A solar controller is an electronic device That controls the circulating pump in a solar hot water system to harvest as much heat as possible, from the solar panels and protect the system from overheating. The basic job of the controller is to circulate the pump when it is hot in the panels, moving the working fluid through the panels to the heat exchanger at the thermal store . Heat is available whenever the temperature of the solar panel is greater than the temperature of the water in the heat exchanger. Overheat protection is achieved by turning the pump off when the store is in place.
Most commercial controllers display the temperature of the hot water in the store and provide general status information about the system, including overall energy production.
The simplest solar controller circuit uses two temperature inputs, one at the solar panel and one at the thermal store ‘s heat exchanger, and an output to control the pump. Commercial controllers use a microprocessor usually with a LCD display and a simple user interface with a few pushbuttons. Power for the controller and the pump can come from a hands electric supply or from a photovoltaic (PV) module. [ quote needed ]
The controller’s main function is to switch the circulating pump on or off. The pump is usually switched on when the solar panel is hotter than the water in the heat exchanger and off when the panel is colder. Switching the pump on the heat in the panel to the store. Switching it off when the panels cool prevents a reversal of the process and loss of heat from the store. The controller measures and compares the temperatures in the panel and the heat exchanger every few seconds.
Commercial controllers do not turn on the pump until the difference in temperature between the panels and the water in the heat exchanger is sufficiently to provide more energy than is consumed by the pump. This temperature difference s’intitule the one differential (usually 4-15 ° C. They turn off the pump When the panels are no follow hot enough to Provide significant heat to the store (the off differential ). The différence entre the ‘wider differentials thesis, These factors are usually set by the solar system, particularly dependent on the efficiency of the heat exchanger and production capacity of the panels.
Controllers provide an overrun time to extract some of the heat energy left in interconnecting pipes after the panels cool off. They may also implement certain safety features such as cooling the store when it exceeds a temperature of 65 ° C, by sending excess heat back to the panels to be given to the environment.
Photovoltaic powered solar controller
A photovoltaic (PV) powered solar controller uses solar energy produced on-site to run the solar-heated transfer fluid to the hot water store.
One claimed advantage of PV power is that it reduces the overall carbon emissions associated with operating the system since it avoids the need to supply this energy from fossil sources. [ citation needed ] However, the energy required to operate the system is very small in comparison to the energy produced by the system and the carbon emissions reduction of PV power fractional addition. [ quote needed ]
The most practical benefit of a PV driver is the result simplicity of the overall system. Rather than using complex algorithms based on solar panels, the pump is driven directly by the PV panel: when the sun shines, the pump runs. In practice this is nearly (90-99%) efficient and easy to understand. [ original research? ]
A disadvantage to the PV powered approach is that the pump stops immediately after the sun is occluded. With solar panels and solar panels, these tubes can be seen in the sun. To avoid overheating the tubes, it is necessary to have a circuit for a short time after the sun, or else to provide a large reservoir of fluid in the header above the tubes. Neither of these options are really compatible with the simple direct-PV pump approach and so such systems are limited to using the less efficient flat panel collectors. [ quote needed ]
A PV powered controller may contain a small amount of electricity when it is used. This electricity store is usually in the form of supercapacitors , since these have a much longer life than batteries . [ quote needed ]
The benefits of a solar powered controller at a cost in a reduced system performance in the range of 1-10%.  This is due to heat losses at times when the panel may be hotter than the water store but there is insufficient sunlight to power the pump. This happens when it is possible to be in excess of the potential for it. [ original research? ]
- Jump up^ Martin C; Watson M (2001). “Side-by-side Testing of Eight Solar Water Heating Systems” (PDF) . United Kingdom Department of Trade and Industry. Archived from the original ( PDF ) on June 30, 2007 . Retrieved 2007-08-04 .