Electricity generation involves many variables, including primary energy source, supply, demand, infrastructure and cost. The availability of hydrocarbons isn’t helping the shift to renewable energy sources; so what are the alternatives? And, what is holding them back in becoming our primary sources of energy?
I recently attend a talk (Offshore renewables long term
) at The Building Centre discussing wind power and energy storage, to learn more with particular reference to renewables and energy storage. Here are some of the key takeaways:
There is plenty of renewable energy; 10,000 times more solar energy hits the earth everyday than we use. The UK is very well placed for offshore wind, representing in the order of 40% of the World market. It is estimated that twice the UK total energy demand could be supplied as electricity if the offshore wind capacity could be captured. Tidal and wave energy are in the mix at a smaller but still meaningful scale.
Renewables come with a range of attributes; sun, wind and tide are delivered free to site with no clean up or handling charges. On the flip side they generally have a cost disadvantage compared to non-renewables and suffer from low energy density and intermittent supply.
So, it’s one thing capturing this abundant energy, but what about storing it?
A wide range of ideas are being explored to provide electricity on demand from renewable sources. These involve various forms of energy storage with a range of energy densities.
Reusing water for peak electricity demand. Above image credit: USGS. Featured image credit: wiseGEEK.
Gravity: Pumped hydro > Pumped hydro has been the traditional way of storing excess electricity from the grid and seems to return about 65-75% of the energy used to the grid.
Gravity: Gravel mechanical battery > Rather than using water a company called Energy Cache is using gravel transported up and down a slope in a similar manor to a ski lift. They claim superior performance at less cost than pumped hydro.
Compressed Air Energy Storage (CAES) > Compressed air can be generated directly from a windmill or electric motor driving a compressor. The compressed air is released through a turbine to generate electricity. Thermal management of these systems is required during storage because compressing the air generates heat and expanding the air significant cooling.
CAES Energy Bag initial test at Thin Red Line Aerospace in Canada. Image credit: Keith Thompson/Thin Red Line Aerospace
Seamus Garvey at Nottingham University, who presented the talk at The Building Centre, has investigated using bags of compressed air under the sea so that the water pressure provides the pressure vessel rather than fabricating large tanks on land. Using salt mines as compressed air storage vessels has also being considered.
Liquid air > Highview Power Storage are developing systems to liquefy air down to -200°C and then evaporating the cryogenic fluid producing gas to drive electricity generating turbines. The efficiency of this system can be improved by locating with other industrial systems that produce waste heat or cooling.
Image credit: Highview Power Storage system
Batteries > Many chemistries of battery are being investigated for large scale storage. These include ideas to use second hand batteries from cars and using large fleets delivery trucks as mass storage.
Heat > Solar power towers store the suns energy as heat, using molten salts with a high heat capacity. Steam produced from this stored heat is used to produce electricity from steam turbines as required.
Food battery >
In their latest book ‘The Upcycle‘
, William McDonough and Michael Braungart (who also developed ‘Cradle to Cradle’
), suggest that intermittent wind power could be used to power LEDs in greenhouses. Any gust of wind at night time could power biological growth through photosynthesis; the food produced could be considered as the stored energy derived from renewable sources.
Challenge for the future…
Despite numerous alternatives of renewable energy and its storage, it looks like the continued development of Shale Gas and Shale Oil is likely to prolong cheap hydrocarbon energy way beyond the conventional supply predictions. The new challenge we appear to be facing is to come up with ideas to make renewables a more attractive option in order to curtail the environmental impacts of our hydrocarbon reliance. This brief overview shows that storage of intermittent renewable energy supply is an area ripe for innovation and creative thinking at all scales. Whether through price reduction, refinement of storage solutions, accessibility or end user engagement, the key to driving these alternatives is to make them more appealing at every level.