My Solar Access %s...should I install?

Using a Solmetric device, I determined that my solar access is as follows:

Solar Access: Annual: 71% -- Summer (May-Oct): 89% -- Winter (Nov-Apr): 48%

Given this info, does anyone know how this would affect my rebate in California?

And, if you had this kind of coverage, would you still install a system?



  • BB.BB. Super Moderators, Administrators Posts: 32,814 admin
    Re: My Solar Access %s...should I install?

    Regarding rebates... As are as I know, you can still get them even if they are installed in a deep forest--I did not see anything on the forms I filled out that checked that they even pointed towards the sun. They list an expected output (5361 kWhrs per year), but nobody asked when mine generated about 4,800 kWhrs in the first year.

    Here are my results (monthly--I also have daily if you want) for San Mateo (near 92/El Camino). Array is 3,500 watts STC (2 strings of 10 x BP4175 or 20x175 watt panels, entire roof clear of shade roughly from 9am to 3pm (at this time of year):

    496 kWhrs for September 2005
    365 October 2005
    285 November
    134 December
    268 January 2006
    354 February
    313 March
    470 April
    523 May
    558 June
    490 July
    495 August
    558 September
    495 October
    377 September
    358 November
    297 December
    213 January 2007
    320 February

    Assuming that mine is, at least 10% from optimum for all year and that I have roughly the same amount of sun as you... You can just take my numbers divide by 0.90 (normalized results for my site without trees)... You can check month by month and see how much energy you will loose.

    Basically, during winter you get 1/2 the energy per month as summer--so loosing 52% of half is not as bad as loosing it during the summer...

    My question is the shading the results of fixed objects that won't change (within reason) over the next 30 years--or is much of the shading tree line which can continue to grow and that either a) you have no control over the growth, or b) it will cost you a lot of money to keep the trees trimmed/topped (which city and tree surgeons don't like to do)...

    Some issues that may help with "payback" are regarding your electrical usage/billing... If you are using more than baseline (for me, about 300 kWhrs per month)--at 130% of baseline, you would be paying roughly 2x for electricity (over ~390 kWhrs)... So, at that level $0.23 / kWhr--even if you are loosing some due to shade--you are offsetting some very expensive power... If you are below 130% of baseline, then at ~$0.12 per kWhr, the economics are not as nice.

    If your roof is not clear of sun 9-3pm, or has shading during 9-3pm from power lines or facing away from true south at greater than +/- 25 degrees--then then you may have more issues...

    One last thing to think about--for me, I have used all of my optimum roof area for solar electric panels... Take a look at your power bill... It may make sense for you to install solar thermal collectors for hot water/hot tub/home heating... Saving money with electricity or natural gas is still money saved (and solar thermal panels are about 1/10th the price of solar electric panels).

    As always, conservation is the big thing. My panels have generated 4,800 kWhrs, but in pure kWhrs, I have only consumed about 3,200 kWhrs through conservation--so I still have extra that I sometimes use for electric heat, dehumidifier (included in the numbers shown) or even that plug-in hybrid in the next few years.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • marksmarks Registered Users Posts: 17
    Re: My Solar Access %s...should I install?

    I understand that there have been significant changes in the CEC rebate program, and that the actual performance does have an impact. Check the CEC website, they probably have the info there.
  • BB.BB. Super Moderators, Administrators Posts: 32,814 admin
    Re: My Solar Access %s...should I install?

    Yep, as of January 1st, 2007, the Solar PV rebates are now outsourced to the utilities... For small systems (under 100kW) there are still, up front, one time rebates. For large systems (>100kW), they will pay $.xx per kWhr generated (requires dedicated meter on solar system). Now also requires 10 year guarantee on systems (no consumer repair costs).
    Incentives for all systems less than 100 kilowatts will initially be paid a one-time, up-front incentive based on expected system performance. Expected performance will be calculated based on equipment ratings and installation factors, such as geographic location, tilt, orientation and shading. This type of incentive is called Expected Performance-Based Buydown (EPBB).

    Appears to have much more (probably reasonable) requirements for Grid Tied Solar PV to obtain rebates and kWhr kickbacks.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: My Solar Access %s...should I install?

    Check also, your local utility for minimum monthly costs. If I read it right, if you get the incentive, then you must commit to a Time-of-use rate. With my utility, that equates to a $7 a month lease rate for the meter, plus the minimum monthly kWh charge of about $5.

    Last year, if you elected just straight metering (called E-1), there would be no lease charge for the meter. And if you got in on E-7 TOU before June, you could just buy the meter, outright. No longer true, even if you get E-7 today. I will gladly take corrections, here, if I've misunderstood. I haven't delved deeply into the matter, because it only makes me feel bad.
  • BB.BB. Super Moderators, Administrators Posts: 32,814 admin
    Re: My Solar Access %s...should I install?

    Ran across this site (mentioned in Solar Guppy's forum) for and looking around, found an interesting solar calculator... Sunpower currently uses Xantrex GT series inverters and Sunpower's 22% efficient panels (for smaller foot-prints).

    I ran through the solar calculator, and if you have no shade--the numbers seem to be pretty consistent with my experience (my 3,500 watt panels produce about 10% less than predicted by my installer and by this program--possibly some morning/evening shading issues). I checked the numbers with my E7 PG&E TOU rate plan and it predicted a -$192. I actually got a -$285 credit (yes I sold more power than I consumed)--Overall the numbers seem to be pretty accurate--the differences are that my bill is not $600 per year, but closer to $500 per year..

    Even though the program is biased towards Sunpower's solution--it does appear to have pretty good list of options you can play with (roof pitch, E,SE,S,SW,W, flat and TOU rate plans by utility, and location in US by ZIP or State/City). A few of the views (like power generated) you have to pay attention when you generate more than you buy--the power generated ends up in two columns.

    Looks like a very good product for doing what-if comparisons for you Black Mountain...

    One word of warning--I compared San Mateo and Pacifica for power generated and got the same results (cities are only 10 miles apart)... However San Mateo is a very sunny/warm climate behind a coastal mountain range--and depending on where you are at, Pacifica can have weather close to San Mateo's or go entire summers without sun depending on where in the city you live.

    So, if you live in a coastal marine area or have other local weather issues--I would take the numbers with a big grain of salt.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: My Solar Access %s...should I install?


    Not sure what your individual benefit will be, but perhaps if you are concerned about the pricetag of PV that you consider Solar Products just for water heating. I was able to generate all of my DHW from two Stiebel Eltron Solar panels which I mounted myself on my roof and Stiebel Eltron Storage tank in my garage. Check out the following link for mor info:
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