The downside of the SMA SPS is there is very little headroom to surge
and start a well pump or a fire pump. There is also the major problem of
sundown.
Dave Angelini Offgrid Solar
"we go where powerlines
don't"
http://members.sti.net/offgridsolar/ [1]
e-mail offgridso...@sti.net
[2]
text 209 813 0060
On Fri, 20 Sep 2019 11:07:12 -0400, Dave Tedeyan
wrote: Hi Mike, For rapid shutdown, we are on NEC2014 in NY. So module
level is not necessary. And the SPS is a huge reason for the SB inverters
on this one. And in this case, it is almost exactly what the homeowner is
looking for. But with the two inverters, can those SPS be wired into a
panel rather than just into an outlet? So far, this customers house has not
even been built yet. The barn is up, which is where the solar is going. So
I am not 100% sure about loads, but there will likely be heat pumps. So
if the SPS's can put power the same panel, then that might be just what I
am looking for in this particular case. Although I am still curious if
others have retrofitted other systems with something like I was initially
talking about for an inverter that does not have a SPS. I think that at
least in this market a low end 3rd party solution could gain a lot of
traction.
DAVE TEDEYAN, PE Senior Engineer | Taitem
Engineering, PC 110 South Albany Street | Ithaca, NY 14850 o. 607.277.1118
x121 f. 607.277.2119 www.taitem.com [3] Solar * Sustainability * Energy *
Design B-Corporation Best for the World 2018 Honoree
On Fri, Sep 20,
2019 at 10:58 AM Harry Mahon wrote:
Dave - how is Rapid Shutdown
being complied with? And what load requires 240V - or is that needed to
"fool" the PV inverters?
With two SB-40s, you have the ability to wire
for the homeowner two Secure Power Supply circuits - and get up to 2000W
(at 120VAC) from each when sun is up and grid is down, no batteries or
extra inverter needed.
This is exactly the "simple industry solution"
you mention, and it has been available in US from Sunny Boys only since
2013.
Best regards -
Mike
SMA America
Michael Mahon
Technical
Trainer, Solar Academy
6020 West Oaks Boulevard, Suite 300
Rocklin, CA
95765
U.S.A.
Mobile: +1 916 918 9412
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FROM: RE-wrenches ON BEHALF OF Dave
Tedeyan
SENT: Friday, September 20, 2019 7:41 AM
TO: RE-wrenches
SUBJECT: [RE-wrenches] Running a grid tied system when the grid is down
Hi all,
I get asked this question frequently, as I am sure many
others do, and of course the first answer is "it cannot be done". But can
it? I have a customer who is very keen on trying to make this happen. After
a few lengthy conversations, he still wants to try it, even after
understanding the limitations (i.e. a cloud passes by and now you cannot
power loads...)
I have some thoughts on how to make this work, and
thought I would post it here to get others comments who I am sure have more
experience in something like this than I do.
-PV system would have to
be backfed, so that they can turn off the main breaker to disconnect from
the utility entirely (and then have to look at the neighbors, or guess when
the grid comes back)
-Have a fairly small 12V off grid inverter/charger
than can be powered by a single 12v battery. This inverter would have to be
manually turned off until after the grid is down and the main breaker is
disconnected.
-Would also need an auto transformer to bump up the
voltage to 240V. Something like the Outback PSX240.
-Once the main
breaker is off and the off grid inverter is on, would it be able to wake up
the grid tied inverters? On this project, there are two SMA SB-40
inverters.
-There would need to be some kind of dump/diversion load to
deal with excess power coming from the GT inverters. I have not used these
in the past, but are the controllers smart enough to just deal with any
excess power in the system?
-Have a trickle charger on the battery to
keep it topped off most of the time.
-Another thought would be to DC
couple. This would involve having a DC switch in one of the strings going
to the GT inverter, such that when the house is islanded from the grid,
they can flip the switch and have that one string go to a high voltage CC.
Then they could just run some small loads off the power from that one
string, or maybe we could allow it to try to wake up the GT inverters as
well.
This particular homeowner specifically does not want much in the
way of batteries and has a smaller budget than will allow something
sensible like a Sunny Island.
At least in upstate NY, there are many
people who would like to be able to take advantage of their solar when the
sun is shining, but who just do not have the budget for a legit battery
system. I am somewhat surprised that there is no simple industry solution
for this yet, although maybe it is more complicated than I am making it out
to be. And of course, you need a very hands on homeowner who very well
understands the limitations of this kind of setup.
I would certainly
appreciate any feedback or comments on this, and also would like to hear if
anyone has tried this kind of setup before.
Thanks much!
-Dave
DAVE TEDEYAN, PE
Senior Engineer | Taitem Engineering, PC
110 South Albany Street | Ithaca, NY 14850
o. 607.277.1118 x121 f.
607.277.2119
www.taitem.com [17]
Solar * Sustainability * Energy *
Design
B-Corporation Best for the World 2018 Honoree
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