Andreas Späth

Green energy’s big flaw?

2011-08-17 07:40

Andreas Späth

“But the wind doesn’t always blow and the sun goes down at night!”

That’s a common response from my friends when I go on one of my regular rants about how we should be investing much more heavily in renewable energy (RE) in this country. Since the wind and the sun are variable and intermittent, they claim, RE can’t provide us with either baseload electricity - the amount that needs to be available 24/7 - or the peak supply required during the most power-hungry periods.

It’s a red herring, of course. The issue can be solved by integrating as many different RE sources as possible over as large a geographical area as possible into an efficient smart grid: a densely interconnected network of large, centralised power plants as well as widely distributed business-, factory-, farm- and household-scale solar and wind installations.

My friends also tend to ignore the rapidly developing field of energy storage which allows electricity generated by RE sources to be stored when it’s not needed and used when there is demand. This technology will play a crucial role in securing a steady supply of green electricity in the future. Here’s a brief summary of what we can expect.

Pumped storage

Pumped storage schemes currently represent about 99% of the global grid-scale energy storage market. Energy is stored by pumping water from a reservoir at a lower elevation to one at greater altitude. When additional electricity is required, the water is released from the upper to the lower reservoir through turbines generating electricity. Local examples include the Drakensberg and Palmiet Pumped Storage Schemes.

Batteries

Banks of batteries are successfully used by off-grid households to store the electricity they generate using wind turbines and solar panels, but much larger grid-scale batteries are already in operation, too. Together with the batteries in parked electric vehicles, these could form a nationwide distributed power storage network with owners allowing the grid to store and discharge electricity during certain periods of the day.

Compressed air

Electricity from RE sources can be used to compress air into suitable natural underground reservoirs or manufactured, above- or below-ground storage tanks. The stored air is released through turbines to generate electricity whenever it’s needed. This technology, which is already in use in Germany and the USA, is capable of storing large amounts of energy for long periods of time at low cost.

Ultracapacitors

Capacitors are devices that store electricity as ions on the surface of electrodes which can be charged and discharged very rapidly. By pimping them with nanotech materials such as graphene, their capacity is vastly increased, promising potential applications in grid-scale electricity storage.

Flywheels

Electrical energy is converted into mechanical energy stored in spinning disks that are levitated using magnets. Flywheels can dispatch bursts of electricity and modulate the intermittent supply from RE sources.

Hydrogen fuel cells

Once this promising technology has become viable, surplus electricity will be used to produce hydrogen which can be stored until it’s converted back into electricity through a electrochemical process in fuel cells.

Superconducting magnets

Electricity is stored indefinitely with little loss in the form of a magnetic field generated by current circulating through coils of superconducting wires. The electricity can be discharged as high power outputs for short periods of time whenever required.

Synthetic gas

RE can be converted into carbon-neutral natural gas by using it to turn CO2 into methane which can be stored and subsequently used to fire power plants.

Molten salt

At concentrated solar power plants an array of mirrors focuses sunlight onto a central tower, heating a liquid salt solution. The molten salt is fed through a steam generator to produce electricity. Because it only loses about 1% of its heat in a day, the salt can also be stored and used for up to 15 hours without any further sunlight. On 3 July, the 19.9 MW Gemasolar plant in Spain produced uninterrupted solar electricity for 24 hours. In future it’s expected to provide electricity for an average of 20 hours a day.

A diversified, smart RE grid with advanced energy storage is the way forward, whether monopoly utilities like Eskom or my sceptical friends like it or not.

- Andreas has a PhD in geochemistry and manages Lobby Books, the independent book shop at Idasa’s Cape Town Democracy Centre. Follow him on Twitter: @Andreas_Spath

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