grid isolation and backup power distribution [RE-wrenches]

[William Miller]

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Davis:

If I understand you correctly, you have a multi-building facility that you 
wish to power with a central battery/inverter system.  The problem is, some 
of the loads in the remote buildings exceed the capability of the inverter 
system.  You are looking for an alternative to running separate feeders to 
each building and segregating loads in those buildings.

One idea is to use the load start capability available with most inverter 
systems.  If the inverter can handle the higher loads for a short period of 
time until a generator can start, the generator will auto-start and the 
loads will see the full through-transfer capabilities of the 
inverters.  (Most inverters can transfer more power than they can create.)

Another idea is to use a wireless or wired control to start a generator 
manually.  The generator feeds the inverter system and transfers 
automatically, again, using the full through-transfer capabilities of the 
inverter system.  This remote can be the Outback Mate, although one is 
still allowed only one Mate (hint, hint to Outback).  This requires users 
to know to activate the remote control before starting the large loads.

Moving up the range of logistic complexity, one can also arrange for a 
remote to start a generator AND transfer the feeds through an outboard 
transfer switch with more ampacity than the inverter can through-transfer.

Lastly, Davis, is it possible that you could pull the existing feeders out 
of existing conduits and pull them back in with additional leads that will 
be fed from the inverter outputs?  This, of course, depends on conduit 
sizing, but it eliminates trenching.

In the final analysis, trenching and conduit can cost less (and be more 
reliable) than fancy transfer and remote control systems.  I'd analyze the 
cost of running the extra feeders and weigh that against more complicated 
solutions.  Emergency call outs are a b***h.

Good luck,


William Miller





At 06:40 PM 10/15/2007, you wrote:

>Wrenches,
>
>I am trying to cook up an idea for back up power distribution for a 
>cluster of buildings that are all fed from the same meter.... One way to 
>go would be to have battery banks and inverters in each building, but this 
>wouldn't work out for space reasons and not all buildings have good PV 
>potential so the idea was to centralize the generation and therefor the 
>battery charging... So I would like to use the existing distribution wires 
>to feed the buildings back up power, using an automatic transfer switch at 
>the service entrance to isolate from the grid and to feed inverter power 
>down to the buildings.. BUT, there are some large loads that would not be 
>practical to backup on battery power... SO the trick is to have some kind 
>of automatic transfer switch that monitors the line in and instead of 
>switching sources, it switches the output over to a critical loads panel 
>and then waits for a manual reset back to the full house load panel once 
>the utility power comes back on... Another trick is to feed the critical 
>loads panel during normal operation in a way that won't backfeed the main 
>panel during critical operation... Does this make any sense?  It seems 
>like it ought to be possible some how instead of laying a second set of 
>wires to all these different buildings when only one set is going be in 
>use at one time anyway... Any ideas would be appreciated... Thanks
>
>--
>Davis Terrell
>Bright Earth Solar
>(802) 492-2273 / brightearthsolar.com


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