What makes a good hydropower site?

Written by: Phil Davis, Managing Director at Renewables First and specialist in hydropower, wind power and solar power system design.
Reviewed by the Renewables First engineering team for technical accuracy.

A good hydropower site is a valuable asset.

You could write a book on what makes a good hydro site, but in summary you need:
• Good head
• Good flow
• Simple site layout with main parts close together
• Good grid connection
• Good site access
• Single ownership of the site, or cooperative neighbours
• Not too many environmental sensitivities

Good Head

Head is probably the most important factor in having a good hydro site, provided the other parameters are satisfactory. The power, and therefore energy output from a site is proportional to head. The cost of a hydro system is to a large degree determined by the physical size of the civil engineering structures and the turbine. As the head decreases there is less water pressure to push the flow through the turbine, so the turbine and associated concrete structures have to get physically-larger to accommodate the slower-moving water. The opposite is true as the head increases; the system gets physically smaller and costs less while at the same time the power and energy production increase, making the return on investment higher.

This doesn’t mean that low-head sites are bad – at the end of the day the head you have is what you have – but it does mean that all things being equal, higher-head sites tend to be better than lower-head sites. It also means that for any site it is always worth doing whatever you can to increase the head and reduce head losses, which can all be done by good hydropower design.

Good Flow

You can’t do anything without sufficient flow, so this is also important. Generally speaking, low- head sites tend to have higher flow rates because they are in the lower-end of a river’s catchment in lowland areas, and therefore have a larger catchment upstream with lots of tributaries. Higher- head sites are usually higher in the catchment where the land is steeper (hence the higher heads possible), but also the catchment is smaller, so flow rates tend to be less.
There is no ‘right’ flow rate, it is just a matter of calculating how much energy you can generate and deciding whether your project will be economically viable.

Simple site layout with main parts close together

This is mainly in relation to construction and installation works. The perfect site from a construction perspective is a green field, with no constraints. As complications arise such as historic structures, public rights of way, historic machinery and natural features (like cliffs, bed-rock, waterfalls, springs etc.) the project gets more complicated and therefore expensive. Very few projects are ‘perfect greenfield sites’, so don’t worry if you have some of the constraints listed above, but be aware that more constraints means more construction cost.

It is also beneficial if the intake, turbine location and discharge are all reasonably close together. On lower-head sites this ensures that the civil engineering (i.e. concrete) structures are relatively small, hence lower cost. On higher-head systems it means the penstock-pipe is reasonably short, which is important because this is often the most expensive part of a high-head hydropower system.

Good grid connection

You may have a cracking hydropower site, but it is no good if you can’t sell the power because there is no grid connection! You not only need a physical grid connection, but it also needs to be ‘strong’ enough to take all of the power you will generate. Generally, you will need a three-phase 11,000 volt supply either on-site or nearby. Ideally you would already have a suitable on-site transformer or substation so you can connect on the low-voltage (LV) side.

Very small systems (<25 kW) may be able to connect to a single-phase supply, and in some cases you can connect up to around 80 kW using a special ‘split-phase’ transformer.

It isn’t possible to tell how ‘strong’ a three-phase 11 kV supply is without formally asking the Distribution Network Operator (DNO). Renewables First can make grid connections applications on your behalf and obtain quotes for any grid upgrade works required. See here for more details.

Good site access

For the construction stage, and to a lesser degree for on-going maintenance, the site will need access for construction equipment, delivery vehicles, and for large systems, cranes. Hence narrow lanes, tight corners, soft ground and obstructions caused by buildings can all cause problems which in the worst-case would prevent the project progressing, and in the best case may just mean additional cost. These issues would all be considered when the hydro feasibility study was carried out.

Single ownership of the site, or cooperative neighbours

In a perfect world the entire site would be owned by a single landowner. This not only makes the environmental consenting easier, but also means that commercial agreements between landowners are not required, which if they are usually means sharing a percentage the revenue. It is surprising how often such commercial agreements cannot be concluded because of irrational greed from one party, so it is well-worth discussing the project and how all stakeholders would be compensated at an early stage and getting the appropriate legal agreements signed before proceeding with the expensive consenting and design stages.

Not too many environmental sensitivities

As discussed in more detail on our website’s hydro consenting pages, the process of getting environmental consents from the Environment Agency (EA) in England or Natural Resources Wales (NRW) in Wales is bureaucratic and slow. It is significantly better under SEPA in Scotland.

In all regions the more ecologically-sensitive a site is, the longer and more expensive the consenting process will be. In general terms hydropower systems can be safely incorporated into all but the most sensitive environments and will always be designed to have no negative impact, and will often provide a net improvement particularly for fish passage.

So environmental sensitivities (like migratory fish, fish spawning, protected species etc.) are not show-stoppers, but do slow the consenting process down and make it more expensive.

For answers to all of your hydropower questions please visit our Hydro Learning Centre.

If you are interested more generally in renewable energy generation, we provide whole-project capability in hydropower, wind, solar PV and heat pumps. Please visit our Net-zero landing page for more information.

About the Author
Phil has worked in the renewables sector since 2001 and founded Hydro Generation, which became Renewables First in 2009.

A qualified mechanical engineer (BEng, MSc Renewable Energy Systems), Phil is a recognised expert in hydropower, wind and solar PV across all project stages.

View all posts by Phil