I have often wondered....

TunerTuner Registered Users Posts: 7
Gents....been reading wonderful info for several hours but the math is escaping me now.

I live in Florida and my energy usage from local power monoply ranges from 1300kwh to 2200kwh/month. I see all sorts of stuff for sale on eBay and elsewhere that seems to good to be true.

Local power company is now offering $.32/kwh in the form of a feed in tariff for a grid tied PV system.

I'm not an apologist for my public school education but I'm having trouble figuring out how large a system I need to cover my usage and create a little additional energy to help stave off proposed construction of a new biomass power plant.

Any thoughts would be much appreciated.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: I have often wondered....

    What do you want to achieve? Lowering your energy bill or eliminating it or making a profit?
    In that order, the first is doable but at expense, the second is most probably unlikely for any reasonable investment, and the third is darn near impossible. :D

    Here's why: we generally figure that a solar electric system produces at a best rate of approximately $1 per kW/hr over the life of the system. That's about three times the cost of your grid power. In other words; profit ain't in it.

    But there are many grid-tied set ups available that would reduce your bill. Since you're in Florida, most of your energy usage is probably from running AC during the day so the solar could help off-set costs at these peak usage times.

    To answer your first question last, 2200 kW per month divided by 30 days in a month is about 73 kW per day. Considering that rate of usage, how about investing in conservation methods first? They will give you the best pay-back per $1 spent.

    Just so you know, those of us who use "solar only" (off grid) try to keep usage as low as possible: I use less than 3 kW/day at my cabin, with "all mod cons". Are you sure you read those numbers right?

    Please stand by for more (and better) answers! :D
  • BB.BB. Super Moderators, Administrators Posts: 32,088 admin
    Re: I have often wondered....

    A quick way of calculating how much GT solar you would need. First go to the PV Watts website. Choose the city nearest to you.

    I will guess Datona Beach Fl. Set panel to 1kW (just an easy number). Use defaults for everything else. 1kW of panels will generate 1,359 kWhrs per year.

    Lets look at an average of:

    (2,200kWhr + 1,300kWhr)/2 = 1,750kWhr per month average

    12 months * 1,750kWhrs per month = 21,000 kWhrs per year

    21,000kWh/1,359kWh per 1kW of panels = 15.45 kWatts of solar panels...

    Assuming it would cost around $8,000 per kW of solar panels (turnkey installed, with permits) and you get a 30% Federal Tax break and Florida pays the $4 per installed watt rebate (cross your fingers on this one--year to year guess if will be funded):

    $8,000 -$4,000 per kW rebate = $4,000 out of pocket
    $4,000 cost * 0.70 fed tax credit = $2,800 per kW of solar panel installation costs

    15.45 kW of solar panels * $2,800 = $43,260 installed cost (after all credits)

    Your costs--assume 20 year life (no repair costs)--plug 15.45kW panel back into PV Watts and get 20,994kWhr per year:

    $43,260 / (20yr*20,994kWhr per year) = $0.103 per kWhr cost of GT power (no loan charges, repair costs, etc.)

    20,994kWhrs per year * ($0.32-$0.103 per kWhr) = $8,880 per year "profit"

    Not bad--but this assumes no repair costs (probably will need to replace inverters at least once in 20 years). And assumes that 50% of your installation cost is offset by Florida's rebate--which may be a gamble--have to install first year, then wait for 2nd year law for rebates to be funded.

    No property tax (home systems), no sales tax on solar equipment, very high Florida rebates (max 25kW system?), $0.32 per kWhr payments (any hidden gotchas?), 30% Fed taxes back.

    "Break Even point":

    $43,260/$8,880 per year "profit" = ~4.9 years

    Does not look bad... If everything works out. Florida has been leading the money give-a-way for solar for a few years now.

    -Bill

    PS: I sized this system based on, what I guessed to be, your 1 year kWhr usage for your home... Of course, you can size this to anything that meets your needs.

    Also, does Florida use a separate meter for your solar GT system--or is the $0.32 per kWhr only on the "net" output (GT system - Home Usage)? Would change the "payback" formula a lot (I based the above on a guess that Florida uses a separate meter for the Solar GT array). You will need to look into the billing details (which can wreck the "profit" if they start throwing in net metering, reservation charges, and income taxes on the payments)...

    Still, a GT system with all of the rebates, still is a $0.10 per kWhr system... Not bad compaired to use in California where we would be paying $0.38 per kWhr if we used over 1,000 kWhr per month.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TunerTuner Registered Users Posts: 7
    Re: I have often wondered....

    Cool....thanks very much.

    My daily average on this month's bill is 58kw based on a 28 day cycle. Total was 1643kwh for $234.85 or $.143/kwh....until you add in the surcharges and taxes.

    The power company's contract limits a residential property to 10kw.:cry:

    I have had CFLs in every socket for years but do have a couple of refers and a freezer running as well as a bunch of vampire usage for TVs etc. The AC/Heat component in summer/winter only seems to add around $75-$150/month to the total.

    Based on what I read above, my best bet it to bite the bullet on solar water heating(expesnisve due to exsinging WH location) and additional insulation.
    in an older house.

    The limitations placed on max kw take the feed in tariff off the table for me but the LPC is also still offering rebates to residential customers for solar panel install with net metering.

    Maybe a 5kw system would take care of most of the 120v stuff and leave the 240v to the grid?
  • BB.BB. Super Moderators, Administrators Posts: 32,088 admin
    Re: I have often wondered....

    There is no "difference" between the 120 VAC and 240 VAC--it is all one circuit... The GT inverter will, most likely be, a 240 VAC device.

    Of-course, you are probably just saying to off-set the power usage of the smaller 120 VAC devices, and letting the larger power hog 240 VAC devices continue to be feed by the grid.

    If the $4.00 per Watt Florida rebate happens again--you will just about break even on power costs (or come out ahead)--but that is a gamble (the government is going to run out of other people's money in the next few years as the Federal government keeps sucking it up).

    In the end, conservation is usually the best place to invest your money... Lots of insulation (>R40 in the attic), double pane vinyl windows, energy star appliances, CFL's no matter how bad they look, using smaller laptop computers instead of large desktop systems--placing them in standby when not used (reducing power in your home reduces A/C costs a lot too), replacing your old A/C with a new heat pump (18SEER?) and use it to help make your hot water with the waste heat (another couple threads here).

    Once you have gotten your power needs down--then, a Grid Tied system will give you a good chance to lock in lower cost solar PV GT rates, and free you from the spiraling costs of grid power (a guess) in the next few years at the $300,000,000 in carbon taxes kick in at the Federal level).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TunerTuner Registered Users Posts: 7
    Re: I have often wondered....

    Thanks again, BB. Insulation should help a lot with the AC/heat. I have a couple of BIG skylights that have marginal tint on them...lowE glass will take a bunch of that heat load away.

    Been watching too much PlanetGreen and seeing wild deals on solar panels on eBay I guess:) Once I get some of this stuff done, I will be back for more PV data....you guys ROCK!
  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: I have often wondered....

    Your last place to look is solar, first is conservation

    2.2 Mw is a crap load of energy ... sounds like you have atypical old house, maybe R5 in the attic , nothing in the walls a SEER 8 AC and resistive heating


    First is get the attic blown in to a minimum of R40, that alone will take 25% off your bill and for an average home costs under 1K. Also while up there check all the duct work for leaks, I've seen home with the duct work litterlaly blowing into the attic do to a register pulled off the duct.

    Next, get rid all the old refrigerators or freezers, I would guess you have so old clunker stuck in the hot garage, they are using more energy than you hot water. Figure out what you need and get a new energyStar rated unit , cut you demand in half for that function

    Next, upgrade to a SEER15 minimum heat pump, this will cut in half the AC/HEAT load, which over a year is more the 50% of the energy used in a typical florda home. installed cost is 5-7K Turnkey.

    With the above, you can at minimum cut your energy consumption by half if not more

    Solar Hot water in Florida is not the best route, Get a DeSuperHeater, which connects to the AC/Heat pump and uses excess heat to heat the hot water, about 1/4 the installed cost of solar thermal with actually more BTU's as a typical solar HW system could provide, it also provides heat whenever the AC/Heat pump runs, unlike solar which at night ( none ) or the rainy season ( lots of clouds 5 months of the year ) can't help in making hot water

    If you've done all of the above, then and only then think about GT solar electric, In Florida it be done for much less than BB's quotes, panels can be had for under3$ watt from SunElec but even at an installed price of 2-3 dollars watt net, there is no point until the home is fixed, otherwise your just wasting that expensive GT energy
  • TunerTuner Registered Users Posts: 7
    Re: I have often wondered....

    Yeah, 2.2 would be July/August here. Walls have maybe R5, cathedral ceiling with maybe R9...no way to fix without removing a lot of sheetrock OR roofing and plywood.

    AC is 10SEER, 3.5 tons with 2.5 in undersized duct board...and probably some leaks. Lots of problems that are expensive to fix. I really like the water heat coming from the heat pump....will check into that.

    The beer fridge in the garage is a new, energy star Samsung:D but it's operating in a hostile environment...pretty hot out there in the summer.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: I have often wondered....

    Sounds like the Sheetrock is attached to the rafters, which I would guess at best is 2x8's no point removing anything, not enough space for R40 which needs 16" plus air space on top of that. Was the house built that way or week-end-warrior to cathedral ... maybe redo to a lower slope to get insulation, that's how new homes are built ( I have cathedral but full access above the ceilings everywhere )

    refrigerator in the garage is nuts, you running 2X the rating of the unit to overcome the heat ... that's some expensive beer

    Your only choice is more efficient AC/Heat pump ... will save some but one might ask why bother with a structure with so many issues
  • BB.BB. Super Moderators, Administrators Posts: 32,088 admin
    Re: I have often wondered....

    Regarding my estimates--They are just guesses based on rough national averages and you may be able to knock a couple dollars a watt off those prices for your area (all the better). I am not involved in the solar/construction business at all.

    Regarding how much it will cost to add insulation... For your amount of energy usage, in Kalifornia--we are already paying $0.38 to $0.58 per kWhr--Take a guess where your bills will be going over the next decade and see if you can justify re-doing your insulation / ceiling / roofline / skylights.

    Also, if you ever decided to install a generator for emergency power (hurricane, etc.)--the lower your power needs the less your emergency fuel needs will be too...

    Your home will probably be much more comfortable too--winter and summer.

    The cost of power is probably going to get worst over the next 4-8 years.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TunerTuner Registered Users Posts: 7
    Re: I have often wondered....

    I've learned more this afternoon on this site than in a year of watching Planet Green.
    Your only choice is more efficient AC/Heat pump ... will save some but one might ask why bother with a structure with so many issues

    And those folks that would ask that would probably be content to continue to watch their energy costs go up:confused:

    The house was built in 79, no way to lower the ceiling due to a loft. However, I can and will insulate the roof and side walls and change out the skylights. A more efficent AC unit that makes hot water is a near term addition once the insulation is done. great suggeston...

    The garage refer could get moved into the man cave for more efficent operation.

    Last will be as much PV as I can reasonably get on the roof of a 35'x45' steel shed.

    Thanks for sharing your time and experience, its been a large help!
  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: I have often wondered....

    I suggest some reading on Geothermal ... the efficiency can be near SEER of 30

    Almost all the Geothermal systems have built in secondard loops for heating water, as that's how they primarily cool. If you a serious do-it-yourself type, you can put a Geo unit in for the same cost as a Turn-Key Air Cooled Heat pump ... advantage over the air cooled Heat pump there is no refrigerant lines to deal in the Geo unit as everything is in one box

    Look on eBay to get an idea on prices
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: I have often wondered....

    pvs have a side benefit in that they absorb the sun's initial brunt and can help keep the house cooler being the house is partially shaded by them. you will need to be sure to have a minimum of 6 inches between the pvs and the roof so the pvs can have some air to cool off somewhat.
    as to the insulation options for you, maybe consult a local insulation installer to see if you have any other cost effective alternatives available to you. loose insulations are not the only types out there either, but it is homes like yours needing the insulation the most so i'm sure they have some ideas of what can be done. if you can't fit or get r40, but can fit or get to r20 then do it. it might not be ideal, but it will still cut in half the btus flowing over what you presently have. also, try to stop any airleaks around doors and windows.
  • mike95490mike95490 Solar Expert Posts: 9,393 ✭✭✭✭✭
    Re: I have often wondered....
    Tuner wrote: »
    Last will be as much PV as I can reasonably get on the roof of a 35'x45' steel shed.

    Beware, the PV can have a bigger wind load then the shed anchor bolts can hold.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Bob McGovernBob McGovern Solar Expert Posts: 25
    Re: I have often wondered....

    What color is your roof? Dark shingles are all the mode today, but they are bad in any climate and suicide down south. The shingles and sheathing break down quickly in the heat, they can lead to moisture cycling issues, and they increase cooling bills 25%. If you have dark shingles, the good news is you can paint them a lighter color. It's really easy, and if done with an artistic eye can look as good as those 'layered' architectural shingles.

    Bad news is lots of Homeowners Associations limit color choices. A mild tan is good.

    ETA: 60-70 kWh/day is really, really high. Double the US median. Definitely work the efficiency/lifestyle angle until that number is below 15, then it's worth talking renewables. As for the utility's 10 kW system "limit" -- have you looked into the capital costs of a system that size? You are talking, what, $80k? Cheaper to knock down the house and start over.:blush: The pure PV footprint would be immense, like 1600 sqft.
  • mike95490mike95490 Solar Expert Posts: 9,393 ✭✭✭✭✭
    Re: I have often wondered....

    Bad news is lots of Homeowners Associations limit color choices.

    That makes me want to get "Trailer Roof Aluminun" color
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Bob McGovernBob McGovern Solar Expert Posts: 25
    Re: I have often wondered....
    mike90045 wrote: »
    That makes me want to get "Trailer Roof Aluminun" color

    Neon pink, man. Makes it easy to find your house on GoogleEarth.:cool:
  • TunerTuner Registered Users Posts: 7
    Re: I have often wondered....

    Update: the roof has R19 and the walls are R11...better than previously thought.

    There are some poorly insulated areas in the crawl space that are being addressed this weekend. Next up is a steel roof with additional foam insulation.

    The old 10 SEER heat pump with the horrible ductwork is going away in favor of a new mini split system that has virtually no start load and runs well on PV.

    No homeowners or deed restrictions to worry about, the new steel shed will be 37 x 48 and wind rated for 120mph and all the PV I want to put up there....starting with 5kw. Local solar company says around $35k installed before rebates and credits.
    LPC still offers rebates for GT systems...I think 5kw will be plenty once the changes are completed.

    Suntex will block heat from the skylights.

    Emergency generator for hurricane season is a 10kw diesel...on a slide in the front end of the motorhome;) More as I think of it, thanks for sharing all your suggestions.
  • mike95490mike95490 Solar Expert Posts: 9,393 ✭✭✭✭✭
    Re: I have often wondered....
    Tuner wrote: »
    Emergency generator for hurricane season is a 10kw diesel...on a slide in the front end of the motorhome;)

    Note about diesel generators - you should keep them loaded to at LEAST 50%, otherwise, they run too cold, and slobber and coke up. Thats why big rigs have covers over their radiators in the winter, to help keep the engine from being overcooled.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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