differing types of invertes question

Re: differing types of invertes question

elesaver wrote: »

I fully understand this rationale. But, what about the opposite situation? The goal is to be off grid but would there be instances where this may not continue to be possible?

I'm trying to imagine what would cause that, other than a conscious decision by the off grid system owner. Is there some other scenario you have in mind?

Re: differing types of invertes question

I built my system primarily as a back-up with batteries. The thought of it just sitting there doing nothing while the grid is available was hard to swallow so I opted for a grid interactive inverter that decreases the electric bill as long as the batteries are topped up. As far as straight up grid tied goes for me there would have been a lot of aggravation to look at all of those solar panels doing nothing during an outage.

Although a generator is a much cheaper back-up option for short outages I feel pretty good about my investment. In today's world you never know what a day will bring.

Re: differing types of invertes question

elesaver wrote: »

After some diligent searching, I have found that the hybrid type of inverters are not recommended for off-grid use. This doesn't mean they CAN'T be used, but they are not recommended. There ya' have it! Thanks all. You are the best!

Please do not overgeneralize. When you are off grid and have to rely on a generator for occasional charging and for large loads like doing the wash or cooking a big dinned with electricity, a hybrid system with what is called "generator support" mode (not just autostart!), as found in some Xantrex models, can make the difference between a good experience and a bad one.
If you do not have that scale of power need, then the added expense of a hybrid system is generally not justified for truly off-grid.
Often a grid tie system and a separate UPS system and generator, without any permanent link to your solar PV, may be the most economical when you want to have standby power in the mix.

Re: differing types of invertes question

elesaver wrote: »

I guess the "boiled down question" is whether or not a hybrid grid tie could be used in a fully off grid situation or are they designed for emergency only off grid use and the use of one for full time power would be harder on the inverter itself?

As the others have mentioned, that is not correct. If you learn about AC and DC coupling, you will have a better understanding of these inverters.

Suppose you want to run a 2500 watt AC load and you have a 4000 watt off-grid inverter and a 2000 watt generator. Your battery bank cannot sustain the load without help from the generator. The sun is behind clouds. Here are three ways to manage the situation: (in the examples, there are no inefficiency losses)

DC coupling:
The generator runs through a stand-alone battery charger to push 2000 watts of DC onto the battery bus.
The off-grid inverter draws 2500 watts from the battery bus.
The sun, through the charge controller, is contributing only 100 watts to the battery bus.
The batteries contribute 400 watts to the battery bus.

Note: all loads and power sources are combined at the battery bus.

AC coupling with two inverters:
The generator output contributes 2000 watts to the AC bus.
The load pulls 2500 watts from the AC bus.
The sun, through a grid-tie inverter, contributes 100 watts to the AC bus.
The batteries, through a hybrid inverter, contribute 400 watts to the AC bus.

Note: all loads and power sources are combined at the AC bus. This can be very tricky... all sources must have their AC waveforms synchronized. One source must be the 'master' to which the others synchronize. There must be a way for the hybrid inverter to tell the grid-tie inverter to stop making power if the battery is charged and there is no load.

Combinations:
You can mix AC and DC coupling. In the above AC coupling example, the sun could make its contribution through a charge controller directly to the battery, but let the hybrid inverter and the generator be combined on the AC bus.

Generally, AC coupling is more efficient. DC coupling is more robust and you can mix and match power sources and loads that do not need to communicate or synchronize.

--vtMaps