Storing up the potential of renewable energy

Renewable energy continues to be one of the fastest growing sectors in the global electricity production industry, with wind and solar power exhibiting the greatest growth.

According to the Global Wind Energy Council, the world’s installed wind capacity is forecast to grow at an average rate of 21 per cent a year between 2009 and 2014, representing the average annual addition of close to 5 GW.

For solar power the growth is even more impressive. In the 30 years between 1979 and 2009, solar energy enjoyed a 33 per cent compound annual growth rate, and there is little sign that this is slowing down.

The renewable energy markets across the global vary significantly in their maturity. While Europe can be seen as the ‘old man’ of renewables, with the USA fast-approaching middle age, the young bright thing is most definitely Asia, led unsurprisingly by China and India.

What is clear for all these markets is that over time the integration of renewable energy sources in the world’s electricity grids will increase. This, however, presents a major challenge for grid operators, and is often cited by some in the more conventional power sector as the Achilles’ heel of the drive towards increasing the contribution of renewable energy in the global generation mix.

In essence, renewable energy resources like wind, and to a lesser extent solar, are intermittent in nature, i.e. the wind does not always blow and the sun does not always shine. When you have significant penetration of such sources on your grid the unpredictable nature of the power output from renewables can result in grid instability and the operator facing load balancing challenges.

To get round this problem there has been, and continues to be, a lot of effort in the area of developing energy storage systems, which as the name suggests can store electricity and release when needed, thereby helping to stabilize the network.

There are a wide number of energy storage technologies available, which vary in size, whether they are mobile or fixed, and in cost. The major technologies are: lead-based batteries; flow batteries, such as zinc or sodium-bromide; advanced batteries such as lithium-ion or sodium-sulphur; and fuel cells.

Having said that, there are some who argue that the development of energy storage technology is not happening fast enough, and is not keeping pace with the explosion in renewable energy fuelled power generation.

An interesting, and potentially important, development in energy storage is the recent release of preliminary results from a wind-to-battery storage project, being conducted by the US utility Xcel Energy.

The project, which began in October 2008, comprises 20 commercially available 50 kW sodium-sulphur battery modules connected to an 11 MW wind farm. According to Excel Energy, the battery modules are able to store 7.2 MWh of electricity with a charge/discharge capacity of 1 MW. When fully charged, the energy storage system could power 500 homes for seven hours.

According to the preliminary results, the energy storage battery system has demonstrated the capability to shift wind power from off-peak to on-peak availability; to reduce the need to compensate for the variability and limited predictability of wind generation resources; to support the transmission grid system through the provision of voltage support, which contributes to system reliability; and to support the regional electricity market by responding to real-time imbalances between generation and load.

As one of the USA’s leaders in wind power distribution, the preliminary results are clearly important to Excel Energy. A final report on the project
is due to be released in summer 2011. The final outcome of this energy storage technology could be very important as utilities across the globe wrestle with integrating variable wind and solar power production with the needs of the power grid.

Kind regards,
Heather Johnstone
Chief Editor

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