how much pv to go off grid

Hi fellows!!

I been thinking to go fully off grid, I already had my system of 1300 w of pv one year ago, my 1530 AH forklift @ 24v will never see a full charge with this much pv. so I been combining solar with grid power, my monthly usage from the grid is between 270 to 320 KW per month, since I might be about half way to be fully off grid all I need is to add more PV, how many watts of panels do I need to get 320 KW per month?, assuming is a shiny every day, cloudy days I'll run my genny to charge the battery and if battery goes on float (with solar) I will charge my 400 AH @ 24v AGM's for back up.

any feed back is apreciated. :confused:

Thanks.

Comments

  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: how much pv to go off grid

    We need to know more about your location. Are you in/near Tuscon, AZ?

    Regards,
    Jim / crewzer
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: how much pv to go off grid

    It does beg the question, (and I'm sure will start an argument) but why, if you have the grid available would you want to leave that great resource behind? Especially since going off grid comes with ongoing maintenance expenses and on average cost about twice as much per KWH as Grid tied PV.

    Tony
  • DapdanDapdan Solar Expert Posts: 313 ✭✭
    Re: how much pv to go off grid

    Hey Homes,

    I am totally off grid. I achieve this with 1560w of pv and consume between 5.5 to 6.5kwh per day. The panels on a great day give me up to 7.5kwh in one day. However my geographic location maybe assisting me since i am in the caribbean at 13N, 59W (Barbados). I have a generator but never use it to top up batteries. When I am low I will simply reduce my usage (like dont watch big screen tv and take the fridge of ice maker). If it gets really bad I would switch the fridge to grid for one day and get the batteries fully charged (I only had to do this once in the pass year when it was overcast for 3 days straight). Hope that helps.

    Cheers....
    Damani
  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: how much pv to go off grid

    My location is Van Alstyne Texas , USA.,

    Tony, the grid is not as great as people thinks, the charges from the cooperative are;

    $18.00 dollars for meter usage per month (use it or not and I can not switch power company to get competitive rates)

    .0225 cts. distribution charge per KW used plus

    .1025 cts. per KW and is variable ( never seen going down) added to all previous charges.

    in few words is $ .18 cts. per KW, if I go grid tied, acording to their 10 pages of rules and requiements, I will have to pay at their discretion for a 2nd. meter which means $18.00 dlls. more for a combined price of meter usage of $36.00, and the catch motivation clause, they will not pay for any excess that I might produce and get charged for whatever KW I use from grid...plus yearly inspections and upgrades to whatever they seem fit.

    this forklift battery I have is about 2 1/2 yrs. old and only paid $300.00 dlls. I expect it to last at least 12 more years if charged properly.

    I'll like to know how much PV watts I need to produce 275 or 320 KW per month.
    my system is 1300 w of PV wired @ 24v., inver/charger 2000w. Samlex S-2024 pure sine, a 1200w MSW 24v. inverter waiting in closet just in case I add more panels for lights or resistive loads, 2 pwm spare controllers plus 3 already installed and the batteries for a combined total of 1930 AH @ 24v. plus a 3500 cont. watts generator.

    so I'M very close to go off grid...most of the money already spent.

    Dapdan, thanks for your reply, I think my wife and I can make it with a system like yours but I have 2 early teen kids at home that will hang around home until they marry:cry:....solar and kids at home do not mix very well :p

    can you guys help with my question, oviously I'm not good at math.

    thanks again.
  • mike95490mike95490 Solar Expert Posts: 8,764 ✭✭✭✭✭
    Re: how much pv to go off grid

    Go to the http://www.pvwatts.org/ website, enter your location, and array info, and it will caculate for you, based on area history, a pretty good guess of what you can expect. If you get a pair of small gensets, to power a backup charger or 2, you would be all set.
    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 ,

  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: how much pv to go off grid

    Mike, small gen set does not has the power to charge a battery bank this big, besides, with the 1300 w of pv I have, I been running lights and tv's and small microwave for 2 weeks of no sun letting the lift battery all the way down to 23v, I really do not want to rely too much on the genny, thats why I asking for some advice.

    Dapdan, do you run your fridge 24hrs. per day every day? is your sys. capable to keep up with your fridge?....I have a fairly new full size kenmore and just run it on sunny days only from 6:30 a.m. to 6:00 p.m. , how do you do it.? i guess the fridge is my greatest hurdle....to keep it running 24/7....., I'm building a batch solar water heater to eliminate the need of running my electric water heater ( now on a timer running only one hour per day every day)

    still, if any body could answer my question, how much pv wats to produce 320 KW per month assuming every day is a shiny day.

    thanks again.:confused:
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: how much pv to go off grid

    Homer,

    I understand your frustration with your utility, and it sounds like it may have some silly/expensive rules that discourage grid tie. My point is that dollar for dollar, grid tie will give you more bang for your buck. Granted you already have batteries/charge controllers/ inverters etc. but in a new installation, the money spent on those items can be put toward more PV. In addition, there are federal and state tax issues that CAN make grid tie cheaper per KWH, as well a possible utility rebates. (I just did a consult for someone and between state, federal, and local tax credits, plus utility credits, the system cost was less than 1/2 net/net, allowing the system to be that much bigger per dollar spent.

    While you are probably never get rid of the $18 per month base charge. On the other hand, the kwh price net/net is indeed going to go up (across the board) but if you are generating ~100% of your power, then it really doesn't matter. Assuming that your utility allows net metering.

    Your battery cost over the life of the battery is likely to be as much as the $18/month.

    Good luck and let us know how it goes,

    Tony

    To answer your question, how big your system needs to be is entirely dependent on how big your loads are. We live just fine on ~300 watts in a very small house with just two of us. Gas cooking, gas hot water heat, and wood space heat.

    PPS Just to be clear, I am not really trying to discourage you from going off grid, but I'm trying to make clear to others who haven't made the investments in batteries etc that you have MAY be better off with straight grid tie.

    T
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: how much pv to go off grid

    So, using the PV Watts program (one of Mike's links), use 1 kW solar panels (minimum program supports), use 0.52 derating, fixed at latitude, for Fort Worth Tx (remember, numbers are based on 20 year average weather--not just sunny weather):
    "Station Identification"
    "City:","Fort_Worth"
    "State:","Texas"
    "Lat (deg N):", 32.83
    "Long (deg W):", 97.05
    "Elev (m): ", 164
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 32.9"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.7 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.32, 66, 6.40
    2, 4.77, 66, 6.40
    3, 5.50, 82, 7.95
    4, 5.98, 85, 8.25
    5, 6.02, 86, 8.34
    6, 6.25, 84, 8.15
    7, 6.39, 87, 8.44
    8, 6.31, 86, 8.34
    9, 5.83, 78, 7.57
    10, 5.56, 80, 7.76
    11, 4.43, 65, 6.30
    12, 4.10, 63, 6.11
    "Year", 5.46, 929, 90.11

    Assuming you want 320 kWhrs minimum per month for 9 months of the year... That would be January/February at 66kWhr per month per 1kW array.

    320 kWhrs per month / 66 kWhrs per month per 1kW of panels = 4.9 kWatts of solar panels

    Your worst month is December at 63 kWhrs per month (not much of a difference):

    320 kWhrs per month / 63 kWhrs per month per 1kW of panels = 5.1 kWatts of solar panels

    Your choice how much power you will want from solar vs genset.

    Obviously, you can play with efficiency numbers (Grid Tied is around 0.77 efficiency):

    0.77 panel+charge controller eff * 0.85 invtr eff * 0.80 batt eff = 0.52

    Also, tracking may be an option too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: how much pv to go off grid

    Bill points out another reason that grid tie gives you more bang for the buck,, system efficiencies that are at least 25% more efficient net/net.

    T
  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: how much pv to go off grid

    Thanks Tony and Bill, we all know that there is not free lunch, while there is net mettering allowed, the cooperative will have the upper hand all the time, just to think that if the price of KW does not go up I have to pay for 320 KW per month a total of $684.00 a year, that is 2 sun 190w panels per yr. so 10 panels will have a ROI in five years or less if prices go up....., I may just go with enough pv's to charge my battery bank to 8% so I can get the 12yrs. left on battery life.

    or perhaps, just enough pv to run my fridge 24/7, it has an energy rating of 4.50 amps @ 115v. 60hz.

    thanks again. ;)
  • DapdanDapdan Solar Expert Posts: 313 ✭✭
    Re: how much pv to go off grid

    Hey homes,

    My Kenmore side-by-side 25cu ft fridge runs 24/7 all year. It is hooked up permanently through a killawatt meter and consumer an average 2.5kwh per day. I should also point out that i have a solar water heater and do not use electricity to heat water (even though there is a heating element in it). My fridge is my biggest consumer and accounts for approximately 40% of my power needs.

    If one were to use my solar harvesting as a real world I would need at least twice my current panel capacity if i were using around 370kwh per month. So go out there and buy 10# 200w panels they are quite cheap now and I dont think the price is going to be at this level for very long and since you are going off grid as opposed to grid tie you would not need Ul certification and that will make the price even lower if you get them from those guys in miami. I think you are in florida as well Homes so you can drive there and pick them up and while you are at it collect 2 for me and mail them to me in Barbados.

    Cheers...
    Damani
  • mike95490mike95490 Solar Expert Posts: 8,764 ✭✭✭✭✭
    Re: how much pv to go off grid
    Mike, small gen set does not has the power to charge a battery bank this big, besides, with the 1300 w of pv I have, I been running lights and tv's and small microwave for 2 weeks of no sun letting the lift battery all the way down to 23v, I really do not want to rely too much on the genny, thats why I asking for some advice.

    2 weeks of no sun is exactly why you need a genset, or you will destroy your 20 year battery in 2 weeks.
    I mentioned 2 small gensets, each powering a charger. If you only need a little charge, alternate gensets on a weekly basis. If you have to do laundry and clean house, fire both gensets up. I'm calling a 2,000w genset, little. Thats more than your 1,300 PV array.
    And you don't want one overloaded genset, that will die when you need it most.
    23V on a 24V battery bank is a pretty drastic discharge.
    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 ,

  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: how much pv to go off grid

    Thanks again guys, adding 2000 w pv is not that bad.

    Dapdan, I live in van Alstyne Tx., for me it will be a long drive to Mimi, it will be just great if we take a family vacation and pick'em up on our way back, the shipping cost will be spend on the motel expenses, a good way to excuse this investmant :D.

    Yes Mike , a 2000 w. genny is small but also gas efficient, B.B. has done the numbers so many times.....8)

    My son and daughter understand the concept., we do the investment and some day they may not have to pay for housing and electric bill. may God bless our kids.

    Thank you guys, Bill, Tony, Dapdan, Mike, Niel....S.G.

    Thanks to the forum. ;)
  • PhotowhitPhotowhit Solar Expert Posts: 5,183 ✭✭✭✭
    Re: how much pv to go off grid

    Something else to consider is that forklift batteries tend to require MORE OFTEN equalizing. something it sounds like isn't happening now. may be time for a serious gen set.

    If it makes you feel any better my Elect Coop charges $25 "line fee" before you buy any electric... I'm off grid but use closer to 40kwh a month. I'll start a thread here soon asking about electric company fees.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: how much pv to go off grid

    40 kwh per month.....I'll never get that close, I think that it will take a lots of conservation from our part to get there, $25.00 for meter charge is high , probably you still have to pay the distribution charge in my case .02 cts. U.S dllrs. per every KWH used..... the power company is hard to beat., ....

    Thanks for your reply.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: how much pv to go off grid

    We are about 18 kwh/month, but use Propane for the fridge, (and it doesn't calculate the power used while the PV is in surplus during the day, so the "real" number is probably closer to 30 kwh/month). In addition all our shop work is done with generator.

    I can't imagine living on much less in any "normal" living arrangement. It would be curios to hear from anyone that lives consistently on under 1kwh/day average.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how much pv to go off grid

    I agree with Tony. Our cabin usage is around 30 kWh/month too. Unfortunately the panels fall short of this, so some improvement is needed.

    That 30 kWh is about 1/20th what the 'on grid' home in the valley uses.
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,186 ✭✭✭✭✭
    Re: how much pv to go off grid
    icarus wrote: »
    We are about 18 kwh/month, but use Propane for the fridge, (and it doesn't calculate the power used while the PV is in surplus during the day, so the "real" number is probably closer to 30 kwh/month).



    Tony


    There is a way to get this data however!

    If you are offgrid logging KWH or AH, the data from the next days reading and you complete the charge cycle is the amount you consumed the previous day including the amount required to replace it. If you complete the charge cycle daily for a month this is your number and it will be fairly close to a system that logs with a shunt if you complete the charge cycle every day.:cool:
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: how much pv to go off grid

    I probably could,,,but I really don't have the motivation.

    T
  • al128al128 Solar Expert Posts: 65 ✭✭✭✭
    Re: how much pv to go off grid
    icarus wrote: »
    We are about 18 kwh/month, but use Propane for the fridge, (and it doesn't calculate the power used while the PV is in surplus during the day, so the "real" number is probably closer to 30 kwh/month). In addition all our shop work is done with generator.

    I can't imagine living on much less in any "normal" living arrangement. It would be curios to hear from anyone that lives consistently on under 1kwh/day average.

    Tony

    Tony, while still not under 1kw per day (we are around 2.2kwh/d) we live a really normal life.

    We are still on grid (i am still trimming fat ;)) ... we are a family of 4 and except for tv (our little doughter pushed it off the rack) we have all the amenendies (?) one might imagine ... we have gas hot water, wood heating, 2 or 3 netbooks, hifi, all cfs and a rather new fridge (0.9kwh/day). We have regular washing machines (clothes), microwave, waffle iron for sandwiches, etc...


    one learning: your first point of attack should be the fridge ... even small improvements go a long way ... like having a 2" styrofoam panel lieing on top of it in the summer (freezer is up on my model) did drive the consumption like 20% down!

    cheers
    al
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: how much pv to go off grid

    Very good to be under 2kw. Like I said, we are ~.6kw on average. Having no TV helps. I also have added insulation to my fridge. Wood heat, demand hot water, etc. No micro or heating stuff like toasters, and our washing machine is a gas powered wringer.

    Tony
Sign In or Register to comment.