Hi Larry;
I'm actually looking at the secondary DC array strategy you mentioned as
well. It's all about those lower charge rates in the absorption and
float stages. The DC array could be sized for a charge rate as low as
C50 and probably have enough current to get the job done.
Meanwhile Enphase is apparently jumping into the battery backup market
as well:
https://enphase.com/en-us/products-and-services/whats-next
Anybody using that equipment or the amazingly promoted Tesla storage?
I'm afraid the energy storage market is filling to the brim with
Vaporware, while us Wrenches keep soldiering on with decade old
methodologies.
I've personally weathered several Tsunamis of BS over the years in the
solar industry, and I think another one may be upon us: might be time to
get to higher ground.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 8/21/2015 7:45 AM, Starlight Solar Power Systems wrote:
Ray,
I’m curious about what you mean by not doing a 3 stage charge. While
PV charging in coupled mode (off grid), the battery will reach your
absorption set point. Is this triggering the GT inverters to shut off
or does the battery inverter absorb timer run at all? I would think
the absorb timer should run until the array current produced is more
than being consumed and then the the GT shuts off.
Just a wild idea here but if you could calculate the AH needed to
reach 100% SoC after the GT inverters shut down, a separate PV array
and charge controller would stay online to finish the charge. No
wasted energy to dump loads and the customer has more usable power
from the system. This may cost more than going to a dump load though.
Larry
On Aug 20, 2015, at 10:56 PM, Ray Walters <[email protected]
<mailto:[email protected]>> wrote:
Hi Folks;
I've done more research on the whole AC coupled issue, and one flaw I
found with both the Sunny Island and the Radian is that they can't
really do a full 3 stage charge for the batteries in off grid mode.
They detect that the batteries are full and disconnect the AC coupled
GT inverters, but this is about as subtle as the very early charge
controllers, and amounts to 1 stage charging. This is fine for
temporary outages, and when the grid comes back, the batteries get a
good 3 stage charge. But these folks are really wanting a design that
could be taken off grid permanently. Also as you my recall, the GT
PV system is Enphase, so we can't use the more sophisticated controls
that SMA offers for the Sunny boys.
I hate to say it, but I might be back to a diversion load with PWM
controller. Not elegant, but we could get 3 stage charging.
Every time I look at AC coupled setups, I just want to start over with
charge controllers.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 8/17/2015 9:39 PM, Mac Lewis wrote:
Hi Ray,
With that size grid-tied system, you would want to use a battery
based inverter(s) near the (6.7/0.8) 8000W range.
The frequency shift of the Sunny Islands will work with kicking out
the enphase inverters but you wouldn't get the same output ramping
that it would offer if it was a Sunny Boy grid-tied inverter. The
Sunny Island can effectively solve your generator backfeeding because
there is a reverse current sensor that will disconnect the AC input
at whatever level you want, 50 mA is default I think. You may need
to give the Sunny Island generator start control for this however.
You can read about it here on page 137.
http://files.sma.de/dl/15216/SI4548-6048-US-BE-en-21W.pdf
You'll need to give the Sunny Island a digital signal that tell it
whether its connected to a generator or a grid as outlined in the
manual.
This is where the Radian is nice because it has two AC Input terminals.
Sounds like an interesting project.
Good Luck.
On Mon, Aug 17, 2015 at 8:36 PM, Jerry Shafer
<[email protected] <mailto:[email protected]>> wrote:
I cant see this working well without some battery based inverter
Jerry
On Aug 17, 2015 10:10 AM, "Ray Walters" <[email protected]
<mailto:[email protected]>> wrote:
HI Esteemed Wrenches:
I am consulting on a system I have never seen, that consists
of a 6.7Kw Enphase roof mounted system, and 2 backup
generators. Each generator has an automatic 200 amp transfer
switch to back up its own 200 amp panel. Both 200 amp panels
are fed by a 400 amp service from the grid.
The Enphase PV backfeeds a subpanel in another building which
then is fed by a 2 pole 60 amp breaker in one of the 200 amp
panels.
Currently they are having issues with the generators kicking
out because of the Enphase inverters. That part I
understand: you can't backfeed a generator, or its voltage
regulation freaks out.
Now we get to the fun part: they want to create a third
critical load subpanel with loads selected from both 200 amp
panels to be powered by batteries and an inverter.
I am considering the Sunny Island since it makes the most
sense with its ability to signal the Enphase inverters to
shut off when the batteries are full. I also see this as a
partial solution to the generator issue, since normally the
Enphase will be connected to the output side of the Sunny
Island. However, when the generator is used to charge, we
will be back to directly coupling the generator output to the
Enphase.
Here are some possible solutions I'm considering:
1) Use a separate charger for the generator so that it will
only feed DC to the batteries, and not be AC coupled.
2) convert the PV back to DC with charge controllers, but
that would involve ditching and adding another conduit run
between buildings.
3) Put the Enphase PV on a relay that would disconnect the
PV when charging with the generator.
4) Something I haven't thought of that one of you clever
folks can suggest......
As always, thanks in advance for all you responses,
--
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760 <tel:303%20505-8760>
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