[RE-wrenches] Generator Controlled Mini Grid

Tue Feb 12 19:03:36 PST 2013

Chris,

I just wanted to say thanks for coming onto the list and giving more detail
of what you have achieved. I have long believed that with a little more
understanding and thought, PV and a diesel (or gas) derived grid will become
common place, and will eliminate the need for a battery bank on many
systems.

Cheers,

Carl Emerson.

Subject: Re: [RE-wrenches] Generator Controlled Mini Grid

I am connecting a Kohler 12RES to my house, the roof has 3.1KW of PV
connected to a SB3000.

I thought we would have problems so we all knew to turn of the solar before
turning on the generator. One day, we forgot, and it all worked. Since that
I have left the solar on each time we ran the generator. As we are in a
small island, power outages are common.

The Kohler has a problem I cannot get to the bottom of and I'm going to pull
a Generac from inventory and install it, so I will find out if that also
works. My home and office is a test lab, I'll try anything there.

On Mon, Feb 11, 2013 at 8:44 AM, Drake
<drake.chamberlin at redwoodalliance.org> wrote:

Chris,

It sounds like you are creating a generator supplied mini grid, if I
understand correctly,  My reading is that your generator is creating the AC
voltage, and the inverter is synchronizing with it, allowing power to be fed
into the system from a PV source. 

This approach could represent a major innovation in solar industry.  I
remember a decade or so ago when it was proposed, on this list, that battery
based inverters could be backfed to charge batteries, and someone tried it.
It worked.  Today AC coupling is standard operating procedure.  

Up to that time, it was only understood that to connect an AC source to the
output of a battery based inverter could damage it.  Maybe the next step is
to AC couple to generator supplied sub panels and allow PV usage during
power outages. 

What inverter and generator are you using?  How many Watts of PV are
connected?

Thank you,

Drake 

At 02:04 PM 2/10/2013, you wrote:

I have a generator and PV system that just works together, despite all the
dire predictions that it won't. from my experience of PV and generators (I
am also a generator tech), the biggest issue is the AVR board and how it
responds to back fed voltage, and the generator controller's over voltage
settings.
I think that it would probably on only require a reprogrammed inverter to
make this work as follows.
The AVR produces excitation voltage to vary the strength of the rotor field
and therefore the induced voltage in the stator. When the PV system back
feeds the generator, the excitation level is reduced to control the voltage.
When there is no load, the inverter keeps raising the voltage to attempt to
push the current to the grid and at some point the generator trips out on
overvoltage. 

 If the inverter was programmed to reduce the production of power in
response to the rise in voltage, it would sync pretty nicely with the
generator. However, this would likely violate the IEEE parameters for a grid
tied inverter. SMA has off-grid mode, I suspect that is the best solution.

In a Sunny Island system, as I understand it, the Sunny Island caries the
frequency to communicate to the inverter to reduce the current output. That
avoid the problem of the inverter raising the voltage.

On Sun, Feb 10, 2013 at 2:45 PM, Drake <
<mailto:drake.chamberlin at redwoodalliance.org>
drake.chamberlin at redwoodalliance.org> wrote:

Hi Kevin,

Thanks for the Eigg video.  What a great place.

I didn't see evidence of any AC coupling of inverter produced AC to a
generator produced mini grid.  I understand this is being done in a homebrew
manner by some.

The current wisdom on the issue is that the less the PV contribution to the
generator supplied grid is, the easier.  It would seem that if a grid tie
inverter output could be regulated, using Sunny Island type controls, it
should be possible to have a small inverter generator create a mini grid
that could be fed by PV.

A system featuring this type of technology was linked in a posting on this
list some years ago, The link seems dead now.  In that case a large
generator was feeding a number of houses, and PV was fed into the system.

The reason for this interest is that battery backup systems are much more
expensive than generators.  We need to find a way to utilize PV arrays
during outages without the expense of battery backup systems.

Drake

At 07:42 PM 2/8/2013, you wrote:

Hi Drake,

SMA has very good solutions for this. Does this out of the box without a
bunch of custom control systems. I have put a few systems in like this, but
the renewables not yet online (generator / battery now). If you google Isle
of Eig you will find some info on what they have done there.

http://islandsgoinggreen.org/about/eigg-electric/

Kevin

-----Original Message-----

From: re-wrenches-bounces at lists.re-wrenches.org

[ <mailto:re-wrenches-bounces at lists.re-wrenches.org>
mailto:re-wrenches-bounces at lists.re-wrenches.org]On Behalf Of Drake

Sent: February 8, 2013 6:41 AM

To: RE-wrenches

Subject: [RE-wrenches] Generator Controlled Mini Grid

A potential customer is interested in a mini grid, set up by a

generator, to connect his array to.

Some years back, on this list, an article was linked about a

community with a central generator that had PV input to the generator

supplied, local grid, using electronic controls.

Has any progress been made in this technology?  Does anyone have a

link to the electronic control equipment or any other relevant information?

Thanks,

Drake

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Cell: 264.235.5670

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