How does hydroelectricity work?

For over a century, the UK has benefited from hydroelectric power or generating electricity from water. In a report generated by the World Atlas of Hydropower and Dams, it found that in the UK we generate over 5885 GWh/year using purely hydro, with an additional 2800 MW capacity of existing pumped storage. We’ll talk more about pumped storage later, but first, let’s talk about the basics of using the power of water to create electricity.

How does hydroelectric generation work?

Put very simply, hydroelectric power is generated using flowing water to spin a turbine which turns a shaft that’s connected to an electric generator. More often than not, hydroelectric dams are used to direct the water downward through the turbine in a way which can be controlled to maximise energy production.

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Run of the river hydro

Unfortunately, this can’t be placed on every river, as hydroelectric dams require large volumes of water with a big drop in elevation. The bigger the elevation and the more water that flows through the turbine, the greater the capacity for electricity generation.

There are four main types of hydro:       

  1. Dams - the most common type of hydroelectric power, using dams to channel the water and drive the turbines
  2. Pumped storage - this method requires the moving of water between reservoirs at different elevations and provides 'on-demand' electricity. 
  3. Run of the river - typically used for smaller generation, where water flowing downstream is used as it passes. This method relies on a constant supply of water to be effective. 
  4. Tidal power - using the predictable movement of tides, large amounts of energy can be created twice a day. Reservoirs here can also be used to generate power during high demand periods. 

How much power can water create? 

Hafod y llan hydro

This completely depends on the size of the generator and the amount of potential power available at the site. A hydroelectric generator can be absolutely huge – like Hoover Dam’s 2,000MW capacity – or as small as 50kW, but the larger the generator the more cost-effective it is to install and run.  In 2011, the UK generated around 1.5% of its electricity from hydroelectric schemes and this number is continuing to rise every year.

What are the advantages of hydroelectricity?

There are lots of benefits of using hydro power to create electricity – the fact that it’s renewable is just one of those!

Hydro can be a very predictable and consistent form of electricity which works well with other forms of renewable energy to match demand. They’re actually one of the most flexible forms of generation, being able to hit maximum capacity in under 2 minutes and being able to be stopped just as quickly.

This means that hydro is perfect for helping meet any peak demands and balance generation throughout the day. Using hydro in combination with other more weather dependent renewable generation such as wind and solar is ideal as it can be turned on very quickly and is far more responsive than gas, coal or nuclear power stations.

Hafod y porth hydroelectricity turbine

Hydroelectric generators also have long lives when compared to other forms of electricity generation. A hydroelectric generator can still be in service 50 to 100 years of working and requires very little labour with low maintenance costs which makes a lot of economic sense.

Does it affect the environment? 

Yes and no. The impact that a hydroelectric project will have on the environment will vary depending on scale and technology being used – for example you can expect a much smaller impact from a small scale run-of-river hydro system than one which requires flooding of land to create a new reservoir which would have a significant impact on the ecosystem both up and downstream.

At Good Energy, we have a Development Charter in place to ensure that the best principles are followed when we are looking at developing new renewable assets such as hydro-generation. The construction of a dam or tidal generator does require some upset of the natural terrain, however, these are rigorously monitored and planned to cause the least amount of damage as possible.

hafod y porth hydro turbine

Once the work has been completed, these locations provide an opportunity for a biodiverse ecosystem to thrive. Additionally, once the water has gone through the turbines to create electricity it carries on their natural water cycle, uncontaminated and unaffected by the process of creating electricity.

What are the disadvantages of hydroelectricity?

There are some downsides to hydro – the most obvious one being that you need to have very specific conditions and elements available in order to generate electricity using this type of system.

Additionally, the initial cost to develop and build a project can be very high. Large-scale hydro electricity projects require significant investment in order for them to be built and even then there can be other permissions that are required which can slow can and even halt development.

Like any form of generation, you’re also dependent on the fuel for production. While certain methods like tidal power are extremely predictable, river run hydro power depends on a constant flow of water which relies on rainfall.

How much does hydroelectric power cost?

The cost of hydroelectric power is largely dependent on the type of generation being used, as the bulk of the cost is in building the system. Unlike other systems, hydro is largely dependent on location which means making a generalisation on cost is extremely difficult as will inevitably vary case by case. That said if you are able to retrofit existing projects with new technology it would typically be much cheaper than starting from scratch.

Tidal hydro power

Once development has been done, operational costs are relatively low compared to other types of electricity generation. Hydroelectricity is largely considered a reliable system which can run for very long periods of time – as such the biggest maintenance costs are clearing debris and replacing damaged intake screens and routine maintenance.

Can I use hydro power to generate my own electricity?

If the means, location and finance are in place and you have access and permission to create your own hydro generation then absolutely, yes you can do it. You may still need to have several assessments on the impact of the system before you can start building the system though. 

Once your site is up and running you can also sell energy back to the grid using our Feed in Tariff or Power Purchase Agreement depending on the size of your generation. 

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