Posts Tagged ‘booster’

Every solar hot water system comes with a booster for the times when there is not enough sun. There are two types of booster technology: electric and gas.

Electric Solar Hot Water Booster

This is the most common way to boost your water heating. It is the most economical as it does not have a large upfront cost. When you start using your solar hot water system, it is best to leave your booster off until you run out of hot water.

Once you know how many days of clouds that takes (for us it is 3, but that will be different for every family, depending on how you use your water), you can turn the booster on before the water goes cold. But it is worth testing it out first.

Is it not Automatic?

The electric booster has a thermostat that only lets it start when the water temperature falls under 60 degrees Celsius. So you could just leave it on and forget about it. However, that would result in wasted energy.

Let us assume that your whole family has a shower early in the morning. The temperature in the tank drops to 55 degrees. That would trigger the booster to heat the water. However an hour later, the sun hits the panels and would have heated the water far more efficiently and cheaper.

It is therefore best to leave the booster off and only turn it on when you really need it.

Which Tariff?

The official government suggestion is to connect the electric booster to Tariff 33. That is the off-peak tariff, which means it only runs for 18 hours a day. It is cheaper than normal electricity, but in many situations you use far less electricity than the minimum payments.

(Over 3 years, we had our solar hot water connected to night tariff. In that time, we used a total of 177 kWh for the booster. On Tariff 11, we would have paid about $30. Because of the minimum quarterly payment to have access to the night tariff, we paid $120 in that time.)

The story is different if you have something else connected to the off-peak or night tariff (e.g. a pool pump). Then it might be the best financial choice.

Gas Boosted Solar Hot Water System

The other booster uses gas. Even though the greenhouse gas savings are slightly higher with this type of system, you basically have to purchase two hot water systems (one solar and one instantaneous gas heater) which are coupled together.

As long as the water heated by the sun is hot enough, it just flows through the instantaneous gas system. When the temperature drops below the thermostat setting (usually between 45 and 49 degrees) the gas system starts heating.

In some instances it is possible to use an existing instantaneous gas system.

One of the issues that came up in the interviews at World Environment Day was the question of the reliability of solar water heating.

Some people have experienced problems with earlier systems that did not have enough capacity to handle a few days of grey skies.

There are three components to that issue

1) Tank Size

All tanks have great insulation, so that the heat-loss over a few days is minimised. The more important factor is how much hot water is used. According to the Sustainable Energy Development Office of WA an average person uses 50 Litre of hot water per day.

The water in the tank heats up to 90 degrees in summer, but gets mixed with cold water when it comes out (to 50 degrees, so that no one gets burnt). That means a 300 Litre tank has a capacity of close to 550 Litre of 50 degree water. So for a family of four, it can last close to 3 days without any sunshine.

So the bigger the tank, the more hot water you bank.

2) Solar Water Heating Collectors

Efficiency of collectors depends on a lot of factors. We check them all on this website and then again before installation to make sure you get the best efficiency out of your system.

We use the highly efficient technology in all our split solar hot water systems that can face anywhere from North-East to North-West to work well. You need to get an absolute minimum of 4 hours of sunlight on the panels to successfully heat your tank.

3) The Booster

The last element in solar water heating is the booster. It has a thermostat that is set to 60 degrees. So whenever the water temperature falls below 60 degrees, it automatically heats it up.

Conclusion

Is solar hot water heating reliable? Yes absolutely. The technology is well matured since the 1950’s. It is highly efficient (up to 80% of the sun’s energy is turned into hot water) and it has a reliable backup with the booster.