Amps = (Watts / Volts)
Parts List:
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 Draw | Output Wattage | Max Runtime |
| 12V @ 1A | 12 Watts | 183 Hours |
| 12V @ 2A | 24 Watts | 91 Hours |
| 12V @ 4A | 48 Watts | 45 Hours |
| 12V @ 8A | 96 Watts | 22 Hours |
| 12V @ 16A | 192 Watts | 11 Hours |
| 12V @ 32A | 384 Watts | 5 Hours |
| 12V @ 183A | 2196 Watts | 1 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: HowStuffWorks.com:
A car's battery has a reserve capacity rating. A typical rating is
80 minutes, which means the battery can supply 25 amps at 12 volts
for 80 minutes. If you consume 120 watts continuously, that means
that you are draining about 10 amps from your car's battery
continuously. A typical car battery can supply power at that level
for perhaps three hours. A deep-cycle battery can supply power at
that level for six or eight hours. Then you will need to recharge
the battery (which takes awhile). However, if you are running two
compact fluorescent bulbs at 15 watts each, total consumption is
only 30 watts, or 2.5 amps at 12 volts. A car battery can supply
power for about 12 hours at that level. A deep-cycle battery can
supply power for a day or two at that level.
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:
It is advisable to match the solar panel's maximum current to the battery's
amp-hour rating (C), a typical battery charging current is C/20, so a 100
amp hour battery should have a solar panel rating of around 5 amps. Consult
the battery manufacturer's data sheets for the best rating.
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.
Ventilation
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.
Inverters
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