[RE-wrenches] High Voltage MPPT units; Adding battery backup

[Darryl Thayer]

We are getting a little wild here, but take the 600 volt line and run one leg at least through the high voltage relay (tyco kilivolt EV2000 series), then use a 3 pole 240 V transfer switch, using one pole to control the series current through the relay coil.  When the 240 volt switch is opened the relay breaks the circuit, and the transfer switch finishes opening without current.  The 240 volt switch is safe with no load just like a do not open under load other devices we use.  
Darryl


________________________________
From: Jeff Clearwater <jeffc at villagepower.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Thursday, November 10, 2011 1:32 AM
Subject: Re: [RE-wrenches] High Voltage MPPT units; Adding battery  backup


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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