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Saturday, August 1, 2015

Energy Storage (Batteries)

I chaired a debate at the PowerGen conference at the CTICC on the 16th July 2015.

Although it was to a technical audience with a technical panel, very many people are asking me for help with understanding battery technology and I thought this summary might be useful.

​People are concerned that renewable energy systems might not produce electricity​ when it is needed, but I think that we can see that even fossil fuel based systems, such as the one Eskom runs, also don't produce electricity when it is needed.

Wind turbine and solar-electric (photovoltaic) systems have to produce electricity when it is needed. Note that this is exactly the same for fossil fuel based systems​ which also have to produce electricity when it is needed.

And both systems waste electricity and produce electricity when it isn't needed. It's just that when the wind or the sun is wasting electricity, it is free, whereas a coal or nuclear power station still costs us money when it is wasting electricity, e​.g. for coal, nuclear power, other supplies.

A well run fossil fuel based electricity grid has 15% "spinning reserve" running all the ​time so that when you turn on the light or your kettle, there is electricity. This electricity is usually wasted, so we need is storage.

The first storage that grids have had for decades is pumped storage dams. At off-peak time, ​or when electricity is being wasted, water is pumped from a lower dam to an upper dam. At peak time​, or when demand exceeds supply,​ the water runs down and creates electricity.

Another storage we have used for decades is the geyser in our house or office, where we store electricity in the form of hot water, for use later​. We should "charge" it with electricity at off peak time, and then use zero electricity for the geyser at peak time​. We still have hot water during load shedding, so you can see that this is a form of "battery" where we have stored electricity for later use.​

And then there are all sorts of batteries, like the ones in your cell phone, or laptop, or watch, or TV​ remote​. All these should be charged from 10pm to 6am, when electricity is really cheap, at the low off-peak tariff.

And then there are newer batteries such as molten salt, where surplus electricity can be stored as heat at 800 degrees celsius and then when this electricity is needed this incredibly hot salt bolts water to make steam which then drives a turbine and makes electricity.​ Concentrated solar systems store electricity in this way. Eskom could also store electricity like this if it wished.

In summary, a battery or energy storage system stores electricity either in a battery or as heat or in a pumped storage system for later use. ​There is nothing new about this. Our fossil fuel grids need it. And our renewable energy grids also need it. The main difference is that in a renewable energy grid, charging the batteries is free.

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