Power Conditioning Equipment for Stand-Alone Systems
Inverters condition electricity so that it matches the requirements of the load.
Photo credit: Trudy Forsyth
Most electrical appliances and equipment in the United States run on alternating current (AC) electricity. Virtually all the available renewable energy technologies, with the exception of some solar electric units, produce direct current (DC) electricity. To run standard AC appliances, the DC electricity must first be converted to AC electricity using inverters and related power conditioning equipment.
There are four basic elements to power conditioning:
- Conversion—of constant DC power to oscillating AC power
- Frequency of the AC cycles—should be 60 cycles per second
- Voltage consistency—extent to which the output voltage fluctuates
- Quality of the AC sine curve—whether the shape of the AC wave is jagged or smooth.
Simple electric devices, such as hair dryers and light bulbs, can run on fairly low-quality electricity. A consistent voltage and smooth sine curve are more important for sensitive electronic equipment, such as computers, that cannot tolerate much power distortion.
Inverters condition electricity so that it matches the requirements of the load. If you plan to tie your system to the electricity grid, you will need to purchase conditioning equipment that can match the voltage, phase, frequency, and sine wave profile of the electricity produced by your system to that flowing through the grid.
A series of requirements for grid-interactive inverters have been developed by Underwriters Laboratories, a leading safety-testing and certification organization. These requirements, referred to as UL 1741, apply to power-producing stand-alone and grid-connected renewable energy systems. Either you or your installer should contact your power provider to see which models they accept for grid-connection; most simply require a grid-interactive inverter listed by an organization such as Underwriters Laboratories.
The cost of inverters is affected by several factors, including:
- Quality of the electricity it needs to produce
- Voltage of the incoming current
- AC wattage required by your loads
- Power required for the starting surge of some equipment
- Additional inverter features such as meters and indicator lights.
When you size your inverter, be sure to plan for any future additional loads you might have. It is often cheaper to purchase an inverter with a larger input and output rating than you currently need than to replace it with a larger one later.
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