Grid tie inverter without anti-islanding?

[Dave Turpin]

Well, obviously to meet UL specifications any grid tie inverter has to have anti-islanding. In other words the inverter has to shut down when the grid blacks out to prevent damage.

But in a hydroelectric application, is there an inverter that can diconnect from the grid when a blackout occurs, and then continue providing AC power to the house? I know that there are grid tie inverters that have battery backup, and this should be similar?

[Rob Beckers]

Hi Dave,

Only the battery-driven inverters can do that. Reason is that a grid-tie inverter that has hydro, wind, or solar as its origin of energy behaves as a current source to the grid. It will raise (or lower) its voltage as needed, to pump enough current into the grid to meet its MPPT target. The battery-driven inverters are voltage sources; they output a set voltage and will raise or lower the current as needed to maintain that voltage. The two are quite different in their fundamental behavior. Granted, with the right firmware you could turn one into the other, but the source (hydro/PV/wind) doesn't cooperate for that: Hydro and wind need to see a set load, to maintain control. You can neither under- nor overload those, it doesn't work. Therefore the inverter would never be able to maintain a constant voltage (at least not if it needs to meet source load requirements).

-RoB-

[Dave Turpin]

What about this guy?

http://www.magnet4sale.com/OutBack-2.5kW-24VDC-Pure-Sine-Wave-Inverter-Sealed-Grid-Tied.html

Edit:

Well, I guess the problem would be that battery backup grid tie inverters require a very limited input voltage range. Hmmm.

[Rob Beckers]

Outback makes fine inverters. Their design is getting a bit dated in comparison to the competition, they do work well though. As mentioned, the source is battery only. You're right, battery based inverters are usually meant for a specific battery voltage. In case you're thinking of substituting the battery for another energy source (ie. wind/hydro), that won't work. The inverter needs the very low impedance voltage source (ie. a battery) to work properly.

-RoB-

[Dave Turpin]

I was actually thinking of maintaining a vestigial battery system with a single deep cycle battery. As long as the alternator continues to make power you would still have power. Problem is that every battery backup inverter I see is designed for solar and has a pretty weak input dc range from the generater.
It was just a passing idea. We rarely lose grid power in Seattle (this week is an exception due to the unexpected snow storm), so it would be probably a waste of money anyway.

[Rob Beckers]

Actually all the battery based inverters I know do not have any charge controllers for wind or solar in them. Those need to be added externally. All they do is just convert battery DC into house-grid AC.

-RoB-