African energy
17
<< Continued from page 15
Gas boilers enjoy the advantage of instant hot water, potentially saving on the heat loss of stored hot water, but the cost per litre of hot water is in theory very similar to an electrical resistance element, based on protection of Eskom’ s prices and the minimum costs of gas as set by the Department of Energy and NERSA.
Heating oil boilers enjoy a cost advantage over gas, not because they are more efficient, but because paraffin does not suffer VAT and is subsidised by the government.
Solar photo voltaic( PV), where electricity is generated from solar panels, is not a suitable option for heating water using the existing electrical resistance elements in the geyser. Comparatively, the costs are up to five times higher than using solar water heating technology.
Based on South Africa’ s high solar radiation, solar water heating should be the winner in terms of cost versus reward( depending on the system chosen).
However, a combination of hot water heating energy technologies may be the best solution, particularly on larger hot water requirements( commercial applications like hotels and hospitals). For example, solar is used to preheat and is then topped up by either gas, heating oil, or heat pumps. PA
James Green is the CEO of Ubersolar and Pay As You Go Solar, and a member of the SESSA Council.
‘ Solar water heaters are rubbish’ – or are they?
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.
By
James Green
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 kilowatthours 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 %
Continued on page 19 >> www. plumbingafrica. co. za March 2017 Volume 23 I Number 1