Bigger Panels not 12V, why?

Jakachira
Jakachira Solar Expert Posts: 47 ✭✭
I have been looking for 200Watts Solar Panel in South Africa, anything above 120Watts is for 24V system.

Why do bigger panels are for 24V?

Another question is how can one charge two different batteries at the same time with one system of solar panels? i mean if you have two 12V batteries, with diffrent discharge, how can you carge then on one controllerwith them sharing the power?

Last question, what is the standard power consumption of a standard satellite decoder.

Before i go, I want to say something people usually overlook. A TV rated 85Watts power consumption may not always use that power everytime. After all, there are many factors that can lessen that consumption e.g volume, light , tuning etc. Its very normal for a TV like this to consume only 60watts. When doing calculations, people should not try to underestimate their systems. For example, on a 105a/h, i have only 50ah to use, 85Watts is close to 7amps. I cant say i will run my TV for 7hours, this can be well close to 12 hours depending on what volume am I playing and so. So people should not be surprised to see some magic happening after underestimating your system. The same goes for any other gadgets.

Another thing is of 5 hours of sunshine per day. :-) Guys here in South Africa, my 250Watts Panels hits 14.25Amps at 8am, 12.25Amps at 5pm. At peak, it reads 15.5Amps. Thats close to 8hours of 13Amps average. I wonder what happen if my panels are mounted and starts at 6am. The isue of getting half of power of your panels on clear skies is also debatable. My panels channels 15 Amps maximum. I once fully charged my 12V 105Ah battery starting 8am to 12pm. That is 5 hours. Average current was about 14.5 multiply buy 5 thats close to 75amps. Thats about 80% of power of my battery that i had discharged earlier. So if you have 250watts of panels it cant be 125Watts per hour, it cant be 4 hours per day also (well here in SA).

Solar System properly installed performs efficiently that you may not see any losses.

Thanks, guys.

Comments

  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Bigger Panels not 12V, why?

    My guess is that the thin wires internal to the panel prevent high currents. So higher wattage panels tend to be higher voltage too.

    You can use a split charger for 2 different banks, such as: http://www.smartgauge.co.uk/smartbank.html
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Bigger Panels not 12V, why?

    Jakachira,

    The reason (as I see it) is high voltage panels (typically > 100 watts) allows them to reduce the wire diameter and keep costs and assembly issues down...

    Remembering Power=Volts*Amps, a 205 Watt 17.5 volt Vmp panel vs a 43 volt panel (using typical Vmp values):
    • 205 W / 17.5 Volts = 11.7 amps
    • 205 W / 43 Volts = 4.8 amps
    • 4.8 amps / 11.7 amps = 0.4 ratio
    So for the same sized panel with the same wattage output you only need 40% of the copper to carry the same power...

    Also, the large wattage panel market is pretty much dominated by Grid Tied installations which use Vmp-array voltages on the order of 200-600 volts or more... So people are already stacking lots of these panels in series to get the needed operational voltage anyway.

    There are, of course, trade offs. For example, off-grid folks typically need to use the more expensive MPPT type charge controllers to charge their battery banks. But MPPT solar charge controllers do allow the Vmp-array to be as high as 100 VDC or so--Which allows the customer to place the array farther away from the battery shed and/or use less copper in their Array to Solar Charger run.

    Regarding your experience, it sounds like you are tracking the sun during the day with your solar panels?

    For example in Harare ZWE, two different setups... One Fixed array and the other Two Axis Tracking with 1,000 watts of solar panels and 0.52 system derating for off grid power:
    "Station Identification"
    "City:","Harare"
    "State:","ZWE"
    "Lat (deg N):", -17.92
    "Long (deg W):", 31.13
    "Elev (m): ", 1503
    "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:"," 17.9"
    "Array Azimuth:"," 0.0"

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

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (Z$)"
    1, 4.99, 71, "N/A"
    2, 5.12, 67, "N/A"
    3, 5.86, 84, "N/A"
    4, 5.76, 81, "N/A"
    5, 5.68, 84, "N/A"
    6, 5.47, 79, "N/A"
    7, 5.78, 88, "N/A"
    8, 6.07, 91, "N/A"
    9, 6.88, 97, "N/A"
    10, 6.52, 94, "N/A"
    11, 6.01, 84, "N/A"
    12, 4.93, 71, "N/A"
    "Year", 5.76, 991, "N/A",
    "Array Type: 2-Axis Tracking"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (Z$)"
    1, 6.06, 88, "N/A"
    2, 6.06, 80, "N/A"
    3, 7.23, 106, "N/A"
    4, 7.30, 104, "N/A"
    5, 7.28, 109, "N/A"
    6, 7.19, 105, "N/A"
    7, 7.54, 115, "N/A"
    8, 7.45, 112, "N/A"
    9, 8.56, 122, "N/A"
    10, 8.10, 119, "N/A"
    11, 7.65, 109, "N/A"
    12, 5.76, 84, "N/A"
    "Year", 7.19, 1254, "N/A",

    So, just changing to a two axis tracker gets you both more power (25%) and longer time period to charge your battery bank.

    Both advantages that Dave_Sparks sees with trackers for his off-grid customers (in spite of the higher costs of a tracking vs fixed array) in this thread:

    Eletrician Going Off Grid - Sizing / Questions

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Bigger Panels not 12V, why?

    You can also use the SunSaver Duo for two battery banks:

    http://store.solar-electric.com/modubachco25.html

    There are other solar charge controllers that will do multiple banks, though I would go with the name brand myself.

    For charging from mains (non-solar) there are lots of chargers that can do multiple banks (Xantrex and Samlex both make them) as well as splitters like this:

    http://store.solar-electric.com/echo-charger.html
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Bigger Panels not 12V, why?

    If you use PWM controllers with common grounding (most all are negative ground--probably need to confirm with a call to tech support) can share a common large solar array (one large array, 2 or more PWM charge controllers to multiple battery banks).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset