Solar Photovoltics

Re: Solar Photovoltics

Where will the system be installed?

For example, say it will be near Long Beach California. Using PV watts website, assuming off-grid with flooded cell batteries derating of 0.52, fixed mounted array, starting with 1,000 watts / 1 kW of panels:

"Station Identification"
"City:","Long_Beach"
"State:","California"
"Lat (deg N):", 33.82
"Long (deg W):", 118.15
"Elev (m): ", 17
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 33.8"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.43, 65, 8.12
2, 5.00, 67, 8.38
3, 5.52, 81, 10.12
4, 6.21, 88, 11.00
5, 6.12, 88, 11.00
6, 6.09, 85, 10.62
7, 6.63, 94, 11.75
8, 6.79, 96, 12.00
9, 6.18, 85, 10.62
10, 5.46, 79, 9.88
11, 4.81, 68, 8.50
12, 4.34, 64, 8.00
"Year", 5.63, 960, 120.00

Say you plan on being Solar Only for 9 months of the year (many places, winter is almost impossible to install enough solar panels for 100% year round solar only power). February is 67 kWH per month per 1kW of panels:

• 13 kWH per day * 30 days = 390 kWH per month:
• 390 kWH per month / 67 kWH per month per 1kW of panels = 5.82 kW of solar panels

Battery bank would be a 48 volt (large system)... 3 days of no sun, 50% maximum discharge, assume all power is used at night, 85% efficient inverter:

• 13,000 WH per day * 1/48 volts * 1/0.85 eff * 3 days no sun * 1/0.50 max discharge = 1,911 AH @ 48 volts

Very roughly, an Off-Grid system will cost you around $10-$20 per Watt (lots of variables, self install vs turn key, etc.):

• 5,820 Watts * $15 per watt = $87,300 (+/- 50%)

Your cost for electricity will be around $1 to $2+ per hour assuming costs are spread out over 20 years (parts, replacement batteries, fuel for genset, etc.):

• 390 kWH per month * $2 per kWH = $780 per month electric costs

If done in the US, you should qualify for 30% Federal tax credit, but usually no state or local rebates. Some states the system will be property tax free/others will charge you property taxes.

Anyway--13 kWH per day is a very large off-grid system... I would suggest that you aim at 3.3 kWH hour per day (~100 kWH per month) for a typical cabin/small home design.

Larger systems, of course, can be done--It is just that they are so darn expensive. Anything you can do to reduce power costs (fewer appliances, Energy Star Rated, laptop computer vs desktop system, using propane/other fuels for cooking and heating, lots and lots of insulation, double pane windows, CFL lighting, etc.) will all help.

It almost always to conserve a Watt than to generate a Watt.

-Bill