Photovoltaic cell energy output: Maximum power output, Pm = Vm x Im

At solar noon on the equator on the Fall or Spring Equinox E = 1000 w/m2. (This is about as high solar irradiation as you can expect). At a typical 12% efficiency would then get a 120 watts per m2 of solar panel.

For Appledore Island a more reasonable irradiance value is 200 – 250 watts/m2. So typical power output would be 24 – 30 watts/m2 during daylight hours.

For Appledore Island: Average annual solar radiation: 4.51 kWh/m2-day Average summer solar radiation: 5.23 kWh/m2-day Average winter solar radiation : 3.56 kWh/m2-day

Note: this isn’t Appledore

Typically, the angle of the solar array is set within a range of between site-latitude-plus 15 degrees and site-latitude-minus 15 degrees, depending on whether a slight winter or summer bias is desirable in the system. Many solar arrays are placed at an angle equal to the site latitude with no bias for seasonal periods. Latitude for Appledore Island = 42.96oN

PV output is low voltage (Direct Current) - usually 6 to 24 volts PV output is low voltage (Direct Current) - usually 6 to 24 volts. The most common output is intended for nominal 12 volts, with an effective output usually up to 17 volts.

To design a system, the total amount of solar radiation energy is expressed in hours of full sunlight per m², or Peak Sun Hours (PSH). This term represents the average amount of sun available per day throughout the year. PSH has units of kWh/m2-day. It is assumed that direct solar radiation for one hour = 1kWh/m2. Thus PSH actually equals the number of “full sun” hours in a day. For Appledore PSH for summer was shown in a previous slide to be 5.23

Design of number of panels required depends on electrical demand. For Appledore typical day’s power demand = 30 kw (This does not include power for R.O. and main saltwater pump). Panels are rated by wattage.

Total electrical demand variation (including R. O Total electrical demand variation (including R.O. and main seawater pump) is shown in the following graph.

For example, a BP 3160 solar panel has the following specs. Max power output: 160 w Voltage : 35 volts Current : 4.5 amps Size : 31 x 63 in.

Since the sun is not full strength for full day the 160 watts output can’t be realized. Energy output from panels = 160 watt x hours sun For the summer this equals 160 x 5.3 = 848 Wh (per panel)

Energy requirement for Appledore is 30kw times the hours of electricity use. Assume this time is approximately 12hrs. Energy requirement = 30 kW x 12hrs = 360 kWh

Number of panels required:

For the BP 3160 panels this number of panels would occupy an area of about 75ft x 75 ft. The total ground coverage would be reduced by tilting the panels. 45o tilt reduces area by 0.707 45o 1 m 0.707 m

Inverters are required to change the DC output of the PV to AC Inverters are required to change the DC output of the PV to AC. The quality of these inverters varies (by price). Some typical outputs follow.

Here is a inexpensive inverter output:

Here is a expensive inverter output without load :

Here’s an expensive inverter output with load

Typical inverter 12V to 110V 6kW capacity Eff. = 90% Wt = 30 lbs 9” x 6” x 26”

Other factors to consider: Island electrical load is not likely to be 30 kw for 12 hrs (likely to be lower). Loss of energy for the inverter. The smoother the sine wave output the higher the energy loss (approx 10 - 25%). Loss of energy in storage batteries (approx. 20%)