Inverters convert your battery voltage (for example, 12 volts) to 120 volts, the typical voltage needed for appliances, computers, tools and many other household items. Lights, fans and water pumps are all available for 12 volt systems. Larger items, such as refrigerators are available as 12 volt and propane but these tend to be expensive. If you plan to be off-grid, it is best to wire the house for both 12 volt and 120 volt. The 12 volt wiring will go to a basic 12V circuit breaker panel then to the batteries. The 120 volt wiring will go to a standard household circuit breaker panel, then to the inverter and then to the batteries. It is possible to wire the circuit breaker panel so that you can use shore power (regular grid power), a generator and an inverter to power your needs. I will cover this in the next installment of this blog when I discuss transfer switches.
In part one of this series, I stated that these blog articles assumed you were designing and building a basic solar power setup costing roughly $3500-5000. Therefore, I will only cover inverters for this setup. I will also assume that your battery bank is setup for 12 volt, not 24 volt or higher. Your first step in choosing an inverter is determining your needs. Inverters are rated in watts; you will need to convert all your appliances and other electrical needs into watts. Lights and other items are easy, they are rated in watts (for example, a 60 watt light bulb is 60 watts). Larger appliances might be rated in watts or amps. If amps, just convert to watts ( Amps X 12 volt = watts). Total up all your electrical needs, do not worry about amount of time used each day, just the total number of items that will run at any one time. If you do not know the energy needs or you worry that the manufacturer has been conservative in their reporting, you can determine the energy usage with a kill-a-watt meter.
Let us assume you have a refrigerator rated at 40 watts, six lights rated at 10 watts each (60 watts total), a vent fan rated at 2 amps (2 x 12 = 24 watts) and a toaster oven rated at 1200 watts. Assuming we use all these items at the same time, the total is (40+60+24+1200=1324) 1324 watts. We would need an inverter of at least 1324 watts to power our system. However, we also need a 10% margin of error (for electrical losses, voltage spikes, etc) so best to get an inverter rated at 1500 watts.
There are two basic types of inverters, modified sine-wave and pure sine-wave inverters. Without getting to technical here, know that some items will not operate or will fail if used with modified sine-wave inverters. Pure-sine waver inverters have the same waveform as traditional grid electrical current. Because the costs have fallen on pure-sine waver inverters, I see little reason to risk failure of your computer, refrigerator or other expensive items. Therefore, I recommend a pure-sine waver inverter.
There is a host of inverters sold from unknown brands to well know brands. I tend to purchase well know brands with the psychology that "you get what you pay for" (within reason). I recommend reading the reviews of others that have used the same inverter, amazon is an excellent site to read numerous reviews.
If you feel that you electrical needs will grow, I recommend purchase a larger inverter now as the cost to change will be at least double your original cost. I wish you luck and good fortune with you developing off-grid system.
This shows my inverter and my other electrical items:
Below are links to a few of the inverters I have tried and found to be quality equipment.