Calculating Solar Panels
July 27th, 2010 by KenricThis post is based on Another Investor’s comments in the previous solar post about my green home.
When the solar power rep was here he pulled up the stats from another home in Scottsdale. This home was a 9.8kW system producing 32kW a day in June. I would assume that this number is close to the maximum that the system could ever produce. I was told that our solar systems are limiting by our 200amp circuit breaker, so even if I had unlimited roof space I couldn’t put a 100kW in my house without upgrading to a 1000amp breaker.
So based on the 32kW a day, I took a look at my electric bill. For June I used 1200kW during 9am to 9pm peak hours. 1200 – 32×30 = 235kW. Which is really good.
But lets look at the whole bill.
Off peak I used 1544kW. Total kW usage would be 1779kW. I pay $0.14 per KW on peak and $0.02 off peak. Just in straight kW savings the solar panels saved me $134.00. But there are all sorts of other fees like delivery charge, etc… that are prorated by kW usage. Without going into the calculation details I guessitmated that I have additional savings of about $35. So total savings from the solar system is estimated at around $170.
My bill was $350 for the month of June, so solar would have cut my bill 50%. I did the same calculation for May and came up with a $158 savings on a $280 bill. Which isn’t bad. But I guess what I’m seeing is that at maximum sun my solar panels can produce or save about $170 a month.
My average bill is $220 a month, so the savings is pretty significant at $170 month. However, that assumes that every month has sufficient sunlight to produce 32kW a day which we know isn’t true.
If it was as easy as plugging $170 x 12 months = $2040 a year of savings, it would be easy to calculate your payback period. I believe that Solar City guaranteed at least 10,000kW of electric generated or they would pay you for any amount under. 10,000kW comes out to 27kW a day.
BTW, I think that a 9.8kW system could only cost $12,000-$15,000 now with all the rebates. At $12,000 we are looking at a minimum 6 year pay back.
Thanks for making me type this out. It really helps me more and I’ll looking into the cost of buying a system or building one.
Posted in Green Home | 7 Comments »
Stumble it!
go to http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/ and plug in your info. This is a fairly common tool in the industry for installers to check savings.
You may also want to look at a solar thermal system. Renewable energy credits aside, these typically have a quicker payback.
By kurt on Jul 28, 2010
I’m currently looking at a short sale in a retirement community in the Northwest Valley. It is a little less than 1,200 sf and has a 4 Kw solar panel system that was installed in 2005 at a cost of $32,000. Per the listing, the electric bill has averaged $50 a month.
I own the same model of house on the same street with a similar lot orientation. Mine has dual pane windows. The listing for the house being sold does not mention dual pane windows.
I have never occupied this house, but the electric bill ranged between $50 to almost $250 in the summer with the 10 year-old A/C unit per the last tenant. Average was around $130. Older folks don’t cook a lot but they stay home much of the time and most watch TV. No CFL’s are installed and the house is all-electric.
The savings are maybe $1,000 a year. Capitalized into value, maybe $12,000 to $15,000, max.
This is a short sale, but the list price is the same or less than other houses in the immediate neighborhood. This house has a converted carport. The house two doors down with an original carport is listed at $5,000 more. There is a VA foreclosure with a covered patio converted to additional square footage and a garage that is listed at $19,000 more. It’s across the street and a few doors down. All are recent listings.
This says to me the market does not add any value for the solar electric system, at least not in retirement communities in the Northwest Valley. The solar companies will tell you the value of your house increases when you install a photovoltaic system. The green advocates say buyers will pay extra for gteen features. I’m skeptical, and I certainly would not factor an increase in the value of the property into my calculations when I was making a decision about buying a solar system.
By Another Investor on Aug 6, 2010
Those numbers just wouldn’t make any sense if you were calculating ROI on panels. 320 months or 26 years to break even for return? They probably only paid $10,000 after rebates and credits.
The numbers do seem close though, 4kW system according to my calcs would save about $75 a month.
I just got another quote for an 8.9kW system leased at $118 a month with nothing down for 10 years. Should save me $153 a month so it nets +$35/mo.
By Kenric on Aug 6, 2010
solar panels for homes are still expensive and requires some large capital to install;;.
By Joe Mason on Oct 6, 2010
solar panel prices are getting lower and lower, soon we can afford to buy those high power solar panels*.’
By PCSO Lotto Result on Oct 20, 2010
we have a solar panel at home that my father built, it can generate 500 watts of electricity :
By Chipboard Sheets · on Nov 9, 2010
I read this one yesterday and thought of you…
http://www.inc.com/magazine/20101201/say-yes-to-solar.html
Have you heard about this one before? It kind of makes sense for you, no?
By Andres on Dec 28, 2010