When we are designing systems, we generally want to keep the currents as low as possible. If we put too much current through a circuit, the energy loss caused by this current increases exponentially. This current creates heat and reduces the overall efficiency of the system. This resistance builds up over distance, which means that the higher the current, the more issues you will have with power loss, particularly over a long cable runs.
To overcome this energy loss, you either need to install thicker and heavier cables, or increase the voltage of the system. If you double the voltage of a system, you halve the current and therefore reduces the energy loss significantly.
For example, let us say that we have two 12V, 200Wp solar panels that we wish to connect together to charge a battery. We have the choice of connecting them together in a series, to create a 24v, 200-watt circuit or connect them in parallel to create a 12v, 200-watt circuit:
- A 12-volt 100Wp solar panel has a current flow of 8.3 amps (100 watts ÷ 12-volts = 8.3 amps).
- If we connect the two solar panels up in series, the solar array also has a current flow of 8.3 amps (200 watts ÷ 24 volts = 8.3 amps).
- If we connect the two solar panels up in parallel, the solar array has a current flow of 16.6 amps (200 watts ÷ 12 volts = 16.6 amps).
It is usually better to double the voltage rather than double the current. Of course, there are exceptions to this rule. If, for instance, you want to use your system at 12 volts, for example, then you may decide to use thicker cables and keep cable distances to a minimum. This does limit the overall size of your system, but this may not matter. So long as you are aware of the problems and design around them, there is nothing wrong with this approach.