Starter system srtup

Options
Newb
Newb Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
How many batteries can 4- 90w solar pannels maintain? I have up to 10 125ah solar batteries
· Share on Twitter

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Options
    Re: Starter system srtup

    Welcome to the forum.

    The missing part of the equation is the Voltage.

    For example:
    90 Watts * four panels = 360 Watts total. Typical panel + charge controller gives an average efficiency of 77%, or 277 Watts.
    Divide this by the system Voltage (lowest you should let it go) and you get the peak potential charge current.
    With 12 Volts that would be about 23 Amps. This is generally considered to be enough for 230 Amp hours of 12 Volt battery.
    Under some circumstances it could support more, depending on how it is used (no load draw during recharge time would benefit the scenario).

    Then there is the Icarus formula for determining how many AC Watt hours you could expect those panels to supply daily:
    360 Watts * 4 hours of equivalent good sun * 50% over-all system efficiency = 720 Watt hours. (Note that number works well with a 25% depth of discharge on the above battery bank.)

    Basically you've got about the right amount of panels for a couple of golf cart batteries giving 220 Amp hours @ 12 VDC.
    If those 125 Amp hour batteries are 12 Volts, it would work for two of them. Three at the outside (beware of parallel battery connections). Ten of them won't be in it no matter what.

    How we doing so far? :D
    · Share on Twitter
  • Newb
    Newb Registered Users Posts: 6 ✭
    #3
    Options
    Re: Starter system srtup

    It is 12V so you are saying 3batteries max. What size controler can i use with that? I have a 10 amp controler thanks for everything i know about 120 v but this solar power blows my mind
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Options
    Re: Starter system srtup

    Since the peak current will be around 23 Amps, you need to use one controller capable of handling more than that.
    It would also be helpful to know the exact panel specifications (Voc, Vmp, Imp, and Isc). At 90 Watts, they likely have a Vmp around 17.5 and an Imp of about 5 and a bit. This means you could use a PWM charge controller like this: http://www.solar-electric.com/ps-30.html or similar. You would not need one of the more expensive MPPT controllers (unless the Vmp is lower or higher than 17.5 by a significant amount). You would also need to fuse each panel according to their Isc rating to prevent any possible problems from three feeding too much current to one should something go wrong. And then there is the issue of Voltage drop in wiring, most notably from the array to the controller.

    Is this to be a DC only system or are you thinking of running an inverter? The application can make some significant changes in system design.

    It's pretty much the same math as 120 VAC, just some different details. :D
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
    Options
    Re: Starter system srtup

    Nominally, we would recommend a 0.05 to 0.13 rate of charge for a battery bank (i.e., a 100 AH battery bank with 10% rate of charge = 10 amps). So, for your array, the rule of thumb would look like:
    • 4*90 watts * 0.77 panel+charger deratings * 1/0.05 rate of charge * 1/14.5 volts charging = 382 AH @ 12 volts minimum
    • 4*90 watts * 0.77 panel+charger deratings * 1/0.10 rate of charge * 1/14.5 volts charging = 191 AH @ 12 volt nominal
    • 4*90 watts * 0.77 panel+charger deratings * 1/0.13 rate of charge * 1/14.5 volts charging = 147 AH @ 12 volts cost effective maximum

    Note that the above numbers are approximations--If you are withing 10% of them, you are OK...

    If AGM, they will work better than flooded cell down towards 5% rate of charge (although, AGM work fine to 13% or higher rate of charge too).

    If flooded cell, would usually be better towards 10-13% rate of charge.

    If the system will be sitting most of the time, you can get away with 5% rate of charge.

    If the system will be used a lot with a lot of heavy cycling, you should probably be looking at 10%+ rate of charge.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Options
    Re: Starter system srtup

    So with three 125 Amp hour 12 Volt batteries you get 375 Amp hours. Of which 23 Amps is just about 6%.

    But remember that charge rate is net: current in less current out for loads. That's why I prefer the 10% target for most applications.

    At 250 Amp hours (two batteries) & 12 Volts 23 Amps is 9% and should work well for most cases.
    · Share on Twitter
  • Newb
    Newb Registered Users Posts: 6 ✭
    #7
    Options
    Re: Starter system srtup

    I dont know what the voc, imp, or isc are. Im guessing that vmp is volts from the panel i have a couple of invertees i have used in the past campint i was hoping one of them would work i have a 375, 800, and a monster 2000.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Options
    Re: Starter system srtup

    Do you know the brand & model of the panels? The specs are out there on the Internet somewhere! :D

    I'll hazard all of those inverters are of the MSW type. And so we come 'round to where we should have started; what are you trying to run? It makes a difference to lots of things, including battery size and recharging.

    Lots of the common terms/abbreviations we use around here can be found in the Glossary: http://forum.solar-electric.com/showthread.php?6136-Glossary

    Voc is Voltage open circuit, Vmp is Voltage at maximum power, Imp is current at maximum power, Isc is current under short circuit. Usually Vmp * Imp comes pretty close to the Watt rating.
    · Share on Twitter
  • Newb
    Newb Registered Users Posts: 6 ✭
    #9
    Options
    Re: Starter system srtup

    Yes all are msw. I was hoping to run some lights in a garden shed maybe a tv and if i had enough maybe a koi pond pump (under 2.5 amps) on a timer how ever long it will last
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #10
    Options
    Re: Starter system srtup

    Voc (voltage open circuit--i.e., solar panel with no load)
    Vmp (voltage maximum power--solar panel loaded to Pmax=Vmp*Imp)
    Imp (current maximum power--see above)
    Isc (current short circuit--Solar panel output shorted in full noon-time sun)

    Solar panels are not "ideal" batteries in any sense of the word. They are actually current sources (i.e., ~Imp from zero volts to Vmp) where a battery would supply its maximum current into a dead short). Also, Voc floats up and gets higher on very cold sunny days--which can over voltage a charge controller.

    And, 4x90 watt panels (360 watts) is not a lot of power--For a typical North American installation, we assume around 4 hours of sun minimum for ~9 months of the year (less in winter). For an AC solar system, the end to end efficiency is about 52% for a typical system. So:
    • 4*90 watts * 0.52 system eff * 4 hours of sun per day = 748.8 Watt*Hours per day...

    A 2kW inverter running a 1,500 watt electric heater would last about:
    • 748.8 WH * 0.85 inverter eff * 1/1,500 watt heater = 0.42 hours = 25 minutes per day of use

    So--If you need a lot of power but only for 20 minutes a day (well pumping, power tool, etc.), you can possibly use a large 2kW inverter... However, if your loads are normally smaller (radio, a few lights, computer, DSL Modem, etc.)--then it would be better to use a smaller inverter that better matches your loads.

    A large inverter may use 30-60 watts before you add any AC loads to it... 10 hours * 60 watts = 600 WH--Most of your late summer, early spring power production just to turn the inverter on.

    So--What are your loads/needs for solar power? If we start there, then we can guide you towards a system--rather than trying to hit you will a dozen different design guidelines at your first posts (can be frustrating trying to drink from a fire hose).

    -Bill
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Options
    Re: Starter system srtup

    Spend $30 on a Kill-A-Watt meter and measure the actual power consumption of those things you want to run for how long you want to run them. You will be surprised, and probably disappointed. 720 Watt hours isn't that much when you're used to unlimited utility power!
    · Share on Twitter
  • Newb
    Newb Registered Users Posts: 6 ✭
    #12
    Options
    Re: Starter system srtup

    As far as brand and model i attached them to the south facing roof of the shed today and i remember the info on the back i will have to look tomorrow. The small panel i did not install was kyocera all the info was on the back of it. I bought a bunch of solar panels at an auction and thought it would be fun to set up and use.
    · Share on Twitter
  • Newb
    Newb Registered Users Posts: 6 ✭
    #13
    Options
    Re: Starter system srtup

    Will it work to use an amp merer and times it by the volts to get watts
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #14
    Options
    Re: Starter system srtup

    maybe you should tell us what it is you mean by maintain those 10 batteries. i interpret maintaining a battery as a float charge which is usually in the 1%-2% range of the battery capacity, but can be a bit more if desired. to charge a battery we generally recommend between 5% and 13% of the battery capacity. as cariboocoot said the voltage the batteries and pvs are configured for also play a part in determining if it will be suitable so we need details on the battery arrangement and type of battery with the full specs as well as possible series/parallel pv arrangement with the full specs of the pvs given.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #15
    Options
    Re: Starter system srtup

    Some basic tools (links to show basic equipment--pick your own vendors/products for your needs):
    • Kill-a-Watt Meter (or similar): Used to measure voltage/current/watts/VA/PF on 120 VAC 15 amp circuits (Euro version too). Allows you to measure kWH usage of cycling loads over hours/days/months/etc.
    • DC Amp*Hour / Watt Hour Meter: More or less the low voltage DC version of a Kill-a-Watt meter (used by Remote Control folks)
    • DC Current Clamp: Much safer and easier to measure DC current in battery system (typically up too 400 amps or more). This is a good enough/inexpensive DC Current Clamp meter (does AC Current + normal DMM functions too). Very nice if you have parallel battery strings or solar panels--Just clamp on and check current sharing.
    • Hydrometer: Need to measure state of charge of Flooded Cell Batteries. Will not work on AGM/Sealed/GEL type batteries.
    • Battery Monitor (Victron good brand too): Basically a "fuel gauge" for your battery bank. Will estimate the state of charge of your battery bank based on Amp*Hours in and AH out (plus fudge factors). Not perfect, but really nice to help keep track of state of charge--and almost a necessity for AGM/Sealed/GEL batteries. Can help you avoid common mistakes of under charging/over discharging/over charging your battery bank. Not cheap ($175 or so minimum cost), so may not be practical for smaller systems.
    • Whole House Monitors: Basically a large Kill-a-Watt meter for your home. Lots of versions/companies out there. Some just monitor your main power lines. Other have multiple current sensors (main power, A/C system, electric water heater, etc. and can work with Grid Tied power (net metering). One company here.

    The whole Amps*Watts bit does work--but we have to be clear what you are talking about.

    For DC Power systems, generally:
    • Power = Volts * Amps
    • Work = Volts * Amps * Time (Hours in our case)

    Working with battery banks, they tend to be pretty close to 100% efficient with Amps*Hours powering ~ Amp*Hours recharging. So you will see a lot of talk about Battery Systems using Amps and Amp*Hours for measurements. And many times you can use Amp and Amp*Hours when talking about sizing your system--However, we need to know the working voltage to get "real" power/work and such.

    Note that a 12 volt DC system and a 120 volt AC system can use the same amount of power but use different Amps... For example:
    • 12 volts * 10 amps = 120 Watts
    • 120 volts * 1 amps = 120 Watts

    So same amount of power, but 10x different number of amps (10x voltage then 1/10th the amperage). Keeping current "low" by raising battery bank voltage (12 to 24 to 48 VDC) or even higher (some solar arrays + MPPT charge controllers)... And using 120/240 VAC inverter for long distance loads with reasonably small wire gauge.

    Back to Power and 120 VAC power... With alternating current, the sine wave voltage can have a phase offsest wrt the sine wave current... And in many cases with electronics, the AC current wave form is not a sine wave, but instead, is a short/high current pulse--In the end, these wave forms cause wires and transformers to over heat.

    One of the AC Power equations is:
    • Power = Voltage * Current * Power Factor

    Power Factor can vary between 1.0 (perfect, such as a resistance heater, or a PF Corrected power supply) to 0.67 for induction motors (un-modified). Or even down to 0.6 or 0.5 for some (typically inexpensive) CFL and LED lighting.

    So, the power equation (and Watt*Hours) has the "PF" fudge factor.

    And, when designing wiring/inverters/generators, we use VA (Volt*Amps) to let us know how much total current is flowing through the wire (not just the part that is doing "work" as in W*H)--So:
    • VA = Volts * Amps

    Most inverters and smaller genset we talk around here have the same VA = Watts rating... So, for example, a generator rated for 1,600 Watts is really rated to 1,600 VA ... If PF=1.0 then both VA and Watts are the same. If PF=0.5 then Watts is 1/2 the VA for that circuit.

    Anyway--that is the real short and condensed (and somewhat "wrong":roll:) Electricity 101 explanation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Options
    Re: Starter system srtup
    Newb wrote: »
    Will it work to use an amp merer and times it by the volts to get watts

    Not really. You're looking for Watt hours. Since the draw on many devices varies over time you would not get accurate numbers by just measuring the Amps & Volts at any given moment and then multiplying by the hours on. The K-A-W will do the math for you, and more accurately than you can do it yourself. The exception to this is motors or anything else that has a high start-up/in-rush current; that's nearly impossible to measure without a very expensive meter.
    · Share on Twitter

Categories