taec™

How to size your solar array

Many people would like to be able to power a conventional all-electric home with solar modules. Sadly to go ALL electric would be cost prohibitive, however it is possible to make great savings on current electricity usage by installing PV panels.

Today’s solar modules can convert approximately 18% - 20% of the solar energy they receive into electricity under ideal conditions. This means the more square-feet of solar array you have, the more power you will generate. However, outdoor temperatures, cloud-cover, site elevation, and shadows from nearby objects will reduce this electrical power output substantially.

If planning a project in sunny southern latitudes, you can expect better performance than those in cloudy northern latitudes. Whilst this sheet will help explain some of the complex challenges, please feel free to call TAEC who will be happy to discuss your requirements in more detail.

Basic array sizing using an average peak output of 10-watts per square-foot, it will take 100 square-feet of solar array/panels for each kilowatt (kW) of solar output required. You will need to leave some space between modules to allow for expansion, and between rows for wiring access (refer to the manufacturer installation instructions.)

Residential-size solar systems typically have a 24 or 48-volt battery-bank, unless they are grid-tied systems without batteries.

Ideally, you should use a module count that is in multiples of two, since most modules have a nominal voltage of 12 or 24-volt. For example, if you intend to install a solar array in the 2 kW size range, you should install 24 modules at 80-watts each (1,920 watts total), but should not use 25 modules just to make it match a nominal output goal. Alternately, look at installing 20 units at 100W to match the nominal output. This approach will enable equal division of the voltage and current among other system components, such as array circuit fuses, charge controllers, and cable runs etc.

A solar panel can be mounted in either direction; however, the location of the cable outlet box on the back of a module can affect the length of cable run between modules.

When selecting the mounting site for your array, keep in mind there should be no shading of any part of the array between 9:00 am and 3:00 pm. Even narrow shadow from a nearby tree partially covering only one module can potentially reduce the total array output by up to half!

The highest yearly total output will be achieved if the array is on a south facing roof, with a roof slope equal or greater than the latitude for your location. However, it is possible to mount solar arrays in all orientations from almost due east to due west, and with all roof-mounting angles from vertical to flat, to accommodate unusual local site conditions or design requirements; so don’t rule it out if your preferred location is less than perfect. Expected system performance & Value.

Yes, the sun shines all day (we hope), but at the lower sun angles before 9:00 am and after 3:00 pm, a typical solar array will have a much lower power output. During shorter winter months this “solar day” is even shorter.

If you are looking for an 'approximate' sun-hour per day value, use 4-hours for winter months, and 6-hours for summer months. Again, those locations in more southern latitudes may exceed these averages, while those in more northern latitudes may have fewer peak sun-hours per day, especially during winter months.

From the earlier example of a 1,920-watt array, we would expect results of 7.68 kWh per day in the winter (4 hr. x 1,920 watts) and 11.5 kWh per day in the summer (6 hr. x 1,920 watts). The average between these two on an annual basis would be in the region of 9kWh per day, or roughly 3,300kWh per year.

So to determine the overall contribution of a PV solar system of this size you would need to know what your total annual kWh unit consumption is.

Typical usage levels for the average family home currently indicate an annual electricity consumption figure of approximately 5,000kWh per annum. Therefore a contribution of 3,300kWh from a PV Solar array like this would equate to approximately 65% of electricity used, and subsequently a significant saving in energy costs.

Commercial figures indicate a usage average of 70,000kWh per annum. Therefore a 20kW System could in principle produce savings of up to 50% of electricity used.

So why not consider reducing your electricity costs whilst reducing your carbon footprint with a PV array system from TAEC™