Solar Power Information

Important Math:
  • Watts= (Volts * Amps)
  • Amps = (Watts / Volts)
    Parts List:
    Solar Charge controller kit 12vDC, 20A Max/240W@12V - Solar Power Center 12vDC 9A $55
    205@24V 7.71A Solar Panel $543.25 ($2.65/Watt)
    400W Wind Turbine (+$578) ($1.445/Watt)
    TOTAL $598.25 (+$578)
    12V 70A (840W) to 110VAC/60Hz Inverter $1000
    TOTAL $1598.25 (+$578)
    OBPS4-VFX3648Q 14.4kw 110/220vac

    This provides a simple system, that provides 12vDC output of 183 Amps. Adding additional batteries will increase the runtime in direct proportion to what is added. Insure that you do not overload your system.
    Battery DrawOutput WattageMax Runtime
    12V @ 1A12 Watts183 Hours
    12V @ 2A24 Watts91 Hours
    12V @ 4A48 Watts45 Hours
    12V @ 8A96 Watts22 Hours
    12V @ 16A192 Watts11 Hours
    12V @ 32A384 Watts5 Hours
    12V @ 183A2196 Watts1 Hour

    Estimated Loss of 1.25-1.5 will reduce your runtime through normal battery loss, as well as loss from an inverter. This reduces 12V@32A (384W) to 12V@25A (307W) or 12V@21A (252W) when figuring your battery capacity.

    Excerpt from:

    Battery Choices and Loading

    While technically you can use a car battery for these purposes, clearly a deep cycle battery will provide the performance you desire.

    It is important to keep in mind that your battery charge time will be extensive. In the case listed above, of a 75W panel @ 12vDC assuming you only get 50% output from the cells, and you get 8 hours of sunlight a day (accounting for dimmer conditions at night), your estimated charge time is calculated as follows:

    (12v*3amps) / 1.25(loss) = 28Wh => 28Wh*8h = 224Wh/day
    That puts the charge time at aprox 1.2 days (or 10 hours)
    Excerpt from SCC3 information page:

    Number of batteries needed

    If you use the numbers from the sample load numbers link at the end of the page, you turn out needing 6310W peak and a total of 20950Wh/day. This comes out at 51 Amps peak, and a total of 174 Amp Hours in a day at 120 Volts. To handle these peak loads, it is important to use electrical wiring of the correct gauge to carry the current. 51 Amps @ 120 Volts (or 526 Amps@12vDC) is hazardous. One should not forget that batteries have a limited life span. Any system should be designed such that you can easily replace batteries without disrupting much of your load. You may need to diagnose to determine what batteries have lost their ability to retain a charge. These will be the long term operational costs of any system. Electrocution occurs when a small, specific amount of electrical current flows through the heart for 1 to 3 seconds. 0.006-0.2 Amps (that's 6-200mA milliamps) of current flowing through the heart disrupts the normal coordination of heart muscles. These muscles loose their vital rhythm and begin to fibrilate. Death soon follows. To provide an example of how small an amount of current it takes to kill; a 15 Watt night light draws about 125mA.

    That being said, if you're going to draw 526 Amps peak from your 12V batteries to feed your inverter, you will need at least 3 of the 183Amp batteries listed above. If you desired to have a 24 hour reserve of power, consuming 20950Wh, you will need aprox. 10 batteries. To avoid deep discharge, I recommend adding another 25-50%. This will increase your runtime in the most extreme situations. I do understand that this becomes quite expensive as well. 10 batteries @ $359 = $3,590. It may be more cost effective in these cases to consider having a gasoline generator to run things, until you bring enough panels and batteries online.


    You also need to provide some ventilation as the batteries charge (consider a low voltage DC fan that runs off the batteries or charge controller.. this will allow it to run only while you are charging). Some information about your ventilation requirements can be found online.


    If you are not trying to run your whole house, and want to go for a more home-brew system to make your important electronics stay alive, there are smaller inverters avaiable besides the one listed in my parts list above.. Here is a sample list of some that could be used to provide the necessary AC voltage. You can also build your own. If you are attempting to run a TV, Computer or other sensitive device, you should pay close attention to if the inverter outputs Square Wave or Sine wave. Some electronics do not operate well unless they have a true Sine wave.

    External Links:
    Zip Code to Sun Hours/Day - (Very useful to estimate)
    Bob's Solar Project - An excellent case of how to use solar shingles
    Solar System Sizing Calculator (have your bill handy)
    Sample Loads numbers
    Load Worksheet
    True Sine Inverter
    6W 18vDC 12"x18" solar panel
    Reasonably priced solar panels
    sample Multimeter for measuring Amp draw
    Sample 5v voltage regulator circuit, with simple instructions to scale up to 12/24/48 volts

    Sample valuable power data

    © 2004-2008 - Jared Mauch - jared @ this host name - send feedback/comments/corrections to this address