Opinions on a grid tie system with net metering

rprr
rprr Registered Users Posts: 14 ✭
in Grid Tie and Grid Interactive Systems #1
I would greatly appreciate the input from forum members here on the following Solar PV system that is proposed.

We live in Hawaii where electricity is quite expensive and therefore decided to install a solar PV system given all the available tax credits and other incentives. The system will be the following. Installer is quite reputable and has done large number of local installations both small and large. There is no shading.

System details:
DC rated power: 3.84 kW
Panels: 16 panels Sunpower E19 240-watt (model SPR-240E-WHT-D)
Inverters: Enphase 210-watt DC-AC micro inverter (model M210-84-240-S12)

Amount of electricity generated by above system:
DC rated power = 3.84 kW
DC-AC derate factor = 0.80
Peak sun hours (avg) = 4.5
Total amount of electricity = 3.84*0.80*4.5*365 = 5000 kWh/year

System is grid tied with net metering.

Installed costs: $29000 (with tax) is almost $7.55 per watt
Federal credit: $8700
HI Tax credit: $10000 (two separate installs)
Net cost: $10300 ($2.68 per watt)

Electricity usage is roughly 5000 kWh/year (14 kWh/day)
Cost of electricity = 40 cents/kWh
Annual cost of electricity produced is = $2000
Minimum power bill per year = $20 * 12 = $240
Annual cost savings = $1760

Payback time (assuming costs remain same) = approx 6 years

I'd very much appreciate your input especially if I have made mistakes and/or made incorrect assumptions. Thanks in advance.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Opinions on a grid tie system with net metering

    Welcome to the forum.

    I'm not a G-T guy, but from the many discussion on this board regarding Enphase inverters it would seem there is no advantage in using them over a central inverter (such as an SMA SunnyBoy) when you have no shading issues and all panels can be oriented the same. It just adds cost, not power.

    What happens to the price if you stick one of these http://www.solar-electric.com/suboysb40wag.html in to replace sixteen Enphase units? Ought to save about $1000.

    Also, the 80% efficiency factor may be a bit optimistic for warm & wonderful Hawaii. Panels don't like heat.
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #3
    Re: Opinions on a grid tie system with net metering

    Cariboocoot -- Many thanks for the welcome and your response.

    Cost: The difference was roughly $800 for us. After a 65% tax credit this works out to roughly under $300. Furthermore, the dealer also pays for the Enphase monitoring for the first 5 years.

    Efficiency: Where I live in Hawaii, the normal (average) highs vary between 78-84 F which is 26-29 C. I also assumed that the roof gets 20 degrees higher. Thus the difference from the STC would be 21-24 C. The Sunpower panels reportedly have a power derating of -0.38%/K which would roughly be 8-9% loss. The panel operating efficiency would therefore be 91-92% assuming no shading etc. The inverter is supposed to operate at 95.5% efficiency. I also assumed all other losses to be roughly 8%. The total derating factor was 0.915*0.955*0.92 = 0.8
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #4
    Re: Opinions on a grid tie system with net metering

    Here is a link to PV Watts. Put your sytem numbers in KW size, Tilt, and Azimuth in degrees True that the panels will point adjust you electric rate as needed and see what the program say's. Does look like your warmer year round temp is derating more. I plugged my system in and it showed about 150 KWh less for the year than here in CA at about 39° North. Same sun here on a cool day, mid 60°F and my GT3.8 inverter will max out being feed by 4600 watt of panels. Today about 80°F and only 3500 to 3600 watts average. Did get over 30 KWh today which makes me happy. Nice to see the numbers roll back on the utility meter.

    Good Luck and enjoy your system. You have some very nice tax breaks there. Just don't double dip on calculating them, Uncle Sam Frowns on that.

    http://mapserve3.nrel.gov/PVWatts_Viewer/index.html
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • Dr. Strangelove
    Dr. Strangelove Solar Expert Posts: 49 ✭
    #5
    Re: Opinions on a grid tie system with net metering
    rprr wrote: »
    ... Installer is quite reputable and has done large number of local installations both small and large.

    Would you mind if I asked who you're using for your install. I have interviewed maybe a half dozen installers and I have only found one that I might trust on my property.
    System details:
    System is grid tied with net metering.

    Installed costs: $29000 (with tax) is almost $7.55 per watt
    Federal credit: $8700
    HI Tax credit: $10000 (two separate installs)
    Net cost: $10300 ($2.68 per watt)

    Electricity usage is roughly 5000 kWh/year (14 kWh/day)
    Cost of electricity = 40 cents/kWh
    Annual cost of electricity produced is = $2000
    Minimum power bill per year = $20 * 12 = $240
    Annual cost savings = $1760

    Can I ask about your numbers too? First, could you break down the gross installation costs - material & labor? What kind of racking are you using?

    Second: how is it that you plan to max out the Hawaii state credit ($5K) twice? I'd love to break my installation down into $14,285 ( $5K / 35% ) increments.

    Third: where did you get the $0.40/kWh delivered price? Are you on a neighbor island?

    Finally, how did the haggling with HECo go? Did you have to upgrade your service to 200A or more? Did you have to do anything else to satisfy our power masters? And how difficult were the permitting and inspection processes?

    Thanks-

    Andrew
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  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    #6
    Re: Opinions on a grid tie system with net metering
    rprr wrote: »
    Inverters: Enphase 210-watt DC-AC micro inverter (model M210-84-240-S12)

    Did you switch this to the new M215 inverters?

    John
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  • Fatawan
    Fatawan Solar Expert Posts: 71 ✭✭✭
    #7
    Re: Opinions on a grid tie system with net metering

    The new inverters won't work with the Sunpower modules
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #8
    Re: Opinions on a grid tie system with net metering
    Dr. Strangelove wrote: »
    Would you mind if I asked who you're using for your install. I have interviewed maybe a half dozen installers and I have only found one that I might trust on my property.
    I live on the Big Island (Hilo side). I am using Provision Inc. This is their website.
    http://www.provisiontechnologies.com/index.html
    Can I ask about your numbers too? First, could you break down the gross installation costs - material & labor? What kind of racking are you using?
    Unfortunately I don't have the break up. I was just given the total cost. Everything was folded in. In order to install Sunpower you have to go with the dealer that they use. I don't know what racking is used.
    Second: how is it that you plan to max out the Hawaii state credit ($5K) twice? I'd love to break my installation down into $14,285 ( $5K / 35% ) increments.
    The following does not constitute tax advice (Please consult your tax preparer or CPA).
    I have read the Hawaii regulations for the renewable energy tax credit. The maximum tax credit is not per installation but is actually per system. There is a very complex way of deciding what constitutes a system. Please see
    http://www.state.hi.us/tax/tir/tir10-03.pdf
    Third: where did you get the $0.40/kWh delivered price? Are you on a neighbor island?
    I am on the Big Island. Last month we paid $0.43/kWh
    Finally, how did the haggling with HECo go? Did you have to upgrade your service to 200A or more? Did you have to do anything else to satisfy our power masters? And how difficult were the permitting and inspection processes?
    There was some issue with getting an Interconnect Requirement Study from HELCO. My system is still being installed. Most likely by middle of next month we hope to be generating our own power and connected to the grid.
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  • Dr. Strangelove
    Dr. Strangelove Solar Expert Posts: 49 ✭
    #9
    Re: Opinions on a grid tie system with net metering

    Thank you for that pointer to that document. I will seek tax advice from my in house counsel (she hates it when I say that). I have been moving towards a three part system: 2 GT inverters and arrays, and one hybrid battery inverter system. If I can keep all three PV arrays the same size, it should be easier to keep the systems up by swapping blocks for maintenance and failover. Adding solar water heating will be a fourth.

    Wow, HELCo is nearly 50% more than HECo! I didn't think there was anyone paying more than us on Oahu. Good on you for your system.

    I've got a good handle on the costs for the electrical bits, it is the structural components and labor that I'm trying to pin down. I'm trying to get my architect to understand that we are starting from scratch so that the infrastructure for the PV array can be architected into the design of the building. We have identified an installer here that he has worked with before, and all three of us have engineering degrees - just different ones. I'd like to get him onboard before we even excavate for the garage.

    Andrew
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  • rprr
    rprr Registered Users Posts: 14 ✭
    #10
    Re: Opinions on a grid tie system with net metering
    Dr. Strangelove wrote: »
    Thank you for that pointer to that document. I will seek tax advice from my in house counsel (she hates it when I say that).
    There are some other documents as well that are referenced in the instructions for filling out Form N-342 (credit for RE). Make sure to read those as well.
    I have been moving towards a three part system: 2 GT inverters and arrays, and one hybrid battery inverter system. If I can keep all three PV arrays the same size, it should be easier to keep the systems up by swapping blocks for maintenance and failover. Adding solar water heating will be a fourth.
    We do have solar water heating as well. For two of us, it is perfect. We do not use any electricity for water heating.
    Wow, HELCo is nearly 50% more than HECo! I didn't think there was anyone paying more than us on Oahu. Good on you for your system.
    The high HELCO prices definitely make the decision to go solar much more favorable in terms of quick payback.
    I've got a good handle on the costs for the electrical bits, it is the structural components and labor that I'm trying to pin down. I'm trying to get my architect to understand that we are starting from scratch so that the infrastructure for the PV array can be architected into the design of the building. We have identified an installer here that he has worked with before, and all three of us have engineering degrees - just different ones. I'd like to get him onboard before we even excavate for the garage.
    It is great that you are designing your house for solar from the get-go. We just bought an older home (built mid-1980s). It does have plenty of roof space for solar.

    Good luck with your install.
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