Solar Hot Water 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.
No Booster Switch?
We always put the booster switch in for all the reasons above and I am pretty sure that most high quality installers do that automatically. But some companies apparently do not have the switch as a standard procedure, so whoever you purchase from, make sure that you get a booster switch.
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.
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Tags: booster
December 16th, 2008 at 6:50 am
Hi
I have a solar system without a booster. Not good. Is there any particular gas booster unit that you would recommend? Are there any considerations outside of size to consider?
Many thanks
Jon
December 16th, 2008 at 1:26 pm
Thanks for your questions Jon,
I would love to give you a clear answer, but I can only makes some stabs in the dark.
1) Do you have access to reticulated gas?
LPG gas is about 8 times as expensive as reticulated (natural) gas. Therefore it is often uneconomical to boost with gas when you are on LPG.
2) Check whether your system has a booster element in it.
I am not quite sure why you have a solar hot water system without a booster. I’ll just assume that you (or whoever put it in) wanted to reduce greenhouse gas emissions and ordered a system without a booster.
I cannot say for certain, but most systems come with a booster. So sometimes plumbers install a solar hot water system without connecting the electric booster to sell a system “without a booster”.
3) There are a range of instantaneous gas units that can be used with solar hot water. They are just added between the solar hot water tank and the shower. If the water is not hot enough, they kick in. The advantage: you only heat water that you are using. The disadvantage: they are expensive and waste a lot of water.
4) What to consider? It is not so much size (as you would not want another storage tank), but how much water they can heat per minute. The Dux solar hot water units that come with a gas booster usually can heat 26 Litre/min.
I hope that helps.
Alexander
December 17th, 2008 at 9:32 am
Thanks for your helpful answers Alexander! We are on LPG. There is an electric booster which is fine for summer, but I fear its a terrible drain on the batteries in deep winter. It would seem a gas booster is the way to go if we can switch it off for the sunny seasons.
I’ll talk it over with the plumber today and get back to you.
Many thanks
Jon