Published on September 22nd, 2018 | by Derek Markham0
Solar Diverters Can Supply Solar Hot Water From A Rooftop Array, Without Adding Any Extra Plumbing
September 22nd, 2018 by Derek Markham
Installing a solar diverter can essentially help convert a home’s hot water heater into an energy storage system, allowing solar homeowners increase their self-consumption during peak production hours.
The conventional method of generating solar hot water, which uses the thermal energy of sunlight to provide hot water either through a direct circulation system or via a heat exchanger, can be an effective solution for providing domestic hot water from renewable energy. And in many places, solar hot water is a great entry-level or gateway option for those looking to both lower their carbon footprint and to save money, without having to commit to the cost of a full rooftop solar array.
However, for those who already have rooftop solar, or are considering it, there’s a way to get domestic solar hot water without adding any extra plumbing, through the use of what’s called a solar diverter. In some places, most notably Australia, solar diverters have been coming into vogue as an additional way to reap additional value from a rooftop solar array’s excess electricity production, which would normally flow back on to the grid but in this case would by stored locally as hot water.
For those with electric hot water heaters, adding a solar diverter can essentially help convert it into a solar energy storage device, and although domestic water heaters aren’t nearly as sexy as a home battery storage system, they are a key part of a home’s energy demand. In fact, this aspect of residential energy use is already being targeted through the deployment of “smart” water heaters and Grid Integrated Water Heaters (GIWH), but depending on the particulars of a given installation and utility, the choice to either add a solar thermal hot water system or to use a solar diverter or to just feed the grid with excess solar electricity and then pay the demand costs to heat water later is a personal one. Due to the wide range of levels of solar electricity compensation, whether through net metering systems or feed-in tariffs, and the variety of electricity costs in different areas across different times of the day, each use case will have to be considered separately.
Although there are simple solar diverter devices that can be added between a solar array and an electric hot water heater, there are also companies manufacturing purpose-built solar electric hot water systems, such as the Solahart Power Store, which it claims is “Australia’s first solar-smart electric water heater.” Solahart’s Power Store system, when combined with a home energy management system (HEMS), is meant to allow the homeowner more control over their own electricity consumption.
Adding HEMS to your Solahart PowerStore® system allows you to purchase energy when it is cheaper by shifting loads away from peak demand periods. It also helps predict solar energy generation from your solar power system by using seasonal and daily weather patterns, and decides on when it’s best to use high energy consuming devices such as air conditioners and pool pumps.
Another option for solar electric hot water is coupling a heat pump water heater with a solar PV system, which setup is said to need “only about 1/3 of the PV modules to generate the electricity for domestic hot water as compared to a resistive electric tank.”
On a side note, in reading up about solar diverters, I was kind of surprised to see that we haven’t really covered the topic here on CleanTechnica very much at all over the years, even though we’ve covered solar thermal and solar hot water quite a bit, but a quick Google search shows a lot of results from Australian websites, which is a curious thing to me. Perhaps the economics of solar and the costs of electricity here in the US aren’t quite to the point where adding a solar diverter to a rooftop PV installation isn’t an obvious choice yet, but the fact that it’s a market to itself in another country seems to indicate that there are most likely a number of other relatively small efficiency and optimization tweaks that could be added to homes and their electricity systems to make them smarter and cheaper and more sustainable.