By Drs. Robert & Sonia Vogl
President and Vice President,
Illinois Renewable Energy Association
Electricity powers much of our modern society. It can be produced and distributed as two different types of current known as AC and DC. Alternating current or AC moves in waves, flowing in a positive, then negative direction. Direct current or DC power flows in one direction at a steady rate.
A household electric range is powered by AC current while a flashlight or a cell phone is DC powered. AC became the standard source of power for much of the industrialized world as it could be easily shipped long distances at high voltage levels but changed by transformers to lower voltage levels to use in households, businesses and industries. With increased use of wind and solar power, interest in shipping electricity along new DC power lines is increasing.
Writing this article on a computer uses both kinds of current. The household outlet into which the power cord for the computer is plugged is AC. The adapter converts the AC power to DC for the computer. The conversion from AC to DC power involves some loss of energy that is released as heat within the converter.
Our renewable energy system produces DC power which is converted into AC to integrate it into our utility service. When drawing solar power to run a computer two energy conversions and losses are involved reducing efficiency. A more efficient system would use the DC output from our solar panels to directly power our computer.
A shed we use as a workshop has both AC and DC circuits. The AC circuit is linked with our household energy supply and is used to power tools and PowerPoint projectors. Another independent circuit consisting of a 60 watt panel with battery storage powers DC lights and a radio. The small system also served as a model for similar systems the IREA installed in Jamaica and Guatemala.
An electrical engineer in Chicago slowly transformed his home electrical service from AC to DC power one room at a time. He left the original AC wiring system in place and used it to run some of his appliances. He installed solar panels and battery storage to power his electronic devices. Over time he abandoned grid service by producing all of his electricity with solar panels.
The introduction of electric vehicles powered by batteries adds to the growing use of DC power. The batteries can also store electricity transferable to the home or workplace in times of need.
As solar panels, fuels cells and batteries produce DC power, converting it to AC power adds expense, loses energy and degrades power quality. The increasing use of electronic technology for LED lighting, computers, entertainment and power controls requires converting AC to DC power adding energy losses.
With the massive investment in AC power and the large costs involved in replacing it with a DC system the challenge is one of finding more ways to make effective use of both forms of power.