Solar Charge Controllers
A solar charge controller is an electronic circuit that adjusts the output voltage and current of solar panels to match the needs of the batteries being charged. In order to charge a battery, your charger--or in this case--your solar panel must be at a higher potential than the battery being charged. In other words, the voltage of the panel must be greater than the opposing voltage of the battery under charge, in order to produce a positive current flow into the battery. But how much more should it be? The current flow can be calculated using Ohm's law: E=I*R; where E is the voltage in expressed in volts, I is the current in Amperes, and R is equal to the resistance measured in ohm's. The effective voltage in this circuit is the output voltage of the solar panel minus the opposing voltage of the battery. We can determine this difference in voltage necessary to cause our desired current flow by plugging our known values into the equation. Assuming a 12 volt battery with a 50 Amp-hour capacity, our target charge rate should be about 10 Amps. There is no resistor in this circuit except for the internal impedance of the battery, which is a fraction of an ohm. In this case we will approximate it to be 0.2 ohms. Using Ohm's law we multiply 10 Amps by 0.2 ohms and we get 2 volts as a result. This means that our solar panel must be 2 volts higher than our battery voltage to maintain our target charge rate. This example is meant to show that the rated output voltage of your solar panel must be greater than the battery being charged for your solar charge controller to work. As I mentioned earlier, the actual values are dynamic and thus the need for a charge controller. Go Green Solar has some excellent solar charge controllers available at a reasonable price, which allow them to adapt to different battery and panel combinations such as 24v, 36v, 48v, etc. These controllers use DC-DC converters to match the voltage and use digital circuitry to measure actual parameters many times a second to adjust the output current accordingly.
The Thermosiphon System
The laws of thermodynamics dictate that certain conditions exist to allow heat to flow properly throughout the system. If these mandatory conditions exist, convection will naturally cause a thermosiphon to occur within the closed-loop system. These physical requirements are as follows:
- The output of the collector must be above the level of the return.
- The hot water storage tank must be located above the collector.
- The output of the collector must be piped to the top of the storage tank or heat exchanger coil.
- The bottom of the tank or coil must return to the bottom of the collector.
- There must be a minimum of hydraulic resistance and heat traps.
Once these criteria are met, the system can function properly. Initially, as solar heat is introduced to the system, the water in the collector tubes becomes less dense, resulting in convection flow upwards toward the outlet of the collector. The heated water rises naturally to the storage tank or heat exchanger. This heated water enters the top of the tank and the cooler water at the bottom of the tank, being more dense, descends down the return pipe to the bottom of the solar collector. Providing there is a minimum of hydraulic resistance, such as sharp bends in the tubing; and the piping does not contain heat traps in the form of dips causing a negative pitch, then the heat will continue its cycle unimpeded.
As more people seek alternative sources of energy to reduce their heating bills or to be free of the grid completely, renewable sources of power such as solar are sought more frequently. The thermosiphon solar collector system satisfies this increasing demand by offering a method of heating potable water or providing a source of radiant heat that is completely free to operate!
- Hot water out
- Storage tank
- Collector output
- Solar collector
- Cold water feed / collector return
