‘Solar water heaters are rubbish’ – or are they?

‘Solar water heaters are rubbish’ – or are they?

By James Green

Untrue headlines, fictional news, and falsehoods. Conspiracy theories are reaching new heights across the world, particularly in the UK (Brexit), in the US (Trump), and, of course, in South Africa.

Having got your attention, there is, unfortunately, a certain amount of truth in the statement, “Solar water heaters are rubbish,” since many consumers and indeed plumbers think exactly that.

The problem is not that the heaters are rubbish; rather, the problem is misinformation, lack of understanding, and unrealistic expectations. While the Department of Energy states, “Water heating accounts for a third to half of the energy consumption in the average household,” and Eskom says, “An electrical element geyser will use up to 40% of the average household’s energy costs,” solar water heater suppliers have claimed savings of up to 40–60% of the home’s monthly electricity bill.
Well maybe, but only if the solar water heater is sized correctly and the power output matches the kilowatt-hours being used to heat water. In more than 90% of cases, this has not happened.

Studying the output of solar water heaters reveals that most solar systems are only about 70% efficient in replacing the electricity normally used in heating the tank’s volume. Amazingly, power output in kilowatt-hours on solar thermal systems is almost never mentioned on information sheets and websites.

At the same time, ‘savings calculators’ for solar water heaters suggest anywhere between 35% and 45% savings on the home’s electricity bills. Contradictions? Misleading information? Or selling on blind faith, hopes, and promises?

Add into the equation that solar water heaters are perceived as being expensive, so the result is a sale of a 150ℓ solar system (because it is cheaper). In most instances, a 300ℓ-sized system is needed for a home of three to six people, based on a relatively conservative 75ℓ of geyser hot water per person.

Choose a solar system based on financial arguments.

Typically, a 150ℓ solar water heater saves around five kilowatt-hours (kWh) per day (60% efficient), and the home’s water heating is running at 15.35kWh. Put another way, the solar system is saving 30% of the water-heating bill, and this, as a percentage of the home’s electricity bill, is only about 10%. (Eskom a few years ago calculated typical savings at 8%.)

Little wonder that the consumer is disappointed. The outcome is not only a shoddy reputation for solar thermal in general, but those that went solar and were disappointed are putting off potential adopters.

However, if the solar supplier were to identify that the system being chosen would save a percentage of the hot water heating bill (or more specifically, the electricity used in heating that volume of water) then the false expectations would be overcome.

Each solar water heater could then stand on its own merits. Payback on investment and investment savings may all still be very attractive, and with the increasing price of electricity, most will achieve payback in three to five years — some considerably less.

Not surprisingly, few homes have any real idea of how much electricity they use in heating water and it is generally far more than they would expect.
A simple home audit is to read the electricity meter on three consecutive days at the same time (20:00 is a good time), calculate the total kilowatt-hour consumption for the home, and average the daily consumption. Then turn off the geyser for 24 hours — at the same time — and back on again the next day, and calculate the consumption. Compare the two calculations and you will have an estimate of geyser electricity consumption. The only niggle with this is that the home will be out of hot water for most of the day.

With this basic approach, the plumber or consumer can easily determine what size of solar geyser they need or, more importantly, they can determine what amount of electricity they want to save through solar.

Choose a solar system based on financial arguments: solar savings in kilowatt-hours, cost per kilowatt-hour, and daily and monthly rand savings.

It is no different to buying a car. If you want performance, buy one model of car; if you want fuel efficiency, buy another model.

It is not that solar water heaters are rubbish; it is that neither the consumer nor the plumber is looking at the opportunity realistically. Solar thermal can and should be one of

the best investments a home can make.

  James Green is the CEO of Ubersolar and Pay As You Go Solar, and a member of the SESSA Council.   
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