Wind Turbines

Wind is caused by the heating of the earth's surface by the sun. The heating of the surface is, however, uneven as time of day, water surfaces and cloud cover cause some areas to heat less quickly. As the heat rises it creates a low pressure area and air from adjacent high pressure areas flows toward this low pressure area thereby creating wind. Wind, like solar energy, is somewhat seasonal thus accurate overall wind measurement is useful.

It is generally recognized that an average annual wind speed of more than 18 km/h (5 m/s) is the required minimum for a stand alone wind-based system to be considered viable. For this reason the East and West coasts of North America, the far north and southern prairies offer the most promise for a primary wind power application. Outside of these areas wind turbines best complement solar systems or conventionally fueled generators to reduce fuel consumption in hybrid applications.

Rated vs. actual energy output

The optimum power of a cell is referred to as its maximum power point (MPP) where the combination of the highest current and voltage, usually 17 VDC, is achieved under standard test conditions (STC) of 1000 w/m² of light and cell temperature of 25° C. Seldom do the modules operate under a clear blue sky and operating temperatures of the cells are generally in the range of 30° C warmer than the ambient air which reduces their output. Photovoltaic modules are typically rated according to their wattage output, under STC.

If a solar module generates a rated 4.4 amps @ 17 volts this equates to a 75 watt rating. In a nominal 12 V battery system, however, the module continues to generate 4.4 amps though at a lower 12 - 13 volts producing a maximum of only 57 watts. Good photovoltaic system design will use the rated amps - the power actually delivered to the battery bank.

What affects PV performance?

Light intensity - The rated power of a solar module is made at a standard test condition of 1000 w/m² light intensity. Their power is directly related to this intensity, thus on a fully overcast day a solar module can be expected to reach about one-tenth of its rated power.

Technology - Different cells have varying degrees of efficiency and operating characteristics. Crystalline modules usually operate in the 0.5 -0.6 V range, however, thin film cells are generally higher.

Cell size - The power generated by the cell is proportional to its size - more sunlight hits a larger cell thus more power is generated.

Seasonality - Most regions of Canada receive at least 2200 hours of sunlight each year. The distribution of this sunlight is of course highly variable with November and December yielding less than 1/3 the direct sunlight that is available in July.

Temperature - With the exception of amorphous modules, photovoltaic cell efficiency improves producing higher currents in cold temperatures. In fact, a modules peak power and voltage will improve by 0.3 - 0.5% for every one degree Celsius below 25° C.

The information contained herein is subject to change without notice.