18 June 2012
There’s money to be made in selling, installing and servicing solar hot water (SHW) for both residential and commercial use. In fact, all indicators point to an expanding market for installing domestic hot water and commercial process heat systems (for sterilizing food and beverage equipment and distilling processes in chemical manufacturing) that use the sun’s rays as the energy source.
There’s money to be made in selling, installing and servicing solar hot water.
In just the residential segment of SHW alone, the Solar Electric Power Association estimates a potential $123 billion market in the US Commercial enterprises accounted for a full quarter of all SHW installations in 2009, according to the Interstate Renewable Energy Council. According to some industry watchers, that share should increase as companies look to improve efficiency and save fuel costs. In Europe, nearly 2.6GWth was installed in 2011, bringing total thermal installations to 26.3GWth. This amounts to 18.8TWh of solar thermal energy, contributing to a savings of 13MMt of CO2. Overall market growth in Europe was 9% in the last ten years, according to a report by the European Solar Thermal Industry Federation.
While SHW equipment has traditionally been low cost to manufacture and many parts have been culled from off-the-shelf commodities, there have been hardware and software developments resulting in more efficient systems. Manufacturers and distributors are also making it easier for installers by selling packaged setups in addition to letting them mix and match the necessary components.
The concept is simple enough: Water circulates through a solar collector where it’s heated by the sun’s rays before heading back into a home or commercial building. For details on different designs, read “Domestic Solar Thermal: Nuts and Bolts of the Technology.”
In cold climates, most SHW systems are active, closed-loop systems. To prevent freeze damage, an antifreeze liquid circulates through the solar collectors in a closed loop and transfers heat to potable hot water at the heat exchanger. A circulating pump moves the liquid, making it an active system.
Power consumption can be further reduced by running the pump off a small photovoltaic panel. When no pump is used, heated water relies on convection to move and the setup is deemed a passive SHW system. In warmer climates, water can move through the collectors, making it a direct or open-loop design, and the water is fed directly to the store.
Water is typically kept in an insulated storage tank often connected to a backup heating supply. Most packaged arrangements include choices of storage tanks for residential applications ranging in size from 40 gallons to 120 gallons. Many tanks are manufactured with stainless steel linings rather than glass linings to avoid corrosion and the need for anode rods. Many of these also include heat exchangers built onto tank exteriors.
Tanks can also be purchased insulated or uninsulated in capacities ranging from 200 gallons up to 1,000 gallons. Some large-volume tanks are built with interior coil heat exchangers. For even greater amounts, some distributors sell modular storage tank systems specifically designed to be assembled on site for retrofit applications. They provide storage from about 300 to 12,000 gallons for multi-residential and commercial systems. The super-insulated (6-10 inches of fiberglass) and pressure-free tanks use integrated high-grade steel corrugated heat exchangers. Drain back tanks allow water from solar collectors and pipes to drain in both freezing and overheating events, and expansion tanks are also generally part of any SHW system.
SHW monitoring systems
The newest advances in SHW hardware and software have come in the form of monitoring capabilities. Most efficient SHW systems include a differential temperature controller that will sense when the collectors are cooler than the water in the system and shut off the pump, preserving the hot water. Controllers can also determine when to re-circulate liquid in a closed-loop to prevent freezing, drain water from collectors in extreme hot or cold events and perform other operations. Many controllers are also equipped with advanced monitoring systems that record operation and can display data on a monitor or send it to a computer or mobile device so service companies, property managers or homeowners can make adjustments. While these add costs to smaller, residential systems, recent advancements can often make the return on investment acceptable for many home systems.
Finally, aside from a long list of piping and connectors that is part of any hot water system, SHW installations often include a number of safety and check valves at various locations. One of the key pieces of the puzzle, especially in cold climates, is a frost valve near the collectors that will bleed off fluid if it starts to freeze. For more on the use of frost valves, see “Solar Solution: Frost valve for solar thermal.”
Whatever the application, it’s important to note that each location will have different requirements. Systems should be designed with the location’s load needs and environment in mind.
Written by Jonathan Gourlay, Contributing Editor, Solar Novus Today
Proximity Hotel: First Light Solar
Solar Circulating Pump: Laing Thermotech
Thermal Storage Tanks: Rheem
Solar Thermal Monitoring System: SunReports