Solar thermal energy, or solar water heating, is a cost-effective, eco-friendly way to generate hot water through solar panels, working in conjunction with a heating system. The concept isn’t new — solar hot water systems have been around since the 1970’s — but recent technological advances have led to a greater selection of equipment.
Examples of advancement include PV thermal (PV/T) systems that capture heat from a variety of sources, including heat from PV modules, and water heating powered directly by PV-generated electricity.
Prices for major thermal components have dropped significantly, too. Gal Moyal, CEO and chief engineer at Free Hot Water, says with ROI in less than three years for large projects, solar thermal is attractive to large commercial natural-gas-boiler and tank-system users.
Monitoring has also entered the solar hot water realm. The ability to see a real-time graph of a functioning solar water heating system, along with the solar gain, tank losses, back up element use and draw was not available just a few years ago.
Photo courtesy of Alternate Energy Technologies
John Alger, manager of engineering at AET, says drainback design, which offers over-heat and freeze protection, high performance and low maintenance costs, also represents a growing trend in the industry.
He says these are the reasons why:
Fewer problematic components: There is no expansion tank, check valve or air vents, along with no need for a heat-dump strategy.
Higher performance: Water is a superior heat transfer fluid compared to glycol and, in most cases, developers only need a single wall heat exchanger when using water.
Lower maintenance: Water does not turn acidic not is it damaged from stagnation in a drainback system. Consequently, there is no need for the annual pH checks, or the five-year system flush and recharge. That translates into more profit for the client.
Lower cost: Drainback is ideal when used with atmospheric tanks because the tank also doubles as the drainback reservoir. Atmospheric tanks are a fraction of the cost of pressurized ASME tanks.
Fewer leaks: Glycol tends to be able to slip by pipe dope and Teflon tape better than water, so it is not uncommon, even with proper installation techniques, to have glycol leaks in the collector loop.
Despite these recent successes, solar thermal power faces several challenges in the marketplace. Among the challenges is a shortage of information and understanding regarding the function and benefits of solar thermal systems. Also, the initial cost of a solar thermal system is sometimes considered too high for consumers. Still, last year, SEIA formed the U.S. Solar Heating and Cooling Alliance (SHC Alliance) division.
As the industry strengthens, Suzan Elichaa of Maine-based Solaris sees a need for more technician education. Techs must be trained to service and repair solar thermal systems, not just install them.
“Solar professionals must understand the advantages and disadvantages of all product options to recommend the right solution for their client,” Elichaa says. “In many states, solar thermal is just ramping up, and there is a real lack of accurate knowledge about the systems.”
One company that has introduced a new system recently is Next Generation Energy. The company has eliminated pumps, heat exchangers and copper lines to create the SunBandit. The SunBandit harnesses energy from PV modules and transfers electricity to a microgrid water-heating component, which warms water in a specially designed tank. A grid-tied element provides a back up for the microgrid, creating a hybrid energy system. It does not require approval from utilities.