[RE-wrenches] Mobile Solar power Center

[William Miller]

Peter:

I have built several of these portable display units.  Allow me to free 
associate some issues:

1. Who will deploy unit?  Our trailer has been damaged more than once due 
to improper hitching, towing, backing, and mis-handling.  If you are at 
every event, then no problem, but it ties up your weekends.  If others will 
tow trailer, write up SOPs and get a signature assuming liability.

2. Will the unit be able to solar charge while parked?  We have developed a 
method of folding panels for travel and storage where most of the panels 
are exposed to sunlight and can keep the unit charged.  It was parked in a 
spot for a while with limited sun exposure in the winter and this caused 
problems with self discharge, but we remedied that by revising SOPs.

3. How do you handle loads in excess of capacity?  This applies to loads 
exceeding the inverter capacity and those exceeding storage capacity.

The last time our unit went out (to the Wiener Dog Races) it was parked by 
the promoters in the shade.  It was supposed to power a PA only but the hot 
dog vendor plugged in and depleted the batteries by 11:00AM.  The unit was 
scheduled to power a fundraiser that night, but I was unable to retrieve 
the unit due to it being surrounded by booths until late that 
afternoon.  This lead to frantic grid charging to get batteries recharged 
in time for the evening gig.

Other times, we have powered lights for a street concert.  During the 
summer, twilight comes later and we have adequate battery capacity.  During 
winter months, twilight is earlier and there is not enough battery 
capacity.  The loads are somewhat greater than 20 amps.  We have access to 
one 20 Amp circuit, but when applied to the Outback inverter, the inverter 
transferred loads and we tripped the 20 amp breaker which is behind a 
locked door.  I wish we had used a Xantrex inverter with true generator 
support so the inverter could assist and defray battery loss without 
applying the entire load to the input circuit.  We eventually installed a 
24 volt battery charger that can charge batteries from a current limited AC 
Source and increase battery life with a given load.

4. Stability when parked:  We have had a trailer blow over with panels 
tilted up.  We still need some type of outriggers.

5. Stability when towing:  You need side to side balance and a 60/40 front 
to back weight distribution.  We numbered all components of any appreciable 
mass and then wrote a simple spreadsheet to calculate moment (mass times 
distance from axle, plus in front, minus in back).  We moved batteries 
around until left to right moment difference was near zero and front to 
back moment was near a 60/40 ratio with the hitch positive.  I have a 
friend that supports weight and balance software for the maritime industry 
and he ratified this process.

Good luck,

William Miller

At 08:49 AM 1/19/2009, you wrote:
>We are designing a "Mobile Solar Power Center" to power Eco-Events and the
>like in Southern California. We will have 1,600 Wp of solar panels, 6 kWh of
>24 V AGM battery backup and a 1kW / 120 VAC inverter. I am designing the
>system from scratch, and I wondered if anyone else out there has put
>together a similar system and was inclined to share notes. When I'm finished
>I'd be glad to do the same.
>
>One stumbling block I have right now, is to find a DC rated 70A in-line
>fuse, to put between the battery bank and the input to the inverter. 70A may
>seem an odd value, but it is the best choice for the surge rating of the
>inverter I'll be using (Xantrex Prosine 1000). Does anyone have a source for
>DC-rated in-line fuses?
>
>Thanks in advance, -Peter
>
>Peter T. Parrish, President
>California Solar Engineering, Inc.
>820 Cynthia Ave., Los Angeles, CA 90065
>Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
>CA Lic. 854779, NABCEP Cert. 031806-26
>peter.parrish at calsolareng.com
>
>
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