I'm thinking about Solar but not sure

magesa
magesa Registered Users Posts: 6
Hello,

I'm a missionary living about 100 miles south of the equator live in an area where we have 330 days of sun a year and there is not enough power for the country so we often have load shedding and no power for 10 to 12 hours a day. When that happens we use a Victron Energy Phoenix 12v-500w inverter that is connected to 2-100 amp hour batteries. This is enough to run lights, fans and the fridge for a little while. When the mains comes back we charge the batteries with a VE Centaur 30 amp charger.

I wonder how it would work if I added some solar panels. Do I just have to buy some panels and a charge controller that I connect to my batteries? Will the batteries recharge as I use them?

I have some more questions too but I will wait.

Thanks,

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,398 admin
    Re: I'm thinking about Solar but not sure

    Off-Grid (battery+inverter based) Solar Power is not very competitive when compared with grid power (at least in countries with good infrastructure).

    Even in the US with relatively low hardware costs--It is not unusual for Off-Grid solar power to cost $1.00 to $2.00+ per kWHour... In the US, when you take into account the cost of an inverter and battery bank (with limited life)--A back of the envelope calculation shows around $0.45 per kWH just for hardware+battery costs.

    It is not hard to make an estimate of how much it would cost you (in $/kWH) for solar power vs your national grid. For a first approximation (no Present Value / Future Worth calculations):
    • (total capital costs + fuel + replacement battery/parts) / (kWH per year production * expected years of life).
    What you have right now with a charger+batteries+inverter is just a larger/home made UPS (Uninterruptable Power Supply).

    If you have emergency power needs (for example a huricane knocks out power for 4 weeks)--Solar Power may be well worth the additional costs for energy security.

    If your power is just out randomly 12 hours per day--then your current topology is probably the most cost effective solution.

    Also--This all depends on how much power you use in a day/month... If you power needs are small (conservation)--Laptop + a couple small florescent lamps--Adding solar is not going to be that much of an added expense.

    However, if you are looking for a fair amount of power to supply fridge/freezer/emergency power/hospital/etc.--Solar can be well out of most folks budget.

    Basically, a good aim point is a system that supplies less than 3.3 kWHr per day (100 kWH per month). That could be done with 1,500 watts of solar panels and 550 to 1,750 AH of 12 volt batteries (1-3 days of "no sun" power storage) (at least during sunny weather)...

    How much would that cost you to bring in-country?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • magesa
    magesa Registered Users Posts: 6
    Re: I'm thinking about Solar but not sure

    Bill,

    Thanks for the very detailed answer. I am not sure yet if I want to go completely off grid. I am going to make a simple solar water heater soon.

    Our power company announced 18% rate increases starting in January so that is another incentive to abandon them.

    Right now I am just wondering if adding some solar panels will increase the life of my 2 batteries. The won't last all day if I am running fans and maybe my fridge at home. If I had some solar panels or some Uni-solar laminate panels would they charge my batteries as I use them?

    If so how many panels and what kind of charge controller would I need.

    thanks,
    Mzungu Magesa.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: I'm thinking about Solar but not sure

    you would need quite a bit to abandon your power company. i would try to concentrate on the supplementation of your power for brown outs and outages. a 30a charger can deliver a great amount of power to your batteries. 30a x 12v = 360w and do this for say 10hrs a day and you have 3.6kwh. with a 500w inverter this will last about 7hrs, but that's only if that 3.6kwh is available in the batteries. 100ah is typical for a battery and i'll use that as an example. if you have 2 of them this is 200ah x 12v for 2.4kwh. btw, it would be the same if those are 200ah 6v batteries times 2. you are short already, but it gets worse. of that power you don't want to use more than half of it to help preserve battery life and you're now down to 1.2kwh usable. you need at least 3 times the batteries to properly store and supply that 3.6kwh that your charger delivered to the batteries in 10hrs. if you can go 14hrs or 16hrs or whatever hours more than 10hrs then you'd need to properly store it in order to be able to use it all.

    at this point it may be good to plan for a bit of solar down the road, but for now work out your current needs by backing up your power into batteries and know your loads for if they are large then it gets more difficult and expensive to do.

    interesting as am i to understand your 500w inverter will run your frig and a fan?
  • magesa
    magesa Registered Users Posts: 6
    Re: I'm thinking about Solar but not sure

    Yes the 500w inverter will run my fridge, lights and fans even sometimes I even run my big freezer at the same time. usually I alternate the fridge and freezer.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: I'm thinking about Solar but not sure

    can you elaborate on them a bit for that is very unusual to be able to do that for that many items and only on 500w.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,398 admin
    Re: I'm thinking about Solar but not sure

    Magesa,

    Usually, our recommendations are 1) conservation, 2) understand your loads, 3) do some paper designs and understand costs, 4) then start buying components.

    In general with solar, it is almost always cheaper (and better) to conserve power than to try and generate it...

    But yes--you can attach solar panels with a charge controller to your existing battery bank and extend its run time (at least during daylight hours).

    Take a look at this thread--The system is larger than the one you are planning--but we had a lot of discussions about many of the same issues (Koj is from Ghana).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: I'm thinking about Solar but not sure

    at this point he would only offset any loads that may be on during the sunny daylight hours with whatever he gets in pv current, but my point is he still can only hold what he holds in his batteries and that may not suffice for heavy night time loads without utility power. another charger can just as easily add to the current to the batteries and would be cheaper to do than pv while the grid is intact. when it's out now that's another story and the op will have to evaluate much of this as it pertains to his needs and not just wants.
    if you are running your batteries down past 50% often this will kill them and lessen their capacity somewhat. evaluate what you may need to power in watthours for the number of hours you'd expect to need in an outage. also tell us the voltage and ah capacity of your batteries while you figure out your power needs in an outage.
  • magesa
    magesa Registered Users Posts: 6
    Re: I'm thinking about Solar but not sure

    So my inverter can surge to 1350w, have 650w short term and continuous power of 500w. So it starts up the fridge and it will run for a few hours if I let it. Also all my light bulbs are compact fluorescent, low wattage bulbs.

    I have 2 12volt 100 ah batteries. But lately they aren't lasting too long. I often do run them till they die because I want to run things in my house.

    I know I am probably not planning this out as well as I can but our grid goes off about 3 out of every 4 days and it is getting to me.

    Maybe I should just buy 4 new batteries rather than trying to use solar but with all this hot African sun I thought maybe I could utilize it.
  • magesa
    magesa Registered Users Posts: 6
    Re: I'm thinking about Solar but not sure

    I should add that our fridge is not like a big American one. It is pretty small but not dorm room small

    Also my inverter shuts off if the batteries reach 9.6v. So I don't know if I am wearing out my batteries by doing this
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: I'm thinking about Solar but not sure

    At this rate, your batteries are not going to survive very long. Battery life span is very directly related to the number of cycles and the depth of those cycles.

    http://www.batteryfaq.org/

    http://www.batteryfaq.org/

    The bottom line is that if you are routinely drawing your batteries down more than ~20-30% you will very much shorten their life. As has been mentioned before, define the loads, and then work backwards. I agree that if you have grid power available for part(s) of the day, you will most probably be better off (financially) using the grid to power your big loads while there is grid power available, including charging the batteries, and then use the batteries for loads at times without grid power.

    The size of your battery bank should be sized according to the average draw loads, and your charging capacity should mirror that draw. For example if you draw your batteries 20 amp/hours/day, you might look to have a battery bank of 100-200 ah capacity. In that case then you should look to have a charge capacity of 5-13amps, making sure that the batteries can come to full charge every day, or certainly every couple or three days. Until you can accurately define your daily loads, then designing a battery/charging/Pv system is impossible.

    Good luck, and keep in touch,

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,398 admin
    Re: I'm thinking about Solar but not sure

    Say you run ~120 watts average load (fridge) and 50 watts for lighting/small radio/etc. for 8 hours at a time. Assume 12 volt battery bank and 50% maximum discharge (for longer battery life).
    • (120+50)watts * 8 hours * 1/0.85 inverter eff * 1/12 volts * 1/0.50 max discharge = 267 Amp*Hours @ 12 volt bank
    That will run the given loads ~8 hours with a 50% maximum battery discharge... If these are deep cycle batteries, they should last ~500-1,000 discharge/charge cycles.

    You could justify upwards of a 3x larger battery bank (longer life, longer battery backup time, more costs).

    Your "ideal" rate of charge would run between 5-13% of battery AH capacity:
    • 267 AH * 5% = 13 Amp minimum rate of charge
    • 267 AH * 13% = 35 Amp maximum rate of charge
    I would recommend not going below 13 amp rate of charge--but you could use a 40+ amp charger without problem (numbers are approximate--showing exact results so you can reproduce my math--errors and all:roll:).

    With a 5% rate of charge, it will take ~10-14 hours to recharge the batteries. With a 13% rate of charge, it will take ~4-8 hours to recharge the batteries.

    If you use a larger battery bank, you need a larger battery charger. If you charge with a genset and/or solar panels, you also need to support the charging current with larger charging devices (there are added costs with larger battery banks).

    And, yes, with this setup, you can add add much solar panels as you wish--recommended maximum is again 13% rate of charge (roughly the cost effective limit):
    • 267 AH * 14.5 volts batt charge * 1/0.77 system derating * 0.13 max charge rate = 654 watts max panels recommended
    You can adjust the maximum solar array size from small to maximum--Probably a minimum worth panel size while would be around 10% of the maximum recommended (~65 watt panel). Any smaller, and you will really not even notice its output.

    For a 0 to 200 watt solar array, probably a PWM controller (less costly) would be fine. For 200-400 watts either PWM or MPPT type charge controller. For over 400 watts, a MPPT (2-5x the price of PWM) would be very nice.

    Other issues--how far from the solar panels to the battery bank--Long wire runs need to be taken into account when doing the design.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: I'm thinking about Solar but not sure

    What is your power grid there - 120V or 250V 50 or 60 Hz ??
    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 ,

  • magesa
    magesa Registered Users Posts: 6
    Re: I'm thinking about Solar but not sure

    today it is off from 8 am til 4pm again and it is a bright sunny day.

    when it is on it is 220v 50 hz.

    You guys sure know your stuff.

    I think I will just make a solar water heater out of some black pipe and not deal with solar power.