If you are looking to invest in solar or already have PV solar panels on your roof, then consider investing in a Solar Thermal Water Heater. A typical electric water heater consumes 4500W every time it turn on – this could be 95% of your 30kW system leaving you only 500W to use in the rest of the house. If your air conditioning in running or any combination of other appliances, then you’ll have to buy electricity from the grid – and buying more from the grid is what we’re trying to avoid.
Solar Thermal works is different than solar PV. Where PV uses solar photons to generate DC electricity at the panel, Solar Thermal Collectors utilizes fluid to absorb solar radiant heat (see images below). (1) Fluid, typically a Glycol® mixture (for freeze protection) is pumped through tubes inside your southern-facing solar panels to absorb the free solar radiant heat. Then (2) heated fluid coils around water heater tank transferring heat to the water. This hot water is ready for use (3), and then the solar pump station (4) monitors hot water thermostats inside tank to pump at the rate needed to satisfy hot water needs. State Water Heaters offers programmable pump stations that allow you to adjust it to your needs and life-style.
Solar thermal allows you to heat your water using far less energy load (around 100W) through the use of the pump than that or a typical electric water heater (4500-5000W). If you are looking to invest into solar PV then adding on solar thermal water heating is worth the extra expense.
Turns out the sun generate a lot of heat. This mean solar thermal heats the circulating fluid to temperatures much hotter than you would ever want your shower to be. However, the heat transfer takes time to heat your hot water tank. Because of this, you want larger storage so that you can take advantage of more sun hours of solar thermal’s radiant heating. Examples: 1) if a smaller 40 gallon tank is used, then when your thermostat inside the tank senses maximum allowed temperature (about midday), then your pump will stop so that you stay within temperature safety limits. At night you’ll only have 40 gallons of hot water before you have to use electricity from the grid to heat water using the backup electric element. Or, 2) use larger storage like 80 or 120 gallons allows you to maximize water heating during your available sun hours and more usable hot water will be available in your house. With larger storage, you have more available hot water available at night or early in the morning (non-sun hours), so you don’t have to tap into the grid for your hot water needs.
For more information on Solar Water Heaters, give us a shout!