Combination Solar Water Heating and
Solar Electricity Generation
Pictured here is the array of solar collectors that directly produce hot water and electricity for use by the home owners.
The 5 panel solar water heating system was installed by the home owner. The 17 panel solar PV system was installed by a commercial supplier.
Location: Murrysville, PA, USA
The 5 panel solar water heating system was installed by the home owner. The 17 panel solar PV system was installed by a commercial supplier.
Location: Murrysville, PA, USA
How Solar Water Heating Works
Typical Domestic Closed Loop Antifreeze Solar Water Heating System
Installation of a solar domestic hot water (DHW) closed loop heating system will include:
Solar Energy Collectors
Fluid Handling Module
Energy Storage Tank(s)
Temperature Sensors and Control Electronics
The fluid handling module will usually have a circulation pump, expansion tank, air separator and air vent, and pressure and sometimes temperature instruments. The temperature instruments will show the temperatures of the fluid entering and leaving the solar collectors. The fluid module will also have fill and drain valves with check valve separation. Two temperature sensors to be installed, one each at solar collector and heat storage outlets to provide inputs to a differential temperature controller. The differential temperature controller starts and stops the circulation pump when solar energy can be collected and stored.
The fluid module is plumbed to and from solar collector panel(s) and to and from a heat exchanger inside a water heat storage tank. There are numerous suppliers of solar collector panels. These panel suppliers can also supply the hardware needed for supporting the panels and attaching them to roofs, etc.
STORAGE TANK NOTES
The solar heat storage tank can be a stand alone electric water heater with conventional electric heating element and thermostat in the upper part of the tank. In this case, solar heating preheats water prior to entering the water heater and the electric heating element adds any additional heat to attain normal hot water temperature.
A more efficient arrangement is to use a two tank system: 1) a special solar heat storage tank with internal heat exchanger and 2) standard hot water heater. In this case the solar storage tank is fed water at its bottom and receives solar heat. Its outlet leads to the cold water inlet of the standard water heater. When the water temperature entering the hot water heater is high, the water heater stays off. When the water is tepid, the water heater runs a shorter time, only long enough to make normal hot water. This two tank arrangement is more efficient because it has a bigger capacity for storing heat.
TEMPERATURE SENSOR NOTES
The two temperature sensors used by the solar controller are to be mounted 1) on the solar collector outlet piping at the high, hot point, and 2) at the cold exit of the storage tank heat exchanger. The pump controller compares the difference in temperature between these points. When the solar collector outlet reaches a typical difference of 9° Fahrenheit higher than the heat exchanger outlet, the controller starts the circulation pump. Later, when the difference falls to less than 4°F, the controller stops the pump. The solar pump controller is shipped with the on/off differential set at 9°F / °4F. The owner may change this by moving dip switches to 18°F / 5°F.
Sensors are installed by clamping a sensor against the pipe surface with a hose clamp. Each sensor has two insulated leads with bare wire electrical connections at their ends. These wires should be connected to signal cable using wire nuts and further covered with electrical tape. The leads can be folded over against the signal cable and taped down so that they are not loose. The entire assembly, sensor with hose clamp & taped wire nuts, should be covered with pipe thermal insulation. The insulation should be installed to prevent direct exposure of sensor and connections to sunlight, rain or snow.
The signal cable can be telephone cable, CAT5, thermocouple wire or any cable with at least one pair of conductors. Where it is exposed to outside environment, it must have weatherproof jacket.
OTHER ITEMS
Recommended extras are an automatic air vent installed at high point of solar collectors to remove air during initial filling. It is useful to have a Flow Meter (rotameter type) to be installed in piping leading to the solar collector. For safety, a tempering valve should be installed at water heater outlet to maintain normal hot water temperature in supply. Pipe insulation is required over all piping to and from the solar collectors and heat storage tank.
Other materials needed for installation are stainless steel hose clamps for mounting temperature sensors to piping, 18 gauge low voltage thermostat wire for connecting sensors to controller and glycol and water mixture, 50%/50%.
Installation of a solar domestic hot water (DHW) closed loop heating system will include:
Solar Energy Collectors
Fluid Handling Module
Energy Storage Tank(s)
Temperature Sensors and Control Electronics
The fluid handling module will usually have a circulation pump, expansion tank, air separator and air vent, and pressure and sometimes temperature instruments. The temperature instruments will show the temperatures of the fluid entering and leaving the solar collectors. The fluid module will also have fill and drain valves with check valve separation. Two temperature sensors to be installed, one each at solar collector and heat storage outlets to provide inputs to a differential temperature controller. The differential temperature controller starts and stops the circulation pump when solar energy can be collected and stored.
The fluid module is plumbed to and from solar collector panel(s) and to and from a heat exchanger inside a water heat storage tank. There are numerous suppliers of solar collector panels. These panel suppliers can also supply the hardware needed for supporting the panels and attaching them to roofs, etc.
STORAGE TANK NOTES
The solar heat storage tank can be a stand alone electric water heater with conventional electric heating element and thermostat in the upper part of the tank. In this case, solar heating preheats water prior to entering the water heater and the electric heating element adds any additional heat to attain normal hot water temperature.
A more efficient arrangement is to use a two tank system: 1) a special solar heat storage tank with internal heat exchanger and 2) standard hot water heater. In this case the solar storage tank is fed water at its bottom and receives solar heat. Its outlet leads to the cold water inlet of the standard water heater. When the water temperature entering the hot water heater is high, the water heater stays off. When the water is tepid, the water heater runs a shorter time, only long enough to make normal hot water. This two tank arrangement is more efficient because it has a bigger capacity for storing heat.
TEMPERATURE SENSOR NOTES
The two temperature sensors used by the solar controller are to be mounted 1) on the solar collector outlet piping at the high, hot point, and 2) at the cold exit of the storage tank heat exchanger. The pump controller compares the difference in temperature between these points. When the solar collector outlet reaches a typical difference of 9° Fahrenheit higher than the heat exchanger outlet, the controller starts the circulation pump. Later, when the difference falls to less than 4°F, the controller stops the pump. The solar pump controller is shipped with the on/off differential set at 9°F / °4F. The owner may change this by moving dip switches to 18°F / 5°F.
Sensors are installed by clamping a sensor against the pipe surface with a hose clamp. Each sensor has two insulated leads with bare wire electrical connections at their ends. These wires should be connected to signal cable using wire nuts and further covered with electrical tape. The leads can be folded over against the signal cable and taped down so that they are not loose. The entire assembly, sensor with hose clamp & taped wire nuts, should be covered with pipe thermal insulation. The insulation should be installed to prevent direct exposure of sensor and connections to sunlight, rain or snow.
The signal cable can be telephone cable, CAT5, thermocouple wire or any cable with at least one pair of conductors. Where it is exposed to outside environment, it must have weatherproof jacket.
OTHER ITEMS
Recommended extras are an automatic air vent installed at high point of solar collectors to remove air during initial filling. It is useful to have a Flow Meter (rotameter type) to be installed in piping leading to the solar collector. For safety, a tempering valve should be installed at water heater outlet to maintain normal hot water temperature in supply. Pipe insulation is required over all piping to and from the solar collectors and heat storage tank.
Other materials needed for installation are stainless steel hose clamps for mounting temperature sensors to piping, 18 gauge low voltage thermostat wire for connecting sensors to controller and glycol and water mixture, 50%/50%.
