The GENTRAN sounds very interesting. The Internet has some for sale,
but so far no detail. Will the 12 circuit panel shed one circuit at
a time? In a nutshell, how does this work?
Thanks,
Drake
At 02:32 AM 11/10/2011, you wrote:
Hi Wrenchies,
Yes and if you use a GENTRAN or equivalent circuit-by-circuit
transfer switch add-on for the output from the offgrid inverter to
your AC panel - then there is no need for a separate dedicated AC
loads panel and rewire like in Larry's original drawing. I've used
this trick for years to avoid a dedicated subpanel for the output of
an off-grid inverter. Combined with the DC transfer switch idea
that high voltage MPPTs enable, (we've been waiting for this) you
have a really simple retrofit for an on-grid system.
And now with Magnum and others offering low-power 120/240 split
phase outputs in one inverter - the grid-tie hybrid retrofit market
is getting more attractive all the time. DC Transfer Switch to MPPT
Charger to 120/240 split phase inverter/battery to GENTRAN
Switch. Getting cheaper all the time.
And hopefully one day not too far off SMA will bring their "Backup
Set S" they show in their European catalog to the States- this is
basically a 2.2 KW version of the Sunny Island - 2 of them would
achieve 120/240 stacked and be a nice cheaper SB enabler as well.
Also your standard 100 AMP 4 pole DPDT transfer switch may not be
rated for 600 VDC explicitly but think of it - the old knife style
units "throw" is like 12" - no way that won't work with 600 VDC.
Hope that helps!,
Jeff
Larry Crutcher, Starlight Solar Power Systems wrote:
Right.... a major rewire and many components...and sacrifices. The
Outback is limited to 30 amps AC and cost much more than you would
need to spend.
With my idea you just add a transfer switch....Done. When the grid
is down, PV feeds HV CC. Then you can use ANY size inverter, with
or without a transfer switch. No rewiring the grid inverter. No 240
volt transformers or dual inverters. No relays, switches or
diversion controllers. Batteries are always properly maintained. No
phantom loads. Very simple.
Thanks for your input. Now if I can just find that darn 600 volt
transfer switch.
Larry Crutcher
Starlight Solar Power Systems
On Nov 9, 2011, at 1:55 PM, Drake wrote:
Any amount of power will AC couple.
If you use an off grid inverter, such as an Outback, to feed the
protected load panel, the inverter should be fed by grid AC power
to supply loads, when the grid is available. Just feed your grid
tie inverter into the protected loads panel. You will need a
relay to shut off power from the grid tie inverter when the
batteries are full. This can be triggered by the fan relay in the Outback.
The on grid inverter will push power into the grid through the
battery inverter's internal transfer switch during normal
operation and AC couple when the power is out. If your grid tie
inverter is 240 volts, you will need to use a transformer or two inverters.
The phantom load of the inverter can be eliminated by using a
transfer switch to send PV power straight to the grid, during
normal grid availability, keeping the inverter turned off. AC
coupling seems much easier than using a charge controller, but
there is no conditioning of the batteries. The charge is just on
and off at the voltage set point. For a back up system, that is
not much of a problem, as the battery inverter can maintain the
batteries when power is available.
At 02:04 PM 11/9/2011, you wrote:
Nice Find, Drake! Thanks.
What is the minimum system for an AC coupled inverter?
Again, the idea is for low cost battery backup of an existing
grid tie. The AC coupled schematics I have looked at require a
major rewire and many components. I would like to hear if someone
has a simple add on solution compared to just switching the array
to the high voltage CC.
Larry Crutcher
Starlight Solar Power Systems
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