Readers’ letters:

Email us and share your ideas, projects, or new inventions; include photos. (If it’s good, you might win a great prize.)

I’m a great fan of Popular Mechanics. When I read your editorial entitled ‘What’s your plan B?’, I thought I’d share with you and the other readers the details of my solar installation solution that I had put in at our home.

My wife works in the financial world, on a full-time basis from home, and because of the deals and contracts at stake she can’t afford to be offline at any point.

I’m in the electronics field, so, having some firsthand knowledge on the subject, I started researching alternative energy-storage solutions other than batteries for our home off-grid power supply. I didn’t want to have batteries, because their efficiency fluctuates in hot and cold conditions.

Also, over-charging of lead-acid batteries can produce hydrogen sulphide, a poisonous gas that’s colourless and has the odour of rotten eggs. The service life of batteries is around 10 years (or 5 000 cycles at 70 per cent depth of discharge, or DoD). Batteries have to be cycled continuously, and deep discharge below 20 per cent can damage them.

Batteries work optimally at 23°C. Maintaining this temperature would mean installing an air conditioner in my garage where the battery would be stored, and that just wasn’t feasible.

My online research revealed KiloWatt Labs, a company that makes supercapacitors, so I ordered myself one. Here are the reasons why I went the supercapacitor route: 1. Their temperature tolerance is from -25°C up to 85°C, a much wider range than you’ll find in conventional batteries. 2. They have a round-trip efficiency of 99.121 per cent with 1 000 000 cycles at 100 per cent DoD. 3. They function optimally

40+ years.

4. They are 100 per

cent recyclable.

5. They have no capacity

degradation.

6. They’re non-hazardous, non-flammable and also non-toxic.

Our system consists of 12 JA 310 W solar panels with a combined output of 3 720 W. We have a Fronius 4 kW inverter for managing the power from the solar panels, a Victron Inverter (with a 48 V input, a maximum output of 8 000 VA, and a maximum charge of 110 amps), and a 6.7 kWh supercapacitor.

Let me use a recent example to illustrate how effective the system is… We experienced a load-shedding event not too long ago (who hasn’t?), from 18:30 to 20:30, and my wife asked if we’d still be able to make supper. She was worried about how much power would be available to run the various appliances. Without any hesitation, I replied that she should go ahead as normal.

I ‘pushed’ the system – we operated the microwave, stove and I ran the hot-water tap for a while, just enough for the heat pump to kick in

(it pulls 1.5 kW). The house’s load jumped to 3.3 kW, and the capacitor bank started discharging from the state of charge (SOC) of 100 per cent. When load-shedding ended, I went to check the SOC, and the capacitor bank was sitting at 49 per cent. The house’s load was back to normal at 290 W.

When the grid came back online, the Victron unit immediately started charging the capacitor bank. It pulled 5.5 kW from the grid, kept the house’s load at 290 W, and pushed 5 210 W straight back into the bank. I timed it, and it took only 28 minutes to fully recharge the capacitor bank to a SOC of 100 per cent.

My intention for writing isn’t to brag about my system, but to instead offer others some solid advice. When it comes to choosing a solution that will protect assets, without the fire risks associated with generators or batteries, I would highly recommend the supercapacitor route.

I have now been running my system for just more than two years, and I haven’t encountered any problems at all.

MARTIN VON GRUENEWALDT

This is a solution that I haven’t heard about before, Martin. Thanks for sharing it with us. Reading your letter made me realise how many different factors should be considered when planning an off-grid set-up, including the increased risk of fire. The lesson here is to always address issues such as this with any industry professionals you consult.

Your interesting contribution has won you the WORX 20 V inflator/flashlight, sponsored by Vermont Sales. – Mark, Editor