Selling the excess back

Discussion about the FX2000 Inverter
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beltrams

Selling the excess back

Post by beltrams »

Hello everybody.

I've been considering a grid interactive with backup system for some time with increasing seriousness. Recently, I became aware of Outback's new products, especially the FX2000 and spent a good deal of time reading the manual (Rev 4.4) as well as nearly every post in every section of this forum.

Like I suppose many people with PV and a grid connection, I'd like to have a system that mainly sells/buys from the grid, but with a minor battery bank for backup too. My question is, after reading all the setup/programming info for the FX2000, it seems that even with the HBX mode enabled, mostly what the FX does under conditions of high battery state of charge is place building AC loads on the inverter/battery combination if and until such inverter loads drew down the battery voltage enough to disconnect the inverter. In the meantime, the pv charger would have presumably increased pv charge current more aggressively to compensate for battery draw down. Specifically, my question is what if I am away on a sunny day and house AC loads are minimal at best? It seems to me as I understand the various FX2000 operation modes that the charge controller is going to wind down the charging as the batteries top out. For it seems that under conditions of a full battery bank, good pv output, and low AC house loads, a good deal of pv output will be wasted as the FX2000 will curtail inverter output rather than divert it onto the grid.

Under these conditions, how does one program the FX2000 to make use of this power, sending the inverter output onto the grid rather than to AC loads that donÔÇÖt exist at the time on the house side of the AC system?

Am I missing something basic to the unitÔÇÖs operation and programming that would be better explained by a dealer?

<small>[ March 03, 2003, 10:23 PM: Message edited by: Steve B ]</small>
wd8cdh
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Selling the excess back

Post by wd8cdh »

Hi Steve,

Basically in the grid tie mode, the inverter controls its output to hold the battery at a fixed voltage. This voltage is slightly below the float voltage. The MX60 will always try to extract the maximum power from the PVs if the battery is below it's setpoint. If the MX60 is putting current into the battery bank, the voltage will tend to go up so the inverter will increase it's output to hold it down. If the household loads are less than the inverters output, the excess power will simply go into the grid.

You can almost think of the inverter as a proportional diversion charge controller and the house loads plus the grid as the diversion load.

It still works fine while you are away. Even with no loads in your house, the grid will take all of the power you produce.
beltrams

Selling the excess back

Post by beltrams »

Thanks Ron for the quick reply.

I guess I can understand where the FX2000 and the pv charge controller are trying to position the battery voltage under a grid sell situation. What I'm still fuzzy on is the programming required by the FX2000 to do it. Is it in the default setup of the unit? Does the HBX mode need to be enabled?

Reading from page 43 of the FX2000 manual I see:

"The high battery transfer system is a way to use renewable energy sources together with a utility grid to power AC loads.
When the battery is charged the FX inverter/charger will automatically transfer the AC loads connected to the AC output from being powered by the utility grid to being powered by the renewable energy system. If the battery voltage gets low, the loads will be automatically transferred back to the utility grid and the renwable energy source will be allowed to recharge the battery system."


This seems to say that the FX holds the battery voltage in a range by shifting house loads onto and then off of the grid. But what if there aren't any substantial house loads at all? Is there another mode besides HBX or is it implicit in HBX mode that if there aren't sufficient and substatial loads on the AC Output terminals and battery voltage is still high, the FX will start looking for such loads on the AC Input terminals (i.e. the grid) instead?

Sorry to be stupid, but what modes, setpoints etc. on what setup menus are needed to enable SELL mode?
wd8cdh
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Selling the excess back

Post by wd8cdh »

Hi Steve,

I think the HBX mode is just for using power from solar on a grid connected system without selling any power to the utility. Basically using the grid as a backup to solar.

I have not actually read the setup for the grid selling yet. It might not be in the online manual since grid tie type testing hasn't been finished yet.

We should defer to Christopher for further details.

Ron

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Steve B:
[QB]Thanks Ron for the quick reply.

I guess I can understand where the FX2000 and the pv charge controller are trying to position the battery voltage under a grid sell situation. What I'm still fuzzy on is the programming required by the FX2000 to do it. Is it in the default setup of the unit? Does the HBX mode need to be enabled?

QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
billvon
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Location: san diego

Selling the excess back

Post by billvon »

The FX2000 is not yet certified to run in grid-interactive mode, and thus cannot be used in that manner yet.
rdmcghie
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Location: Chico, California

Selling the excess back

Post by rdmcghie »

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Steve B:
<strong>Thanks Ron for the quick reply.

I guess I can understand where the FX2000 and the pv charge controller are trying to position the battery voltage under a grid sell situation. What I'm still fuzzy on is the programming required by the FX2000 to do it. Is it in the default setup of the unit? Does the HBX mode need to be enabled?

Reading from page 43 of the FX2000 manual I see:

"The high battery transfer system is a way to use renewable energy sources together with a utility grid to power AC loads.
When the battery is charged the FX inverter/charger will automatically transfer the AC loads connected to the AC output from being powered by the utility grid to being powered by the renewable energy system. If the battery voltage gets low, the loads will be automatically transferred back to the utility grid and the renwable energy source will be allowed to recharge the battery system."


This seems to say that the FX holds the battery voltage in a range by shifting house loads onto and then off of the grid. But what if there aren't any substantial house loads at all? Is there another mode besides HBX or is it implicit in HBX mode that if there aren't sufficient and substatial loads on the AC Output terminals and battery voltage is still high, the FX will start looking for such loads on the AC Input terminals (i.e. the grid) instead?

Yes, that other mode would be SELL mode and no the inverter will not do this in HBX mode, as best as I can tell. The grid presents an essentially infinite load, so the inverter cannot use load but must use available PV power to determine its output. In SELL mode the grid either supplies the deficiency or accepts the surplus and inverter output power is based on available PV power, not load. Except for a very limited trickle charge to keep the batteries at their float setting very little current flows into or out of the batteries.

Sorry to be stupid, but what modes, setpoints etc. on what setup menus are needed to enable SELL mode?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Steve, what is being described is not SELL mode.

I assume Outback has blocked SELL mode and access to its menus to prevent the FX2000 from being used in SELL mode until the required approvals have been obtained. I expect that you will see an addition to the manual on how to setup SELL mode once this has been done.

Robert
beltrams

Selling the excess back

Post by beltrams »

Thanks for all the replies.

HBX mode did indeed sound like something other than SELL.

Somewhere along the line I forgot how new this inverter was and assumed it was already set up and certified for grid intertie use. I take it then, that certification is a multi-step process? I noticed that the FX was certified to UL 1741 back last September under "Inverters for Use in Independent Power Systems." What time frame are we looking at for interactive certification, if indeed, this is the next step?
dgsalkeld

Selling the excess back

Post by dgsalkeld »

Greetings Stsve B,
According to your description The FX 2000 is capable of selling power back to the grid, but has it passed testing at a listing agency as yet?

Thanks
Robin Gudgel

Selling the excess back

Post by Robin Gudgel »

The best estimate we have at this time for grid tie will be August. Remember that this is just an estimate and things can change, but since we get asked this a dozen times a day, this is the official guess for now. Grid tie is a very major change to the inverter. Before we start modifying the computer code for grid tie, we would like to get most if not all of the other major configurations put to bed. The 48volt unit has shipped a few beta units and production is right around the corner. Greg Thomas will need to assimilate the 48 volt code into our 24v code so that there is one reference computer code. After this revision has been verified, then we have a few more versions to widdle away (230VAC 50HZ, 12VDC etc). Once this is completed and tested, we then will have the baseline required to start grid tie. We expect the other versions to be fairly straight forward, but even at that they require alot of qual testing and tweeking. Hope this helps.
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