Hydro FAQ’s

How do micro hydro-electric projects work?
Standard hydro-electric projects take water from high ground and run it down hill and into a water turbine. The turbine is connected to an electricity generator which generates electricity from the motion of coiled wire through a magnetic field.

In terms of physics, the potential energy associated with water being at the top of a hill (mgh), is converted into kinetic energy associated with it gaining speed as it runs down out of a pipe and through a turbine (1/2mv2). The kinetic energy associated with the spinning turbine is then converted into electrical energy. (m is the mass of water, usually considered as the mass available per second, g is the acceleration due to gravity, taken as 10m/s2 , h is the height difference or “head” between the intake works and the power house of the system.

What works are required to install a micro hydro-electric project?
There are four main elements to most micro-hydro installations. These are:

Intake works This is where the water is captured from a stream or river and diverted into the hydro system. Usually a concrete weir and screen are built into the stream bed to form the intake. The concrete can then be disguised with natural stone etc to improve its visual appearance. For low head projects it is often sensible to make use of existing weirs left over from old mill sites.
Head race or penstock This is the pipework or channels used to convey the water downhill from the intake to the power house. The pipes can be buried or run on the surface, depending on environmental issues and they need to be specified correctly in order to contain the pressure and to minimise energy losses due to friction between the pipe and the water.
Power house This is where the water enters the turbine and the potential energy of the water is extracted and converted into rotational energy in the turbine. Different types of turbine are suitable for different water flows and pressures so the designer will specify an appropriate type of turbine for the project.

The power house also contains the electrical generator, which converts the rotational energy from the turbine into electricity.

The electricity then passes through an inverter which ensures it leaves the facility at the correct voltage, frequency and phase to match the electricity in the grid.

After the inverter there of course the generation meter, which measures how much electricity has been produced and is used to claim the Feed in tariff.

Grid connection It may be that some power lines are required to connect the hydro system to the local electricity distribution network. Depending on site location this may be anything from a few meters to a few kilometers

What type of sites are best?
As the source of the energy is derived from water at height, it follows that the best sites have lots of water and the opportunity for it to descend from as high a height as possible over as short a distance as possible. From a construction cost perspective, sites with lots of height (known as “head”) but less water are more cost effective to construct than sites with plenty of water but a low head.

As a minimum, it would be nice for sites to have around 10 metres of head and a stream catchment area of around 3 square kilometres.

Old mill sites typically have higher flows of water but lower heads. These can still be developed but sometimes prove to be more expensive than a high head, low volume site.

I think my site may be suitable, how can I check?
If you think you may have a suitable site then please give us a call. The first thing to do would be to procure a pre-feasibility study. This might be as little as quick walk around for free, and if it looks suitable you may need to pay around £1000 for a full pre-feasibility study.

How much does a micro-hydro project cost?
This obviously depends on the size of the project. Small projects utilising upland streams may cost £50,000 to £100,000 to install, although operating costs should be very low and the amount of electricity generated is usually considerably more than for competing technologies such as PV.

Larger projects, perhaps based larger upland streams or around old mill sites or weirs on larger rivers can cost more than £1m to develop.

How much energy can I generate from a micro-hydro project?
It’s worth observing that a 4kW micro-hydro project and a 4kW solar PV project actually generate totally different quantities electricity over a 1 year period. As an example, a 4kW solar PV project in Yorkshire could generate around 3,300kWh of electricity per year, whereas a 4kW micro-hydro project in the Pennines, Lake District or Yorkshire Dales could generate 15,000kWh over the same period.

Hence although the micro-hydro system might cost more than a PV system, it will generate around 5 times as much energy.

What return could I earn from a micro-hydro project?
Returns are very project specific, but most people aim to generate a financial return that exceeds 10%.

I think I have a good site, but I don’t have spare money for the capital investment?
Given the costs involved this is not uncommon. We may be able to help in a number of ways, depending on whether you want to take some entrepreneurial risk or whether you would prefer someone else to. One option would be to help you raise finance for the development. Such finance might include a bank loan and or an equity investment.

A second option would be for 350 Hydro to rent the site off you and pay you a percentage of the income generated from a successful micro-hydro development.

How efficient are micro-hydro projects?
Every project is different, but as a rule of thumb, around 50% of the potential energy we calculate as being available in theory, is actually exported from the site as electricity.

In comparison, a typical coal fired electricity power station is around 30% efficient, a modern CCGT gas power station is up to 60% efficient and a solar PV panel is around 14% efficient. It’s worth remembering however that 14% of a carbon neutral and free resource could be much better than 60% of a fossil fuel that has to be purchased!

What are the environmental issues associated with micro-hydro power?
When water is extracted from a stream to run a micro-hydro project it could potentially have an impact on the stream eco-system. The environment Agency therefore imposes limits on the percentage of water from any given stream that can be borrowed for a hydro project. Hence it is always necessary to leave some water behind.

There may also be potential impacts occurring during the construction phase, particularly from the works in the stream to construct an extraction weir and possibly to lay pipes between the extraction point and the turbine house.

Most planning authorities will therefore ask for an environmental impact assessment to be undertaken prior to granting of planning permission.
For upland stream projects aquatic and river bank eco-systems are often a key issue. For lowland mill site projects the needs of over river users such as fishermen and boaters need to be considered.

The environmental upside is of course hydro’s contribution to the 350 objective!

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