Recently an article in the Green Building Advisor suggested that Solar Thermal (solar hot water) is dead. The article claims it is more affordable to heat water with solar electric systems than solar hot water systems. Perhaps the author was putting forth a thought provoking statement to stimulate dialog amongst the renewable energy community – appropriate dialog for our time.
Due to the fact that solar electric panel (PV-photovoltaic) prices have dropped about 50% in the last year one can heat water with solar electricity for less money than solar thermal, in many cases. Strengthening this argument is the fairly recent addition to the marketplace of the heat pump hot water heater that is more efficient than a traditional electric hot water heater.
The costs vary considerably for solar thermal and electric. Outside of the numbers one should consider recovery time of the hot water heater, other practicalities, preferences etc. that often is not reflected in a strict quantitative analysis.
It is common for solar electric system costs to vary from home to home. The costs and ROI can vary by region, state incentives, site specifics, technologies, mounting options etc. Costs can vary based on the quality/efficiency of panels and inverters, orientation, tilt, shade issues etc. All these factors can impact production and thus ROI. Is the system mounted on the roof, the ground? How far is the ground mount from the electrical panel? Trenching and wiring costs can add up fast on a distant ground mount. Costs vary on the type of roof mount — composition (shingle), metal, or tile? A home in the northeast of the U.S. may be better off using solar electric to heat their water than a home in southern California, which may be better off using solar thermal.
What type of fuel costs are you offsetting with your solar thermal? If it is propane, then the solar thermal (and electric) system will have a fairly quick payback and good long term ROI — not to mention protection against energy price volatility.
Natural gas is at such a low price (for now) that it is difficult for solar thermal to compete. If you are considering solar electric or have already decided to invest in solar electric, by all means give strong consideration to adding some extra solar electric panels to offset an electric hot water heater. If you have very low electric bills and high propane bills for hot water then a stand alone solar thermal system may be the best way to go.
Size up your current and future hot water and electrical usage, assess your options, and consult a professional. Regardless, I think most people would agree that solar (electric and/or thermal) is a good investment.
Potential disadvantages of a solar thermal system:
- Most solar thermal systems have moving parts –pumps, sensors, valves etc. and thus need maintenance and eventual replacement of some parts.
- Solar electric essentially has no moving parts.
- Generally speaking a solar electric system will have a longer life than a solar thermal system.
- Freeze damage is a concern in some climates with solar thermal.
- Most owners of solar electric systems can get credit for their overproduction of electricity. It is sent to the grid and credit is given for it.
- Excess solar thermal production is typically wasted or unused. Generally on average a solar thermal system might produce 50-75% of a families hot water needs. Very little production in the short dark days of winter versus overproduction in the long hot summer days.
Experienced solar thermal designers and installers can create a system that does not need pumps or sensors, but these types of systems have their limitations. More modern solar thermal kits make for easier installation, better reliability, and increased efficiencies. One advantage of solar thermal is that it is most often less of an investment than a solar electric system. Most agree solar thermal is better than solar electric in an off grid application. And commercial hot water applications may be better off with solar thermal. Solar thermal is not dead. Solar thermal still has its place, its applications, and by all means is still alive!
PS- One thing not addressed in the GBA article is that a 30% tax credit with solar thermal that might also be applied (check with your CPA) to the back up heat source for hot water. I wrote about the Altherma last month. It supplies hot water for the home like boilers and tankless hot water heaters. A 30% tax credit (via the solar thermal) may apply to the back up heat source – which might pay for all or much of the solar thermal itself. This is an important point to consider if you are involved in new construction, a remodel or changing out a hot water heat source.
