Hydro-Electricity
Good - but there are limited suitable locations
There are two fundamentally different types of Hydro electric plants, called “Run of the river” and “pumped storage"
Run of the River
If a country has high, steep mountains, and reliable rainfall, then it is likely it will also have high energy rivers which are suitable for damming and a hydro scheme. Diverting water from waterfalls, e.g. Niagara, can also be helpful. Having upstream natural lakes, also makes the generation less dependent on the seasonal rain pattern.
Norway has a lot of suitable sites, so they make good use of hydro-electric power. Sadly, some countries, e.g. England, do not have this combination of geological features. Globally, it is not a sufficient solution to our energy problem.
Energy Storage
Pumped Hydro-Electric systems – for Energy Storage
Pumped Hydro-electric power can be used for energy storage. What is needed is a relatively large lake at a higher altitude, and another one not far from it, but further down the mountain. Water can be pumped up to the higher lake when there is spare electrical capacity available from the grid, and when electricity is needed, the water can be allowed to run down to the lower lake, turning turbines as it passes, to create electricity.
If countries have sufficient appropriate geographical sites where these could be built, they could be a useful addition to the energy storage options.
France has many such sites and hopes to build more.
Grid Stability
Pumped Hydro-Electric systems – for Grid Stability
The turn-around time for a pumped HEP system, to start producing electricity when needed, is typically 60-90 seconds – much faster than the time to start most power plants. Dinorwig in Wales takes only 15 seconds to come fully on-stream, and thus it is kept as an emergency reserve power station and is switched on very rapidly if another plant in the UK fails and disconnects from the grid.
Dinorwig has an end-to-end efficiency of 74% meaning that it returns 74% of the power it consumes.
In the UK we have a three pumped hydro-electric schemes, one in Scotland, two in Wales, but they are relatively small and reserved for back-up power if there is an unexpected, or even a predictable, surge in demand. One of them was historically held in reserve should we ever need to restart the electricity grid after a complete nation-wide black-out, though with the better inter-connectivity of the UK grid with Europe, and the presence of some battery storage, nation-wide blackouts are becoming less likely. In the UK there are insufficient sites with the appropriate geography to create enough back-up energy storage for the renewables we have, or would like to install. It also takes a long time to build these schemes and there are inevitably ecological effects from building and running them.
References / external websites:
https://theswitch.co.uk/energy/producers/dinorwig-power-station
European Energy Research Alliance analysis of Pumped Hydro Energy Storage
https://eera-es.eu/wp-content/uploads/2016/03/EERA_Factsheet_Pumped-Hydro-Energy-Storage.pdf