Green energy technologies are often criticised on the grounds that they cannot provide a steady supply of energy, nor can they provide energy when the wind stops blowing or the sun stops shining. The primary issue here is with energy storage to overcome this intermittency. One high-tech solution in the development pipeline is the development of large and efficient chemical batteries – something being worked on by Tesla. There are however a number of drawbacks with such technologies including inefficiencies as the energy can often decay or leak over time, very high cost and their components have their own environmental problems with their extraction and disposal. Despite these issues, when these, and other, issues are cracked the potential of these batteries is great. There are, however, a number of ‘low-tech’ options which I would like to discuss which could indeed be cleaner, cheaper and often a little more off the wall than a chemical battery (literally in the case of the Tesla Powerwall).
Many low-tech energy storage options make use of gravity allowing energy to be stored as potential energy which has the advantage of not depreciating over time. A common principal is to use excess electrical energy to raise a mass which then can then be ‘dropped’ in a controlled manner when needed to drive a motor or generator and thus regenerate electrical energy. Check out the ‘gravity light’ for a very small scale example of this idea which is summarised in three steps below.
1) Excess electrical energy used to raise a mass.
Many low-tech energy storage options make use of gravity allowing energy to be stored as potential energy which has the advantage of not depreciating over time. A common principal is to use excess electrical energy to raise a mass which then can then be ‘dropped’ in a controlled manner when needed to drive a motor or generator and thus regenerate electrical energy. Check out the ‘gravity light’ for a very small scale example of this idea which is summarised in three steps below.
1) Excess electrical energy used to raise a mass.
2) The energy input is now stored as potential energy.
3) Dropping the mass back down converts potential energy back into electrical.
A good option for the mass, especially in wet and hilly places, is to use water, pumping it up hill into a reservoir before releasing it down through turbines. This has the advantage that dams or reservoirs can be pretty big meaning more mass and therefore are able to hold significant amounts of potential energy. Other possibilities include lifting actual solid weights however these are only really appropriate for smaller scale operations such as for individual houses. This is because you need very large masses to store and generate significant amounts of energy. However, it is not too hard to imagine a house that has an array of solar panels able to use some of the energy on a sunny day to crank up a heavy block of concrete (or other potential waste material like scrap metal) before dropping it down through a high resistance hydraulic turbine to power the lights and TV at night before raising it back up the next day.
The concept is relatively straight forward and there are as many ways of implementing it as the imagination allows and one example in particular has caught mine and others attention. A left-field suggestion for using this concept has been cooked up which looks to reuse existing resources and infrastructure in America, namely trains and train tracks, and will work particularly well in the drier parts. The idea involves using excess energy from wind and solar plants to drive electric motors on heavily loaded trains to move them up hill. When needed, the trains rumble back down hill and now turn the electric motors the other way so acting as generators to produce electricity. This system has some advantages over vertical lifting systems of solid weights, which generally need unrealistically tall lifts to operate at such levels, as the trains on tracks act more like water being able to run along slopes rather than vertically and therefore are scalable (just strap on more loaded carriages).
3) Dropping the mass back down converts potential energy back into electrical.
A good option for the mass, especially in wet and hilly places, is to use water, pumping it up hill into a reservoir before releasing it down through turbines. This has the advantage that dams or reservoirs can be pretty big meaning more mass and therefore are able to hold significant amounts of potential energy. Other possibilities include lifting actual solid weights however these are only really appropriate for smaller scale operations such as for individual houses. This is because you need very large masses to store and generate significant amounts of energy. However, it is not too hard to imagine a house that has an array of solar panels able to use some of the energy on a sunny day to crank up a heavy block of concrete (or other potential waste material like scrap metal) before dropping it down through a high resistance hydraulic turbine to power the lights and TV at night before raising it back up the next day.
The concept is relatively straight forward and there are as many ways of implementing it as the imagination allows and one example in particular has caught mine and others attention. A left-field suggestion for using this concept has been cooked up which looks to reuse existing resources and infrastructure in America, namely trains and train tracks, and will work particularly well in the drier parts. The idea involves using excess energy from wind and solar plants to drive electric motors on heavily loaded trains to move them up hill. When needed, the trains rumble back down hill and now turn the electric motors the other way so acting as generators to produce electricity. This system has some advantages over vertical lifting systems of solid weights, which generally need unrealistically tall lifts to operate at such levels, as the trains on tracks act more like water being able to run along slopes rather than vertically and therefore are scalable (just strap on more loaded carriages).
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| Beacons of hope? |
Another really exciting, but slightly less low-tech technology being developed for energy storage I wanted to include here is high-temperature solar thermal. The concept here is the use solar energy to directly heat a medium such as water, salt or oil and the release of heat can be used to drive steam turbines to produce electrical energy. Some of the most interesting examples of these include so called 'power towers'. Here, thousands of mirrors track the sun and concentrate its energy on a central tower where salt is heated to extremely high temperatures (over 500°C) such that it melts. This hot molten salt is stored in insulated tanks to minimise heat loss and then this heat can drive a steam turbine when power is required and especially at night. The first working commercial example of this, an 11MW plant that uses water rather than salt, was set up in the hot, sunny dry south of Spain. Morocco, another hot and dry country just across the straight of Gibraltar, has also been investing (or rather been invested in by the EU) heavily in solar and was even touted as a potential base for providing solar for west Europe (investment, not charity!). They have recently finished the first stage on a plant that aims to produce 580MW with up to 8 hours energy storage using molten salt as the storage medium but with a different design to the power towers. Despite solar energy being in plentiful supply in these locations, water is not which is a problem as a lot is required not least in cleaning the mirrors (although a dry cleaning method is being developed) to keep them shiny and effective!
As I hope you can see, there are alternate options out there to help make more sustainable energy sources more reliable and our slow progress should not be blamed completely on a lack of energy storage systems, it is still largely a lack of will and investment. A range of smaller scale low-tech options exist which means poorer regions can benefit from green(er) energy despite not being able to afford the expensive batteries when they arrive. Our future energy solutions will require imagination and policies that match and optimise the local conditions – one size does not fit all.
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