[RE-wrenches] Very small PV systems for surveillance or other "micro" loads

[Exeltech]

+1 on Ray's comment about exact load.
+1 on Ray's recommendation of measuring it yourself.

+2! on Dan's "load creep" comment.

I own a fairly respectable solar trailer, with adequate power and reserves for many needs.  Three years ago, I provided solar power for an "environmental chili cook-off" fund raiser.  Organizers assured me the total load would consist of nine small crock pots for the contestants.  The crock pots were rated 140 to 200 watts each, and I was told they'd need power only for two hours to keep the chili hot for judging, and sales of chili to the public afterwards.  The chili was to be made at home and brought to the event for judging.

I arrived early and set up.  At first, it appeared the organizers were fairly close on what they'd told me.  11 contestants, all with crock pots.  Close enough.  Then some "professionals" showed up.

Bottom line .. 22 contestants (not 9), some with institutional cookers using up to 1800 watts.  Total load: 14,500 watts.  I had 12,200 watts of sine-wave inverter in the trailer, with 24 kW-h of battery reserve.  Peukert was in full effect that day.  Even with a 2,500 watt Honda generator assisting, the batteries were dead just as the judging began.  Fortunately, the chili was still steaming hot for all involved, so the contest wasn't affected .. but it was a painful lesson learned.
Admittedly, I *did* get some very good cups of chili that day .. but the batteries in my trailer paid for it.

Ray's and Dan's comments (below) are absolutely 100% on target.  Don't trust the customer to tell you what power they need.  YOU validate the actual loads .. and hold the customer to it.


Dan

--------------------------------------------
On Tue, 1/21/14, Dan Fink <danbob88 at gmail.com> wrote:
 
Subject: Re: [RE-wrenches] Very small PV systems for surveillance or other "micro" loads
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Date: Tuesday, January 21, 2014, 11:26 AM
 
I also see lots of "load creep" Ray...."oh, forgot to tell you....we need to add some all-night LED area lighting to the system. It won't use much power......"
 
Dan Fink
 
 
On Tue, Jan 21, 2014 at 10:22 AM, Ray Walters <ray at solarray.com> wrote:
 
On these small projects, its very important to nail down the exact load, to keep the pricing sane. I list on the estimate what the system is designed to do; for instance 18 w load 24 hrs/ day.  Then if something goes wrong and they are running more than they should you just gently
point out that that was not what the system was designed to do.
 
I learned a long time ago, that you can't take name plate power draw numbers, or count on the manufacturer to provide those numbers; you've got to confirm it with your own monitoring equipment.
 
R.Ray Walter
CTO, Solarray, Inc
Nabcep Certified PV Installer, 
Licensed Master Electrician
Solar Design Engineer
303 505-8760