Grid offseting system for 10-12 homes, Colorado [RE-wrenches]

Kurt Nelson sunwise at cheqnet.net
Thu Mar 18 14:30:32 PST 2004


-----Original Message-----
From: Jeremy Rodriguez [mailto:allsolar at ris.net] 

I am trying to put together a system or systems for 10-12 homes that
would be grid connected and use pv to offset the loads.


Hey Jeremy,

This sounds a little like our solar/utility hybrid systems.  No
interconnection agreement as we don't back-feed the grid, just stage
loads on and off the solar during the day.  A small to moderate sized
battery smoothes things out and allows for some back up of critical
loads.  In the smallest that I have done, 150 watts of PV runs their
chest freezer from a couple hours after sunrise until a little after
dark and then back it up in the event of a power failure.

In another, they run their whole kitchen circuit off of a slightly
larger array during the day and a Link Choice meter and power relay
transfers the circuit back to the utility late in the evening.  Battery
is used very little/shallow so it is still there to back up some loads
if there is a failure of the utility power (including well pump in this
house).  This one actually uses a DR inverter and while I would
recommend Outback to those not on a very tight budget, a pure sine-wave,
utility synchronous inverter is of course not required in this set-up.
I recommend using a primary load(s) that runs during the day, and
perhaps runs more frequently during hot and sunny summer months.  I
would not, for instance, use a lighting circuit as a primary transfer
circuit in such a system as it is backwards from the solar input.

The above mentioned system has five outlets on the wall next to the main
load center in the basement.  One is always solar, one is always
utility, one transfers on and off the solar/utility based on
state-of-charge and backs up to the solar regardless of SOC during an
outage, one transfers on and off but does not back up in a power outage
(dehumidifier plugs in here) and another double outlet is always on the
utility unless there is a power outage.  The hard-wired deep-well pump
is also always on the utility unless there is an outage.  

With a little extra electronics, multiple staging can allow for greater
use of the power produced, and if you use the proper relays and
switching, I don't see where the utility should have any say in such a
system as they are just on the side and never see the sun.

Kurt Nelson
SOLutions

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