Solar hot water systems are usually designed to provide 90% of the building’s hot water needs during peak production. Although there is still the need for a backup source, solar energy can reduce a home’s fuel consumption by 80% or more.
In fact, for systems being operated on a continuous basis, if financed at market rates, the system earns money from day one—that is, the cost savings per month exceeds the monthly loan payment. Depending on the size of the system, it will pay for itself entirely in just a few years.
Mass Clean Energy Center has expanded its rebate program MCEC renewable energy rebate programs
Solar hot water is among the most cost-effective means of supplying energy to a home. It is less expensive than grid-based sources of electricity including coal, nuclear, and natural gas. Solar hot water use has doubled in the United States over the last ten years, and it could provide 5% of commercial energy demand and 15% of residential demand by 2015.
There are a few versions of solar hot water systems; drain back, direct solar open-loop with water, and indirect solar closed-loop (with glycol to guard against freezing in cold climate regions).
Since we service the New England area our example outlines the main components of a closed-loop solar hot water system.
- Solar collector panel. Usually mounted on your roof, the collector captures the heat from the sun and transfers it to the liquid circulating through the panel.
- Solar storage tank. The solar storage tank is where the heat energy captured by the collector panel is stored for later use.
- Heat exchanger. The heat exchanger transfers the heat energy captured by the collector panel is transferred to the potable water that is stored in the solar storage tank. In our pressurized system, the heat exchanger is integral to the solar storage tank. In our drainback system, the heat exchanger is in the drainback tank.
- Control system. The control system consists of the differential controller and the circulating pump.
The differential controller compares the temperature difference between the solar storage tank and the collector panel. When the collector panel temperature is 20 degrees higher than the storage tank temperature, the controller turns on the pump(s) and circulates the water through the system until the temperature difference is only a few degrees, then turns the pump off.
How Does It Work? Solar collector panels or evacuated tubes containing a heat transfer fluid (a mixture of water and food-grade glycol) are installed on the roof at a favorable angle to the sun. Temperature sensors are installed on the collector panel and on the storage tank. When the temperature in the collector panel is 20 degrees higher than the temperature in the storage tank, the differential controller turns on the system pump(s) and circulates the water from the collector panel through a heat exchanger where the heat is transferred to the storage tank. Water continues to circulate until the temperature of the water in the storage tank is within a few degrees of the collector temperature. Then the differential controller turns off the pump(s). As hot water from the storage tank is used, this cycle is repeated.
Radiant Heating Systems For Your Home
You can also use a solar hot water (or thermal) system to heat your home. Rather than transferring the heated water to a domestic hot water heater, the solar hot water system can connect to a radiant floor and/or wall panel radiator.
You can make the collection and distribution system as simple or complicated as you like depending on your location, climate, and intended use. Most radiant heating systems use the collection array to heat water and store it in a large thermal collection tank so that you have enough heat to last at least throughout the night. A general rule of thumb is to have a collection tank that can store 1½ to 2 gallons of water for every square foot of solar collector. That water, in turn, is piped via plastic tubing under floors to create an effective heating system.
Radiant floor heating systems have many advantages. They are typically 40 percent more efficient than a forced air heating system and can be zoned so that each room has its own thermostat. Furthermore, radiant floors distribute heat beneath your feet where it naturally rises providing a cozy and evenly distributed heated living space.