[RE-wrenches] PV harvest in grid-tied systems

[Chris Mason]

So if I understand you, your problem is that you have a grid tied battery
backed system XW based system that ought to be exporting power. I have
installed the same system near my office. You are finding that the
customer's electricity cost has not decreased as expected.
I know that when I stand in front of the utilities mechanical meter at
noon, especially when the owners are not in residence, the meter spins
backwards at a rapid pace.

In order to make that work, I programmed the inverter to a "Charge Off"
setting. I let the batteries charge by solar only.

The XW is a pig to setup , I used the outback GFX seriesafter that
installation.

The biggest issue is the hybrid setups like this have poor reporting so it
is hard to know what is going on without moving in. In your case, I would
put one of my eGuage metering units on the utility feeder and look at the
export and import in real time. I would also put CTs on the inverter feed
to measure the production and consumption. Let me know if you need help
with that, I resell these devices.


On Mon, Apr 16, 2012 at 10:56 AM, William Miller <william at millersolar.com>wrote:

>  Chris:
>
> I would willingly clarify but I am confused about what you are confused
> about.  I think we are saying the same thing about off-grid systems:  If
> you don't consume power, battery voltage stays high and charge controllers
> reduce energy harvest.
>
> William Miller
>
>
>
>
> At 06:57 AM 4/16/2012, you wrote:
>
> William,
> I must confess to being totally confused by your post.
>
> I am currently at my office writing to you using electricity from our
> off-grid solar system. We only have the solar power, no grid power.
>
> We get exactly as much power as I predicted we would, in fact a little
> more. But, there is an intrinsic issue with off-grid systems that many
> people miss. Unless you have a use for the power, it won't be "harvested".
> If you allow the inverter to charge the batteries from the grid, there will
> be nowhere for the PV power to go.
>
> To give you an example, our warehouse and office has 2,580 watts of PV on
> a 60 amp charge controller and a 3.5KW outback inverter, with 250Ah of VRLA
> batteries (4 x 12V).
>
> Each day, I read the amount of power the charge controller makes. It
> averages about 12KWh, depending on how much we used that day and the state
> of the batteries at the beginning of the day. We have found that the loads
> did not adequately exploit the power product capabilities of the system, so
> we moved our freezer from the house to the warehouse to use up some more
> power.
>
> As we are in the Caribbean, the insolation levels are pretty continuous,
> so it does make calculations easier.
>
>
> Chris
>
>
>
> On Mon, Apr 16, 2012 at 1:50 AM, William Miller <william at millersolar.com>
> wrote:
>  Friends:
>
> There has been recent discussion on this forum about PV production in
> grid-tied with battery systems.  I have been faced with this same problem
> in a 3 XW system installed in 2009.
>
> The customer's power bill never went down.  PV harvest was abysmal.  The
> system would create great short circuit current but would not harvest into
> the batteries.
>
> It is starting to appear the XW firmware was at fault.  The inverters
> would charge the batteries too high so the charge controllers would back
> off.  Upgraded firmware seems to be helping, but the data set is still
> limited.
>
> Remember this:  just because a PV system can produce does not mean it
> will.  The charge controller knows only one thing:  battery voltage.  If it
> is high, production is curtailed.
>
> Off-grid production will also be reduced is consumption is curtailed.
>
> Charge controllers that can be set for grid-tied applications help, but
> only if the inverter(s) do not keep the battery voltage too high.
>
> William Miller
>
>
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-- 
Chris Mason
President, Comet Systems Ltd
masonc at cometsystems.co
www.cometsystems.co
Cell: 264.235.5670
Int: +1305.767.2094
Skype: netconcepts
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