Need Help To see what I would ned to start

chris4864chris4864 Registered Users Posts: 7
I have checking my electric meter for 24 hrs. I am using about 86 KWH.
That is about 2564 KWH per month. If I would like to buy some solar panel to make me a 0 electric bill in a month how many 240 watt panel would I need, I have full sun and live in Louisiana. Thanks

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need Help To see what I would ned to start

    Welcome to the forum

    The first thing you need to buy to get your electric bill down is a Kill-A-Watt (or similar) meter. Start measuring everything plugged in and see what is hogging the power and needs to be unplugged. You'll get more return on that $30 expenditure than you will on anything else. And faster too. 100 kW hours per day is murder.

    Second, the cost of taking your utility-fed house off grid will be far more than paying the electric bill, regardless of how much power you use. Off-grid power cost from $1 to $2 per kW hour over the life of the equipment, and requires a large capital expense up front.

    Third, depending on what sort of incentives are available to you through your local utility and state & federal governments you may find the most practical way to include solar in your power program is with a grid-tie system. They are much more economical than off-grid, producing power at about $0.50 per kW hour.

    If you were thinking about solar for back-up emergency power, think about a generator instead. Unless your utility rates are even higher than Hawaii's or your grid is as dependable as a politician's promise off-grid solar power does not make good economic sense.

    And this is probably the only solar power forum on the Internet where you'll get told that. :cool:
  • chris4864chris4864 Registered Users Posts: 7
    Re: Need Help To see what I would ned to start

    I am sorry. I check again at my meter after I read your answer and it is 107 KWH for 2 days. That would be 1500 KWH in a 30 day period. I would like to be tie to the Grid, but would like to know about how many 240 panels would be good for me to be even. Thank
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need Help To see what I would ned to start
    chris4864 wrote: »
    I am sorry. I check again at my meter after I read your answer and it is 107 KWH for 2 days. That would be 1500 KWH in a 30 day period. I would like to be tie to the Grid, but would like to know about how many 240 panels would be good for me to be even. Thank

    Even 107 kW hours in two days is 53.5 kW hours per day. (We tend to think in single days for off-grid systems because the goal is to recharge daily.) The advice for the K-A-W meter still holds, as it is useful for any situation. Conservation methods give you a better return on your investment than generation methods. :D

    One of the nice things about grid-tie solar is that you don't have to meet a specific target: any amount will help offset the utility power, and large amounts can even give you that zero bill - or a bit more. The capital costs are not insubstantial though.

    Just as a "for instance" if you were looking to eliminate 54 kW hours per day, you have basically 4-5 hours of "good sun" to do it in. That means you have to generate almost 11 kW per hour to make that much. Given the inevitable system losses (panel output is an average, heat reduces panel output, every wire and component uses some power) you'd need quite a large array. Possibly as much as 14 kW. Maybe more. At an installed cost of $6 per Watt (more or less) that gets mighty expensive. That's why reducing usage is so valuable.

    You might want to try a few theoretical systems on PV Watts http://www.nrel.gov/rredc/pvwatts/ for your area to see what you might expect through the year and what it would be worth.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Need Help To see what I would ned to start

    Lets say you are near Baton Rough LA, using PV Watts, everything set to defaults and 1,000 watts (1kW) of solar panels. We would get:
    "Station Identification"
    "City:","Baton_Rouge"
    "State:","Louisiana"
    "Lat (deg N):", 30.53
    "Long (deg W):", 91.15
    "Elev (m): ", 23
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 0.8 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 30.5"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.1 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.72, 85, 6.89
    2, 4.22, 87, 7.05
    3, 4.96, 111, 8.99
    4, 5.48, 113, 9.15
    5, 5.58, 118, 9.56
    6, 5.45, 109, 8.83
    7, 5.27, 109, 8.83
    8, 5.60, 115, 9.32
    9, 5.11, 104, 8.42
    10, 5.69, 122, 9.88
    11, 4.37, 94, 7.61
    12, 3.80, 86, 6.97
    "Year", 4.94, 1254, 101.57

    So, you would average around 109 kWH per month in June/July or about:
    • 109 kWH per month / 30 days per month = 3.63 kWH per day per 1kW of solar panels
    • 1,500 kWH per month power bill / 109 kWH per month per 1kW of solar panels = 13.8 kW of solar panels for June/July
    A grid tied system (if your local utility allows GT systems) would cost you around $5,000 to $8,000 per 1kW of solar panels installed (professional turnkey installation). You might do it for 1/2 that amount yourself:
    • 13.8kW system * $6,000 per kW = ~$83,000
    With a 30% Federal tax credit:
    • $83,000 * 0.7 credit ~ $58,000
    Done with 240 watt panels:
    • 13,800 watt system / 240 watt per panel ~ 58 panels (240 watts per panel).
    Some round figures... In general, conservation is a better investment for your money--so we always ask have you insulated (lots of attic insulation, double pane windows, weather stripping), have a very energy efficient AC system (older models are around 0-13 SEER, you can get air based systems upwards of 26 SEER which would cut your A/C power requirements by about 1/2), looked around your home to use more efficient appliances, TVs, Computers, turning things off when not needed, replaced old filament based lighting, etc....

    Not a Grid Tied system must be approved and allowed by your utility. And different utilities/states have different Grid Tied Metering plans (net metering). Some are pretty good for the customer, and others not very good. Also, there are lots of smaller utilities and coops that do not allow net metered power at all.

    Also, pure solar Grid Tied systems (what I sized above) are about the most cost efficient way of producing your own power... However, they do not operate if your utility power fails (storms, pole knocked down, etc.). Off grid capable power systems cost a whole lot more to install and operate (with batteries, backup genset, etc.).

    Lastly, I priced the system based on one months worth of power usage--typically utilities offer 1 year net metering and you would size you system based on 1 year worth of power usage (and power that a GT system would produce).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Need Help To see what I would ned to start

    Most grid tie systems should be rated for annual usage if the utility allows credit of power month to month. If you June/July usage is that high you also need to know what your Jan - March usage is as well, as you will probably over generate in those months. I have summer days in AZ where I use well over 100Kwh, but only generate about 60Kwh, but I have a bank of power with the utility to draw against. Last Saturday was a prime example with outside temps soaring to 118F and inside temps held @ 78F our usage well out stripped our production. Just think about that temp delta, it is the same as a delta on a typical refrigerator and in our case about 27,000 cubic feet to cool.

    Grid tie generally isn't sized by peak consumption but by annual consumption. That cuts the outlay to usually 1/2 of peak consumption.
  • chris4864chris4864 Registered Users Posts: 7
    Re: Need Help To see what I would need to start

    I check with my power company in my area and they do a tie end on there electric lines. I would like to know how many 240 watt panel I would need to install with a total for a year of 31,101 KWH of electric power that I use. Thanks!! Chris
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Need Help To see what I would ned to start

    Regarding your power company, you still need details about their program to be sure (is this one year net metering, do they have/require Time of Use peak/off peak billing, do they tiered pricing--an east/west cost billing thing--, etc.?).

    Also, you should confirm (or not) that Baton Rouge is near your location and/or has similar weather...

    Assuming my above guesses where correct, then for a 1 year net metered system near Baton Rouge LA GT system will generate around 1254 kWH per year per 1,000 watt of panels. Or:
    • 31,101 kWH per year / 1,254 kWH per year per 1,000 watt of panels = 24,800 Watts of solar panels
    • 24,800 watts panels / 240 watts per panel = 103 panels
    Note, for many states/utilities, systems over 10kW of PTC Rating (roundly 12.5 kW of solar panels) treat them quite differently than under 10kW systems. You may be charged for utility infrastructure upgrades (local distibution wiring and transformers), you may not qualify for a 1 year net metered program but be put into a different billing plan, and you may have other requirements placed on your system (power reporting/logging, etc.--although--this last stuff is typically a California thing).

    A 24.8 kW system is probably going to cost around ~$120,000 minimum to install ($5,000 per kW minimum). You can get a 30% federal tax credit and may qualify for other local tax credits).

    That is a fair amount of power usage even for a good sized home (in my limited experience)... Have you looked at conservation (insulation, new A/C high efficiency A/C system, replacing electric hot water/heating with heat pumps, get the kids to turn stuff off when not in use, etc.)?

    For less money, and frequently without changing your lifestyle much--people that have never tried before can cut upwards of 1/2 of their power use with extensive conservation efforts.

    It is almost always less expensive (and has better resale value) to do conservation vs adding an "over sized" GT solar array. Plus the homes are typically much more comfortable (less noisy, more even temperatures, better humidity control, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • chris4864chris4864 Registered Users Posts: 7
    Re: Need Help To see what I would ned to start

    Thanks BB. You are saying that I would need 131 panels ( 240 Watt panels )to produce 31,000 KWH in a year . I divided that 31,000 Kwh per year by 12 months and that a average of 2,591 KWH per month. My Electric company would buy my Electricity at the same price that I use. Thanks!! Chris
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Need Help To see what I would ned to start

    Actually, 103 panels for 31,000 kWH per year...

    Note that the math is a three step calculation...
    • The first step is to see how much power 1,000 watts of solar panels will generate in your area... Used PV Watts
    • Then divide that into your power requirements and that is how many watts of solar you will need. See below
    • Lastly, take the size of array and divide by your 240 watts per panel to get number of panels. See below

    • 31,101 kWH per year / 1,254 kWH per year per 1,000 watt of panels = 24,800 Watts of solar panels
    • 24,800 watts panels / 240 watts per panel = 103 panels
    Note, the above numbers are based on ~20 year average sun for Baton Rogue--Actual sun may vary by 10-20% month by month or year over year (natural weather patterns)...

    Also, used a 77% efficiency for the system... In very warm climates with solar panels mounted tight to roof, you may be slightly less efficient and need a few more panels to keep up (hot panels do not generate as much energy as small panels)....

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • chris4864chris4864 Registered Users Posts: 7
    Re: Need Help To see what I would ned to start

    Thanks BB. I would have not believe that it would have taken over a 100 240 watts panels to produce 85 WHh of power per day to brake even on my Electric bill . Also I would have put my panel on poles. Thanks for your help. There is no way I would spent that much money on solar power. Thanks for your advise. Chris
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Need Help To see what I would ned to start

    you don't need to break even as you can offset your usage somewhat by getting a smaller more manageable system. many people do that.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Need Help To see what I would ned to start

    Chris what are you running that requires so much power? While your peak/day/week month might lead you to believe that much is required it seems extreme for a residential installation.

    I have three 3 ton AC units, one is a mini split, a swimming pool pump, electric stove, three full-time computers and a plug in electric car and don't use that much juice. What is your overall annual usage? Do you have variable rate plans, where just replacing youth on peak time of use would be cost effective?
  • chris4864chris4864 Registered Users Posts: 7
    Re: Need Help To see what I would ned to start

    I have three 3.5 ton AC units, a swimming pool pump that run 24 hrs., electric stove, three full-time computers and 3 freezers , 3 ice boxes. and a small 2220 volt air condition to cool my wife cake shop that is connected to the house. I burn about 2600 KWH per month. I just wanted to know about how many 240 watt panels That I would need to lower my electric bill to almost 0 . Any input would be great . Thanks Chris
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need Help To see what I would ned to start

    I think you'd get more benefit from reevaluating your loads. For instance electric stove is a big power user that can be replaced with natural gas or propane either of which is bound to be cheaper. The pool pump; somewhere on this forum is a discussion about lower-power pool pumps that are available. Likewise the AC units are not necessarily the most efficient, nor the refrigeration units. Certainly the computers can be reduced: laptops can do the same job on a lot less Watts. This may sound like an odd way to go about it, but the cost of supplying that much power with PV could easily pay for some significant improvements in the efficiency of the loads.

    And that is always where you have to start.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Need Help To see what I would ned to start

    I have a VFD based pool pump, runs 4hours a day max along as the pool is not in trouble. Check with you utility on AC unit upgrades rebates. Look at switching to some thing like MAC mini computers, desktop kind of features with lap top type of power draw. Look at energy star appliances as well.

    This sounds like more than a typical residence, while it is possible to lay in that much solar, it won't be cheap. My system is 72 175 watt panels into a 400 amp service, about the limit before having to do some serious derating of the service main breakers.

    Would suggest looking at your annual usage and go from there. Is the 2600kwh a peak summer consumption?
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Need Help To see what I would ned to start

    Here is some production number on a monthly basis off my 12.5Kw solar setup with a Time of Use plan 9AM-9PM Mon-Fri as on peak and a difference on summer and winter rates:

    Month Power Cost
    Jun 11 -2057 kWh $ -309.52
    May 11-2064 kWh $ -300.84
    Apr 11 -2052 kWh $ -257.09
    Mar 11 -1969 kWh $ -258.98
    Feb 11 -1591 kWh $ -213.40
    Jan 11 -1613 kWh $ -198.71

    Given the above numbers I still purchased some off peak power from my utility for weekday overnight usage at cheap rates. I produced much more on peak than I consumed in the first 5 months of the year (nearly 2900kWh extra), but in months 6-9 I will consume more than I produce. In months 10-12 I will produce more than I consume again and the utility will settle up with me on Dec 31 for the excess watts at about $0.062 per kWh credit on my account. It is all about annual planning, not a single month usage.

    Let's assume that 2600 kWh is your summer peak consumption and now lets assume again that your winter usage is half your summer usage. If you could reduce your peak summer consumption by say 20% a 10Kw Grid tie should easily meet your needs. That puts you in the 40-50 240 watt panel range. But before you run off and buy, you need to do the planning to avoid the "Ready, Fire, Aim" syndrome so common in solar deployments.

    All of this is dependent on your location, your utility method of accounting on Watts sent back to the grid, your billing plan. The right thing to do is to look at your ROI and get the most bang for the buck. Locally I can get Grid tie installed for slightly under $5 a watt right now, hit that with any utility rebates and the 30% Fed tax credit you should get a feel on your ROI. Zero electric bill is a lofty goal, but if you can buy off peak power cheaply, then just offsetting the on peak portion of the bill can be pretty cost effective depending on your electric rates.

    I would say more information is required to determine a best course of action. Can you give us your location, the monthly consumption numbers, the utility rates and possible rate plans and how does your utility handle the excess production in the low usage months?
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need Help To see what I would ned to start
    BB. wrote: »
    Actually, 103 panels for 31,000 kWH per year...

    Note that the math is a three step calculation...
    • The first step is to see how much power 1,000 watts of solar panels will generate in your area... Used PV Watts
    • Then divide that into your power requirements and that is how many watts of solar you will need. See below
    • Lastly, take the size of array and divide by your 240 watts per panel to get number of panels. See below

    • 31,101 kWH per year / 1,254 kWH per year per 1,000 watt of panels = 24,800 Watts of solar panels
    • 24,800 watts panels / 240 watts per panel = 103 panels
    Note, the above numbers are based on ~20 year average sun for Baton Rogue--Actual sun may vary by 10-20% month by month or year over year (natural weather patterns)...

    Also, used a 77% efficiency for the system... In very warm climates with solar panels mounted tight to roof, you may be slightly less efficient and need a few more panels to keep up (hot panels do not generate as much energy as small panels)....

    -Bill

    Baton Rough, Baton Rogue... are you doing that on porpoise? :D
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Need Help To see what I would ned to start

    The Baton Rogue I will cop to a typo... Don't know where Baton Rough came from.:blush:

    Although, I am really frustrated with this integrated mouse bad on my pretty new Toshiba--Keeps activating every keyboard short cut there is on Firefox--Including 1/2 I never knew about. :grr

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need Help To see what I would ned to start
    BB. wrote: »
    The Baton Rogue I will cop to a typo... Don't know where Baton Rough came from.:blush:

    Although, I am really frustrated with this integrated mouse bad on my pretty new Toshiba--Keeps activating every keyboard short cut there is on Firefox--Including 1/2 I never knew about. :grr

    -Bill
    Post #5. I lived in BR for a while, and it is a bit rough in places... ;^)

    Mouse bad? Bad mouse!

    Speaking of funny typos:
    http://damnyouautocorrect.com/

    Don't go there unless you have a lot of time to waste sitting at your computer giggling hysterically.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Need Help To see what I would ned to start

    Ok--I am going to take a break... Mouse pad.

    Talk among yourselves.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need Help To see what I would ned to start
    BB. wrote: »
    Ok--I am going to take a break... Mouse pad.

    Talk among yourselves.

    -Bill
    Hey, I didn't mean anything by it. I don't mention typos unless they are funny. Freudian Typos, as it were. :D

    I once was on a forum discussing Cozumel and we were talking about a big new shopping mall that had been built right on the waterfront to cater to the cruise ship crowd, which they had to tear down a lot of cool old buildings and residences to build. They named it "Punta Langosta" (lobster point), but in a post I accidentally called it "Puta Langosta". Puta means "prostitute". Freudian Typo.

    Now I call it that on purpose. :cool:
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Need Help To see what I would ned to start

    Sorry--I had fun reading about my typos... Should have added the ;).

    Yea--there is a Putah Creek in California....
    The true meaning of "Putah" in Putah Creek has been the subject of discussion and speculation. It was originally called "Arroyo de los Putos" (1844) and "Puta Creek" (1845), but the "Puta" form was rejected by the United States Board on Geographic Names, likely because of the resemblance to the Spanish puta, meaning whore.[5] Some consider the resemblance to be "purely accidental".[6] "Puta wuwwe" may also mean "grassy creek" in native Miwok,[6][7] but other possibilities (including "whore") are discussed by historical sources.[5]

    Fun and games with languages...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • chris4864chris4864 Registered Users Posts: 7
    Re: Need Help To see what I would ned to start

    Hi Again. My electric bill average about 245.00 per month in a year. I pay about 7 or 8 cent per KWH in my area. My Electric company is Slemco and they will buy back my Electity at the same price that I pay for it. I use about 2500 KWH per month average. Someone said I would nee 101 240 Watt panels. Is this correct. I do luive about 50 miles west of Baton Rouge. Thanks. Chris
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need Help To see what I would ned to start
    chris4864 wrote: »
    Hi Again. My electric bill average about 245.00 per month in a year. I pay about 7 or 8 cent per KWH in my area. My Electric company is Slemco and they will buy back my Electity at the same price that I pay for it. I use about 2500 KWH per month average. Someone said I would nee 101 240 Watt panels. Is this correct. I do luive about 50 miles west of Baton Rouge. Thanks. Chris
    Usually net metering is a little more complicated than that. Will they write you a check at the end of the month if you have produced more than you have used? At the end of the year? Or at all? Do they let your meter run backwards and forwards all year and then just zero it out? It is very unlikely that they will write you a check at the end of the month for full retail value for excess kWh's you produce.

    Every utility has its own interconnect and tariff agreements, and there are several different strategies that they employ. You need to get familiar with how they are going to deal with your excess, should you have any, before you plunk down on a system that will ever generate excess power, even for a little while.

    I don't know how whoever told you how much solar you would need came up with that number, but it looks suspiciously like they just multiplied 101 modules times 240 Watts to get close to 2500. If that is the case, that person is someone you should NOT be getting advice from.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need Help To see what I would ned to start

    101 * 240 = 24,240 Watts. Times how many hours of sunshine? That's what equals Watt hours (not including derating).
    Where you'd put that many panels is another question. A 240 Watt panel is almost 20 square feet in itself. Times 101 is over 2000 square feet of space. That's a lot of roof.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Need Help To see what I would ned to start
    ggunn wrote: »
    I don't know how whoever told you how much solar you would need came up with that number, but it looks suspiciously like they just multiplied 101 modules times 240 Watts to get close to 2500. If that is the case, that person is someone you should NOT be getting advice from.

    See post 5, 7, and 8 above... Don't have to listen to me--and it is always possible I have done the math wrong.

    Baton Rouge seems to have have weather issues (high humidity, cloudy summers?)... Almost a 1-2 hour a day sun "deficit" when compared to "sunny San Francisco Airport" during summer...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need Help To see what I would ned to start
    BB. wrote: »
    See post 5, 7, and 8 above... Don't have to listen to me--and it is always possible I have done the math wrong.

    Baton Rouge seems to have have weather issues (high humidity, cloudy summers?)... Almost a 1-2 hour a day sum "deficit" when compared to "sunny San Francisco Airport" during summer...

    -Bill

    Well I got 115 240 Watt panels for 85 kW hours per day, but then I'm a pessimist. :p
Sign In or Register to comment.