PV Collectors

PV Panels are one way to Get Solar Gain.

The solar energy striking the earth's surface at any one time depends on weather conditions, location and orientation of the collector, but overall, it averages about 1000 watts per square meter on a clear day with the surface directly perpendicular to the sun's rays.

In Nova Scotia we have a fraction of this to work with. This chart gives the most helpful numbers, that is, average kWh per day available in various months in Halifax. This is a useful number because it gives you the amount of energy you have available each day. Multiply this number by the efficiency of your collector (12% for commercially available panels, to 18% for experimental) to get something in the range of 0.4 - 0.6kWh/day per square metre of panel.

Keep your panels pointed Solar south, not magnetic south. Angle is critical for maximum solar gain; the Optimal Solar Panel Angle depends on several factors.

The Nova Scotia Power page on net metering indicates that you can "bank" kWh for 12 months. You can't reduce your kWh below zero and get paid, however.

Most PV enthusiasts will quote a 20-year payback period; payback on [[Hot_Water_Collectors?]] is much faster.

Example Calculation

A house in Halifax heated by oil with perhaps one electric baseboard uses 14000kWh annually -- about 38kWh per day on average.

The chart above shows that the house receives, averaging over the year, 3.72kWh per square metre of sun per day, times 12% for the efficiency of commercial collectors of turning the sun into electricity, so we would expect them to collect 0.45kWh of electricity per square meter per day.

If I need 35kWh each day, we divide by 0.45 to get 85 square meters of panels -- a 10m x 8.5m array -- to break even over the year.

The key is that most people have to reduce their electrical consumption by 90% before they can live on solar panels.