Jan 14, 2010

How Inverters and Batteries Work

This post talks about the definition of inverters and the types and sizes of inverters needed for your home solar power system.

What is an inverter and how does it work?

An Inverter is a device that converts one type of voltage (direct current, or DC) into another type of voltage (alternating current, or AC). The conversion is usually from 12 volts DC to 110 or 220 volts AC because that is what the power company supplies us with in our electric sockets, but the output you want really depends on the appliance you want to power.

Solar batteries (also called lead-acid batteries) are usually 12 volt batteries so as you begin to rely on them at night, the inverter changes the 12 volts of electricity into 240 or 110 volts.

What size of inverter do you need?

If you need to power small appliances, like laptops or light bulbs through solar power, you’ll need a small inverter, say 150 watts of power. If you’re thinking about an air conditioner, you may want a large inverter with a power value of 3000 watts. Here’s a list of sizes which were originally published by ExplorOz:
  • 150 watts - Charger for cameras, laptops, and small power tools; DVD player; coffee grinder; kitchen mixer; printer; very small television
  • 250 watts - Small TV, slow cooker, desktop computer, electric blanket
  • 500 watts - Small fridge, freezer, small angle grinder, drill, large TV, washing machine (no heat)
  • 1000 watts - Breadmaker, microwave (600 watts - keep in mind that the input power for a microwave oven is around twice its specified cooking power level, due to inefficiencies in converting to the very high frequencies needed for cooking - 2 thousand million hertz!)
  • 1500 watts - Toaster, small air conditioner, chainsaw, vacuum cleaner, iron
  • 2000 watts - Microwave (1200 watts), hair dryer, fan heater, iron
  • 3000 watts - Large air conditioner
What Type of inverter do you need?

Again, this depends on the type of appliance you wish to run. Here are the two common types of inverters (Modified and Pure Sine Wave Inverters) and the appliances they usually run, (credit, DonRowe.com):
Modified Sine Wave Inverters (MSWI) – these deliver power that is consistent to a reasonable degree and will therefore run most devices fairly well. These are both affordable and popular. The appliances supported are:
  • Most computers, with the exception of some laptops, printers and monitors (computer crashes, weird printouts and electrical noise on screen are possible)
  • Microwave ovens and motors (run slower and noisier compared to Pure Sine Wave Inverters)
  • Fans, fluorescent lights, audio amplifiers, TV Game consoles, Fax, and answering machines (audible and electrical noise is possible)
Pure Sine Wave Inverters (PSWI) – these deliver a highly consistent amount of power to your appliances, very similar to that provided by power companies. All sensitive and heavy equipment will run normally on these and even those that are designed specifically for using MSWI. Naturally, this inverter is expensive and highly efficient. The appliances supported are:
  • Any appliance with electronic temperature controls, e.g. bread makers and light dimmers
  • Laser printers, photocopiers, magneto-optical hard drives
  • Power tools employing "solid state" power or variable speed control
  • Some battery chargers for cordless tools
  • Some new furnaces and pellet stoves with microprocessor control
  • Digital clocks with radios
  • Sewing machines with speed/microprocessor control
  • X-10 home automation system
  • Medical equipment such as oxygen concentrators
When in doubt over which one to buy, go for PSWI if you have deep enough pockets because they will run all appliances well, but the MSWI may end up damaging a few.

The down side of inverters
  • The input power of inverters is less than the output power because inverters have an efficiency rate of about 80% to 90%. The rest of the power is lost as heat.
  • Inverters can get damaged if there is a sudden surge in the DC volts level and for that reason, you need to have a controller too.
  • Risk of electrocution and over-heating if proper care is not taken
You can avoid buying inverters altogether but you’ll need to get appliances that run on 12 volts DC, and these may be hard to find and expensive. Plus, certain inverters allow you to sell back excess solar power to your power company as credits.

Home Page