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How do photovoltaic arrays produce power?

Photovoltaic arrays produce electrical power; that we understand, but how big does the array have to be?

Photovoltaic arrays produce electrical power; that we understand, but how big does the array have to be?

And how efficient are they?

The silicon cell that makes up the array converts about 30 per cent of the sunlight into electrical energy.

This efficiency rating varies between manufacturers, due to construction techniques and type of silicone cell used, either poly-crystalline or mono-crystalline. But when the arrays are assembled the efficiency is taken in consideration before the power rating is assigned to the panel.

ISO standards demand that if a panel is rated at 210 watts then it must produce 210 watts in full sunlight.

Array efficiency is further affected by positioning; trees, other buildings, and the direction and angle the array is pointed, all have significant effects on total power output.

These factors are difficult to change in existing home sites but can be designed into new constructions.

As I have talked about before, solar trackers have evolved to the point that they will add 40 per cent to the arrays total power output by keeping the array continuously pointed at the optimum angle to the sun and thereby maximizing sunlight capture.

The amount of power needed from a solar array is a very important consideration in off-grid living; as opposed to a grid-tied home which has the primary objective of reducing the power bill.

A growing family with young children and teenagers would require more power than a home of “empty nesters” whose jobs keep them away during the day.

Also, lifestyle comes into play, do you like every light in the house on in the evening, and are you interested in installing the latest power saving appliances with an energy star rating.

Generally speaking three kW of solar will provide all the power needed for most families if it is supplemented with one or two kW of wind power.

Wind power has the advantage of producing energy at night, a feature the winter season often presents.

For larger families, again in rural settings, 5kW of solar may be required with 2 or 3kW of wind turbine.

In Alberta temperature also has an effect on solar power production.

The colder it gets the more power a photovoltaic panel will produce, and even though the days are shorter during winter, the gain from the cooler temperatures and the reflected light off the snow, will greatly add to the output when the sun is out.

The higher the efficiency of the solar array, the less the backup generator has to run.

Storage of the power produced is a problem all during the year.

It is not unheard of to have a couple weeks of fogged in weather in the winter. Not a problem because common sense, and insurance requirements dictate a backup generator, but in the summer there is a surplus of available power and not enough storage space in the battery bank. If we could find a way of storing all we produce, then we would really be ahead of the game.

Lorne Oja can be reached at: lorne@solartechnical.ca