Solar Thermal Water Heating
The basic function of a solar thermal system is to pre-heat incoming city or well water to reduce fossil fuel consumption. Typically, incoming city or well water is supplied at 45F to 55F. Since most hot water heaters store water at 120 to 140F for domestic use (showers etc), preheating greatly reduces gas or electrical use.
System components
- Collectors
Solar collectors are the portion of the system that actively absorb the sun's energy. Collectors are classified as "flat plate" or "evacuated tubes". Regardless of the style, collectors use glass and copper to heat a liquid - typically glycol or water - which in turn heats water in a storage tank.
- Supply Lines
Copper supply lines connect the solar collectors to the storage tank in a loop (supply and return). One to three gallons of heat transfer fluid - usually non-toxic freeze-protected glycol - is circulated through the loop to transfer heat to the solar storage tank.
- Pump Station
Consisting of a small pump, valves, and gauges, the solar pump station circulates glycol from the collectors to a heat exchanger that transfers heat to water in the solar storage tank.
- Solar Storage Tank
A solar storage tank resembles a typical hot water tank with one important exception - it has a heat exchanger. The heated fluid from the collector flows through this heat exchanger to heat the water held in the tank. This preheated water (as low as 70F and as warm as 160F) is fed to the backup water heater, which now has to do a lot less work.
A general rule of thumb is that for every 1 square foot of collector there should be 1.5 to 2 gallons of solar storage. - Controller
The performance of the solar thermal system is managed through a controller. The controller turns on the pump when there is enough solar energy to heat the storage tank. It provides digital readout of tank temperatures, monitors system performance and has numerous other features.
Solar Thermal Space Heating
A solar thermal system for space heating heats domestic hot water and supplements a building's radiant heat system. It uses the same components as a solar water heater but requires more collectors and more solar storage.
Use of solar thermal for space heating is not as economical as domestic hot water (DHW) because mid-winter — the period of the highest heat load — corresponds to the time of year when solar energy is least available. That said, solar thermal systems do reduce space heating costs during all but the shortest or cloudiest days of the year, and especially early winter, late winter and even early spring.
Solar space heating systems are most effective when:
- Radiant floor heat is used.
- The building is well-insulated. If not, we recommend first spending money on insulation or perhaps limiting solar thermal to domestic hot water pre-heat.
- Solar collectors can be mounted vertically (70 to 90 degrees). This helps maximize winter solar exposure and reduce summer overheating. This orientation also promotes reflection from snow, which can increase collector production and eliminates snow loading. Ground- or wall-mounted arrays allow for vertical collector orientation.
- Solar components can be incorporated into a building early in the design process; ideally collectors become an architectural asset.
- There is space for larger (160 to 350+ gallon) solar storage.
Contact Us
Mailing Address
702 E. Peach St.
Bozeman, MT 59715
Physical Address
605 N. Wallace, No. 2
Bozeman, MT 59715
(406) 581-1972
liquid.solar@mac.com
