPPT inverter compares the output from the photovoltaic module with grid voltage and then fixes it at the most efficient voltage, to allow you to export the maximum amount of kWh of electricity back to the grid. An MPPT charger in your solar photovoltaic system will improve your power gain by 20-45% in the winter and 10-15% in the summer.



      The battery

      One of the major issues with solar PV systems is that they only produce electricity when the sun is shining. If you are looking to go ‘off-grid’ or have battery back up in times of grid blackouts, you will need batteries within your solar PV system.

      In these systems, electricity produced from the solar cells is either used in the home as required, or if there is no demand in the home, it is converted to chemical energy in the form of batteries. These batteries can then produce the electicrity at night to allow you to use your solar PV system ’24/7′.

      The electricity produced by your solar system is stored in deep-cycle lead acid batteries that look very similar to the ones found in most cars today (although structurally different). The two most popular types of battery are GEL and Absorbed Glass Mat (AGM), which store the charge very well and do not degrade nearly as fast as the common lead acid (wet cell) battery. Both types of batteries are designed to gradually discharge slowly and recharge 80% of their capacity a multiple number of times.

      An automotive battery is a shallow-cycle battery, and this is designed to discharge only about 20% of its electricity so is unsuitable for solar photovoltaic set-up. The reason being is that if any more than 20% is drawn more than a few dozen times, it will get damaged and no longer take charge.

      Solar photovoltaic batteries tend to operate at 12 volts, and can be arranged in banks (multiple batteries), increasing the storage potential of your solar photovoltaic set up. A bank of batteries organised in a series increases the capacity of your storage but also increases the voltage delivered from your bank, while multiple batteries organised in a parallel circuit increase the capacity, but keep the voltage the same (mains electricity runs at higher voltage, so if you have a grid tie system it is likely you will try to match this by running the batteries in series).

      Solar Charge Controllers

      Solar Charge Controllers (also known as Solar Charge Regulators) are used in solar photovoltaic systems to prevent the batteries from being overcharged. If you decide to implement a ‘grid-tied’ system, a solar charge controller is not necessary, as any excess electricity that you don’t use at any particular moment is sold directly back to the grid.

      However, for any of the other three setups, a charge controller is necessary; it acts to regulate the flow of electricity between the solar photovoltaic modules, the batteries and your appliances (known as the load).

      When the load is drawing power (e.g. you are watching television), the charge controller allows electricity to flow from the solar panels directly (if the sun is shining), or from the battery, or from a mixture of the two. The charge controller also prevents damage to the battery by monitoring the flow of electricity in and out. For instance if your system overcharges the battery, it will damage them. The same is also true if you completely discharge all the charge held within the battery.

      At night, when the solar units are no longer producing electricity, the solar charge controller prevents reverse current flowing from the batteries back into the solar panels.

      Solar charge controllers also are equipped with highly effective charging programs that maximise the charging speed, while still preventing overcharging.

      Most are also equipped with maximum power point (MPPT) charging. The principle of MPPT is to extract the maximum available power from the photovoltaic module by making them operate at the most efficient voltage (known as the maximum power point voltage). The algorithm included in the MPPT solar charge controller compares the output from the photovoltaic module with the battery voltage and then fixes it at the best charging voltage, to get the maximum charge into the battery. The maximum power produced by the solar photovoltaic module is dependent on the amount of sun hitting the solar cells and the temperature of the cells. Incorporating a MPPT charger into your solar photovoltaic system will improve your power gain by 20-45% in the winter and 10-15% in the summer.

      Solar array mounting

      As discussed earlier, the amount of power that your solar photovoltaic system produces is dependent on the intensity of light hitting your solar array. There are three types of mounting you can get for your solar panels to help maximise the amount of light that they receive.

      Fixed solar array mountings

      These are the simplest of all the mounting systems, and also the cheapest. In this system, the solar panels will not move at all at any time during the year, so you want to ensure that when you put in the panels they are facing the equator to maximise sunlight.

      Manually adjustable solar mountings

      These can be changed a few times a year to adjust for the winter and summer sun. The sun is highest in the sky during the summer months and lower in the winter, so by being able to adjust the angle of your solar array ensures that the sunlight hits the array at the best angle to avoid reflection.

      Fully automated tracking solar mount

      These mountings track the sun, to ensure that at all times the angle of the solar array is maximising sunlight. These are certainly the most expensive type as they are constantly moving, but they are also by far the most efficient. Despite this, it has been proven to be more cost effective to add an extra solar panel to your array and use the fixed or adjustable mountings.

      Installing Solar PV

      Are you thinking about installing a solar PV system at home? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

      If you would like us to find you a local installer to help install a solar PV system in your home, just fill in the form below and we will be in touch shortly!

        Types of Solar PV Setup


      Each solar setup has its own benefits and limitations, and it is important to gain a real understanding of these before you invest in a potentially expensive solar PV system, to help avoid disappointment further down the line.

      Grid-tied solar PV Systems

      99% of solar systems installed on people’s homes in the UK are what’s known as ‘grid-tied’ systems. These grid-tied systems allow you to use the free electricity you create from the solar PV system, as well as electricity from the National Grid. This gives you flexibility, since you have a constant supply of electricity, whether or not the sun is shining.

      Any shortfall in supply from your solar PV array can be met by additional electricity supplied via the grid, but there is also the added benefit of being able to sell any surplus back to the grid. In essence, a grid-tied system will go some way to reducing your dependence on the utility companies, and also save you money, while still giving you the comfort of as much electricity as you need from the grid. The lack of batteries also makes this type of solar setup cheaper to install.

      Grid-tied solar PV installations have become incredibly popular in the UK recently due to generous government subsidies (guaranteed for 25 years from the date of installation).

      Off-grid/standalone solar PV systems

      Producing 100% of your own electricity in a clean and sustainable manner is the dream scenario for many people; the thought of never paying another electricity bill, and never suffering from grid blackouts is obviously a very attractive proposition.

      However, an off-grid system does not need to be very sophisticated and grand in scale – it can simply power a light in your garden shed, or a water fountain in your garden. For this reason, off-grid installations are the most common type of solar installation across the globe, providing electricity to any isolated location (normally where no other electricity source is readily available).

      The disadvantage is that you essentially become the utility company, so any costly repairs fall under your remit. Also, if there is a problem with your supply for any reason, you will not have electricity. Solar power is also an intermittent source (i.e it doesn’t power 100% of the time), so if you need electricity during the night (for lighting etc), you will need to install batteries within your system. These enable you to store energy during the day and use it when you are not generating.

      The rewards for installing an off-grid system are clear; however the increased responsibility of owning your home’s electricity supply could make this kind of system a potentially daunting task for solar PV beginners.

      Grid-tied with battery backup systems

      The issue with this system is its added complexity compared to the grid-tied solar PV system described above. The batteries will require additional maintenance and add significantly to the final cost, and they will also introduce additional inefficiencies within your system – potentially a 15% loss in overall performance.

      Grid fallback systems

      This is where electricity is taken from the batteries and run through an inverter to provide the electricity required in the home. Once the batteries begin to go flat, the system automatically switches over to grid power, allowing the solar panels to once again charge the bank of batteries, and the process starts again.

      Installing Solar PV

      Are you thinking about installing a solar PV system at home? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

      If you would like us to find you a local installer to help install a solar PV system in your home, just fill in the form below and we will be in touch shortly!

        Gujarat Solar Park, India

      Demand for Renewables Sources of Energy in India

      India has been plagued by power shortages, more than 400 million people go without electricity every year and consumption demands are forecasted to double by 2035. While it is obvious that the gap in supply and demand will, in the short term at least, have to be filled with a majority of non-renewable sources, India has realised they cannot solely rely on them going forward. This is shown by the recent expansion of renewable energy installations within the country, especially solar PV parks as a result of its hot sunny climate.

      Gujarat Solar Park – Key Facts

      In April 2012, the Charanka Solar Park (part of Gujarat Solar Park), located in Northern India was switched on. This solar PV installation provides 214 MW to the grid, which makes it the largest standalone solar PV installation in the world (surpassing the 200MW Golmud Solar Park situated in China). The Charanka Solar Park in association with other smaller installations located within the Gujarat region make up the Gujarat Solar Park. In total, 21 companies are involved in the Gujarat Solar Park, including four from the USA.

      The Gujarant SolarPark was developed in less than two years, an incredibly short period of time when compared to other power plants. This, along with other similar installation has resulted in India being viewed as pioneers in renewable energy.

      The region, made up of 5000 acres of desert wasteland hardly able to sustain any life, receives on average 330 days of sunlight per year creating an ideal situation for a solar PV park. Due to this, the solar PV Park in Gujarat has received very little opposition. Combined, the Gujarat Solar Park produces 600 MW of electricity to the grid, which accounts for two thirds of India’s total 900 MW of solar power production.

      Besides simply producing a large sustainable source of electricity for India, the investment in the Gujarat Solar PV Park has dramatically reduced the unit cost of solar energy, from Rs.15 to Rs.8.5. This has made it far more cost effective as a power solution to help lessen the country’s lack of electricity. It is almost certain that following successful installations of this magnitude, similar Solar PV parks will be rolled out across the country to give even more Indians access to electricity.

      Future of Solar PV in India

      In India itself, coal power plants produce 55% of the total electricity and even though approximately a third of the population are without electricity, the country is still the world’s fourth largest carbon emitter. At present, renewable energy accounts for only 6% of India’s 185 GW capacity. However, the government led by the Prime Minister Manmohan Singh, via the National Solar Mission, hopes to increase this figure to 15% or more by 2020, with solar energy anticipated to make up 3 percent of that increase.

      The Indian government has gone on record to say that, due to the opening of the Gujarat PV Park, as much as 900,000 tonnes of natural gas will be saved and carbon dioxide emission will be reduced by almost 8m tonnes per annum. Every little helps and in terms of future projections, India certainly seems to be doing their bit towards a greener age.

        Crescent Dunes CSP, USA

      Crescent Dunes Solar (CSP) Energy Plant Background

      In September 2011, construction began at the Crescent Dunes Solar Energy Plant, a 110MW concentrated solar power (CSP) plant located near Tonopah, Nevada.  SolarReserve, a US-based developer of large-scale solar power plants, is developing the Crescent Dunes Solar Plant utilizing its market-leading solar power technology with integrated energy storage to deliver clean, reliable electricity on-demand, 24-hours a day. The 540 foot solar power tower, which is located in the centre of the overall plant layout, was completed in February 2012.

      Crescent Dunes Solar Energy Plant Key Operating Facts

      Unlike most solar plants, which are made up of rows of interconnected solar photovoltaic (PV) unit, the CSP technology at the Crescent Dunes Solar Energy Plant uses thousands of mirrors to concentrate the sun’s energy to the 100-foot tall heat exchanger that sits at the top of the central tower and captures the sun’s energy using liquid molten salt, which is heated from 500 to 1050 degrees Fahrenheit.

      The Crescent Dunes Solar Energy Plant will use approximately 10,000 mirrors, called “heliostats”, to direct sunlight towards the receiver at the top of the solar tower, each heliostat continually moving to track the sun and maximise the amount of thermal energy that the tower receives. In technology similar to SolarReserve’s, the heat is used to superheat water to generate steam to drive a steam turbine, but this is not the case in SolarReserve’s technology. SolarReserve’s technology uses molten salt to both capture the sun’s energy and then store the energy, which allows the plant to generate steam for a traditional steam turbine whenever electricity is needed, even after dark.

      Comparing Traditional Solar PV to SolarReserve Technology

      Previously solar energy, such as Solar PV, has largely been considered an intermittent energy source (like wind farms), meaning that the plant can only generate electricity when the sun is shining. Traditional solar plants can’t produce electricity at night, and even cloudy days or other forms of shading impact the total output of the solar plant. However, SolarReserve’s technology has found the solution to intermittency through the use of integrated energy storage. The molten salt solar thermal power technology that will be used at the Crescent Dunes Solar Energy Plant allows the plant to produce electricity 24×7.

      At the beginning of the day, the “cold” molten salt, which is held at a temperature of about 500 degrees Fahrenheit, is pumped up from the “cold” storage tank, up the tower, and into miles of piping that run through the walls of the receiver that sits at the top of the solar tower. Here, the molten salt is heated from 500 degrees to 1050 degrees Fahrenheit by the sun’s energy and then pumped back down the tower to the “hot” salt storage tank where the thermal energy is stored.  When electricity is needed, the hot molten salt is used to generate superheated steam to drive a standard steam turbine. After the hot salt is used, the cooler molten salt is then pumped back into the cold salt storage tank for the process to be restarted once again.

      Crescent Dunes Solar Electricity Potential

      As the electricity generated by the Crescent Dunes Solar Energy Plant will provide electricity to Las Vegas, this 24/7 electricity generation potential is perhaps a prudent measure! SolarReserve will sell 100% of the electricity generated to NV Energy, Nevada’s largest utility, under a 25-year Power Purchase Agreement.

      It is estimated that Crescent Dunes Solar Energy Plant will generate approximately 500,000MWh of electricity per year, which is double the amount of electricity that would be generated by a similarly-sized PV plant, and is enough electricity to power over 75,000 houses during peak electricity periods.

      Crescent Dunes Solar Power Plant Environmental Impact

      Despite producing an abundant, clean source of electricity, the CSP plant may impact the environment. Obviously the mirrors are concentrating an incredible amount of heat at a very small area, posing a danger to anything that gets in its way. Any wildlife, such as birds, that come into contact with this sort of heat will be in serious trouble. In addition, the diameter of crescent Dune mirrors is 2 miles, so it is taking up serious acreage to fulfil its role.

      On the whole though, the Crescent Dune Solar Energy Plant seems like a great engineering feat, providing clean electricity 24/7, in a much more efficient way than existing solar PV technology.

        Getting Solar PV on your roof – is it worth it?!

        April 16, 2013

      As part of the Green Deal, I am going to a lot homes at the moment and solar PV tends to come up a lot. People are unsure about how the numbers stack-up, they have heard in the news about the recent drop in the Feed-in-Tariff payments, but they are also aware that energy prices are going up substantially every year. So is getting solar PV installed on your home still worth it?!

      In a word – Yes!

      But the speed of payback is actually fairly dependant on when you use the energy, as you will see in a minute. So here goes and if you want to query any of the numbers, please drop a comment at the bottom of this post. A typical system is about 3.6kW (3,600 watts) in size, which will cost you approximately £6,000.

      How much electricity will your Solar PV system Generate?

      If you take this figure (or the size of the system you are interested in getting – obviously the bigger it is the more electricity it can produce) and multiply it by 0.8 it will give you the approximate number of kWh the system produces in a year, so in this case a 3.6kW system would work out as follows.

      So 3600 x 0.8 = 2880kWh

      To give you a rough guide, the average home uses about 4,800kWh each year, although your energy bills will reveal what you actually use.

      The Generation Tariff – payment for every kWh of electricity produced

      As part of the Feed-in Tariff, the Energy Suppliers are obliged to pay you 15.44 pence for every unit of energy you produce, regardless of what you do with it – this is known as the Generation Tariff and is guaranteed for 20 years, i.e. regardless of whether the FiT drops over the coming years, you will get this payment of 14.90 pence for every kWh you produce.

      2880kWh x 14.38 pence = £414.14

      But there is more!!

      The Generation Tariff is only half the story!

      Now unfortunately, as anyone who has done GCSE science will be able to tell you, it is not possible to store electricity so you can either use the electricity as it gets produced by the solar PV system or you can export it back to the electrical grid (you have have battery back-up, however in the UK 99% of homes with Solar PV have grid-tied systems).

      The final payback of the system is dependant on the ratio of using the electricity in the home compared to the amount exported.

      The Export Tariff – payment for every kWh of electricity exported

      For every kWh produced and sold back to the grid you get 4.77 pence (this is known simply as the Export tariff), but for every kWh you can use in the home, it means you don’t need to buy it from the grid at approximately 15.32 pence / kWH.

      I hope you can see therefore that it is about 3 times better (financially) to use the electricity you produce rather than export it back to the grid.

      Having said all that – it is worth bearing in mind that most residential solar PV systems installed in the UK don’t come with a export meter, so they will simply half the generation meter reading and assume you export that this – this means you will be paid as if you exporting 50% regardless of whether you use all the electricity in the home or none of it.

      As a result of this – in an ideal situation you would use 100% of the electricity in the home and you would still be paid as if you were exporting 50% of it to the grid – so a nice little bonus!

      In the scenarios below however, I am going to include the export calculations as if you have an export meter, since the move to smart meters will unfortunately remove this nice little bonus!

      Maximising the return from your Solar PV investment

      So the key here is obviously to have lots of panels, all facing south, and use every kWh of electricity that they produce, however in most cases this simply isn’t feasible.

      Imagine being at work all day, your solar system is producing lots of electricity, but you aren’t there to use it. Conversely, a stay at home mum would be much better placed to use all the electricity.

      So in the next section I am going to look at 3 scenarios which will determine the amount of electricity a household can use in the home and how much they need to sell (remembering you can’t store the electricity), and therefore their total yearly return from installing a 3.5kW solar system within their home.

      Scenario 1 (Parents both working, children at school)

      In this scenario, it makes sense that the family will only be able to use their energy early in the morning and when they get home in the evening (obviously they can set washing machines / dishwashers to run as they leave the house), but lets say they use 25% and sell 75%.

      Export tariff – 75% x 2880kWh x 4.77 pence = £103.03

      Saving on Energy Bill – 25% x 2880kWh x 15.32 pence = £110.30

      Total Yearly Return = £414.14 + £103.03 + £110.30 = £627.47

      Scenario 2 (1 Stay at home parent, other at work and children at school)

      In this scenario, while parent at home will use a decent proportion of the electricity produced, it will be nowhere near the usage if all the family where at home at the weekend for example. In this example lets say usage is about 50% and therefore 50% needs to be sold back to the grid.

      Export tariff – 50% x 2880kWh x 4.77 pence = £68.69

      Saving on Energy Bill – 50% x 2880kWh x 15.32 pence = £220.60

      Total Yearly Return = £414.14 + £68.69 + £220.60 = £703.63

      Scenario 3 (retired grandparents at home for the majority of the day)

      In this scenario, the vast majority of the electricity that is produced will be used in the home, so I am going to use the ration 80:20.

      Export tariff – 20% x 2880kWh x 4.77 pence = £27.47

      Saving on Energy Bill – 80% x 2880kWh x 15.32 pence = £352.97

      Total Yearly Return = £414.14 + £27.47 + £352.97 = £794.58

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        Maximising Solar PV Return


      Maximising your solar PV return

      It goes without saying that the bigger your solar array, the more electricity it will produce, but how else can you be sure you are maximising your return?

      Orientation of the panels

      Solar panels in the northern hemisphere perform best when facing due south. This ensures that they receive the maximum exposure from the sun as it travels east to west. There is little point putting solar panels on a north-facing roof, so you may need to install them on a solar array mounting on the ground to ensure you can get the panels angled in a southerly direction.

      There are different types of solar array mounting, but you can get fully automated tracking solar mounts. These mountings track the movement of the sun to ensure that the angle of the solar array is maximising exposure to sunlight at all times. These are expensive, but they also make sure you are getting the best yield.

      Casting shadows on your solar PV array

      It is important to ensure that shadows won’t fall on the solar panels during the peak sunlight hours, as this will obviously adversely affect the output of your solar system.

      The effect of shadowing is amplified if your solar PV array has been set up with string inverters. In this setup, each panel is connected to the next panel in a series of strings, with each panel feeding a DC current to the inverter. When a cell underperforms, bypass diodes reroute the current around the underperforming cells. The problem is that rerouting the current loses not only the potential energy from these cells, but also lowers the entire string’s voltage.

      The inverter then has to decide whether to optimise the voltage of the underperforming string or maximise the energy harvest from the unaffected strings. Normally the inverter chooses to optimise the voltage of the underperforming string, causing the performance of the whole string of panels affected to drop significantly. Just 10% shading of a solar PV panel can result in a 50% decline in output in this type of setup.

      Solar arrays with micro inverters do not suffer anywhere near as badly from shading compared to the arrays with string inverters.

      As a result of the shading issue, it is important to ensure that shadows won’t fall on the solar cells during peak sunlight hours as this will obviously adversely affect the output of your solar system. It is also important to have the foresight to predict tree growth in the coming years, as solar panels should go on producing electricity for 25 years; therefore trees that are currently of no concern could very easily grow to sufficient size in 15 years to cast shadows, diminishing the power producing capability of the solar photovoltaic system.

      Keeping your solar panels clean

      The operating efficiency of a solar PV panel is dependent on the amount of sunlight that hits it, so if you panels are covered in dirt they are going to produce less electricity. It is suggested to wash your solar panels 2-3 times per year for maximum efficiency. We cover the various techniques for cleaning your solar array here.

      You should also coat your solar panels with protectant to reduce reflection and increase transmissivity.

      Ambient temperatures of the panels

      One of the key factors impacting the amount of electricity your solar panels produce is the temperature at which they operate. It is easy to presume more sun and therefore heat results in more electricity but this is wrong. Different solar panels react slightly differently to the operating ambient temperature, but in all cases the efficiency of a panel will decrease as the temperature increases.

      The negative impact of temperature on solar panel efficiency is known as the temperature coefficient.

      Solar panels are power tested at 250C, so the temperature coefficient percentage illustrates the change in efficiency as it goes up or down by a degree. For example if the temperature coefficient of a particular type of panel is -0.5%, then for every 10C rise, the panels maximum power will reduce by 0.5%.

      So on a hot day, when panel temperatures may reach 450C, a panel with a temperature coefficient of -0.5% would result in a maximum power output reduction of 10%. Conversely, if it was a sunny winter’s morning, the panels will actually be more efficient.

      It is therefore really important to maximise airflow around the panels to try to keep them cool so their efficiency isn’t negatively impacted. Rather than installing panels flat against your roof, you could try lifting them slightly to allow air to circulate underneath.

      Use more of the electricity in your home

      As mentioned in the solar PV costs section, it is best to use the electricity you produce from your solar PV array in your home, since that means you don’t need to buy it at 15p from the electricity company. Selling the electricity back to the grid means you are eligible for the export tariff which is only 4.5p/kWh.

      One way to do this is with a solar diverter. These send excess energy that isn’t being used by your appliances to your immersion heater instead, helping to heat your water.

      You can also make behavioural changes to ensure that you are using as much of your self-generated energy as possible. It is worth changing some of your energy usage behaviour. For example, it is better to run washing machines and dishwashers during the day – so set them to start as you leave for work.

      The other way to use all the electricity you produce is by incorporating batteries into your solar PV array. Batteries will increase the upfront cost of your array and will require maintenance, but can be really worthwhile in the long run. Any electricity you produce during the day can be stored in the batteries and then used as and when you require it.

      Final thoughts on investing in a solar PV system

      Having received quotes for solar PV installation, you need to run the numbers to see if it makes financial sense for you to invest. It is important to bear in mind though, that solar photovoltaic arrays are modular, therefore new panels can be introduced at later dates as finances allow, further increasing the electrical output potential of your system.

      Installing a solar photovoltaic array on your property should not be solely a financial decision though; you should also take into account energy security.

      As demand for electricity in the UK continues to increase, the supply side is not keeping up. Over the next 3 years, 8 of the UK’s coal power plants are going to close, due to EU legislation on emissions, and by the end of the decade some of our nuclear capacity is also due to be decommissioned. Experts have predicted that the UK could face blackouts in the next few years.

      A solar photovoltaic system can therefore reduce your reliance on energy companies, helping to minimise the impact of energy scarcity on you and your family in the future.

      Installing Solar PV

      Are you thinking about installing a solar PV system at home? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

      If you would like us to find you a local installer to help install a solar PV system in your home, just fill in the form below and we will be in touch shortly!

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