Harvesting solar energy
The driving force for a solar hot water system comes from the solar collectors – in particular, the absorber plates. Covered in a black (or very dark surface) the absorbers are exposed to the sun. The energy contained in the solar radiation is converted to heat (that is, into thermal energy) by the absorbers. To understand how Envirosun systems maximise the amount of solar energy absorbed, read: More heat than light.
To reduce re-radiation from the hot absorbers back to the environment, they are placed within a collector case that is insulated and fitted with a glass cover. To learn more about how Envirosun solar glass works, read: Our solar glass The results are clear.
The absorbers are filled with a liquid, which provides the means of collecting and transferring the solar energy to a heat store. In most (but not all) cases, the heat transfer liquid is simply water – the same water that will eventually come to hot water taps. In some cases, the liquid in the absorber plates is not consumed but instead re-circulates between the absorbers and the heat store as part of a closed-circuit.
The way energy is transferred from the absorbers to the tank depends on the system type:
Thermosiphon systems, such as the Envirosun TS range rely on the natural tendency of hot water to rise and displace cooler water above it. The hot water leaving the absorbers flows into the mid-point of the tank to be replaced by cooler water from the bottom of the vessel. This means that the top half of the tank quickly fills with hot water while the collectors add heat to the cooler water lower down. To understand this process in detail, read: Our connections.
Active systems, such as the Envirosun AS use an electronic controller and circulating pump to make the transfer. Just like the thermosipon systems cool water is drawn from the bottom of the heat store and returned to the mid-point as solar-heated water. To learn how this is controlled, read: Our pumps and controls.
The heat store comprises an insulated, water-filled storage cylinder. Generally the stored water forms part of the open-circuit that connects to the absorbers and eventually flows as hot water into the home. Sometimes, the water in the heat store is not directly connected to the absorbers but instead is separated by a heat exchanger that is wrapped around or immersed in the heat store. To read how Envirosun tanks hold more heat, read: Our insulation.
When hot water is drawn into the home it comes from the hottest part of the heat storage tank. This happens because the hot water outlet pipe is located at the top of the tank (and is often fitted with a scoop which reaches up). Cold water that flows into the tank to replace the drawn-off hot water enters at the bottom (often through a ‘diffuser’ that prevents un-wanted mixing and tempering).
There will always be times when solar energy can’t meet all of the hot water needs. Whether it’s because of poor weather or high hot water usage, it is just not practical to entirely rely on the sun. For these days, most solar hot water systems are provided with some form of back-up heating. The most common method is to immerse an electrical heating element inside the heat store controlled to operate when additional hot water is required. Other solutions involve feeding the outlet of the solar hot water system into a separate electric or gas heater to boost the hot water temperature. To learn about the auxiliary heating options that Envirosun offers, read: Our back-ups.