If you have been following this column, you now know that photovoltaic cells produce direct current. This form of electricity commonly abbreviated as DC is great for charging batteries, and even that function has to be controlled so it does not boil the battery dry or otherwise destroy it due to too much electrical current.
That, however, does not do us any good in the home because our household appliances use alternating current. So what is alternating current and why the two types?
To be brief, alternating current, abbreviated AC, is a form of electricity where the positive and negative polarities change. This change is a function of how the alternating current is produced. Each change is called a cycle and most of the common electrical equipment in North America runs on 60 cycles per second. Alternating current cannot be stored, but it has the advantage of being able to travel great distances. Direct current has the advantage of being able to be stored, but it is difficult to get it to travel any distance. DC is great for the car battery, but it sucks in the home.
With alternate current being the standard for all electrical appliances, a problem is posed when using solar panels. How do we get the direct current that photovoltaics produce into the more common usable form of alternating current? Let me introduce you to a piece of electronic equipment called an inverter.
An inverter is an electronic device that has the ability or capability to convert DC into the form we all use in our home, AC. It does this with advanced electronics that have been in use in industries for decades but as with all things electronic, is now being carried over to the residential market.
Not only do inverters change direct current to alternating current, but through the marvels of modern programmable electronics, can meet the varying load demands of an “off grid” electrical home by starting a generator when the electrical load exceeds preset limits or when the batteries get to a low level of charge, or even maintain them by running an equalizing cycle.
Inverters can simply take the power of one solar panel and convert it into acceptable AC electricity suitable for sending down the power line should your electrical production exceed your demand.
More complex systems can monitor your input of power into the grid, track your sales, charge a backup battery bank in preparation of a power outage and probably the most important function of all: shut off your home’s power production to the hydro lines should the power go out. This protects the utilities service people who work on the system to bring the electrical power back online.
Inverters allow us to use TV and dishwashers, fridges and deep freezers, microwaves and normal 110-volt AC lighting, all the normal conveniences. They make green energy viable for our modern world.
Lorne Oja is an energy consultant, power engineer and a partner in a company that installs solar panels, wind turbines and energy control products in Central Alberta. He built his first off-grid home in 2003 and is in the planning stage for his second. His column appears every second Friday in the Advocate. Oja, who lives in west Central Alberta, can be contacted at lorne@solartechnical.ca