Solar Energy in the home: your FAQs answered

Sun power: It's only just dawning on Malta

This has to be one of our most info-rich articles here at Malta Inside Out, thanks to Charles Yousif of the Institute of Sustainable Energies at the University of Malta who is also Secretary General of the Malta Energy Efficiency & Renewable Energies Association. Charles’s clear information should help answer many householders questions on the whys and wherefores of installing a solar water heater, and more. There’s a lot of options on the market, and a lot of word-of-mouth advice around. Here are some facts.

The good old geezer

Q. How much energy does an electric boiler consume?
A: It depends on the use, the temperature and the number of people in the household. In general, 4 people consume between 3 or 4 kWh every day, at least for 9 months i.e. a total of between 800 and 1,000 kWh/year, assuming no losses. So, a geezer could account for around 20% of your electricity bill.

Q. What do you mean “assuming no losses”?
A: If you leave the geezer on all the time and the only control is its thermostat, then you will have heat losses from the hot boiler to the air surrounding it. These could account for an added 20-30% extra power.

Q. Geezers are normally insulated, so how come there are losses?
A: The insulation is generally very thin and inadequate. In addition, there are areas at the bottom where the electric element is connected which are not insulated and they are a source of heat loss too.

Q. Do you mean that one would save if the geezer is switched on only when needed?
A: Definitely. Using a timer could also help to reduce the hassle of switching it on and off.

Now to Solar Water Heaters

Q. If I install a solar heater, would it save on my energy bill?
A: Yes, provided that it is installed properly and sized properly.

Q. What are the important points about installing a solar heater properly?
A: There are 4 important aspects:
1) For domestic use, when the home owner will use hot water between September and May, the ideal inclination angle of the panel should be between 45 and 55 degrees to the horizontal.
2) The panel should be facing south.
3) The hot water delivery pipes should be well insulated and the insulation well protected from UV radiation and sealed at the edges to stop rain water from seeping in.
4) Last but not least, the amount of water in the hot water storage tank should be proportionate to the area of the solar panel. For a flat-plate collector, the ratio should be 50-60 litres per square metre of collector. For an evacuated-tube system, the ratio should be 80-90 litres per square-metre of cross-sectional area of the vacuum tubes.

Q. This is complicated: Can you give an example?
A: A typical 200 litre hot water system should have 4 square metres of solar flat-plate panels or 2.5 sqaure metres of cross-sectional area of vacuum tubes

Q. So does this mean that a vacuum tube collector is better than a flat-plate collector?
As long as you keep to the above 4 rules, both systems should give you more or less the same output.

Q. But people say that vacuum tubes work better in winter because they absorb the UV radiation.
A:The UV radiation is available on sunny days be it in winter or in summer. On cloudy days, the UV radiation is very low. Therefore, this statement is untrue.

Q. But experience shows that people who have evacuated tubes fair better in winter.
A: This may be true because normally flat-plate systems are under-sized for the needs of the family and tend to suffer in winter. On the other hand, evacuated tube system could dangerously over-heat in summer. The conclusion is that Malta has over 300 sunny days a year and both systems should work properly on most days. Sometimes, the problem would also come from the user because as time passes by they either start connecting the solar system to other parts of the house or the family increases in number and they don’t realise that they need more hot water, which the solar system cannot provide alone, having been designed originally for lower demand.

Q. What do you suggest for a normal houshold – a gas heater or a solar heater?
A: Gas is a fuel and pollutes the environment. It has to be bought and its price may change in the future. Solar heating uses free energy and provides a relaible and clean source of energy.

Heat Pump Water Heaters

Q. But some households have no roofs, so how can they install a solar heater?
A: That is a problem and MEPA, so far, does not allow installation of solar heaters on the facade. There are heat pump water heaters, which could save energy too. This is simply an air-conditioning unit that heats water instead of heating air. it saves around 60% of the electricity consumed by a geezer. This should be supported by Government because a heat pump has been accepted by the European Commission as an electric component that may contribute to renewable energy

Q. What do you mean? A heat pump needs electricity to operate the compressor, so how can it generate renewable energy?
The heat pump absorbs energy from the air which is renewable energy and passes it to the water to heat it up. If the energy absorbed in the water is more than the energy used by Enemalta to generate electricity to drive the heat pump compressor, then the difference between these two values is actually a contribution to renewable energy.

Q. Are these heat pumps available in the market?
Yes. One has to aim to buy a high efficiency heat pump with a COP of 3 or above. However, the prices are still relatively high due to the small market in Malta.

Further Information
The Institute for Sustainable Energies offers a technical inspection of installed, domestic, solar water heaters. For an appointment, call Eur. Ing. Charles Yousif on 2165 0675. See the Institute’s site for details too.

Malta Resources Authority (MRA) operates government’s support schemes including subsidies for first-time installation of domestic solar water heaters as well as schemes for photovoltaic panels.

Photo: Courtesy of Peter Grima, Know Malta