Solar for me?

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Mass Solar
Mass Solar Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
Excellent site here. Had some basic questions based on my scenario for possible solar power. I am located in Central Ma, and the roof faces South East. Reviewed last years utility use, and we used 5100 KWH last year..appx 425 per month...pretty frugal for a family of 5. Here are my specific questions:

1.) I hear that running an electric water heater is not the way to go using electrcity, but one should get a solar hot water system. Right now, the entire house and water is heated with oil, and with oil at 4.25 gallon, I don't mind a 30% increase in electric use if I can generate it myself. Although we have a family of 5, 3 are kids under 5 and we don't use much hot water. (all boys)

2.) Shading? How much shading affects the solar output of a panel. i.e if there is a small shadow on the panel that covers 10-15% of the panle, how much would this affect performamce. (Our house is right for Solar, but we would need to do some tree cutting for the panels to make sense in Nov-Feb.

3.) Here in Mass, its looks like we would qualify for a $5Wt rebate due to our income, home value, and supplier. (Evergreen in Marlboro) Am I better off placing a system that generates a bit more than we need during the summer months to make up for the winter vs cutting down tons of trees and having the MRs's upset for a while? (At $5/wt rebate, it seems like more panels vs less trees is an ok option)

I know I should have provided more details, so if anyone needs more info please let me know. This site is great. (Sorry about the typo's..in a rush right now)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #2
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    Re: Solar for me?

    OK, the basics... Go here to find out how much your system will generate. Use defaults for now (set for Grid Tied system).

    Looks like a system with 4.1 kWatts of solar panels will generate 5,099 kWhrs per year (based on Boston area weather). This calculator has been pretty accurate for me--but you can see +/- 5-10% based on weather and what not.

    Generally, with 1 year net metering (if offered by your utility), you would design the system to generate exactly what you consume--many (most all?) rate plans will not rebate you any cash at the end of one your (account is zeroed and you start over).

    Regarding trees... For now, assuming they provide 100% shade Nov thru Feb--you would loose ~1,300 kWhrs per year or increase the cost per kWhr... Assuming you pay around $0.12 per kWhr over 20 year system life, your installation cost is around $8-$10 per watt:

    4.1k * ($10/w install costs - $5/w rebate) / 5,100kWhrperyr*20yr = $0.20 per kWhr

    4.1k * ($10/w - $5/w) / 5,100-1,300kWhrperyr*20yr = $0.27 per kWhr

    If you have Time Of Use metering--and can offset your power usage from noon-6pm to off peak times--that can help you too (of course, TOU must be available, what are peak/off peak times, and rate plan, tiers, etc.).

    Problem with trees, is they grow. You may have to address the issue in the next few years anyway.

    And shade can really kill the output of a solar pv system... My 3kW system (with two parallel arrays), basically looses about 1/2 of its output if much more than a small portion of 1 out of 20 panels are shaded... With solar electric, assume any shading is a bad thing. Even power lines can cause 20%+ loss in power output.

    In the end, it is a tough call... Trees are pretty, neighbors (and cities) "like trees" (until they shade/fall/root damage their properties) and for me--to get a tree professionally cut starts around $1,500. Way more than the lost electricity costs for a year.... But that shade repeats and grows over the next 20-30 years--it does hurt to not cut/prevent shade.

    Economics wise, for heating, use a solar thermal system. They are only 1/4 the roof space for the same heat (80% efficient vs 20% or less for solar PV), less costly (1/4 the cost to install?), and solar thermal panels only loose energy generation based on the percentage of shading (10% shade would be 10% heat reduction). With oil (or electric) heat--solar thermal heating can make a lot of sense (can be much easier conversion vs a natural gas installation--gas water heaters and the gas itself is so cheap compared to electric/oil system fuel costs).

    For your area, you will have to take freezing weather into account. Plus, solar thermal systems have more maintenance issues (pump/tank leaks, anti-freeze, etc.) than solar Grid Tied systems (install, turn on, wash panels if you want, and that is about it).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #3
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    Re: Solar for me?
    Mass Solar wrote: »
    Excellent site here. Had some basic questions based on my scenario for possible solar power. I am located in Central Ma, and the roof faces South East. Reviewed last years utility use, and we used 5100 KWH last year..appx 425 per month...pretty frugal for a family of 5. Here are my specific questions:

    1.) I hear that running an electric water heater is not the way to go using electrcity, but one should get a solar hot water system. Right now, the entire house and water is heated with oil, and with oil at 4.25 gallon, I don't mind a 30% increase in electric use if I can generate it myself. Although we have a family of 5, 3 are kids under 5 and we don't use much hot water. (all boys)

    2.) Shading? How much shading affects the solar output of a panel. i.e if there is a small shadow on the panel that covers 10-15% of the panle, how much would this affect performamce. (Our house is right for Solar, but we would need to do some tree cutting for the panels to make sense in Nov-Feb.

    3.) Here in Mass, its looks like we would qualify for a $5Wt rebate due to our income, home value, and supplier. (Evergreen in Marlboro) Am I better off placing a system that generates a bit more than we need during the summer months to make up for the winter vs cutting down tons of trees and having the MRs's upset for a while? (At $5/wt rebate, it seems like more panels vs less trees is an ok option)

    I know I should have provided more details, so if anyone needs more info please let me know. This site is great. (Sorry about the typo's..in a rush right now)
    Just a few things I've found with my 6 flat panel hot water solar system over the past year. First, you can't heat a doghouse with these from Nov. to Feb., you'll just barely do your domestic hot water in this time period if you're lucky. Second, shading kicks the daylights out of even solar hot water systems. I know, I have a tree and I keep records. Min. 20% loss with minor shading. I can only imagine what shading does to PV. The tree is coming down......
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