Water heating can be responsible for up to 25% of your energy consumption. Especially for households relying on electricity for water heating, a solar hot water system can save significant amounts of money. With a bit of planning (for instance, taking showers in the evening, after a sunny day), a solar hot water system can save you up to 80% of your water heating costs. So what’s the best solution for your household? Read on for an overview of solar hot water systems available in Australia, how they work, and the pros and cons of each.
Flat Plate Collectors for Solar Hot Water
A solar flat plate collector, a.k.a. thermosiphon or roof-mounted system, typically consists of a water tank and a large heat-absorbing plate, both installed on the roof. The flat plate collector is something of a hot box, or a greenhouse: the surface, or plate, absorbs the sunlight energy and traps it inside in the form of heat. Here, a series of copper pipes start heating up and cause the water contained within to warm up, as well; the latter circulates back and forth between tank and tubes until it’s hot enough, at which point it runs back down and into the household’s plumbing system.
While flat plate collectors tend to be cheaper and easier to install with respect to evacuated tube collectors, they are not very efficient due to their surface area being, well, flat. They work best when the sun is right above the roof and perform less at most other times, including the winter. Besides, flat plate systems can be heavy, to the point of potentially deforming the roof underneath, which then becomes a safety concern.
Evacuated Tube Collectors for Solar Hot Water
A second solar water heating method is called evacuated tube collectors. Also known as a split- or low-line system, this technology uses a similar mechanism to that of flat plate collectors. Instead of a flat surface, however, this type of solar hot water panel employs cylindrical tubes that absorb solar energy while at the same time limiting heat loss. The tube has no water in it: instead, it fits into a copper manifold, and the heat is then transferred across to the water. A sensor checks the temperature differential and coordinates a circulating pump, which sends cold water up to the roof and hot water back down and into the storage cylinder.
The main benefit of this technology is that the individual, rounded tubes increase the area perpendicular to the sun’s rays at any given time of the day, making them up to 33% more efficient vs flat plate collectors, as well as faster. It can take as little as three to four hours to collect a full tank of hot water, compared to six hours for flat plate collectors. Naturally, increased efficiency attracts higher-value STC’s, as well. In addition, were a single evacuated tube to be damaged during a storm, the rest of the system would not be impacted, and repair would only take 10 minutes, at minimal cost.
Compared to flat plate systems, evacuated tube collectors perform well in cold and overcast weather and are resilient even in challenging situations, such as heat waves or subzero temperatures. While evacuated tube technology may require a higher initial investment, they recoup this quite well over the years. One weakness of this system, however, is the water pump, a device that, while for the most part reliable, only has a 2-year warranty on it.
iStore Technology for Solar Hot Water
The newest technology available on the market and which wins our recommendation is called iStore by Solargain. It is virtually an air conditioning unit sitting on top of a tank, but working in reverse: through the use of a heat pump, it heats water up, instead of cooling it down. According to the Melbourne Energy Institute and the ‘Beyond Zero Emissions Report: 2013’, this type of heat transfer is 80% more efficient than electric or gas hot water systems. Added bonus: since the water tank sits at ground level, there is no need for any plumbing through the roof, which significantly reduces installation time and costs. As a guideline, an iStore system may only take two hours to put up, compared to a roof-mounted plumbing system where anywhere from five hours to a whole day may be necessary.
This system is unique in that it allows to store excess production in the form of hot water, because water is an energy storing system. Its storage capacity is comparable to that of a 6kW battery. iStore fits perfectly with our vision of making a household as efficient and self-sufficient as it can be—especially when coupled with a solar panel system. In fact, when your production has been at its highest for a few hours, your batteries are full, and you’ve got excess electricity that would otherwise go to the grid, water can act as a real energy storage device.
We hope that our overview has helped you appreciate what a solar hot water system can do for you. The average family may save 50% to 80% of their heating bills by switching to solar hot water, and in the sunniest of climates, that figure may be nearly 100%. Get in touch with us and see how we might help you minimise your hot water heating costs.