Traditional gas and electric water heaters are powered by fossil fuels, and emit large amounts of CO2. A solar water heater can reduce CO2 emissions AND your energy usage for heating water from 60% to 80%. Solar Water Heating systems convert solar radiation to heat for domestic hot water, space heating, radiant floor heating, or pool heating. A typical solar water heating system can reduce a household’s CO2 emissions by 6,000 lbs. This is roughly equivalent to removing 1.5 cars from the road. Solar hot water systems qualify for generous state rebates and federal tax credits.
Active Solar Hot Water Systems
Active systems utilize pumps to move the water through the collectors and back to the storage tank. Active systems can be closed loop or open loop.
Pressurized closed loop systems (see animation below) transfer the heat energy from the collectors to the storage tank by pumping a fluid, usually a mixture of water and glycol, hrough a heat exchanger. This fluid never comes into contact with the water in the storage tank. These systems use the least amount of electricity compared to other active systems, and since the fluid is a closed loop, the system components like pumps and valves avoid contact with the “hard” city water which extends their service life.
Drainback systems have a small accumulator tank which stores the fluid which flows through the collectors. When the system becomes active, the water is pumped from the accumulator tank through the collectors. An additional pump transfers the energy from the accumulator tank to the primary storage tank. Drainback systems are optimal when the hot water usage is sporadic or seasonal. Draining of the collectors prevents overheating and damage to the heat transfer fluid, as well as protecting the collectors from freezing.
Active open loop systems pump the city water through the collectors and into a storage tank. Active open loop systems transfer the suns energy very efficiently to the tank, although the tend to have a shorter life span than closed loop systems. As a result of being exposed to hard city water, open loop systems are more susceptible to internal pipe corrosion, and unreliable freeze protection often results in freeze damage to collectors. Open loop systems are generally undesirable in areas with hard water such as San Diego.
Passive Solar Hot Water Systems
Passive systems by definition use no electricity for pumping water through the collectors. Passive systems fall into two basic categories; Thermosyphon and ICS (Integral Collector Storage). Thermosyphon systems use the principle of convection to heat the water in a storage tank. These systems place the storage tank above the collectors, and as the fluid in the collectors heats up it rises up to the storage tank where the energy is transferred, and the cooled fluid returns to the collector.
ICS systems consist of storage tanks enclosed in a case which are usually painted black, and transfer the sun’s energy directly into the water in the tanks. Both ICS and Thermosyphon systems are quite heavy, and the roof structure should be inspected by an engineer prior to installation to ensure the roof can safely carry the weight.
- Reduces CO2 emmissions for heating water 85% or more
- Reduces pollution associated with natural gas and coal
- Greatly reduces your gas or electricity usage for heating water
- Protects you from utility rate increases and fluctuations
- Tried and true technology
- Long system life of 30+ yrs
Solar Hot Water Case Studies