Is gas boosted solar hot water better for the environment than electric boosted solar hot water?
First of all, there are two types of gas boosting for solar hot water. Pre gas boosting heats all of the water in the storage tank using gas. Post gas boosting only heats the water via a continuous flow gas booster as you are using it. It does not heat any water in the storage tank. I only recommend pre boosting where customers do not have a reliable source of electricity. In this article gas boosting will mean post gas boosting.
I am always asked are gas boosted solar hot water systems better for the environment than electric boosted solar hot water systems. My answer would be ” Yes gas boosting is better for the environment under ideal conditions and if the installation is completed as per the manufacturers guidelines.” I would go on to say, ” Yes gas boosting is better for the environment if there is never a chance of a breakdown and if humans weren’t humans.”
However, we know a breakdown will occur one day and humans do tend to use more of something when that something is limitless. Additionally, many people do not know that most electric boosted solar hot water systems can be installed and altered so they use less water, have less embodied energy and produce lower green house gas emissions than their gas boosted counterparts.
To understand why this is possible, we need to look at the differences in the systems and how home owners interact with them under real life conditions.
Some gas boosted solar hot water systems are more efficient than others. Some use solar bypass valves and some require the water from inside the solar storage tank to pass through the gas booster. However, in every case, the booster will ignite when a hot tap is turned on -in some cases for a minimum of 20 seconds. This will occur when the water in the tank is hot enough for use also.
This will not occur with any electric boosted solar hot water system.
Our hot water servicing experience anecdotally points to it taking longer for most owners of gas boosted systems to realise they have a fault with the solar hot water side of their system. This is because the gas booster will continue to provide limitless hot water, even when there is a leak in the system or a fault in one of the solar components. As most storage tanks are out of sight and many leaks occur on the roof, it can be a long time before leaks or other faults are noticed.
This can waste water and energy leading to more catastrophic failures and costing lots of money.
Electric boosters cannot provide a limitless supply of hot water. Therefore, home owners tend to realise something is not working as well as it should sooner.
My experience with any hot water system that provides limitless hot water is that homeowners tend to use more hot water. Gas boosters provide limitless hot water. Electric boosters do not.
Gas continuous flow systems are notoriously slow at providing hot water. This is because there is always 2-3 litres of water held in tubes inside the system. This water is nearly always cold and is run-off down the drain (along with the additional water in the pipes between the outlet of the system and the tap) while you wait for the hot water to arrive at the tap.
Because the water in electric boosted systems is always hot, you only need to run the water off that is in the pipes between the outlet of the storage tank and the tap.
As explained in the section on energy consumption above, leaks on the roof collectors or around tanks are much more likely to be noticed with electric boosting systems.
The gas booster comprises of a 16kg continuous flow gas hot water system. This is strapped to the front of the solar storage tank. It is made from copper, plastic , aluminium and steel. With an average of 90mj/kg the booster contains 1540mj of embodied energy. This energy would provide 3 people with hot water for 28 days. The above has not even considered the 500-1000mj of embodied energy in the copper gas pipe for the booster.
Making electric boosted systems use less energy for boosting
It is possible to install an electric boosted solar hot water system to make it work so efficiently that it is better for the environment than gas boosted solar hot water systems. It is also possible to alter most existing electric boosted systems to get similar efficiencies as the brand new electric boosted systems we install.
On new systems, we start with larger capacity storage tanks. Large tanks act like a battery-storing excess hot water for the periods when the sun does not shine or when demand for hot water is high. Depending on hot water usage we would usually install mid element tanks to reduce the overall amount of water being boosted in the storage tank.
On all systems, we restrict boosting to specific times. We change the pitch and orientation of the solar hot water collectors, alter the pipe work for minimum resistance and we may change the pumps and control stations. We then tune the system for optimum performance.
It is possible to get electric boosting down to an average of 28 hours per year.
These views are based on my 30 years experience in servicing, repairing, supplying and installing all types of hot water systems in the Canberra and Queanbeyan region.
I have restricted electrical, plumbing and gas fitting licences. I studied at The Solar Hot Water Institute previously at Mossvale, NSW.
I have served as a Director of Master Plumbers Australia and as President of Master Plumbers ACT.
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