Many homeowners prefer to go off-the-grid to become completely energy independent. The thing is that off-grid solar systems aren't connected to the electricity grid, so they will continue working even if the public power grid is not functioning. However, this is only achievable with reliable solar equipment, such as a good off grid inverter.
How off grid solar inverters work
PV modules use the solar power and turn it into direct current (DC). It can power lighting in your home and chargers for small devices, like a smartphone. But most home appliances function on alternating current (AC). This is where an inverter comes into play: it turns direct current into alternating. The efficiency of an inverter is close to 100%, which means that almost no power loss occurs while it's working.
DC-AC converting is not its only function. Solar off grid inverter also gives the owner an option to monitor the functionality of the whole system. Besides, inverters can act as power output maximizers: they track the voltage of panels and identify the optimum operational power for the whole array.
How is an off-grid inverter different from a grid-tied inverter?
You can’t use a grid-tie inverter for an off-grid solar PV system. It can easily damage the whole system and here is why.
Grid tied inverters have a control device to match the inverter cycles with the utility grid cycles. They need to be in phase, otherwise the voltages will cancel each other out. When there is no reference cycle, like in an off-grid system, the matching circuit disconnects the solar power to prevent electricity from backfeeding into the grid.
Are off grid micro inverters any good?
Microinverters are more popular in America than anywhere else. This type of inverter is installed directly on a panel, so that DC turns into AC right on the spot. It is a good choice when your panels are subjected to shading, because weak performance of one panel doesn't affect others. Microinverters make a system more efficient and don't occupy a lot of space. That is why a lot of homeowners prefer microinverters for off grid systems.
How to size an off grid inverter
The size of a solar inverter is usually measured in Watts. When purchasing an off grid inverter, you have to make sure it suits the size of your solar panel system. For example, if your solar panel array has a combined power of 5kW then a 5,000 W inverter should be just right for it. Consult with the manufacturer when in doubt and read the guidelines. Keep in mind, that if your inverter is not sized properly for your system, in case of malfunctioning you might not be able to get compensation through the warranty.
How to choose the best off grid inverter
There is a range of off grid inverters suitable for different budgets and energy needs. When looking for one, consider the following things:
- Efficiency. This is how much power the inverter delivers from the batteries to your home under the perfect conditions. A good efficiency rating is from 94% to 96%.
- Self-consumption. It shows how much power the inverter will consume when idle.
- Battery charger output. Many off-grid inverters have a battery charger to recharge the batteries in winter with a backup generator. A good off-grid inverter will have a battery charger in the range of 50-100 amps DC.
- Temperature range. Inverters are sensitive to weather extremes. If possible, it is best to place an inverter in a garage or in another sheltered location, where it's safe from rain, snow and direct sunlight.
- Warranty. Normally, inverters come with up to a 10 year warranty.