How much PV would I need?

ThatSolarGuy · 04-12-11, 01:40 AM

I agree for the most part with Xringer's math. I use 5 hours a day in SoCal. 5 hours may seem low, but when you factor the entire year (cloudy days), 5 hours is actually pretty good. In your region 4-4.5 might be more accurate.

Here's the calc I use everyday

MODULE WATTAGE x # OF MODULES X .76 x # HOURS = kWh/day

FYI .76 is a factor derived from...
most inverters are about .96 (96% efficient)
most modules run at.90 of their nameplate (the CS 200's generate about 180Watts
voltage drop is max of .98 (system designers will select conductors to max this at 2%)
system design is .90 (system design is the delta from ideal positioning of your array) ideal being true south and angle or tilt = your latitude. So .90 assumes your losing 10% due to less than ideal mounting conditions.
When you multiple all those factors you get .76

So I'm going with 9.6kWh per day from (14) CS 200 polys in the N.E. ALL your hardware could be procured for about $3.15 per watt (DC watts that is) or $8,820. Now that's before any rebates or incentives, and as Xringer says, that's a lot of years of electricity at just 400kWh/month. Google DSIRE for rebate info in your area.

Blue Skies,
Jeff

BTW Right now module prices are plummeting. Modules make up about 65% of the hardware cost. My current favorite is the Canadian Solar 250mono, lots of power and great price.

04-12-11, 01:40 AM	#11
ThatSolarGuy Lurking Renovator Join Date: Apr 2011 Location: Murrieta California Posts: 3 Thanks: 0 Thanked 1 Time in 1 Post	- calcs for solar production I agree for the most part with Xringer's math. I use 5 hours a day in SoCal. 5 hours may seem low, but when you factor the entire year (cloudy days), 5 hours is actually pretty good. In your region 4-4.5 might be more accurate. Here's the calc I use everyday MODULE WATTAGE x # OF MODULES X .76 x # HOURS = kWh/day FYI .76 is a factor derived from... most inverters are about .96 (96% efficient) most modules run at.90 of their nameplate (the CS 200's generate about 180Watts voltage drop is max of .98 (system designers will select conductors to max this at 2%) system design is .90 (system design is the delta from ideal positioning of your array) ideal being true south and angle or tilt = your latitude. So .90 assumes your losing 10% due to less than ideal mounting conditions. When you multiple all those factors you get .76 So I'm going with 9.6kWh per day from (14) CS 200 polys in the N.E. ALL your hardware could be procured for about $3.15 per watt (DC watts that is) or $8,820. Now that's before any rebates or incentives, and as Xringer says, that's a lot of years of electricity at just 400kWh/month. Google DSIRE for rebate info in your area. Blue Skies, Jeff BTW Right now module prices are plummeting. Modules make up about 65% of the hardware cost. My current favorite is the Canadian Solar 250mono, lots of power and great price.