Off grid system to run HVAC only, doable?

[DanKegel]

? The solar panels would generate and send all their power to the grid as normal; only if the grid was out would he throw the switch to run the A/C straight off the inverter's 'secure' output. Since that would almost never happen, I don't see how efficiency would be affected.

But it's moot anyway; from what I can tell, the secure output is not enough to run an A/C.

[jflorey2]

Agreed - battery could be smaller with HBX, but will also be driven harder thus reducing its life.

Dan - that would eliminate the normal production of the inverter and would result in far less energy overall.

[DanKegel]

Too bad sunnyboy's secure power supply outlet is only 1.5kW. That and a manual switch might have made a cheap way to scratch the off-grid itch.

[ButchDeal]

Yes but doing it with grid available would allow the inverter, battery and array to be smaller than if off grid completely, thus minimizing the costs, and maximizuping production. Though this just cuts the losses to minimum

[jflorey2]

I'm still not interested in a typical grid-tie but maybe a grid switch? Solar panels to a small battery to handle startup and then switch over to the grid when the sun goes down?

Sure; Outback has a mode that does just that (HBX.) You still have the same problem with battery costs though.

[inetdog]

Often a 3kW inverter will not be able to start even a 1500W motor.

[Sunking]

Finally ! I've asked this question a few times and never got a clear answer. It's the batteries that wreck the math!

Big time. Battery cost alone will be 5 to 7 times more than you pay the mean ole power company. Size of bank you would need requires a permit because it contains over 500 pounds of toxic material. You get to go through that pain of inspections and paper work with the Employment Prevention Agency. For the quantity of batteries needed will require its own room with reinforced floor. You are talking 5000 to 6000 pounds of batteries costing $15K to $20K every 5 years.

You got that kind of money to throw away?

[Logan5]

Yes, if you are trying to save money grid, tie is the only way to go. Almost anything is possible with enough money, so yes it can be done. Very few solar, battery salesmen will tell you this though. Until a new battery storage options come to market it's grid tie, or spend more, I have seen solar hybrid split AC units that run on 220 VAC and have built in solar assist. so not to feed back grid but assist a known heavy load.

[ButchDeal]

it is not cheap and you will by cycling the battery a lot more than grid tie but much less than off grid completely.
It is pretty much my set up with a different program configured on the inverter.
because of the battery use it will be the best option for working without a net meter configuration but still very much what SunEagle is talking about for costs.

[SunEagle]

Yeah but at post #2 I still had a deathgrip on NOT tying to the grid

Unfortunately when you add batteries of any size to a solar pv system (even a hybrid connected to the grid), the cost of those batteries ends up costing you much more /kWh then to just run directly from the grid.

Unless you are paying above $0.30/kWh a battery system will cost you much more and is not financially smart thing to do.

[hertfordnc]

Yeah but at post #2 I still had a deathgrip on NOT tying to the grid

[ButchDeal]

This is what I suggested in post #2 BTW.
Any time the solar/battery is not enough it will pull from grid. You could set the discharge limit for the battery that it would be allowed to discharge to before pulling from the grid as well. It can be programmed to never back feed as well.

[hertfordnc]

Finally ! I've asked this question a few times and never got a clear answer. It's the batteries that wreck the math!

I'm still not interested in a typical grid-tie but maybe a grid switch? Solar panels to a small battery to handle startup and then switch over to the grid when the sun goes down?

[Logan5]

A solar PV system with hard cycled batteries will not only never pay for it's self ever, but will actually always cost many times more forever as long as you run that system. 1 dollar per Ton hour is an example only. It's probably much worse. unless you are cooling a very small place, your battery need could be the size of a mini van and cost 10's of thousands of dollars and have to be replaced every year to 3 years or so. I would get a fork lift for the annual ritual.

[jflorey2]

Sounds like you're saying solar never pays for itself?

Solar+battery never pays for itself due to the ongoing cost for batteries.

So the first question is, how much battery do I need to deliver 600 watts for 24 hours and how much solar do I need to replenish that battery on a clear day in summer?

600*24/.95 (inverter efficiency) = 15.2kwhr

So for lead acid you need 30.4kwhr per day (no more than 50% discharge.) That means about 90kwhr of batteries total for 3 days of autonomy (an often-used standard.)

Minimum solar for that battery size will be about 9kw (for C/10 charging.)