Rather give households solar power than try to reform Eskom

Early in the current load-shedding wave, independent energy expert Ted Blom ridiculed the idea of renewable energy as a solution. There are times when the sun doesn’t shine and there’s no wind. What he says is true but is an outdated view.

Renewable solutions rely on a variety of sources that generate in excess of the average requirements since they might not all be available at once and energy storage is an important part of the mix.

One form of storage is heat. A solar thermal system, instead of relying on photovoltaic panels to convert sunlight to electricity, stores energy by using concentrated solar energy to melt a salt mix. The amount of storage depends on the quantity of the salt mix and the number of mirrors. Such systems make most sense where sunlight is very reliable.

Eskom’s main form of energy storage is pumped storage – hydro schemes that can operate in reverse by pumping water uphill when excess energy is available, and allow it to flow downstream to generate power. Three such schemes total about 2.7 gigawatts, about 5% of Eskom’s total generating capacity. However, for these to work, there has to be excess capacity for at least part of the day.

Better in terms of efficiency is batteries – pumped storage is about 80% efficient whereas a good battery is over 90% efficient. The main advantage of pumped storage is its longevity. The best lithium ion batteries last 10 to 15 years, depending how much and how often they are drained, whereas a hydro plant should last 50 to 150 years without performance deterioration.

However, building new hydro plants takes time and needs a significant water resource that won’t be depleted and sufficient space for water storage below as well as above the scheme, so grid-scale battery storage is increasingly attractive as batteries improve.

While lithium ion chemistries continue to improve, and other promising chemistries could do even better, batteries have an inherent limitation – discharging them is a chemical process and each charge cycle reduces their ability to hold charge. The best current technologies can tolerate 5 000 to 10 000 discharge-recharge cycles and can discharge as much as 95% of their capacity without damage. This is a vast improvement on lead-acid batteries, the previous standard for off-grid backup. These batteries seldom last more than two to three years if heavily used.

However, there is an even better idea out there than batteries that last over 10 years and incremental improvements on how often and how deeply they can discharge – supercapacitors.

A capacitor stores energy by storing an electric charge on conductive materials separated by an insulator. There are many ways capacitors can be made but a common property is that the charge they store leaks. A common type of computer memory uses a capacitor to store each bit, for example, and needs a refresh cycle to top it up. Capacitors are also good for storing very small amounts of energy; larger-scale capacitors are increasingly difficult to construct. 

However, supercapacitors promise to change all that. They have up to a million times the ability to store charge compared with ordinary capacitors. Unlike batteries, charging and discharging causes no damage and they can discharge fast and completely without damage. Up to recently, supercapacitors were a bridge technology with limited use because they were best suited to short bursts of power. One application is hybrid vehicles, where a sudden power boost could be useful. Another is the “black start” of a power station (when there is no other power source). Unlike batteries, they leak power relatively fast.

New York-based Kilowatt Labs claims to have changed all that with supercapacitor storage (supercap for short) that is practical for renewable back-ups. Their Sirius supercap systems cost about twice as much as an equivalent lithium ion battery but are rated at a million cycles and 45 years of life, close to the low end of the lifetime of pumped storage. 

This is a relatively new technology so a promise of being good for 45 years has not yet been put to the test in the real world. I am sceptical of these numbers until I see an independent test; based on a patent they have been awarded, I suspect that this unit is actually a hybrid – supercapacitors plus conventional batteries. This being the case, they need to explain how coupling batteries with supercapacitors triples the lifetime of the batteries and how the control electronics can last that long. And one million cycles over 45 years means a complete discharge-recharge cycle every 25 minutes, so it’s a meaningless claim.

Despite my scepticism of the Sirius claims, battery technology is improving rapidly and will make a big difference to grid-scale storage and, if supercaps really are the solution, plenty of people are working on making that happen.

But in a context where big projects often fail catastrophically, is grid-scale storage the best option?

Home systems can scale up as they become affordable for mass adoption.

A home solar-plus-battery system for R200 000 can reduce electricity bills substantially. A system like this can recover the cost in saved electricity bills in about 10 years – at current prices. This may seem like a lot of money but a 10-year payback time makes it possible to add this sort of cost to your home loan. 

If 100 000 homes added about 5kW of solar to the grid with sufficient storage to cut their demand on Eskom, this would make a big difference. While the entire 5kW times 100 000, totalling 500MW, would not be available all at once, batteries smooth out the demand on grid power. The key is batteries that are not damaged by being used this way – some of the latest lithium ion chemistries can discharge up to 95% of rated capacity and are expected to last 15 years.

Eskom’s load-shedding aims to cut 1GW of demand at a time; stage 2 does this for up to four hours in one day. If 500MW of solar is available for eight hours of the day, that would be equivalent to what stage 2 load-shedding saves. In cloudier weather, it would not be as good but this is an indication of what a lot of solar could do – particularly with batteries to make it available outside of sunny hours.

Not everyone could afford this solution but it could be coupled with a larger number of households with a smaller smaller amount of solar or no batteries – for example, all RDP houses could be equipped with a 300W solar panel as a contribution to a free electricity allowance.

All of this is far better than reforming Eskom for a number of reasons. There is no single large tender to defraud. There is no large dysfunctional organisation to reform. And individual households have a strong incentive to ensure that it is done right as they will save money.

Yet President Cyril Ramaphosa is talking about creating another Eskom to compete with the existing state-owned enterprise. If we can’t get this right once, why is doing it twice better?

The views expressed are those of the author and do not reflect the official policy or position of the Mail & Guardian.

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Philip Machanick
Philip Machanick is an associate professor of computer science at Rhodes University

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