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K & C Stork Solar Power Consultants

Inverters PDF Print E-mail

An inverter is used to convert DC electricity (usually from batteries) to 240 volt AC power. There are two broad categories of inverters recommended for power supply applications, modified squarewave and sinewave. The sinewave inverters also can be broken down into two further categories, stand-alone (usually powered from a battery) and grid interactive (for feeding into the national electricity grid)

Grid-Interactive Inverters
not only convert the DC electricity from solar modules (or any other suitable source such as fuel cells, turbines etc) into pure sinewave grid quality power, they have to actually monitor the grid waveform and duplicate it exactly. They must also disconnect from the electricity grid if it fails for any reason (such as being switched off for maintenance). Any electricity generated not used in the home is exported through a special meter into the main electricity supply. Some of these inverters have a feature called "Maximum Power Point Tracking" or MPPT, where the inverter will determine the maximum input voltage and current values to get the maximum power possible out of your investment. Some Grid-interactive inverters have battery backup facilities, which can supply power to your requirements during blackouts, as well as "sell' electricity to the grid. Please call or email us with your requirements.

Modified square wave inverters
(also called modified sine wave and quasi sinewave) produce a step-shaped output, which will operate most AC loads, but may upset equipment with timing functions such as TVs, VCRs, computers and induction motors. Recommended for: most applications, including power tools, general lighting etc
Not recommended for: electronic flow control pumps, and any appliance with older switch-mode power supplies or microwave ovens as they both require the sinewave peak to operate efficiently.
We do NOT recommend the use of cheap square-wave inverters in any application, as these usually have very bad output waveforms, and the high voltage spikes on the output could damage your appliance. We have seen some of these "hobby inverters" trip surge guard protectors with nothing plugged in! Also make sure that the inverter you are looking at purchasing is fully isolated and M.E.N. compliant if using it in a fixed installation. All inverters listed in our catalogue are compliant. These requirements are covered in the Australian Standards AS3000, and are required by law. Almost all of the cheap inverters available do NOT comply with these standards and are suitable for mobile applications only.

Pure Sinewave inverters
produce a smooth output similar (sometimes better) to that from the mains grid. The power output is much higher in quality than modified square wave inverters and has a greater voltage stability than the grid. However, they are also the more expensive of the two types, due to the complexity of re-producing the sinewave from a pure DC source.
Sinewave inverters are quickly becoming the industry standard, are readily available and are not much more expensive than modified square-wave inverters. Again, there are many cheap sinewave inverters that do not comply with AS3000 for fixed installations, be aware of this if purchasing an inverter for a particular application.

Inverter/chargers
combine an inverter (either modified or pure sinewave) with a battery charger. These can be either simple or complex devices used for many things, such as a simple back-up power supply, an automatic battery charger and change-over to the grid in a mobile home, back-up generator charging right through to complex load-sharing systems. The end use will determine the actual inverter/charger that is used. Please call or email us if you have a special requirement.