Solar Water Heating

Solar water heating, also known as solar thermal systems, are a proven technology that has been used successfully for over 30 years. These systems transfer heat from the sun into a solar fluid and then to a home’s domestic hot water, space heating system, or both.

Domestic Water Heating Systems

Domestic water heating systems use the sun’s energy to provide a portion of your home’s hot water needs. In Wisconsin, these systems can provide up to 75% of a home’s annual water heating requirements. The solar water heating system will typically supply nearly all of the home’s hot water during summer months. Your existing water heater acts as a backup during winter and cloudy periods.

Space Heating Systems

Solar water heating can be used to provide heat for your home, too. Since space heating needs are greatest when there is the least amount of sun, these systems are much larger than domestic water heating systems. Typically, domestic hot water heating for the home is also provided by the same system. In Wisconsin, up to 50% of annual space heating needs can be met with a solar hot water space heating system.

Domestic Water Heating System Diagram

The numbers used in the following text refer to the system diagram below. The main components of this system are: the flat plate collectors (1), the heat exchanger/storage tank (2), the circulating pump (3), the photovoltaic module (4), and the mixing valve (5).

When the sun shines on the collectors (1), it heats up the fluid. At the same time, that sunlight provides power to the circulating pump (3) via the photovoltaic module (4). The heat absorbed by the collectors is transferred to the potable water in the storage tank (2) via a built in heat exchanger in the bottom of the tank. Cooler fluid exits the heat exchanger and returns to the collectors to be reheated by the sun.

The solar heated potable water in the storage tank (2) is fed directly to your conventional water heater where additional heat may be added (if needed). From the water heater, the hot water enters the mixing valve (5) that provides scalding protection in case the storage tank water is hotter than the desired hot water tap temperature. The output of the mixing valve is connected to the house hot water supply.

Solar Space Heating/Dometic Hot Water System

The numbers used in the text below refer to the system diagram on the following page. The main components of this system are: the flat plate collectors (1), the heat exchanger/solar storage tank (2), the circulating pump (3), the photovoltaic module (4), the supply loop (5), and the demand loops (6, 7).

When the sun shines on the collectors (1), it heats up the fluid. At the same time, that sunlight provides power to the circulating pump (3) via the photovoltaic module (4). The heat absorbed by the collectors is transferred to the water in the storage tank as it is circulated through the supply loop (5) in the bottom of the solar storage tank (2). Cooler fluid exits the source loop and returns to the collectors to be reheated by the sun. This part of the system is a closed loop meaning that the same fluid is continually circulated and no fluid is lost or gained.

Heat is removed from the storage tank for use in the home via two demand loops (6, 7) near the top of the solar storage tank. One loop (6) provides space heating to the in-slab radiant heating system while the other (7) provides domestic hot water.

The space heating loop will transfer solar heat from the storage tank into the slab. The cooler fluid will return from the slab to be reheated by the demand loop (6). This part of the system is also a closed loop where the same fluid is continually circulated. If the heat present in the solar storage tank is not adequate to supply heat to the slab, the system will automatically switch the heating function to the LP boiler. This can occur during periods of extended cloudy weather and/or extreme cold. A mixing valve is present at the output of the storage tank to prevent high temperature water (>140° F) from entering the in-slab loops.

The domestic water heating demand loop will transfer solar heat from the storage tank into the hot water heater. Cold water is supplied to the demand loop (7) by the well pump. The water is then heated as it passes through the demand loop. If the heat provided by the solar storage tank is lower than the water heater setting, the water heater will turn on to boost the temperature as needed. A mixing valve is present at the output of the water heater to prevent scalding temperatures at household water outlets. This is an open loop system component in that water is continually added (from the well) and removed (shower, washer, etc.)