Grid tie/batt backup system sizing using utility bill info

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System
System Posts: 2,511 admin
in Grid Tie and Grid Interactive Systems #1
Hello, I am designing a system for my home; grid tied with battery backup. We do not have netmetering but I don't feel comfortable going totally off-grid. My past 14 months' info averages to around 3400kWh per month and I am wondering what setup to use; maximum amount of my power from solar as possible. Thanks
Monthly usage
(kWh)
July 2008 5371 June 2008 4712 May 2008 3090 April 2008 3225 March 2008 1588 February 2008 2657 January 2008 2934 December 2007 2612 November 2007 2310 October 2007 2938 September 2007 4657 August 2007 3487 July 2007 4553 June 2007 3209

Also, will need to allow for adding a solar jack or equivalent pump. I have spent the past week sizing systems but i don't know if I am doing it in the right way so thanks for any help you can offer. direct pointing at a setup would be appreciated :)
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
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    Re: Grid tie/batt backup system sizing using utility bill info

    Well, you should be looking at conservation first

    Your July Bill is an average of 179 kWh/day ... you would need about 45 kW of solar panels ... or about $350K solar system ( gridtie no batteries ), double that for off grid

    Your way out of even thinking about solar ... I'd suggest you read a bit about how to understand your energy usage and ways to bring down the consumption side and things like insulation, high efficiency appliances, better windows ect.
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #3
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    Re: Grid tie/batt backup system sizing using utility bill info

    Cpdd,

    I agree with SG that sizing a system for your described loads would result in very large system. And, borrowing from the refrain that “it’s cheaper to invest in energy conservation than in energy generation”, looking for ways to reduce the energy load (home? business? both?) would probably make sense.

    However, one alternative would be to size and buy a PV energy system that would be grid-interactive (sell to the grid and/or reduce main panel loads) but would provide backup power to a select group of “essential” or “critical” downstream AC loads via a separate subpanel. Such systems are fairly common. This way, essential loads could be backed up while other non-critical loads lie dormant during a power outage.

    We can provide some amount of design assistance here on the forum. The site’s host also offers design services, as do the installer’s on the list below. Let us know if you’d like to explore this further.

    See: http://store.solar-electric.com/capr.html
    And: http://www.homepower.com/files/featuredinstallers/installersdirectory.pdf

    HTH,
    Jim crewzer
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #4
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    Re: Grid tie/batt backup system sizing using utility bill info

    You can review various programs for Mississippi (if that is where you are from) for loans/rebates/local laws to reduce your power use/solar Grid Tied/etc. on this site.

    TVA appears to offer a green tag program where they will buy your power for 2-3x your going rate--with approval of your local supplier. May allow you to go Grid Tie / virtual net metering... Appears to be a small program--but there is a chance your utility+TVA would approve.

    If AC is your major power usage--looking at insulation/double pane windows/new high SEER system (possibly including ground sourced Geo Thermal)/interior-exterior air heat exchangers/etc. would be a good place to start... If you use electric heat--then solar thermal for domestic hot water/pool would also help.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #5
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    Re: Grid tie/batt backup system sizing using utility bill info

    Cpddprice,

    One way to look at how you should proceed, you are probably paying around $0.10 per kWhr, or less...

    Here in Kalifornia... Where the government is trying to get everyone to conserve, they give OK pricing to people who don't use much power ($0.09 to $0.12 per kWhr), and hose people who use a lot...

    Right now, for somebody using over ~1,000 kWhrs per month (residential), they would be paying from $0.35 to $0.53 per kWhr... So, what would you do if all of a sudden, you had to pay around $900-$1,200 per month for your electricity instead of some $300 or so per month...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #6
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    Re: Grid tie/batt backup system sizing using utility bill info

    cpddprice

    Hopefully we did not scare you off like they did on the other board. Stick around, we may not have the answer you where looking for right now.

    Note to all: He/she does not have net metering, so we should look at sizing a system that will meet his/hers daily needs without turning the meter backwards. Something to offset their current usage.

    crewzer is going in the right direction about what loads need battery backup.
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