What is wave energy?

There are many different designs out there that harness the energy from our oceans’ waves. Wave energy uses the movement of waves to generate electricity. The technology is continually being modified so that it may one day be able to contribute a large proportion of the energy needed to power coastal countries. If the UK were to harness this technology it could supply a lot of power to the coastal towns and villages. Australia, for example, could supply over 60% of its own energy from wave energy alone. It certainly also helps when countries also have over 300 days of sunshine and can harness solar power as well.

How does wave energy work?

Below are three examples of wave energy, technological solutions:

Oscillating water column (OWC)

For OWC technology, it is not the waves that move the turbines directly, but a mass of compressed air that is pushed by these waves. This involves a structure usually located in a breakwater, the upper part of which houses an air chamber (thus the compressed mass of air) and its lower part is being submerged under the water. In this way, the turbine takes advantage of the movement caused by waves, both when they come in and when they go out, and the doubly-fed generator (both by its rotor or mobile part and by the stator or fixed part) to which it is coupled then feeds energy to the grid.

Floatation platforms

The platforms draw energy from wave power by floating with the rising and falling motion of waves. The floats are attached by arms to a platform that stands on legs secured to the sea floor. The motion of the floats is transferred via hydraulics into the rotation of a generator, producing electricity.

Channelling the wave

A third approach is to use channels near the shore to store the energy in an elevated reservoir.  Then as the water flows back out of the reservoir a standard hydroelectric water turbine is used to generate electricity.

Seafloor carpets

Harnessing the power of waves from the seafloor has often been touted as the best possible way. This is because of the lack of disruption to fishing, leisure and shipping that is often caused by surface-based technologies. These seafloor carpets use the turbulence created by the waves above to power pistons and create hydraulic pressure, which can be turned into electricity to power homes, or used for desalination.

UK wave energy development

In the UK, wave energy is classified as part of marine energy, along with tidal energy. This is why in policy terms sometimes these two areas are referred to interchangeably. In January 2012, there was an announcement of the creation of the first Marine Energy Park (MEP) in the south-west of the UK. This will allow the collaboration between the private and public sector to embark on wave and tidal projects from Bristol to Cornwall and the Isles of Scilly.

Wave energy like tidal power is supported by tradeable ROCs. The current level of support is 2 ROCs per MWh of electricity generated. After the 2011, the level of support is to increase to 5 ROCs per MWh. The idea is that for the next few years the UK government needs to support emerging technologies so that they can become the cutting edge solutions of the future. As the technology in this is still developing, the output cost of electricity produced is greater than for fossil fuels. It is for this reason that both UK and Scottish Governments have a large role to play. The Green Investment Bank, when it goes live, is more likely to lend to projects that are close to mass scale expansion rather than funding any research and development stages.

Berkeley, California, and the seafloor carpet

A team including, Reza Alam and Marcus Lehmann, have come up with a revolutionary way of tapping the constant 24/7 power of the wave. Instead of trying to harness the energy from the surface, potentially causing disruption to shipping, fishing and leisure, they have come up with a renewable energy source based on the sea floor. They suggest that just one square metre can power two homes and just 10m of Californian coastline can provide as much electricity as a whole football, or ‘soccer’ as they say over in the States, field’s worth of Solar Photovoltaic Panels.

The idea was first thought of when it was realised that patches of muddy ground found off the coastlines of Northern America, reduced the dominance of waves hitting the shore. The oscillation of the waves would gently push the mud up and down, causing a build up of heat as a result. This turbulence, absorbed by the muddy floor, would be the perfect 24/7 dense form of energy generation.

Double action cylinders, holding a carpet that is currently a thin sheet of rubber in testing but due to change to an alternative durable substance, which are forced up and down by the waves, create hydraulic pressure. This can then be passed along the sea floor and onto the shore where it then can be exchanged and transformed into electricity.

Thought to be made commercially available before 2026, this is certainly the next big thing regarding sustainable, renewable wave technology.

Hydroelectric power on a residential scale

It is well known that energy is generated by building dams over giant underwater turbines; however it is possible to use micro hydro generators (<100kW) or pico hydro generators (<5kW) on more modest water flows. In this section we explore where the technology can be used in a small scale area, for example the home or a community project. More about industrial size dams and solutions can be found in the green commercial section.

Obviously, there is a fundamental requirement on a steady stream of moving water, however they have an advantage over solar power (both solar PV and solar heating) and wind, in that they can run day and night and in any weather conditions provided the we don’t have a prolonged drought period where streams and brooks can dry up.

The amount of energy produced is reliant on two things:

The flow of water

The flow of water is simply the quantity of water flowing in the water source, which is measured in litres per second.

The head

The other key factor is the head – this refers to the pressure at which the water hits the turbine blades, and is the vertical distance from the water source to the generator. The larger the distance that the water falls before it hits the blade, the higher the head. Ideally both the flow and the head will be high, however if one of these is particularly high, while the other is low there is still the potential for a rich source of electricity.

You can estimate the number of kilowatts of energy produced by multiplying the flow (litres/sec) by the head (m) and multiplying by 9.81 (gravitational constant). Remember a typical house uses 4500kWh per year.

Busting energy saving myths

Read more

How does micro hydroelectric work?

The type of turbine that is used varies depending on the type of flow available, however typically a residential generator uses a pipe to collect water from a river or a stream. Using gravity the water moves through the pipe ‘downhill’ and a generator situated within the pipe acts to change the kinetic energy from the water flow into electrical energy.

When you have high head (the vertical distance from the water source to the generator), you are best using an impulse turbine (such as a Pelton turbine). This turbine is not submerged in the water, instead it sits in the air, and consists of buckets around a central hub. The nozzle at the end of the pipe converts the water into a fast moving jet. This jet of water is directed at the buckets, and the force of the the water causes the turbine to spin generating the power. The smallest type of high head turbine requires a head of at least 10-14 metres, and a water flow of 3-4 litres/ second, and this is rated at producing 200 watts of power.

For medium head water flows, it is best to use a reaction turbine. With a 3-12 metre head and a water flow of 45 litres/ second, you can get a reaction turbine that will produce about 3000 watts of power. Obviously as with the high head turbines, if either the head or the flow increases, you will see dramatic increases in the potential electricity your system is capable of generating.

For low head water flows, you obviously require a high flow rate, and in this situation an old style water wheel is the best. So the water fills the buckets which fill up, then pulling the wheel down, so the next bucket is filled, and this process is continued so the wheel spins (albeit very slowly). However the advantage of this type of system is that any potential blockages just simply wash through the system. Gearing can be used in conjunction with water wheels to increase the speed that the generator spins to help electricity production. Water wheels are also aesthetically pleasing on the eye!

Summary of micro hydroelectric power

If you are lucky enough to have a water flow source on your property that either has high head or sizeable flow, a micro hydroelectric generating system may be the perfect solution for your energy needs. Despite potential seasonal fluctuations in flow and head, a micro hydroelectric system will provide you with electricity 24/7, with very little maintenance necessary.

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.

What is OTEC?

OTEC stands for Ocean Energy Thermal Conversion. It is all about using the differences in warm and cold temperatures of oceans to produce useful products like electric power for coastal or island communities. With increases in energy prices and technical innovations over the last few years, OTEC systems, such the one produced by the Ocean Thermal Energy Corporation, are becoming viable technological solutions to help provide some of the world’s energy requirements.

OTEC technology cannot currently be used across the globe because the heat gradient needed for the OTEC operation needs to be of a sufficient level. Therefore it tends to be concentrated among the hottest parts of the planet which are between the tropics. Therefore, it may not be suitable as an electricity energy solution for some European and Northern countries. UK companies and people interested in this technology do read on, because although the processes may not be suitable for direct electricity generation, indirectly, companies such as BG Group, BP and Shell can exploit existing offshore infrastructure, which includes existing oil and gas rigs located in the warm parts of the world, upgrade for OTEC technology, and supply hydrogen, the next generation fuel, for cars and household boilers to be used all round the world.

OTEC is not like wind power or solar power (which are intermittent), because the technology can operate on a 24-7 basis. Oceans act as incredibly large solar energy collectors, absorbing about 80% of the sun’s energy. This means that every day, the oceans on our planet absorb solar energy equivalent to 250 billion barrels of oil, and if we could convert 0.1% of this energy into electricity each day, it would supply a significant proportion of  electricity and fresh water requirements for agriculture for tropical, coastal regions of the world.

How does OTEC work?

OTEC Warm and Cold Water

OTEC (Ocean Thermal Energy Conversion) works by using the temperature gradients found in large bodies of water, where the temperature of water found on the surface is significantly higher than the cold water found deeper down. The largest water temperature gradients exist in tropical oceanic regions, because not only do you have the very warm water, but you also have oceanic depth to make use of cold water currents. For example, just off the coast of Puerto Rico, you have an oceanic depth of about 3000 metres, and therefore the temperature of the surface and deep water can vary by more than 20 °C, which is absolutely perfect to exploit the OTEC process.

OTEC Process

An OTEC power plant works by pulling in warm ocean surface water and this is used to heat a ‘working fluid’ such as ammonia or propane into a gas. These fluids have a low boiling temperature, which when turned into gas, moves the steam into pressurised shafts that are then used to drive turbines. The turbines then drive the generator, which converts mechanical energy into electrical energy. You may now know this part from the heat Rankin Cycle, which underpins electricity generation for current processes such as biomass, nuclear and fossil fuels. A long pipe accessing the very cold water from the depth of the ocean is used to cool and liquefy the gas back into working fluid, so the process can start again.

As the ocean water can only heat the working fluid by about 20oc, the steam produced from the OTEC process unfortunately doesn’t carry much energy. However, as the resource, which is ocean water, is abundant, an OTEC power station can harness much of the energy it produces by counting on the large volumes of hot and cold water it requires to operate which goes some way to counteract the lack of efficiency problem.

OTEC technology can be harnessed to produce Seawater District Cooling (SDC). This is when pipework takes in deep water, which is cold. It then harnesses this cold water for district air-conditioning as opposed to using lots of electricity and chemicals seen in current systems. These types of systems can save up to 80% or more on electricity usage.

Seawater/air conversion

The extensive difference in temperatures found between seawater and air in coastal arctic regions can be exploited using a similar technique to OTEC. Where ammonia or propane is used in OTEC systems, liquid butane has to be used in arctic locations due to its lower boiling point. The relative heat of the seawater is used to transform butane into a gas that drives turbines, before the winter arctic air temperature, which can fall to -22 °C, rapidly condenses it and allows for the continuation of the cycle. Although this technique is in its infancy, the fact that it requires half the amount of seawater extraction pipes compared with the OTEC system makes it potentially less expensive and therefore a more efficient concept.

OTEC Industry Development

OTEC Company Innovation

OTEC technology was pioneered in the late 19th century, but it has only been recent technological advances in heat exchangers that have made the technology a viable commercial source of energy. Companies such as Lockhead Martin, Ocean Thermal Energy Corporation and Makai Ocean Engineering, who have become leaders in the development of this technology, are looking to bring it to market on a large commercial scale. They have managed to gain leverage from the expertise in Hawaii, for example, which has the right ocean temperature variations and depth required for this technology to work. Since the 1970s, the US established Natural Energy Laboratory of Hawaii, has become the leading test facility of the energy source due to the region’s warm water surface, and very deep, very cold water.

OTEC onshore vs. offshore facilities

OTEC technology is not all about electricity generation, it has a much wider scope than that. An onshore OTEC facility can for example not only create electricity, but other products that include fresh water and hydrogen that can promote agriculture and be used as a fuel, respectively. The upwelling of cold water from the depths of the ocean also helps aquaculture thrive, through its fertilising capabilities. Together with a SDC system it can provide the power requirements of an island or coastal community, create jobs and safeguard energy security at low cost which doesn’t cause damage to the environment.

An offshore OTEC facility, as previously mentioned, can be harnessed by companies and countries that are currently involved in deep sea mining exploitation in remote locations. For instance existing deep water, offshore platforms can be upgraded with OTEC technology for the production of hydrogen fuel. It seems evident that oil and gas companies that also have the transportation facilities can use existing machines to transport this fuel around the world.

The future for OTEC

We need to move away from the burning of fossil fuels and move to a technology like OTEC to not only produce the energy requirements, but to produce an alternative fuel like hydrogen, that can be combusted as an alternative. Fossil fuels are wasted in the combustion processes as this deprives future generations of key materials (e.g. plastics) required for commercial and domestic purposes. OTEC is not suitable for all locations, but tropical waters are abundant, so can be used in conjunction with other renewable energy sources to help drive a world free from fossil fuel dependence.

Maximising wind turbine returns

To maximise the electricity contribution that a wind turbine can provide you with, two interlinked questions need to be considered:

• How much electricity you would like to produce?
• How much electricity you can produce on your property?

How much electricity do you need your turbine to produce?

You first you need to decide exactly what you are trying to achieve by installing a wind turbine on your property. Are you trying to become completely independent from the grid? Are you simply trying to decrease you electricity bills having received a capital lump sum that you can invest? Do you simply want a wind turbine to power a light in your garden shed? Obviously the larger the turbine, the more electricity it will produce; however larger turbines will be more costly.

By looking at utility bills from previous quarters, you can get a feel for your total electricity usage over a year. You can get more accurate readings if you go around your property and complete an energy assessment of your current load (simply the total energy that each appliance in your house uses over a certain period of time). This involves producing a table with each appliance, its draw in watts (measured using a watt plug in meter – sometimes known as a wattmeter), and the estimated time of use in a 24 hour cycle. With all this information you can complete a much more accurate total yearly assessment of usage of your house (by multiplying usage for a 24 hour cycle by 365 days).

Having a feel for your total energy usage should help you decide what you are trying to achieve with your turbine. There are several wind turbine setups which we have described in more detail below.

How much electricity can your system produce?

It is really important that you have a target electricity figure in your mind that you are aiming to achieve, be it 50% of your total energy requirements, or becoming fully self sufficient. However, this may not be possible if there are constraints on your property, such as lack of space or low average wind speed.

Wind speed

This is the key factor and we usually use average wind speed as the measurement for your particular location. You cannot directly affect the average wind speed at your home; however your choice of site and tower height can have a dramatic impact on the wind resource. The power available for the wind that is blowing is the cube of the wind speed – this is absolutely fundamental, and this can be seen in the simple sums below:

• 3mph – 3 x 3 x 3 = 27kWh
• 6mph – 6 x 6 x 6 = 216kWh
• 12mph – 12 x 12 x 12 = 1,728kWh

This is excellent news, as the further you get away from the surface of the earth and its many obstructions (e.g. houses), the higher the wind speed: therefore the more power in the wind. This means it is important to try and maximise the height of any tower you use, to try to maximise the wind potential of your wind turbine system.

Swept area

The swept area is the circle that the turbine produces when spinning, so this is the diameter of the blades. The blades are driven by the power in the wind, so the larger your swept area, the more energy you can harness. Again the easiest way to illustrate this is with some more simple sums (apologies for those adverse to maths!), where the area of a circle is half the diameter² x π. (π = 3.14)

• 3 foot diameter = 1.5 x 1.5 x 3.14 = 7ft²
• 6 foot diameter = 3 x 3 x 3.14 = 28ft²
• 12 foot diameter = 6 x 6 x 3.14 = 113ft²

Taking into account these two factors, you can see the maximum electricity you can produce. Remember that wind speed is free (although towers obviously cost more money the higher they are), while investing in bigger and bigger turbines gets more expensive.

What size turbine should you be looking at?

The size of your wind turbine is therefore determined by the amount of electricity you are looking to produce (but potentially constrained by windspeed and space), and secondly the amount of cash you have available.

Unlike solar photovoltaic cells that can be added to fairly easily as additional funds become available, the turbine blades would need to be replaced, and potentially the generator changed if you want to produce more power in the future. Home scale generators normally are between 8 and 25 feet in diameter (so a swept area of between 50 – 500 feet²). If you have an average wind speed of 10 mph, these could produce between 1,000 and 15,000 kWh. An average house uses approximately 4,800 kWh per year, so a 25 foot diameter turbine is going to produce a serious excess of power to sell back to the grid, or power more than one house.

Final thoughts on wind turbines

Planning permission

Contact your local council to ask about planning permission if you’re considering installing a wind turbine. The majority of local authorities are keen to encourage the installation of renewable energy systems. However it is a good idea to consult your neighbours before investing time and money into the planning phase, to allow them to voice any objections.

Average wind speed

Before you even consider investing in a wind turbine, you need to check your average wind speed. The Carbon Trust have created a tool that allows you to estimate the wind yield at your home location. You are looking for an average wind speed in excess of 5m/s. By providing simple information regarding your location and type of turbine, the tool will give you average wind speed and potential energy output.

Subsidies

In the UK, as a wind turbine owner you can benefit from the Feed-in tariffs. There are different allowances depending on the power output of your equipment. Wind turbines above 5MW are classified as commercial and alternatively benefit from the Renewable Obligation Certificates. The Feed-in tariffs basically provide you with a source of income for every kWh of electricity you produce. This is independent from any excess electricity you sell back to the grid, which you further benefit from in the form of the export tariff. This can really help a wind turbine become an economically viable system to put into your house.

What are ground source heat pumps?

Ground source heat pumps use the earth as a heat source, taking advantage of the stable temperatures in the ground to provide heat and hot water for the home.

Ground source heat pumps are not a new concept and have been around since the 19th century. This technology became very popular in Sweden in the 1970s and since then units have been sold worldwide.

In the UK, there has been a sudden surge in demand in heat pumps since the launch of the Renewable Heat Incentive, which pays homeowners for each unit of hot water produced. Although rates are no longer as high as they were, they can still cover much of the initial install costs of the systems.

How do ground source heat pumps work?

A ground source heat pump system uses heat trapped beneath the ground and boosts it to a higher temperature using a heat pump. This heat is then used to provide home heating or hot water. The heat pump performs the same role as a boiler does in a central heating system, but uses ambient heat from the ground rather than burning fuel to generate heat.

Initially, a heat transfer liquid (normally glycol) is pumped through pipes buried deep in the ground. As the liquid travels through the pipework it absorbs ambient heat from the ground and warms up, before returning back to the ground source heat pump unit. Once it returns, a heat exchanger removes the heat from the liquid and it then continues to travel round and round the pipework in a continuous cycle.

The low-grade heat is transferred through the heat exchanger, then passes through a heat pump compressor which drives the temperature up to a level that is usable for heating and hot water.

How much pipework does a GSHP require?

The length of the ground loop depends on the size of your home and the amount of heat you need – longer loops can draw more heat from the ground, but need more space to be buried in.

The pipework can either be laid horizontally or vertically. If laid horizontally, the pipework tends to be buried in trenches 2-3m deep, spread over a huge surface area to ensure the heat transfer liquid has the opportunity to increase to a sufficient temperature. If the pipework is installed vertically, boreholes get drilled in to ground (at a cost of £6,000 – £8,000 for each borehole!). These need to be drilled by professionals and will regularly exceed 100m in depth to ensure that the heat transfer liquid again has the opportunity to absorb enough heat.

There are two types of ground source heat pump, and both have a few components in common – they consist of a ground heat exchanger, a heat pump and a heat distribution system (e.g. underfloor heating or radiators).

Closed loop ground source heat pump

The majority of ground source heat pumps installed today are closed loop heat pumps. As the name suggests, no outside liquid enters the loop of pipework at any point. In this set up, a sealed loop of high density polyethylene pipe is laid either vertically or horizontally in the ground. The heat transfer fluid is in a completely closed system travelling through the pipework and returning back to heat pump.

Open loop ground source heat pump

The open-loop ground source heat pump uses ground water to pump around the system; however the number of installations of this type are decreasing, mainly because you need a source of groundwater. Also an additional associated issue with the open loop ground source heat pump is that the quality of the groundwater can actually have a detrimental effect on the system.

Ground source heat pumps require electricity

The fact that ground source heat pumps run on electricity suggests that they are expensive to run (electricity is approximately 15p / kWh while gas is just 4p / kWh). However heat pumps are in fact incredibly efficient.

In fact, ground source heat pumps are even more efficient than air source heat pumps, converting each unit of electricity (required to run the pump and compressor) into 3.5 – 4.5 units of useful heat. Compare this to a brand new energy efficient boiler, which converts each unit of gas into just 0.9 units of useful heat.

The efficiency of air source heat pumps is measured by the Coefficient of Performance (CoP), which is simply how many units of useful energy are produced from each unit of electricity consumed to operate the system. With air source heat pumps, the coefficient of performance changes throughout the year. This is because since in the winter months, the unit needs to work harder (and hence uses more electricity) to drive the temperature up to an acceptable temperature.

For ground source heat pumps the coefficient of performance is relatively consistent – this means that even in the middle of winter, when hot water and heating demand are at a maximum, the GSHP should be running equally as efficiently as it does on a red hot summer’s day. This is because the temperature underneath the ground remains relatively constant all year round – and this is one of the key advantages of GSHPs over air source heat pumps.

Heat pumps do have some impact on the environment as they require electricity to run, but the heat they extract from the ground is constantly being renewed naturally, hence they are considered a renewable heating source.

Installing a ground source heat pump

The Energy Saving Trust (EST) recommends households considering a ground source heat pump to consult a Microgeneration Certification Scheme installer and only use a properly accredited professional to complete the work. During its trial, the EST found a variety of heat pumps incorrectly installed, which therefore didn’t perform as efficiently overall as they could have. It is essential to use an MCS-approved installer to qualify for the Renewable Heat Incentive.

It is important to shop around and we always recommend getting several quotes before choosing the best option for you. Studies have shown that most suppliers tend to exaggerate the savings in energy costs this system will produce.

Renewable Heat Incentive

Heat pumps are part of the Government Renewable Heat Incentive (RHI) scheme. It means that you can get paid for every unit of renewable heat you generate. You can get a significant chunk of the cost of installation back over 7 years of payments – not to mention the savings to be made from the heat pump itself. Read more on that here.

Benefits

• Ground source heat pumps can lower fuel bills, especially if you are currently using conventional electric heating (saving of £420), LPG or oil (saving of £50).
• Ground source heat pumps are often classed as a ‘fit and forget’ technology because they need little maintenance, and no fuel deliveries are required, however they provide space heating and hot water 24/7.
• Can reduce your carbon footprint: heat pumps can lower your home’s carbon emissions, depending on which fuel you are replacing.

Limitations

• Ground source heat pumps require a reasonable amount of land outside to lay the coils underground. If this is unavailable the technology will not be suitable for your home.
• If you have a vertically submerged closed loop system and there is a leak, it can be difficult to gain access to.

Cost

• From £13-20,000.

Installing heat pumps

Are you thinking about getting a heat pump? 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 heat pump installer, just fill in the form below and we will be in touch shortly!

What is Hydroelectric Power?

Hydroelectric power is a very well established form of providing energy. In the last decade, 20% of the world’s electricity came from hydroelectric plants (88% of the renewable energy supply). This balance will change as there are now competing renewable energy generating sources like solar PV, and wind power. Hydroelectric power means harnessing power from moving water using an electric generator. In the UK, total hydroelectric power capacity is just under 2%, which makes up under a fifth of the total renewable energy generation capacity. When people around the world think about hydroelectric power, they probably think of the Hoover Dam, which is located on the Colorado River in the USA, between Arizona and Nevada. It was completed in 1936 and had a maximum generating capacity of 1.3GW.

How does Hydroelectric Power Work?

Power is generated as massive turbines spin, which is caused by water flowing over them. When the turbines spin the magnets in the generator, this causes a conversion of kinetic energy to electrical energy. The amount of power generated varies depending on the volume of water that passes over the turbines and the difference in height between the water source and the water’s outflow (known as the head). There are different bands of hydroelectric power plant, divided by the amount of energy they can produce. The power plant divides are as follows – large (few hundred MWs to 10GW), small (up to 10MW), micro (up to 100KW) and pico (under 5KW).

One of the major advantages of hydroelectric power is that it can be harnessed within seconds depending on demand, and as such is one of the only means of storing large quantities of electrical energy for peak demand. This is achieved by holding large amounts of water in a reservoir behind a dam with a hydroelectric power plant below. For example Dinorwig, in Wales can help provide emergency power to fill the demand gaps from a city such as Liverpool. Most power stations, including fossil fuel and nuclear have to stay on at all times as they take time to warm up to produce the power, and cool down for maintenance. As a result, these are used to service base demand, then hydroelectric power can service any spikes in demand, and then water can be pumped  back up into the reservoirs when demand is less (during the night).

Types of Hydroelectric Power

Hydroelectric Power Dam Storage

This is the conventional hydroelectric power station most people refer to when discussing hydroelectric power. It involves building a dam across a river, which traps the water creating a large artificial lake or reservoir behind it. To create electricity, gates are opened at the bottom of the dam and gravity pushes the water through the gates and down a pipe known as penstock, which delivers the water directly to the turbines built into the structure of the dam. This fast flowing water turns the turbines, and the generator system converts this kinetic energy into electrical energy. An example of a hydroelectric power dam, is the Kielder Water reservoir, located in Northumberland, operated by RWE Npower and is the largest system in England.

Hydroelectric Power Pumped Storage

Pumped storage hydroelectric power, as described in the Energy Storage section requires two reservoirs, one at high altitude and one at low altitude. When the water is released from the high altitude reservoir, energy is created by the downflow which is directed through high-pressure shafts, linked to turbines. This pressure drives the turbines which in turn power the generators that create the electricity. When the high altitude reservoir is empty, water is pumped back to it from the lower reservoir. This is linked with a pump shaft to the turbine shaft, using a motor to drive the pump.

In the UK, Dinorwig Hydroelectric Power plant uses pump motors that are powered from electricity from the grid, when the electricity is cheaper overnight, and demand is at its lowest. Hydroelectric power pumped storage generation therefore offers a critical back-up facility during periods of excessive demand, whilst being efficient in storing energy during periods of low demand.

Run-of-the-river Hydroelectricity

Some hydroelectric power systems utilise the natural flow of a river to create electricity without needing to build a dam. These types of hydroelectric power station involve forcing the river flow through penstocks and turbines to create the electricity, but the structures that are put across the river are far smaller than used in the hydroelectric power dam storage described above.

In Beeston, Nottinghamshire, the hydroelectric power plant run by United Utilities is the largest run-of-the-river system in England. The difference between a dam and a run-of-the-river system is that the latter uses free flowing water, and has minimal storage capacity, which has its advantages and disadvantages. The system requires volume of water passing through and without storage capacity may lack the power of velocity. The dam and the river systems can both be example of diversion schemes, where they can both use water that is channelled from a river or a lake

Hydroelectric Power Industry Development

In the UK, the largest hydroelectric power station is at Dinorwig, which is capable of generating 1.8GW of power in just 12 seconds. However looking around the world, this is dwarfed by the largest hydroelectric power station, the Three Gorges Dam located in China. This hydroelectric power plant has a generating capacity of 20.3GW, which at the time was expected to service 10% of China’s electricity needs, however since their demand has increased so dramatically in recent times, it currently only services about 3%.

Hydroelectric power generators in the UK are eligible for Renewable Obligation Certificates (ROCs) with stations commissioned after 2002 that have 20MW of power output and for all that are below this level. According to the DECC, there is no national strategy for nationwide development of hydroelectric power, but the government is committed to do everything in its power to support developers, community initiatives and small scale developers being able to invest and build hydro projects. In addition, schemes up to 50kW can only apply for FITs, whereas schemes between 50kW and 5MW can choose between FITs or ROCs.

What is Geothermal Power?

Geothermal power is utilising energy that comes in the form of heat from beneath the earth’s crust/ surface layer. Essentially this is utilising the same scientific principles as used in ground source heat pumps, but on an industrial scale. Geothermal power relies on large generators and infrastructure that can provide both heat and electricity to multiple dwellings and commercial properties.

Geothermal power is a renewable heat source that can provide energy for electricity production as well as heating for a number of applications and appliances. Currently in the UK there is one working geothermal power plant in Southampton, which is providing a local district heating solution rather than being used an electricity generating power plant.

Some areas of the world have much more geothermal activity (such as Iceland, West Coast of the US, Rotorua in New Zealand, etc.), and these are more obvious places to harness the earth’s geothermal power. However, if you dig deep enough, heat is available anywhere across the globe (including the UK) so we could definitely roll out this technology more, and build on expertise to harvest the heat in more effective ways.

The science behind geothermal power is relatively simple; heat is continuously flowing from the Earth’s core by conduction (travelling from hot to cold) to the surface and is therefore considered as renewable source as long as the Earth continues to have an active core. It is estimated that geothermal power could produce 44million MWs of power, so even if we could tap a very small percentage of this it would service most of our energy needs.

Geothermal Power for Electricity Generation

Utilising geothermal power requires accessing high temperature fluid that is heated deep underground. Historically this fluid has existed underground, formed by rainwater passing through cracks in the crust. The water is heated by hot rock underneath and compressed by pressure that maintain it its liquid form. The water potentially then finds a path through the Earth’s crust, and presents itself on the surface as hot water springs or geysers.

Nowadays, in addition to this naturally occurring phenomenon, we can also artificially mimic this by pumping cold surface water down into the earth’s crust, where it gets superheated and returns to the surface via circulation pumps. Existing Geothermal Power plants have either tapped into the naturally occurring process or mimicked this to produce the steam necessary to drive turbines to create electricity. As we can now have the technology to drill deeper than ever into the Earth’s crust, by utilising the man made process, we can implement geothermal power stations anywhere in the world.

Three common Geothermal Power generating systems

Dry Steam Geothermal Power

Dry steam geothermal power plants use geothermal steam directly to turn the electricity producing turbines. To have this structure in place requires steam directly travelling to the Earth’s surface, which is quite a rare phenomenon, so there are only few examples of this type of power station worldwide. The geothermal steam, which is superheated (above 1000C) is forced up through cracks in the ground under great pressure. The pressure of hot steam is driven through pipe shafts, which then rotate the turbines. The turbines drive a generator, which creates the electrical charge. Hot steam is then cooled in a cold heat exchanger and the cold water is then pumped back into the ground, which then kicks off this cycle again.

Flash System Geothermal Power

Flash steam geothermal power plants rely on highly pressurised, superheated water instead of steam. The highly pressurised liquid is pushed through a series of pressure tanks. In turn, these holding tanks reduce the pressure of the liquid, allowing it to turn into steam. This process is repeated several times in different depressurised chambers with the steam then collected and ’flashed’ through to drive a turbine generator system to create electricity. As with the dry steam geothermal power system, the excess hot liquid is cooled and / or condensed and then pumped back into the ground so the liquid is replenished.

Binary Cycle Geothermal Power

Binary cycle geothermal power plants use lower temperatures to produce energy and use technology much like that used in OTEC, using the heat gradient to turn a working fluid, such as ammonium and/ or propane into steam to drive the electro generating system. This type of system can be implemented using lower ground temperature as a working fluid has a lower boiling point than water. Once the working fluid passes through the turbine shafts, it is condensed back into the liquid and reused over and over again.

Geothermal Power for Heating

We have talked a lot about electricity generation in the above section, however geothermal power can also be used for heating solutions. Like ground source heat pump systems used in the home, a geothermal power system can be implemented as a district heating solution. In the UK, this would be optimal in areas that are not covered by the current gas grid. Using residual heat from the dry steam or flash system geothermal processes, local homes and businesses could be supplied with heat all year round.

The slight issue in the UK, is that the infrastructure requires investment by the generation companies to make this a feasible proposition, it would however allow them to supply both heat and power (CHP cogeneration) to consumers. These types of solutions are currently more common in Scandinavian countries, and therefore the UK is playing catch up as far as geothermal power goes.

Where is Geothermal Power now?

In the UK, there is enthusiasm about the prospects of geothermal power, but thus far DECC has not provided the additional support that the technology really needs to make a suitable foothold. Currently geothermal power qualifies for two Renewable Obligation Certificates (ROCs) per MWh of electricity generated, but the investment community believe this support should be closer to four ROCs, so that investment doesn’t go to other parts of Europe like Germany.

Geothermal power electricity is currently produced in 24 countries across the planet with the total combined installed capacity being approximately 10,715MW. The largest capacity is in the USA (3.1GW installed in 2010), however by 2015 this is expected to increase by 75%, taking installed capacity to 18.5GW. Geothermal power as a heating solution is much more widespread, and currently used in over 70 countries worldwide.

The largest geothermal power company in the world at present is the Calpine Corporation which taps geothermal electricity primarily in the geysers in California. The 19 geothermal power plants it has in this location provide 25% of the green energy to California. In the UK, the Eden Project in Cornwall was granted permission to build a hot dry rock geothermal power station in December 2010, which will power Eden and supply enough energy for 5000 additional houses in the surrounding area.

There is an estimated 300m miles³ of water present on the earth. Of this, 96% is found in oceans, another 2% of water is tied up in glaciers and ice caps, and 1% sits in the atmosphere. This leaves only 1% of the water present on earth available for human and animal consumption, and even a large percentage of this is inaccessible. Demand is growing as a direct result of an increasing population and increased economic development, and has tripled over the last 50 years alone. To cater for this increasing demand desalination may be the only answer in the years to come.

What is desalination?

Desalination describes a range of processes which are used to reduce the amount of dissolved solids in water. It is most often used to describe the process of converting salt water (e.g. sea water) to fresh water that can then be used for drinking (potable water) and irrigation. Used for sometime on ships and submarines, this process now has new focus to provide fresh water for human use in areas where it is currently limited.

Large scale desalinisation plants tend to use large amounts of energy to produce the water as well as costly infrastructure, therefore when compared to drawing fresh water from rivers and groundwater, desalinated water is very expensive. However, you tend to find desalination plants associated with electricity generating plants, from which electricity and waste heat are readily available making them more cost effective. This combined use of resources is explored more in CHP cogeneration.

The quantity of dissolved solids in a liquid is known as total dissolved solids (TDS) and is measured in mg/l. Typically sea water has a TDS value of over 30,000mg/l, while drinking water sits within the range of 0-1000mg/l.

What are some of the desalination techniques?

There are many techniques involved in desalination, each with their own advantages and disadvantages, but broadly speaking most techniques sit within two camps.

1. Thermal distillation – evaporating the pure water from salt water using heat. The processes that fall in this category are as follows and explored below in more detail: a) multistage flash distillation, b) multiple effect distillation, c) vapour compression and d) solar humidification-dehumidification

2. The use of semi permeable membranes – processes explored that fall in this category are reverse osmosis and electro-dialysis reversal.

Desalination using Multistage Flash Distillation

Approximately 85% of desalination worldwide is completed by multi-stage flash distillation (MSF) – this is a type of thermal desalination. This process involves distilling sea water by flashing a portion of the water into steam in multiple evaporating chambers (known as stages) of what are essentially counter current heat exchanges. The process is as follows.

• The sea water enters the system, and via heat exchanges it is heated as the water travels through the top of each of the main evaporating chambers (stages).
• Eventually, once the water has travelled through all of the stages, it enters a brine heater which heats it up further to the optimum temperature for the process to take place (heating it first in the evaporating chambers limits the energy required by the brine heater).
• This water then enters the first stage, where lower ambient pressure causes the seawater to instantaneously boil, releasing heat and water vapour until reaching equilibrium with the conditions in the chamber.
• This water then enters the next stages one after another, where successively lower ambient pressure in each of these causes the seawater to again instantaneously boil as soon as it enters without reheating each time.
• The vapour from each of the stages is condensed against the heat exchanger tubes (with the heat being used in step 1), creating the freshwater which is pumped away and then the remaining brine enters the next stage and this process gets repeated.
• The sea water increases in salt concentration from stage to stage as distilled water leaves the solution. This can simply be pumped back into the original source.

Desalination using reverse osmosis

Another popular method for desalination is reverse osmosis, which involves the use of a semi-permeable membrane. Osmosis is a phenomenon used by plants to absorb water and move it within the plant itself.

Osmosis involves the movement of a solvent across a semi-permeable membrane into a solution of higher solute concentration. It results in equilibrium being met, where the two solutions on each side of the membrane have equal solutes. The difference in the concentrations is known as osmotic pressure, and the higher this is, the quicker the solvent will move. This process can be reversed if the pressure applied to solution with the greater solute concentration is higher than the osmotic pressure.

In reverse osmosis, pressure is applied to the feedwater, forcing the water molecules through a semi-permeable membrane. The water that has passed through the membrane leaves the unit as product water, and most of the dissolved impurities remain behind and are discharged in a waste stream.

There are however major problems associated with this, firstly the process is very slow, and the membranes are very delicate so can tear easily. In addition the water needs to be filtered first so that large particles don’t damage the membrane, and additives may need to be added to prevent build up of salts on the membrane.

These two methods account for most of desalination that takes place across the world. There are other methods which are described very briefly below.

Desalination using Multiple Effect Distillation

In multiple-effect distillation, evaporators are situated in series, so the energy in the steam from one series is used to evaporate water in the next one. The saline water is usually applied to evaporator tubes in the form of a thin film so that it will evaporate easily.

Desalination using Vapour Compression

The technique of vapour compression uses a mechanical energy source, such as an engine or electric motor, to power a compression turbine. The feedwater is evaporated and the turbine compresses this raising the temperature of the exhaust vapour. The vapour is then passed over a heat exchanging condenser, where it returns to the liquid state as product water. The heat removed during condensation is returned to the raw water to assist in the production of more vapour.

Desalination using Electrodialysis Reversal (EDR)

In EDR, an electrical current is used to separate out salt and impurities in the intake water. Most of the impurities in water are present in an ionized (electrically charged) state and will conduct electric current. When direct current is applied, the impurities migrate towards the positive and negative electrodes; these ions are pulled through a semi permeable membrane resulting in two streams, a desalinated stream (which is tapped off as potable water) and a salt water stream. These membranes can become blocked by ions and other impurities; however by reversing the current the solutes that attach themselves to the membrane dissolve back into the water, so this combats efficiency reductions. However, this process is only possible for brackish water; it does not work effectively on purifying seawater. Click here for an EDR example.

Desalination using Solar Humidification-Dehumidification Method

This process mimics the natural water cycle, however takes place over a much shorter period. The simplest example is using a solar still, where the sun enters a glass covered box heating water held in the bottom of the box (which is black to absorb more heat). This then causes the water to evaporate, and this then condenses on the glass cover where it gets collected. More sophisticated designs separate the solar heat gain section from the evaporation-condensation chamber. An optimised design comprises separated evaporation and condensation sections.

Thermal distillation vs semi permeable membranes for desalination

• The performance of distillation technologies is relatively unaffected by feedwater salinity
• Distillation technologies have a higher total energy consumption than membranes
• For low salinity feedwater, membrane technologies have a higher rate of recovery
• Reverse Osmosis requires pre-treatment before the desalination process, in which all solid and suspended particles are removed, its pH value is adjusted and appropriate chemical inhibitors are added to ensure scale deposits
• Distillation suffers from higher rates of corrosion and scale formation due to the higher temperatures involved.

Desalination industry development

The scarcity of fresh water is already critical in many arid regions of the world and this will increase in importance in the future. It is also highly likely that the availability of fresh water (along with fossil fuels) will be a determining factor in world stability in the future.

According to the International Desalination Association in 2009 there were over 14,000 desalination plants, producing 60million m³/day of potable water. Approximately 70% of desalinated water is currently produced and used in the Middle East, the largest plant currently in operation is the Jebel Ali Desalination Plant producing 60million m³/year, and this is a MSF plant.

Closer to home, during 2010, Thames Water opened a £250m desalination plant in Beckton, East London. The plant is the first of its kind to be built in the UK, and will be able to supply 150m litres of potable water each day. The Beckton plant is run using 100% renewable energy and uses Reverse Osmosis to produce the drinking water. It is due only to be used in times of drought and to maintain supplies in the event of an incident at another water treatment facility, but will be able to service 400,000 homes in London and the surrounding areas.

We have to wait and see whether desalination will prove to be profitable for investment in the UK, given that recent water shortages have subsided.

How does a wind turbine work?

When air hits the wind turbine, the blades spin, converting the wind’s kinetic energy into mechanical energy. This rotary motion then travels down the shaft and drives a generator where the electricity is produced. Typically most wind turbines are mounted in the horizontal plane (like the propeller of a plane), and therefore it is key the blades are facing directly into the wind.

The yaw angle is the difference in angle between the wind direction and the direction in which the rotors are facing. The aim is to minimise the yaw angle as much as possible, so most residential wind turbines tend to have tails which orientate the turbine to best capture the wind. Wind turbines should therefore be able to rotate 360⁰ on yaw bearings.

The turbine

There are 2 main styles of urban wind turbines:

Horizontal Axis Wind Turbines (HAWT)

This is a propeller type rotor mounted on the horizontal axis. As mentioned previously, the blades need to be aligned with the wind and this is done by either a simple tail, or an active yaw. These are more efficient at producing electricity than VAWTs however they are impacted more by changes in wind direction.

Vertical Axis Wind Turbines (VAWT)

These are aligned in the vertical axis (like the rotor blades on a helicopter). These are only really deployed within urban areas, where the flow of air is more uneven. Due to their alignment, wind direction has little impact on this type of turbine; however it is apparent that these are less efficient than their HAWT cousins.

In addition to HAWTs and VAWTs there are hybrid turbines that are cylindrical (imagine a gyroscope) – such as the energy ball.

At TheGreenAge, we suggest sticking with the HAWTs as they are the more proven technology, and are offered by more suppliers, so you will be able to get better value for money.

Most turbines tends to have two or three blades, two bladed turbines are cheaper but suffer from blade chatter which puts stress on the system, which can lead to increased maintenance further down the line. If you can afford to get a three bladed turbine, we suggest doing so, as these don’t suffer from this problem at all.

The tower

Three types of tower exist: tilt-up, fixed guyed and free standing. The purpose of these towers is to position the turbines in the best possible position to take advantage of the wind.

Tilt-up towers are held in position by four guy ropes one of which can be released, allowing you to lower the tower, so you can work on the turbine.

Fixed guyed towers are similar to tilt-up towers, except they are permanently fixed in place so you need to climb the tower to do any maintenance.

Free standing towers have no guy ropes. As such they require a very solid foundation. Therefore these are certainly the most expensive, but may well be the most aesthetically pleasing.

The inverter

Most wind turbines produce AC current, so this should be able to be directly fed into your home and the grid, however the voltage and frequency of the power produced is very erratic, so an inverter is used to convert the erratic AC to DC, then back to a smoother AC which can be synchronised with the grid, or for use directly into your home. Battery-based wind turbines normally operate at 12 or 48 Volts, and therefore the inverter must also act to convert this relatively low voltage to high voltage (UK mains is 240 volts). Battery-less systems may produce electricity with a voltage significantly higher (100 volts or more). Therefore in this situation, the inverter needs to be able to handle this higher voltage.

Batteries

In most wind turbine systems, the electricity does not power any appliances directly. Instead the electricity produced is stored in deep-cycle lead acid batteries which 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 hundreds 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 cell set-up. The reason is that if any more than 20% is drawn more than a few dozen times, it will get damaged and no longer take charge.

Wind turbine batteries tend to operate at 12v, and can be arranged in banks (multiple batteries), increasing the storage potential of your wind system 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 the voltage stays the same.

Charge controllers

Charge controllers are used in wind turbine systems to prevent the batteries from being overcharged. If you decide to implement a grid tie system, a 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 battery setup, a charge controller is necessary as it prevents damage to the battery by monitoring the flow of electricity in and out. If your system overcharges the battery it will damage it. The same is also true if you completely discharge all the charge held within the battery.

Most charge controllers associated with wind turbines have dump load capability associated with them. This allows any additional charge to be diverted from the batteries when they are full, potentially to a hot water heating system (so the electricity is not completely wasted). Obviously if you are connected to the grid, this electricity would instead be sold there, providing you with an additional income stream.

Most charge controllers are also equipped with maximum power point (MPPT) charging. The principle of MPPT is to extract the maximum available power from the wind turbine by making them operate at the most efficient voltage (known as the maximum power point voltage). The algorithm included in the MPPT charge controller compares the output from the wind turbine with the battery voltage and then fixes it at the best charging voltage, to get the maximum charge into the battery.

Safety equipment   

Disconnects are simply switches that allow you to isolate parts of the system so you can troubleshoot or repair faulty parts without the risk of being electrocuted. In addition many wind turbine systems are grounded, so that if there is surge in current anywhere in the system it is safely dissipated rather than damaging the system or more importantly you!

Installing a wind turbine

Are you thinking about installing a wind turbine 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 wind turbine at home, just fill in the form below and we will be in touch shortly!