24 volt solar wire diagram

BalzackgooBalzackgoo Posts: 7Registered Users
Here is a basic drawing of a small PV system for emergency backup power. I wanted the system to be 24 volts and will possibly expand its capacity over the next few years. Can somebody please take a look at the wiring diagram and see if there's something I've gotten wrong, forgotten or missed. Any input would greatly be appreciated.

Attachment not found.

Comments

  • offgrid meoffgrid me Posts: 119Solar Expert
    Re: 24 volt solar wire diagram

    Two things come to mind. You would want circuit breakers on the feeds from the batteries to the charge controller and the inverter. I do not see any kind of grounding shown.
    Ned
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: 24 volt solar wire diagram

    Welcome to the forum.

    Okay, you don't actually need a fuse on the panels. You should have one on the charge controller output and especially on the inverter.

    Next, a 100 Watt panel isn't going to put out 10 Amps. More like 5. In series this will still be 5, but at 24 Volts instead of 12. This is important because that 5 Amps is not going to do much for charging 212 Amp hours of 24 Volt battery. It will be a peak charge rate below the 5% minimum. It will be about 2%, which is only enough to maintain the batteries.
  • BalzackgooBalzackgoo Posts: 7Registered Users
    Re: 24 volt solar wire diagram
    offgrid me wrote: »
    Two things come to mind. You would want circuit breakers on the feeds from the batteries to the charge controller and the inverter. I do not see any kind of grounding shown.
    Ned

    Ok, will add some fuses to the leads for the Charge Controller and the Inverter. The Solar Array is grounded and the inverter is grounded as well, although the diagram doesn't show this.

    a 100 Watt panel isn't going to put out 10 Amps. More like 5. In series this will still be 5, but at 24 Volts instead of 12. This is important because that 5 Amps is not going to do much for charging 212 Amp hours of 24 Volt battery. It will be a peak charge rate below the 5% minimum. It will be about 2%, which is only enough to maintain the batteries.

    I do realize that that the panel isn't going to put out 10 amps, but they are rated as "max" 10 amp panels, so on paper the circuit had to handle 10 amps. I do understand what you are saying that the 2- 100W panels are not going to be enough to charge 212AH 24v battery bank, what I need to understand is how to the determine peak charge rate you're referring to.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: 24 volt solar wire diagram

    The current from the panels will be the Imp: Amps at maximum power. This is the most they can put out to a circuit. The rate is expressing that current as a percentage of the battery bank capacity:

    Imp * 100 / Amp hours = peak charge rate percent.

    So 5 Imp * 100 / 212 Amp hours = 2.3%

    Most battery manufacturers recommend a minimum 5% rate, and that is exclusive of any loads.
  • BalzackgooBalzackgoo Posts: 7Registered Users
    Re: 24 volt solar wire diagram

    Excellent, thank you very much for the input. I'll put that info to good use and revamp my idea.
  • BalzackgooBalzackgoo Posts: 7Registered Users
    Re: 24 volt solar wire diagram

    Attachment not found.

    Ok, I revamped the idea to a 12V system and decreased the number of batteries while keeping the capacity at 212AH. The DC circuit breaker is basically a circuit disconnect, it's rated at 10amp, but trips at 13amps. The panels are rated at a max output of 6.2 amps (so the circuit breaker should be alright). I also added the grounding for the panels and inverter and the fuses for the the charge controller and inverter. The fuse sizes i chose should be able to handle everything at peak and still have overload protection. Any input is welcome again. According to my calculations, at 10amp (2 - 5amp panels in parallel), the peak charge rate is slightly less than 5% (4.7%), not ideal,but i do plan to expand in the near future.
  • BB.BB. Posts: 24,528Super Moderators admin
    Re: 24 volt solar wire diagram

    Why a 2.5kW inverter?

    A nominal 200 watt solar array will supply a typical 9 month minimum energy of:
    • 200 watts * 0.52 system efficiency * 4 hours minimum sun per day = 416 Watt*Hours per day

    A 2.5 kW inverter may draw 10-20 watts just turned on... Running the inverter 24 hours per day:
    • 24 hours * 20 watts = 480 Watt*Hours per day

    So--Just running the inverter 24x7 can use use most of the power your solar array generated in a typical spring/fall day.

    The only way I see running a large inverter like this on a small system/battery bank is if you 1) manually or automatically control the DC power to the inverter, 2) have a load that has high starting surge and/or high power required for short periods of time--such as water pumping, and 3) you use AGM batteries that can supply high surge currents and are more efficient/lower self discharge than flooded cell batteries.

    We have two ways we can proceed here--First would be to backup and define your loads, then design a system to run them. Or second, we can just run the numbers (like above) on what the system would be capable of supporting.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: 24 volt solar wire diagram

    The size of the inverter depends on what you want to run. It is doubtful that you'll need 2.5 kW output (greater than one standard outlet which is 15 Amps @ 120 Volts = 1800 Watts) and as Bill said the bigger the inverter the greater its self-consumption. So check the numbers on that for any inverter you look at, as it has to be included in the over-all load.

    212 Amps hours @ 12 Volts gives you about 1 kW hour of power to work with at 50% depth of discharge.
    200 Watts of panels will 'harvest' about half that on a good 5 hour day.

    I don't know where you're getting 100 Watt panels from (hopefully not homemade), but most of the 12 Volt panels available these days are around 140 Watts and that extra 80 Watts would be welcome.

    Further, using two 12 Volt batteries in parallel will not work as well as two 6 Volt batteries in series due to the possibility of current sharing differences. A couple of golf cart batteries may cost less too, and give you about 220 Amp hours @ 12 Volts.
  • BalzackgooBalzackgoo Posts: 7Registered Users
    Re: 24 volt solar wire diagram

    Ok folks, I appreciate all this input. I'll have to look into 6V golf cart batteries. Basically this system is designed for use when the grid fails. The solar panels charge the battery bank till full and maintain a float charge.

    When the time comes and power is needed, I will use this to run appliances like the freezer (around 700-900W) and an additional 500W or so to run fish tank heaters and pumps. I only will be using the power in 1-2 hours bursts, just to maintain. I went with the 2500W inverter because I do want to eventually expand the panels and batteries to be able to power stuff for longer.

    The 100W panels are from grape solar http://www.grapesolar.com/index.php/products/modulesandkits/gs-s-100-ts/
  • BB.BB. Posts: 24,528Super Moderators admin
    Re: 24 volt solar wire diagram

    It is really difficult to "grow" an off grid solar system over time... The differences in equipment, batteries, inverters, battery voltage, etc. is usually too large if you want to grow a system by more than ~2x without major changes.

    I would suggest you start with a Kill-a-Watt type power meter and measure your AC loads... Your system, as designed, will supply 1/10th to 1/20th the power used by the typical north American home... Not really enough to even be helpful running even a single refrigerator.

    For a "small" system, you are looking at something that can supply 1-3.3 kWH (1,000 to 3,300 Watt*Hours) per day to run a very minimal/energy efficient home on off grid solar power.

    If you are looking at short term outages--If you can justify a small genset (Honda eu2000i, Yamaha 2xxx inverter/generator family) and 10-20 gallons of fuel (syphon car tank, etc.0--A genset is typically a better solution. You could still use a small off grid/solar + battery system for lights/radio/etc. at night and avoid the generator noise/fumes during the quiet time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BalzackgooBalzackgoo Posts: 7Registered Users
    Re: 24 volt solar wire diagram

    Ok, so the 12V system in the diagram would best be used to power minimal stuff (lights and radios) and at most can power a 250 watt inverter for approx. 2 hours a day (give or take), correct?

    Also, What sort of array/battery system would be the best to plan for if I was going to build a system that would allow for it to be expanded in the future?
  • BB.BB. Posts: 24,528Super Moderators admin
    Re: 24 volt solar wire diagram

    It really depend on what makes sense to you (bang for the buck, what sort of outages are you planning for).

    When we start with loads--We don't even look at hardware/batteries/etc... We look at your needs.

    For short term outages (1 day to 2 weeks)--Solar Power is difficult to justify from a dollar and cents point of view. For security of your home and family--It can make sense, but you have to be very sure what your minimum needs are that you wish to support.

    Say you can run a genset for 1 week to power a fridge + freezer. The fresh food will be gone in a week--And you will have to decide how much you wish to pay to support a freezer after that... For somebody living off the land (hunting), running a fridge for 3 months may make lots of sense.

    For a city dweller (like myself), the lack of water (no well) and sanitary sewer (no city power/pumping) may force me out of the home before a couple of weeks.

    For me--I sort of look it as camping--Just enough lights, some way to get clean water (filter, chemical, boiling) and cooking/rehydrating dried/canned foods, etc. I don't need much electricity for that.

    If you only want enough power for LED lights, small tv, computer, etc... 1 kWH per day may be enough on a 300 Watt TSW inverter.

    If you want to run a fridge+above+well pump+washing machine -- Probably closer to 3.3 kWH per day on a ~1,500 Watt TSW (recommended) inverter.

    The system you started with is closer to 0.5 kWH per day--So 2-6x larger (and more costly).

    Also--Do you want it to be "portable" or permanently attached? Size of solar panels can be an issue (140 Watt panels are easier to move around vs 250 Watt panels--But 250 Watt panels are much less expensive). Something like $2 per Watt for smaller panels and $1.20 per Watt for larger panels (of course, the price of panels is highly variable--So you may do better or worse--Need to look at price delivered to your door step including shipping+insurance+taxes etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BalzackgooBalzackgoo Posts: 7Registered Users
    Re: 24 volt solar wire diagram

    Thanks for all the input, you have certainly given me a lot to think about. I'll have to do some deep thinking on what it is i'll need. Thanks for the time and input.
Sign In or Register to comment.