obala's solar panel + charge controller questions

hi everyone.
i have five panels in tolal
two are the same 180watts : voc: 30.0v
isc:8.37
vmp:23.7
i would like to wire that together with the other 3 panels :
1) panel from solarex 65watts : voc:21.4
i sc:4.05
vmp:17.1
2)panel 70watts voc:21.5
isc: 4.35
vmp:16.9
3) solar module rsm70 : i think is 75watts 12volts panel
what is the best way possible. and what kind of inverter and regulator should i use . thank you

[Obala, this is your only post--it was not repeated--I moved it to its own thread--so you are fine. - Bill "moderator" B.]

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Mixing Solar Panel size in System
    obala wrote: »
    i have five panels in tolal
    two are the same 180watts : voc: 30.0v
    isc:8.37
    vmp:23.7
    i would like to wire that together with the other 3 panels :
    1) panel from solarex 65watts : voc:21.4
    i sc:4.05
    vmp:17.1
    2)panel 70watts voc:21.5
    isc: 4.35
    vmp:16.9
    3) solar module rsm70 : i think is 75watts 12volts panel
    what is the best way possible. and what kind of inverter and regulator should i use . thank you

    Two options... One with "cheap" PWM controller, and another with "expensive" MPPT controller:

    To use PWM controller: Put all 5 of them in paralllel, get a simple PWM controller, and connect them to a 12 volt battery bank.
    • 4.x amps (#3?) + 4.14 amps (#2) + 3.8 amps (#1) + 2*7.59 amps = 23.32 amps
    So, a 30 Amp PWM controller would work... Your charging energy into the battery bank (on a good sunny day):
    • 23.32 amps * 14.5 volt batt charging = 338 watts maximum
    If you have very hot days, and cool batteries, the Vmp=16.9 volt panels may not provide full current when you try to equalize the battery bank.

    Note: Forget the following--I was thinking of something else when I was typing this out and forgot to erase it before posting.

    A MPPT controller could be setup for a 24 volt battery bank--But the miss-match would be pretty severe and could cause issues when doing Maximum Power Point Tracking.

    Place the two 180 watt panels in series put that in parallel with other 3 panels placed in their own series string:
    • Vmp 180 watt panels = 2x 23.7 volts = 47.4 volts
    • Imp 180 watt panels = 7.59 amps (series connection)
    • Vmp other 3 = ~17 volts + 16.9 + 17.1 volts = 50.9 volts
    • other "3" series current 3.8 amps max
    Maximum average output power from MPPT controller (assume 0.77 derating for "real" power) which would support either a 12 volt or 24 volt battery bank (note: I forgot to multiply by the 0.77 derating factor--the 415 watts is the correct value):
    • 47.4 volts * (7.59 amps + 3.8 amps) * 0.77 = 415 watts
    • 415 watts / 14.5 volts charging = 29 amps into 12 volt bank
    • 415 watts / 29 volts charging = 14 amps into 24 volt bank
    If I did not make any math errors (not a good bet lately; and I understood your specifications correctly)--the MPPT controller will give you almost 50% more charging power to your battery bank and support either a 12 volt or 24 volt battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: obala's solar panel + charge controller questions

    Obala,

    I moved your question to its own thread--easier to keep track of your setup.

    -Bill :D
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: obala's solar panel + charge controller questions

    forgive my ignorance . i might sound funny here . but 338 watts out of 540watts panels . i am loosing lots on first option. i can get that connecting just the 2 big panels 180watts in serie. the second option i am ok with but very concerned with seriouse issue you mentioned with mppt. can you please shed more light. another thing is if take off panel 3 and connect 1 and 2 in parallel and then connect this string in serie with the two 180 panels connected in serie also . this is really challenging .too many questions in my head . thank you kindly for all the help.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: obala's solar panel + charge controller questions

    Obala,

    I am sorry--that paragraph was about something else--and I forgot to delete it (should have been commenting on the PWM controller to 12 volt battery bank miss-match).

    So, If you want a 24 volt bank, either a 24 volt PWM or 12/24 volt MPPT controller would work... To quote the previous post for MPPT 12/24:
    Place the two 180 watt panels in series put that in parallel with other 3 panels placed in their own series string:
    • Vmp 180 watt panels = 2x 23.7 volts = 47.4 volts
    • Imp 180 watt panels = 7.59 amps (series connection)
    • Vmp other 3 = ~17 volts + 16.9 + 17.1 volts = 50.9 volts
    • other "3" series current 3.8 amps max
    Maximum average output power from MPPT controller (assume 0.77 derating for "real" power) which would support either a 12 volt or 24 volt battery bank(note: I forgot to multiply by the 0.77 derating factor--the 415 watts is the correct value--I will fix my previous posts):
    • 47.4 volts * (7.59 amps + 3.8 amps) * 0.77 = 415 watts
    • 415 watts / 14.5 volts charging = 29 amps into 12 volt bank
    • 415 watts / 29 volts charging = 14 amps into 24 volt bank
    And the same setup running a PWM controller into a 24 volt battery bank:
    • (7.59 amps + 3.8 amps) * 29 volts charging = 330 watts
    • 330 watts / 29 volts charging = 11.4 amps into 24 volt bank
    You are in Morocco? I assume that the temperatures are not too extreme for most of the country--but with any controller you need to check the Voc (voltage open circuit cold) and Vmp (voltage maximum power hot) to make sure that the high voltage (very cold solar array can over voltage controller) and low voltage (very hot solar array may not charge battery) do not exceed your working range.

    In your case, your voltages should be fine for most controllers. You have to find what is appropriate for your location (availability and price)... Do yo have any you are looking at?

    One of the controllers (15-30 amps depending on PWM/MPPT) Xantrex, Morningstar, and probably Outback would be fine for your setup. You should have other choices from Europe.

    If you have access to products from the US, our host NAWS has a webstore you can look through.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: obala's solar panel + charge controller questions

    i can.t thank you enough for the valuable informations sir. now that i know what i can get out of my solar panels, i need to know what i can run with it . will i be able to run a small fridge for example . tv . computer and lights . and what size of battery bank i should be looking into . we use 240volts here . i have a power inverter dc to ac 300watts. i was using with panels 1,2,3 in series before i got the 180watts pannels. that should go i think .
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: obala's solar panel + charge controller questions

    Obala,

    From my previous calculations:

    Maximum average output power from MPPT controller (assume 0.77 derating for "real" power) which would support either a 12 volt or 24 volt battery bank (note: I forgot to multiply by the 0.77 derating factor--the 415 watts is the correct value--I will fix my previous posts):
    • 47.4 volts * (7.59 amps + 3.8 amps) * 0.77 = 415 watts
    • 415 watts / 14.5 volts charging = 29 amps into 12 volt bank
    • 415 watts / 29 volts charging = 14 amps into 24 volt bank
    You need to find out your average amount of sun for your location.

    One common term is "hours of sun per day"... The average full noontime sun is around 1,000 Watts per square meter... So, Hours of Full Sun is assuming 1,000 watt/sqmtr... Some approximate numbers:
    • 2 hours of sun in winter/coastal areas
    • 4-5 hours of sun average for regions with decent sun
    • 5-6 hours of sun for average clear summer days
    • 6-7 hours of sun for some desert regions
    From this presentation (solar radiation map in presentation):
    Morocco has an excellent Solar potential :
    4,7 - 5,7 kWh/day (2800 hours/year in the North, more than 3000 hours/year in the South of Morocco).
    So, if you are in the coastal region, more towards 4.7 hours of sun per day and more towards the higher number for central-eastern Morocco.

    Now, note that that is the average over one year... It is very easy to have 2 hours of sun in winter and 5+ hours in summer. Frequently the "cost effective" estimate is to toss out the three months of winter and size the system for the other 9 months of the year.

    For example, using the PV Watts website for the city of Nouasser Morocco, 1kW (1,000 watts) of solar panels (sorry, minimum accepted by website), and 0.52 derating (solar panel, charge controller, battery bank, inverter losses), we get:
    "Station Identification"
    "City:","Casablanca/Nouasser"
    "State:","MAR"
    "Lat (deg N):", 33.37
    "Long (deg W):", 7.58
    "Elev (m): ", 206
    "Weather Data:","IWEC"

    "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:"," 33.4"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","-99.0 dirham/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (dirham)"
    1, 4.24, 62, "N/A"
    2, 4.80, 65, "N/A"
    3, 5.91, 87, "N/A"
    4, 5.50, 79, "N/A"
    5, 5.83, 85, "N/A"
    6, 6.52, 91, "N/A"
    7, 6.67, 96, "N/A"
    8, 6.73, 96, "N/A"
    9, 6.01, 84, "N/A"
    10, 4.95, 72, "N/A"
    11, 4.40, 63, "N/A"
    12, 3.58, 53, "N/A"
    "Year", 5.43, 935, "N/A",
    We get about 63 kWhrs per month of useful 240 VAC per 1,000 watts of solar panels. Your systems rating is approximately:
    • 47.4 volts * (7.59 amps + 3.8 amps) = 540 watts rated
    To work out your system's output for November:
    • 63kWH per 1kW * 1/30 days * 1,000 W/kW = 2,100 Watt*Hours per day per 1kW of panels
    • 2,100 WH per day per 1,000 watts of panel * 540 Watts of panel = 1,134 WH per day
    If you plan on using the system during summer, you can get almost 50% more power...

    But, how much power can you use... What you need to know is how much power your AC appliances consume. Say you have a 13 Watt CFL (compact florescent lamp--"twisty bulb") and a 30 watt laptop.
    • 13 watts + 30 watts = 43 Watt load
    • 1,134 WH per day in November / 43 Watt load = 26 hours of use
    Your 300 watt inverter is too small to power a refrigerator (you probably would need a 1,000-1,500 watt inverter minimum to handle the starting current of the compressor motor in the refrigerator). Also, 1,100 Watt*Hours per day is just about what a small / energy efficient refrigerator uses in 1 day--so with the correct inverter, your system would only be able to power a fridge in the summer months.

    You also have to size the battery for your system... The starting rule of thumb is to plan for 3 days of no-sun and 50% maximum battery discharge...

    Say your average load is 1,100 WH per day and you have a 12 volt 85% efficient inverter:
    • 1,100 WH * 1/12 volt batt * 1/0.85 eff inv * 3 days * 1/0.50 max discharge = 647 Amp*Hour battery bank @ 12 volts
    Notice that the battery bank is fairly large and expensive--if you want a full time off-grid system for power.

    To really know what the power usage of any of your appliances are--you need to measure their usage (labels on appliances are usually very high estimates of power usage). A Kill-a-Watt meter is one very nice way (and reasonably inexpensive) to measure the Watt*Hours per day usage of your devices. Kill-a-Watt meters are now available in 230/240 VAC models now.

    In general, an Off-Grid solar electric system is a fairly expensive way to generate electric power... It is always best to conserve as much power as you can (small, efficient appliances) first.

    I hope this all helps.

    -Bill

    Regarding a refrigerator... Here is an example of how you can really save power by "thinking outside the box"... This project uses about 1/4 the amount of power vs a regular refrigerator.

    Chest freezer as a chest refrigerator

    Saving power is always cheaper vs building a larger solar array + battery bank...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset