Date:         Thu, 28 Sep 1995 11:27:48 -0500 (CDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         dakhlia@wuecona.wustl.edu (Sami Dakhlia)
Subject:      how to plan solar

Source: Solar Electric, Inc, San Diego.

SOLAR ELECTRIC (PHOTOVOLTAIC) MODULES convert sunlight directly to D.C.
electricity without moving parts, pollution, noise, maintenance or wearing
out. They are connected to the CHARGE CONTROLLER which regulates battery
charging to prevent overcharge as well as stopping back-flow from the
battery to the panels at night. The charge controller is connected to the
DEEP CYCLE BATTERIES which accumulate the power as it is produced to make
it available to you 24 hours a day.

Ideally your battery bank should be sized for five days of storage. For
example, if you use 10 Amps of current for five hours each day (10A x
5hours = 50Ah) times 5 days (50Ah x 5 days = 250Ah) you need 250 Amp hours
of capacity. 

Carrying our example farther, if you were using 50Ah per day you will need
this number to figure panel size as well. Take your total daily power
requirement in Amp hours (50) and divide by your average hours of full sun
daily. (5 hours here in San Diego, call for help on this one, we have
averages for most areas on file)(50/5=10) Take this number and divide by
the amperage of your solar array. For our example we will use a Quadlam
rated at 5.1 Amps. So ten divided by 5.1 is 1.96 = 2 panels. 

All this leaves to figure is the charge controller which is sized by the
total amperage output of your solar array. In our example we would need a
controller that can handle at least 10 Amps.

If we would like to run household appliances on our solar system we will
need to have an INVERTER to change the 12 volts D.C. to 120 volts A.C.
Again, we will size the inverter to handle the maximum wattage that we
will be using at any one time. For example, a microwave oven that draws
1,000 watts is running while we watch a 70 watt TV in a room illuminated
by 2 27 watt compact fluorescent lamps (total 1,124 watts). This could be
handled by a Powerstar UPG 1300 (1,300 watts continuous) or a Statpower
1500 (1,500 watts continuous). Or if we only have the TV and the lights
(124 watts) the Powerstar POW 200 (140 watts continuous) or the AC Genius
ACG 200 (200 watts continuous) will do.

[Comments: 

1. when mounted on your van's roof top, the panels will be horizontal and
not oriented towards the sun in the most efficient way. That cuts down on
your average full daily sun figure. 

2. the deep-cycle battery in your bus/vanagon will also be charged by the
alternator when you're driving and you can also supplement the charge with
shore power when camping at a site w/ electr. hookups. 

3. the ratings for the Quadlam are conservative. The 15 Amp breaker switch
popped open twice last week, here in Missouri. Note that David Schwarze
rewired my array to produce more Amps and less tension. (thanks, David)

4. Expect to spend money. I paid $340 for the Quadlam (4ft. by 4 ft.). $80
for a deep-cycle battery. $80 for the inverter. Add another $50-$100 for
various supplies (wire, circuit breakers, solder iron, connectors, bolts,
nuts and washers, drill bits, and countless trips to the hardware store.)
Do not value time, but value the "cool" factor.

Sami -- end comment]

-- 
Sami ('75 Westf.)
dakhlia@wuecona.wustl.edu
http://wuecon.wustl.edu/~samid/