Off grid Islanding [RE-wrenches]

[Joel Davidson]

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In the 1980s Wm Lamb Company made a direct drive pool filtering system using a DC surface pump, a large open-flow filter about the size of a half 55 gallon drum, 6 each 30-cell Arco Solar modules and an MPPT controller. On sunny to partly sunny days, the system filtered over 20 gallons per minute. I"ll bet Dankoff Solar has something similar.

Pool owners in southern California run their pumps 8 hours/day. Energy conservative people run their pumps 4 hours/day unless their pool gets a lot of use and/or debris from trees, etc. get in the pool.

-----Original Message-----
From: Ray Walters <ray at solarray.com>
Sent: Apr 14, 2005 7:45 PM
To: RE-wrenches at topica.com
Subject: Off grid Islanding [RE-wrenches]

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Hi All;

I've got an interesting addition to a large off grid system I did a few 
years ago. The customer now wants to add a swimming pool complete with 
solar heating. The problem is the existing 4 SW4048s are running close to 
their capacity already, and the existing array location is out of unshaded 
area to add more modules. I had a crazy scheme that between using high 
efficiency pumps, not circulating 24/7 , adding more inverters, and adding 
PV modules near the pool, I could meet this new load. The pool would be 
almost 400 ft from the battery room, so I was exploring the idea of using 
something like the SunnyBoy Island inverters to feed the new PV modules 
power back into the main system. I figure the Sunnyboy wouldn't play well 
with the SWs, but I can power a separate AC load center at the battery side 
with one or 2 sunny boys, and then connect via AC to the pool system and 
additional Sunnyboy(s) there.
I've considered building a separate system, or running higher voltage DC 
for the distance, but since I need to add inverters anyway, I thought this 
might work. Anyone try the Sunnyboy Islanding Inverters? BTW, I want 
to  use the main system, since it is backed up by a 30 kW Kohler on auto 
start.
Another possibility, was running the pool circ pumps array direct with DC 
pumps. Do pools really have to circulate 24/7 or would 8 hours a day be 
adequate? The pool will be in an insulated glass enclosure built into a 
hillside with lots of passive solar gain. Any experience with running pool 
pumping systems, integrated with active solar heating, and all run off grid 
would be greatly appreciated. ( I know this has some environmentally 
dubious aspects, but this stuff keeps me in business to do all the other 
systems that help the planet more) Hey and getting experience with these 
islanding systems will prime me for helping villages out in other countries.

Thanks for your help,

Ray Walters
ray at solarray.com
President, SolarRay, Inc.
NABCEP Certified Solar PV Installer
BS Mechanical Engineering, UT Austin 88
Returned US Peace Corps Volunteer 

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