Micro Hydroelectric Power


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.

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.

    Sloy Hydroelectric Plant, Scotland

Background to the Sloy Hydroelectric Power Plant

In May 1945 construction began on the Sloy Hydroelectric Power Station on the banks of Loch Lomond in Scotland. The power station was completed 5 years later and was opened on 18th October 1950 by the late Queen Mother. Even today it is still the largest conventional hydroelectric power plant in the UK. The Loch Sloy Dam, built as part of the project, is 56m high and 357m long and raised the surface level of the loch by approximately 47m. The resulting Sloy Reservoir has a 17km2 direct catchment area, although various pipes and intakes have provided a further 63km2 of indirect catchment area. The total volume of water held in the reservoir by the dam is approaching 36million m2, and the potential energy contained within this mass of water is equivalent to 14million kWh of useful electrical energy. A 3km long tunnel takes water from Loch Sloy to a valve house positioned approximately 197m above the tank. From the valve house, four 2m steel pipes carry the water down into the powerhouse that is situated on the west coast of Loch Lomond.

Extending the Sloy Hydroelectric Power Plant

When the plant was initially built, a vertical Francis turbines was installed in each pump and these were rated at 32MW giving the plant a total output capacity of 128MW, however in the late 1990s a £113m refurbishment resulted in three of the turbines being replaced with larger 40MW turbines. As a result of this refurbishment, the total output of the plant now stands at 152MW. In Sept 2010, Scottish & Southern Energy was given planning permission to extend the Sloy Hydroelectric Power Plant by installing a pumping station, which will give the plant pumped storage capability. The proposed pumping station will house two 30MW pumps each capable of pumping 10m3 / second of water. These would be adjoined to two of the existing pipes, allowing water to be pumped back from the powerhouse on Loch Lomond all the way to Loch Sloy. With the 2 pumps running for 6 hours at a time, 432,000 m3 of water would be pumped out of Loch Lomond, resulting in only a 6mm fluctuation in the water level! The purpose of this pumped storage extension will be to take advantage of excess energy in the grid during evenings and times of low demand, to help the grid in times of especially high demand. The cost of this proposed work is £40m and it would provide an extra 200GWh to the grid. Work on this installation is due start in late 2012 and is due for completion within 27 months.

Environmental Impact of Sloy Hydroelectric Power Plant

One final point to highlight is the risk to wildlife by installing this new pumped storage facility within the Sloy Hydroelectric plant. Ruffe which were introduced by Anglers into Loch Lomond are actually a pest species, however the new facility creates the possibility of these fish being pumped into Loch Sloy, which would threaten the established population of Powan fish in the higher Loch as the Ruffe feed on Powan eggs.

    Dinorwig Hydroelectric Plant, Wales

Background to the Dinorwig Hydroelectric Power Plant

The Dinorwig hydroelectric power station is an example of a pumped storage power station, where water is pumped into a reservoir above the turbines (called Marchlyn Mawr) when electricity is cheap and demand is low, the gates can then be opened providing a high supply of energy (although for a relatively brief period of time) to meet demand, as the water rushes through the turbines to the reservoir at the bottom of the power station (called Llyn Peris).

The plant construction started in 1974 at a cost of £425m taking a further 10 years to complete, and is still the largest pumped storage power station in Europe. In total, 16km of underground tunnels deep within Elidir Mountain where excavated, accounting for some 12 million tonnes of rock. To support the tunnels, one million tonnes of concrete, 200,000 tonnes of cement and 4,500 tonnes of steel were required.

The six fully reversible turbines sit within the mountain in what is actually the largest man made cavern in Europe. The turbines are reversible, allowing water to be pumped back up to the top reservoir when demand for electricity is low (in the middle of the night for example), while also producing an enormous amount of electricity if the water is allowed to follow the natural gravitational path downwards through them.

Why Was Dinorwig Chosen for Hydroelectric Power

When the water is stored in the top lake the energy that is being stored is known as gravitational potential energy, and the greater the vertical distance between the two lakes, the higher the potential energy stored. This is key to why Dinorwig was chosen, as the vertical drop between the two reservoirs is naturally very large, therefore little additional work had to be undertaken to increase the natural gravitational energy potential.

As one might expect pumping the water back up into Marchlyn Mawr (the top reservoir) is significantly more energy intensive than the energy it provides when working as a power station, in fact it uses almost 33% more energy to get the water back up than it produces. However where this hydroelectric power plant is unique is the ability to react quickly to meet peak in demand and instantly provide the power required (unlike Nuclear and Coal power plants). It also takes seven hours to pump the water up to the Marchlyn Mawr reservoir, however will only generate power for five hours.

Why Is Pumped Storage so Important to the UK

This kind of plant is very important to our energy mix in the UK, as most electricity generating plants are very slow to react to changes in demand. For example nuclear power plants can take a few days to reach full power from a shut down state, while coal will take hours to fire up and get up to the temperatures required to drive the electrical and combustion processes. In 12 seconds the plant can go from shut down state to full operating capacity, allowing it to meet very sudden high demand, such as a TV soap advert break when people put their kettles on!

The plant however does suffer from one disadvantage, which is that if all the water is in the Llyn Peris reservoir at the bottom of the power plant, it can produce no power whatsoever. Therefore, governments need to ensure that the majority of peak demand can be met via the less reactive power stations such as nuclear.

Potentially, one might not even consider the Dinorwig as a renewable power station, but simply a means of storing electricity / energy produced by other power stations, however it still has a key role to play in our grid that we rely on every day, vastly increasing our flexibility of supply.

    Warren Buffett – The Man With A (solar PV) Plan!

    January 10, 2013

2013 started pretty well for the renewables industry with news that Warren Buffett is investing a further £1.5bn in what will become the largest solar PV development in the world.

Mr Buffett is widely regarded as the most successful investor of modern times. Although coming from a fairly privileged background, his shrewd investments resulted in him amassing billions of dollars. In 2012 he was voted the fourth richest man in the world with a net worth of around $46.4bn, according to Bloomberg.

Time and time again Mr Buffett has made the right investment decisions, despite an uncertain market, therefore if he feels that now is the time to expand his investment in renewables, one can take it as a very positive sign that they are going to play a major role in the future, not just because the ‘greenies’ are banging the drum, but because they are going to offer excellent returns.


 The latest investment sees Mr Buffett’s MidAmerican Energy Holdings investment company striking a deal with SunPower to acquire and build 2 solar PV projects in California. The two projects acquired by Mr Buffet have a combined capacity of 579MW, and will be completed in 2015. In December 2011, his investment company acquired another 550 MW solar PV plant from First Solar. Already MidAmerican Energy Holdings has invested more than $10bn in wind and solar energy, and we hope there is more to come!

According to a report completed by the Federal Energy Regulatory Commission’s Office of Energy Projects, for the first nine months of 2012, 43.8% of the new capacity added in the US was from renewable sources (e.g. wind, solar, biomass, geothermal and water power). Renewables accounted for 13% of total electrical generation during the first six months of 2012 in America.

In the UK, renewables supplied 11.7% of our energy requirement in Q3 2012, but this figure may have been significantly higher if there had been more rainfall during the year (hard to believe, but there were actually hosepipe bans in place in March 2012!). The installed capacity for 2012 was also up 46% on the previous year, due to large wind projects being completed and the conversion of the Tilbury Power Plant to run on biomass.

So despite all the doom and gloom around the economy, it appears investment in renewable energy is looking very healthy!

    1st August 2012, Changes To The Feed-in Tariff

    August 2, 2012

The Headline Cuts To The Feed-in Tariff

On the 1st August 2012, the solar PV Feed-in Tariff saw another round of cuts, with the subsidy dropping from 21p to 16p per kilowatt-hour. This latest fall in the subsidy comes hot on the heels of the previous cut in April this year, where the feed-in-tariff was reduced from 43.3p down to 21p.

Besides the cut to the subsidy, the other major announcement was that the feed-in-tariff payments will now only be guaranteed for 20 years as opposed to the 25 years offered previously, therefore reducing potential future returns.

The Detail

The exact details of all the tariffs are summarised below.

Solar Photovoltaic with less than 4kWp with an EPC band D or higher will drop to 16p/kWh, while band E or lower will drop to 7.1p/kWh.

Export tariff rates will increase to 4.5p/kWh across the board for all new installations erected on or beyond the 1st August 2012.

The Reasons Why & What It Means For You

The feed-in tariff was designed to drive uptake of solar PV systems by homeowners, which it certainly achieved, with over 80,000 homeowners opting to take advantage of the scheme.

Unlike the Renewable Heat Incentive, which is to be funded by HM Treasury, the money set aside for for feed-in-tariffs is paid for by consumers through additional charges in their electricity bills. The idea is if more people start installing solar PV, then more are eligible for feed-in-tariff payments and this adds more cost to the consumer, which may be seen as unfair. So in the interest of fairness in these tough economic times, the government has probably tried to make a balanced decision by cutting the current tariff on offer. On the one hand still committed to feed-in tariffs by keeping them, whilst at the same time trying to protect the ordinary consumer (by lowering the tariff) who perhaps haven’t taken advantage of this scheme as of yet.

The news is not all bad though, despite the feed-in-tariff being cut by over 20%, if you were to go and buy a 4kW solar PV system today, the price you can expect to pay is around £7,000 – £9,000, whereas the same system only 12 months ago could well have cost you in excess of £13,000.

The increased competition in the Solar industry, largely driven by the massive production facilities being built in China and improvements in technology has caused these price drops, and they are expected to continue to fall as time goes on.

The other good thing to come out of the latest feed-in tariff is that the export tariff has been increased to 4.5p / kWh across the board, to better reflect the value of a kWh of electricity bought from the homeowners.

So fear not, the feed-in-tariff has taken a bit of a hit, but installing a system in your home still has a 8-10 year payback period, and perhaps more importantly, it will offer some protection against the utility price rises that appear to have become a permanent fixture in our daily lives.

    Smart Export Guarantee

    Financial Incentives

What is the Smart Export Guarantee?

After the closure of the Feed in Tariff (FiT), the government introduced The Smart Export Guarantee (SEG) which launched in 2020. The scheme allows growth in electricity generation from green microgeneration technologies.

How does the Smart Export Guarantee work?

Licensed electricity suppliers can offer a tariff and make payment to small-scale low-carbon generators for electricity exported to the National Grid (considering certain criteria are met).

The following low-carbon, renewable technologies are eligible for the SEG:

If you decide install any of the above renewable generation for the home, you should be eligible for the SEG tariff, providing you meet certain criteria.

Savings on electricity bills

Every kWh of electricity that you create yourself and then use in your home means that you don’t need to buy that unit from the electricity company. Electricity is currently priced at about 15 pence/kWh when you buy it from any of the big six energy companies, so the more electricity you produce and use in your home, the more you save.

Smart Export Guarantee registration

In practice in the UK, the energy companies with over 150,000 customers (British Gas, EoN, SSE, Scottish Power, EDF and NPower, etc) are required by law to provide the SEG to homes and businesses. Other smaller electricity suppliers may not offer the SEG as it is not compulsory for them to do so. The full list of registered SEG licensed suppliers is available on the OFGEM website here.

Once you have the product installed through the MCS, you should receive a certificate confirming MCS compliance. Speak to your energy company  that is approved for the SEG – express your interest in receiving the SEG. Your supplier will confirm your eligibility, cross checking your details to the MCS database. On confirmation of the SEG your details will also be added to the OFGEM Central SEG Register.

You may also need to agree a process for meter reading and whether you want to opt out from export tariffs. An important point to note is that it is far more economical to use as much of the electricity you produce in the home as you can, rather than selling it back to the grid. Using a kWh of the electricity you produce in your home saves you buying it from the energy suppliers at 15p, while you can only sell it back to the grid for 4.77p.

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