Pumped Water Storage - the emerging cost efficient method of energy storage

There is a huge demand for energy storage today. Solar energy can only be collected in daytime and therefore part of the the energy generated in daytime has to be stored for night use. There are several effective ways to store energy today, and different storage models have different advantages and disadvantages.

 

Batteries are the most prevalent today, but lithium has serious disadvantages for the environment.

Hydrogen is very clean, and only needs water, but is till more expensive per stored kilowatt than kinetic storage.

Kinetic storage is also clean and can be used with both material weight, or with water. The use of material weight is still under development, so pumped water is today the most cost effective storage of energy.

 

Pumped Water Storage is quite simple. The basic construction consists of an upper and a lower dam. From the upper dam the water goes through a pipeline connected to a  turbine generator, just like any normal hydroelectric power plant. The difference is that the turbine in a pumped storage facility can be reversed into a pump in daytime for pumping water back up to the upper dam - for night use.

There are about 530,000 potentially feasible pumped hydro energy storage sites worldwide, with a total storage potential of about 22 million GWh.

These astonishing numbers come from a report recently released by Professor Andrew Blakers and other researchers with Australian National University’s RE100 Group.

Pumped hydro already constitutes 97% of electricity storage worldwide because of its low cost, ANU says, and the proportion of wind and solar photovoltaics in the electrical grid is extending considerably. This means “additional long-distance high voltage transmission, demand management and local storage is required for stability.”

The massive storage potential of about 22 million GWh “is about one hundred times greater than required to support a 100% global renewable electricity system,” ANU says. An approximate guide to storage requirements for 100% renewable electricity, based on analysis for Australia, is 1 GW of power per million people with 20 hours of storage, which amounts to 20 GWh per million people.

The identified sites are outside national parks and are mostly closed-loop (not river-based). Each identified site comprises an upper and lower reservoir pair plus a hypothetical tunnel route between the reservoirs, and includes data such as latitude, longitude, altitude, head, slope, water volume, water area, rock volume, dam wall length, water/rock ratio, energy storage potential and approximate relative cost. Brownfield sites (existing reservoirs, old mining sites) will be included in a future analysis.

Most of the indicated sites are for quite large storage facilities, but there are also smaller versions of Pumped Water Storage (PWS):

1) Small riverside PWS systems:

Small PWS are quite common alongside major rivers, but are limited in capacity, firstly by the head available and land available for the upper reservoir.

2) Off-river pumped water storage

A concept, developed by the Australian national university and based on small scale PWS is pairs of reservoirs, typically 10 ha each, are separated by an altitude difference of between 300 and 700 m, in hilly terrain or ex-mines and away from rivers, and joined by a pipe with a pump/turbine. Water circulates between the upper and lower reservoirs in a closed loop to store and generate power.

Very little water is apparently required relative to conventional fossil fuel power stations. Estimated stations could be in size from 50 to 500 W and with a storage time of 4 to 20 h.
Problems with initial filling and compensation for evaporation and leakage. Such a network of small scale PWS is claimed to be able to provide sufficient storage capacity to allow operation from 100% renewable energy sources.

These smaller versions of PWS are a quite cheap, reliable and alternative for storage in hilly regions. Some energy developers have picked up on these small PWS. There are several combinaqtions of storage possible today, and can be modelled relating to the specific environment. One example of a company working with this  is energy company Power One, which is specialised in electrification of previously non electrified areas in Africa. They have now developed a combined storage system of both PWS and hydrogen to be integrated in its projects in East Africa. Through this system Powerr One can double its storage cost efficiency, at the same time as the company can provide both night time electricity and hydrogen for transports to its customers. In other areas the combination can be different, depending on natural preconditions.

In the comprehensive global atlas presented by Australian National University’s RE100 Group, pumped hydro energy storage sites provided by users can browse to any part of the world and zoom in to obtain detailed synthetic images. Users can explore thousands of sites in specific locales, sorted by size and capital cost. Clicking on a reservoir or tunnel route produces pop-ups containing detailed information.

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