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Old 03-19-2017, 07:33 PM   #16
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Re: Run central air on battery


I've been toying with going solar for a while and the idea of running central A/C on solar is something I looked at myself, when you need it most, there just happens to be lot of sun out. There's various options such as only putting some stuff on solar, or whole house etc. They all have their pros and cons from complexity (splitting up circuits etc) to cost. For motor loads such as AC or even washing machine you need a very powerful inverter that can handle the startup load, and that will get very expensive. I'm sure it's doable though.

Something like this could probably work:

http://outbackpower.com/outback-prod...ategory_id=529

One MIGHT be enough but I'd probably put at least 2 in parallel.

The inverter is probably going to be your biggest cost, you can choose batteries based on how long you want to be able to go for. Start with cheap Canadian Tire or equivalent batteries, and later on get better ones. Of course TOO big of a battery bank and your solar panels may not be able to charge it fully fast enough within the day. So need to size appropriately. Oversizing is never a bad thing if you can avoid discharging it fully though. Ex: if you only use 10% each day and it fully charges then those batteries are going to last very long.

If your solar array can actually provide enough power to run the A/C + some left over power then you can probably get away with a smaller battery bank, as you can run off solar during the day when it's hottest and sun will be at it's peak. Then run a bit longer off the batteries then by then it will be "off peak" and you can switch back to commercial hydro. Could possibly automate that.

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Old 03-19-2017, 09:18 PM   #17
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Re: Run central air on battery


any of this is doable. It boils down how much do you want to spend and what is his ROI.

But i would submit, that *we* on the forum do not have the expertise to give sound financial advice on this matter.

I will stick with my first assessment, Even living in sunny Texas, this would be cost prohibitive. His solar array would have to be fairly large and his Battery bank would therefore be fairly expensive.

I would also strongly suggest he call these guys

https://www.wholesalesolar.com/

They can give you an accurate quote on the cost involved

p.s.: I have no affiliation with these guys and only suggest calling experts in this field
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Old 03-20-2017, 07:29 AM   #18
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Re: Run central air on battery


Conceptually speaking. If you consider the Powerwall as a generator, use a transfer switch to change power sources. You need to isolate the battery from the grid to prevent backfeeding if there was a grid outage.
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Old 03-20-2017, 07:49 AM   #19
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Re: Run central air on battery


I think there is a device that has not been invented yet. Something that produces more energy than the energy needed to power that device. An electronic version of a gear system. A small gear that uses little power but attached to a larger gear that is doing more work than the smaller gear.
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Old 03-20-2017, 08:03 AM   #20
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Re: Run central air on battery


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Originally Posted by djlandkpl View Post
Conceptually speaking. If you consider the Powerwall as a generator, use a transfer switch to change power sources. You need to isolate the battery from the grid to prevent backfeeding if there was a grid outage.

thats is what a Power wall is (or battery bank), This "generator" has to be big enough to run whatever appliances you want without help from the grid.

The issue is replenishing the batteries.

In the Northeast you need enough battery to last 3 days without recharging. Or you need to be tied to the grid or you need a (fossil fuel) generator to charge the batteries if you don't have any sun for three days or more. Which up here is quite common.

you have other considerations too. Your Inverter to the house must be "pure sine wave" type. Because almost everything nowadays has a computer. Computer do not like 'dirty electricity' they also don't like spikes. Pure Sine Wave Inverters are NOT cheap.

In Texas, it's probably not that big a deal as they get WAY more sun that we do in the Northeast.

If I lived in Texas, I would go completely off grid with a Wind/Solar Hybrid system. Generally speaking, if you don't have sun, you DO have wind.....generally speaking.

Now some people maybe able to get away with a Forktruck battery. But their are issues. The first and most obvious, weight! These things weigh a ton ( or more)

second, they are expensive but they have a ton capacity

Third, you're going to need a LOT of solar panels to charge the battery over the course of a day.

The OP ( original poster) should call a solar professional, tell them what he wants to do and they can put a package together for him

The rest of us are just guessing
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Old 03-20-2017, 11:47 AM   #21
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Re: Run central air on battery


Solar fill would be down the road. Here is a typical price curve to Houston, On that day in the hour of 4-5 PM I'd make $.70 x about 5 kwh. Then refill at night for $.02.
Of course sometimes the high prices last longer and get up into the dollars range. If it hit $9.00 for two hours I'd make $90. More, if I could sell some extra back into the grid. Making a quick profit is not my primary goal, though. This is the Green Forum, after all, right?

It'd be nice if my transfer switch could get real-time informed about prices!
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Old 03-20-2017, 03:00 PM   #22
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Re: Run central air on battery


Im a little confused? what do you mean by "refill at night"
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Old 03-20-2017, 07:16 PM   #23
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Re: Run central air on battery


Do you know how your utility's policy for net metering? I have grid-tie system and all that matters is the meter reading at the end of the month. If it's less than the start, they credit my account in dollars. If it's more I pay/deduct the credit. My rates are fixed regardless of time of day. Depending upon your utility's policy, you could use the grid as your battery.
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Old 03-20-2017, 07:55 PM   #24
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Re: Run central air on battery


The credit you get would be like 10¢/kwh, the average price for the month. I want the credit to be at the peak pricing, which is when I delivered the kw.
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Old 03-21-2017, 11:18 AM   #25
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Re: Run central air on battery


Deep thoughts - How many stages of cooling do you have? If by chance it's two stage, you could lock out the second stage for the price of a timer and some wiring. It would reduce your peak use and still provide some cooling.
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Old 03-21-2017, 02:01 PM   #26
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Re: Run central air on battery


Quote:
Originally Posted by jeff00 View Post
Im a little confused? what do you mean by "refill at night"
Refill the batteries from the grid for $.02.
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Old 03-21-2017, 05:07 PM   #27
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Re: Run central air on battery


Quote:
Originally Posted by puttster View Post
Refill the batteries from the grid for $.02.
I think you're wasting your time and money. You need to go look up 2 volt solar batteries

The batteries alone are going to run you about $8000-$9000. A Trojan 2 volt deep cycle battery will run you about $350 EACH. and you're going to need a lot of them ( like 24 batteries) to have enough power to run a 4 ton a/c..

AND you're are going to want Flooded Lead acid batteries. NO ONE has come up with a better battery for off grid applications, not even the Musk Powerwall, which is about $5000 and you'll need two of those

You're going to want a 2v deep cycle for their storage and DOD (depth of discharge)

you need to research 'solar batteries'

I understand you desire to "beat the system" but I think this maybe a waste of money.
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Old 03-22-2017, 07:06 AM   #28
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Re: Run central air on battery


so after doing a bunch of looking around, I found THIS from wholesale solar:

https://www.wholesalesolar.com/14408...FdmKswodmm8HHg

AND it puts out 240v......there ya go, Good luck
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Old 03-22-2017, 04:24 PM   #29
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Re: Run central air on battery


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Originally Posted by puttster View Post
I would like to put the four ton A/C compressor on a timer or a meter of some kind and have it switch over to a battery for an hour or two per day. Just the A/C, so of there is a power issue it won't bring the whole house down.

I am thinking about using a Tesla Powerwall but maybe regular batteries will do. The stats on the Tesla are
•Inverter: Fully integrated
•Energy: 14 kWh
•Power: 5 kW continuous, 7 kW peak
•Round Trip Efficiency: 90%
•Price $5,500
Initially I will fill the battery at night when the rate is low but eventually I'd like to fill it with solar.

So my question is about the feasibility of a project like this and thoughts on the electrical hook up.
I'm not sure a 7KW peak draw is enough to start the A/C condenser on a hot day.

Condenser would need a hard start kit to get the compressor up to speed as quick as possible to get the KW draw down fast.

Does your A/C have a TXV or piston metering device. Easier to start against a piston than a TXV.
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Old 03-24-2017, 04:47 PM   #30
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Re: Run central air on battery


Thanks, Been, good info. I have a Lennox XC16 model 048 two stage scroll compressor that uses a TXV and the manual says a hard start kit is required where voltage is less than 230V. With all the neat stuff I read about those kits it seems like I should put one in there anyway to save compressor life. Might cut down on startup racket, too, the unit is just outside the bedroom window.

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