Spring, summer and fall, I take pride in keeping the electricity to my geysers off. The water is heated purely by the sun. With a little bit of luck I can even make it through one overcast, rainy day with the hot water stored in my tanks.
But when we were hit this weekend by three successive gloomy, soggy days, I threw in the towel. With the electricity flowing, I sensed an opportunity, however. I had always wondered how much I was saving with my solar hot-water panels. When I installed them, I was making a hundred other changes to my house. Simply comparing my electricity consumption before and after the solar panels won’t answer that question.
So yesterday morning, I decided to experiment. Assured of no sun, I switched off the pump to the panels and recorded my municipal electricity meter reading. [Switching off the pump was essential because even in cloudy weather, solar panels will warm up enough to heat water to a small degree. Waiting for a cloudy day was essential to avoid overheating the fluid in the panels that was not circulating.]
This morning, I ended my experiment and checked the meter again. My household had used 45 kilowatt hours of electricity in 24 hours, compared to 26 kilowatt hours on a normal weekday in recent months. (I monitor the meter rather obsessively.) This means the solar panels are cutting my electricity consumption by approximately 42 percent.
If we have 300 days a year of decent sun, the panels are saving about 5,700 kWh a year. That translates into sparing the atmosphere 5.7 tons of carbon dioxide annually. My financial savings are not quite as dramatic—and not as important in my mind—but still worth noting. At the current Johannesburg charge of 31.18 cents per kilowatt hour, I am saving R1 777 per year. At this rate it will take me at least 20 years to pay back my large and complicated solar hot water system. Simpler systems cost less than half as much and will pay for themselves much more quickly.
Is my 42% saving typical? Dylan Tudor Jones of Solar Heat Exchangers, the company that installed my system, tells customers that they may save up to 50 percent on their electricity bill. Given that my house used to have two electric geysers, I may have cut back that much. I doubt, however, that most people can slice their electricity consumption in half with solar panels. I have a larger-than-average system—3 panels and 600 litres of storage—and my vigilance against wasting power throughout the house means that geysers were using a disproportionate share of the total. But whether a solar hot-water system saves 20, 30 or 40 percent, it is the smartest step a South African can take toward creating a greener house.