Here is what makes a solar panel high voltage or low voltage.
A low voltage solar array has an output voltage slightly higher than the battery voltage. In this case, you don’t need to modify the voltage to charge the batteries or power the inverter. Typical battery voltages in this setup are 12 volts, 24 volts, and 48 volts. A low voltage solar panel array usually has many panels or short strings connected in parallel.
A high voltage solar array outputs a much higher voltage than the battery voltage. The output is usually hundreds of volts. Also, the system must modify this voltage before it can charge batteries with it. A high voltage solar panel array usually has long strings of panels connected in series.
Here is how they influence conductor sizing.
A low voltage solar panel array needs thicker wires going to the charge controller. Also, such an array will need more parallel sets of strings. This demands more wiring and more fuses or circuit breakers.
To illustrate this, let’s look at 2 example solar arrays. Both are 4,800 watt arrays made of ten 48 volt solar panels. The high voltage array outputs around 240 volts and 20 amps. The low voltage array outputs around 48 volts and 100 amps.
High voltage example
This consists of 2 parallel strings with 5 panels in each. It needs 2 pairs of wires going into the combiner, and it needs 2 circuit breakers or fuses. It needs a pair of 12 AWG wires from the combiner to the charge controller.
Low Voltage Example
This consists of ten solar panels in parallel. It needs 10 pairs of wires going into the combiner. The low voltage array also needs 10 circuit breakers or fuses. It also needs a pair of 1 AWG wires from the combiner to the charge controller.
1 AWG wire can be up to 10 times as expensive per foot as a 12 AWG wire from the same manufacturer.
Here is how transmission losses affect them.
The low voltage array will need higher amperage for the same power. This often results in hotter wires and higher transmission losses because of ohmic resistance. So, high voltage solar panel arrays are more efficient than low voltage arrays, especially when they are far from the house.
Here is the type of charge controller you need for each one.
A high voltage solar array needs an MPPT (maximum power point tracking) charge controller. An MPPT charge controller converts the voltage with very little power loss. It does so by increasing the amperage when it reduces the voltage. A pulse width modulated (PWM) charge controller also reduces the voltage. But the amperage doesn’t increase, so it loses a lot of power in the conversion. Therefore, an MPPT charge controller is better for a high voltage solar array.
A low voltage solar array does not need to convert the voltage. So, a PWM charge controller doesn’t cause a large power loss. For this reason, either a PWM or MPPT charge controller will work with a low voltage system.
A PWM and an MPPT charge controller cost roughly the same per watt. So, you might as well use the MPPT charge controller, which can work with both high and low voltage arrays.
Here is how they affect your need for a rapid shutdown system.
The rules for a rapid shutdown system apply to any solar power system mounted on a building. It must be able to reduce the voltage to 30 volts or less for conductors outside 1 foot from the array, or more than 3 feet into the building. This voltage is measured from any 2 conductors or any conductor and ground. The rapid shutdown system should also reduce the voltage within 1 foot of the array to 80 volts or less. These rules are to prevent electrocuting firefighters. These requirements don’t apply to solar arrays on pylons away from the house.
A high voltage solar panel array will need a rapid shutdown system. That is unless the array is on pylons away from the house.
A low voltage solar panel array might not need a rapid shutdown system, depending on the system. A 12 volt or 24 volt array will not need a rapid shutdown system. A 48 volt array will need a rapid shutdown system unless it is located away from the house.
In summary, a high voltage solar panel array is more efficient than a low voltage solar panel array, especially if it is far from the house. It allows smaller wires and lower transmission losses. This will give you greater flexibility in where you locate the array. A high voltage solar array also needs fewer fuses or circuit breakers. You will need a rapid shutdown system if the array is on your house, but the superior efficiency is worth it. This is why high voltage solar panel arrays are so popular.