[RE-wrenches] Solaredge inverters w/ backup generator

Chris Mason cometenergysystems at gmail.com
Sun Feb 9 09:00:22 PST 2014


That's total nonsense. Most of our installs involve a generator, as
generators are very common here due to intermittent electrical supply and
hurricanes. We also sell and install generators and I am a tech.
A decent heavy generator will produce electricity that will fall within the
IEEE 1547 specifications for grid tied interconnections. Additionally, in
our area, we alter those settings to widen the windows as the electricity
supply on an island is not as stable as a large grid.

My rule of thumb is that no lockout is required if there is no risk of
backfeeding the generator, that is, if the load will always exceed the
solar output by a reasonable factor. We have customers that have constant
loads in the 40 to 80KW range, and so 20KW of PV will never cause a
problem. Residential is the larger issue, as there is often no load.
A generator's output is controlled by the Automatic Voltage Regulator or
AVR. It senses the voltage at the terminals of the alternator and changes
the excitation to keep the voltage constant.
Usually the generator's controller has voltage sensing and will stop the
generator if the voltage exceeds limits.
If the solar inverter is making power and there is no load, it will
increase the voltage until it finds enough load, or trips. If the generator
sees the increased voltage and the AVR cannot reduce the excitation enough
to control it, the controller MAY shut down the generator.
A generator's controller and AVR presumes it is the only source of power on
the electrical system. The inverter presumes it is connected to an
infinitely large grid system that can absorb all power generated.

Our usual solution is to put a contactor in front of the inverter
controlled by voltage from the generator, or ideally by a contact on the
transfer switch.

It may be possible to program the generator to run faster or slower so as
to keep the frequency outside the inverter limits, but you run the risk
that a future tech will adjust the inverter or generator.





On Sat, Feb 8, 2014 at 11:32 AM, Kirk Herander <kirk at vtsolar.com> wrote:

> Hello,
>
>
>
> I recently posed the question to Solaredge tech support, wondering if
> their inverter, in this case a 20kw 480 3-phase, would have any issues if
> it were connected to an AC panel backed up by a generator. They told me no
> problem, for the inverter's anti-islanding will work if it sees the
> "generator frequency" and therefore will not try to push PV power to the
> panel. But isn't 60 hz, 60hz regardless of origin? There's got to be more
> to it than that. I question this because I asked the same to SMA several
> years ago and they were hard-set against connecting Sunnyboys to a panel
> with generator backup, so I always would establish the point of
> interconnection upstream of the generator feed. Comments? Thanks.
>
>
>
> Kirk Herander
>
> VT Solar, LLC
>
> dba Vermont Solar Engineering
>
> NABCEPTM Certified Inaugural Certificant
>
> NYSERDA-eligible Installer
>
> VT RE Incentive Program Partner
>
> 802.863.1202
>
>
>
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-- 
Chris Mason
President, Comet Systems Ltd
www.cometenergysystems.com
Cell: 264.235.5670
Skype: netconcepts
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