Inverters
The INVERTER is the major electronic component that converts the 12, 24, or 48 volt DC current from the battery into 220 volt AC current, the same as utility power for standard household lights, outlets, and appliances.
There are basically two types of inverters on the market today: modified sine wave and sine wave. The differences between these two types of inverters are subtle but significant in the way they operate certain types of loads.
Modified sine wave
Inverters can adequetely power most household appliances and power tools. It is more economical, but may present certain
compromises with some loads such as microwave ovens, laser printers, clocks and cordless tool chargers.
Sine wave
Inverters supply power of better quality than the power company, and work correctly with any appliance.
A small 150 Watt true sine wave inverter might be used when you have just a few smaller appliances that require true sine
wave power.
Inverters are rated by their continuous wattage output and are capable of briefly sustaining much higher loads than they can run continuously, because some electric loads, like motors, require a surge to get started. The more they can put out, the more they cost initially. So you don't want to buy a bigger one than you need. On the other hand, an inverter that's too small is going to frustrate you because you'll need to limit usage.
If you only have a single appliance or two to run it doesn't take much. For example, say you want to run a 14-inch TV, a VCR, and a light all at once. Total up all the wattages, about 40W for the TV, 20W for the VCR, and 14W for a compact fluorescent light, a total of 74 Watts. Pick an inverter that can supply at least 74 Watts continuously, and you have it.
To power a whole house full of appliances and lights it will take more planning. Obviously not every appliance and light will be on at the same time. Mid-size inverters of 500 to 1,000 Watts do a good job of running lights, entertainment equipment, and small kitchen appliances, in other words, most common household loads. What a mid-size inverter will not do is run a mid- to full-size microwave, a washing machine, or larger handheld power tools. For those loads you need a full-size 2,000+ Watt inverter. In truth, most households end up with one of the full-size inverters because household loads tend to grow, and larger inverters are often equipped with very powerful battery chargers.
All inverters produce a small amount of waste heat. The harder they are working, the more heat. If they get too hot they will shut off or limit their output to protect themselves. Give the inverter plenty of ventilation and keep it dry.
We have been painting a rosy picture up to this point, but let us now have a little brutal honesty to balance things out. If you know about these problems beforehand it is usually possible to work around them when selecting appliances.
Modified sine wave inverters work fine for 99% of the appliances, with notable exceptions listed below.
The problems discussed here are caused only by modified sine wave inverters. A small sine wave unit is sometimes employed
to power a specific appliance or two, while the rest of the household runs on the cheaper and more efficient
modified sine wave inverter.
Some audio gear will pick up a 60-cycle buzz through the speakers. It doesn't hurt the equipment, but it's annoying to
the listener. There are too many models and brands to say specifically which are a problem and which aren't.
We've had better luck with new equipment recently. Manufacturers are starting to put better power supplies into their gear.
Some top-of-the-line audio gear is protected by SCRs or Triacs. These devices are installed to guard against power
line spikes, surges, and trash (nasties which don't happen on inverter systems). However, they see the sharp corners
on modified sine wave as trash and will sometimes commit electrical hara-kiri to prevent that nasty power from reaching
the delicate innards. Some are even smart enough to refuse to eat any of that ill-shaped power, and will not power up.
The only sure cure for this (other than more tolerant equipment) is a sine wave inverter.
99.9% of computers run happily on modified sine wave. In fact most of the uninterruptible power supplies on the market
have modified sine wave or even square wave output. Many laser printers are equipped with SCRs, which cause the problems
detailed above. Laser printers are a very poor choice for renewable energy systems anyway due to their high standby
power use. Inkjet printers can do almost anything a laser printer can do while only using 25 to 30 watts instead of
900 to 1,500 watts. Most variable speed ceiling fans will buzz on modified sine wave current. They work fine, but the
noise is annoying.
Phantom loads many modern appliances remain partially on when they appear to be turned off. Anything that can be powered up with a button on a remote control must remain partially on and listening to receive the "on" signal. Anything with a clock-VCRs, coffee makers, microwave ovens-uses a small amount of power all the time. Mobile phones answering machines, or anything that uses a "power cube" in the AC socket (These usually run a horrible 60% to 80% inefficiency) use very tiny amounts of power, maybe only a watt or two, but they make the inverter stay turned on and running 24 hours per day. One of these loads, if it is large enough to awaken the inverter from stand-by (where it uses only 0.1 to 1.0 watt), it consumes its own load plus the inverter's overhead, which can be 2 to ten watts. While this sounds like grasping at straws to those unfamiliar with the demands of an independent power system, over 24 hours this much power lost to inefficiency can add a 500euro solar panel or two to the size of the array needed to keep from going bankrupt energy-wise.