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Business Unusual

South Africa needs batteries, here are some we might use

14 October 2020 7:15 PM

Over 1000 MW of renewable energy will be added to the grid in the next year, we need a way to store it.

One major drawback that is often made about renewables is that they don’t work when the sun does not shine or there is no wind. That is true but a greater drawback is that often when they do work, we have enough power but not enough during the peaks.

An age old issue has been how to store enough energy efficiently so we can use everything we generate.

Right now power stations produce too much energy during the middle of the night only to be short during the morning and afternoon peak. It is unlikely we can get everyone to use electricity in a way that there is no peak, so we need another solution - storage.

We tend to rely on pumped water as the main method but it takes up a lot of space and requires a suitable elevation and availability of water. Ideally we need a solution that can be built anywhere, is small but scalable, is reasonably efficient and safe to be located near the areas that need the power.

Here are some alternatives that could do the job.

Home

You might not think we might be a big part of better gird management, but as batteries with lithium ion or lead acid are becoming more common and slightly cheaper, the option to have a few hours battery storage in your home does not only get you through the current load shed periods, but in time might be the thing to lower the demand during the peaks especially if Eskom offers a special low rate to charge them in the middle of the night.

There is an experimental option that impregnates red clay bricks with a solution that turns them into capacitors, in theory the actual bricks in your home become the battery. It would only serve to manage the peaks or should the power fail. It could be charged when demand is low or via wind or solar. If the cost of the brick is not much more than a regular brick and they are easy to connect and are safe it could be a great additional option.

Neighbourhood

Eskom or local municipalities would like to have some local capacity and there are a few options that can deliver what is needed.

Large installations of lithium ion batteries are already in commercial use. They are excellent for responding very quickly and supplying the full potential albeit for a limited time.

These are perfect for regulating the grid which as we move from a few large power stations to many more smaller and different types will be useful to keep everything stable for short bursts.

A novel use of older electric car battery packs that can’t store enough charge is to convert them into electric car recharging stations, but they can also work as grid stabilisers at the same time, drawing power when it is good to do so while dispensing it to vehicles or back to the grid as needed. They can also be configured to supply a short by fast recharge making a quick stop at a charging station enough to give you a 50km boost to get to where you are going where you can fully charge at a slower rate again.

There is a fire risk, but as the technology improves the potential drops, if a large array of lithium ever did catch fire it would be a difficult fire to manage.

City

While lithium works at a city level too, a better option are vanadium redox flow batteries. They are larger than lithium ion batteries, contain liquid chemicals that can be harmful but pose less of a fire risk as they do not get as hot as lithium nor do they contain highly flammable materials. They can be run completely flat with no harm and are able to do many more cycles that lithium batteries. While they are bigger, a space the size of a factory could store a significant amount of energy. Building them at strategic points around a city would not only further stabilise the grid but also supply local power in the event of damage to the broader distribution grid in a storm or after a fire.

They are not that popular yet and so have not become cheaper, but the materials to construct them are cheaper and more easily available than lithium.

District

The next options can be used in addition to the options above or in conjunction with them.

Mechanical batteries are a class that works and consist of stored potential energy using weights that are raised. There are a few options which were covered in a previous Business Unusual. Hydro storage can also be considered a mechanical battery as it is effectively the weight of the water that is the energy source.

They could be constructed at the sites of renewable energy sources and if large enough to store the full day's energy output, it might be able to run like a base load supply in areas with smaller peaks.

Building them at strategic points along the national grid network would also provide grid stability and allow for much smaller network breaks are most areas would have access to a short term backup while the network can be restored.

One option that exists is liquid air storage. The process to liquify gas is well established and the ability to scale it to very large plants is already possible. One of the advantages is that the storage material is effectively just air. It could be just the nitrogen which would allow the 20% liquid oxygen to be used for something else. Rockets and aircraft may be one option as the aviation industry looks to move away from fossil fuels.

The process could also scrub the air of carbon dioxide. The liquid nitrogen can be used for energy production while the carbon dioxide could be diverted for intensive farming using green houses with much higher CO2 levels.

The plants are safe and can be built to be quite small or massive. Excess energy is used to cool air until it is a liquid. Once it is allowed to warm again, the pressure in the tanks increase and can drive generators with the only by-product being air. The process can be repeated many times with little maintenance and ambient air is used to heat the cooled air which in turn requires less energy to liquify it.

The trick is to use a mix of the options and to include the use of coal, natural gas and nuclear which for all their down sides do still have some very big positives. Coal and gas in areas where they are abundant can make them affordable. It might be worth using liquid air plants with coal and gas to capture the output air. It may be harder to cool the warmer gas but removing the higher concentrations of CO2 and other emissions at the source will make for a more balanced return in terms of costs and environmental impact.

The technology and materials for all except the lithium does not require specialist materials so they could be constructed everywhere and while there is some impressive engineering needed, the work opportunities should be able to offer work for a wide range of skill levels.

South Africa could both build its way out of a power pinch, but do so using sustainable options that can be taken throughout Africa and spare the continent the need to go through a dirty fossil fuel stage. It may even be good for these power plants to earn carbon credits which countries that are still heavily reliant on fossil fuels can purchase to offset their impact by paying those utilities and countries that have focussed on greener options from the start.


14 October 2020 7:15 PM

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