Separate ac

What i want to do create a 2nd fuse panel ran entirely off solar.

For the easy of math i only want to run one window air conditioner, 12000 btu. (This will be scaled up at a latter date)

15 amps at 115 volts= 1720 watts

I would need 6 x 320w solar panels just to run in a 100% efficient world

If i went with 9 solar panels
48v battery bank
60 amp controler
2500 watt inverter

It would just run while the sun is out.

How much more would i need to run 24 hrs a day?
This is in phoenix arizona.

Still too much factors involved. Size of room for the BTU, insulation, temperature, efficiency of ac, etc. Your max ratings at 15A is too high, but it really depends. Look at the yellow sticker and maybe it'll tell you how much kwh it uses per year. Then assume your Arizona temp to be high. If you already have the A/C, then hook up a kill-a-watt to it and record the usage. Then you can begin to size your panels accordingly.

For solar, always assume 10% loss in MPPT, and 10% loss in inverter. That's a minimum. Then you also have some idle loss depending on how efficient the inverter is. Could range from 20W to 100W(or more!).

My one window unit will pull around 12A when the compressor is running, so 15A isn't to far off.

You need to find out how much kWh it uses during the day under heavy load. Then you build your battery pack accordingly. Solar would need to be almost 50% or more of what you'd need to run so you can charge the batteries up. Otherwise they'd never get charged.

Another thing to consider is the surge of the A/C unit. 15A may be running amps, but startup amps will be around 30A or so. Your inverter needs to be able to handle that, or about 4500W surge

If you plan on expanding later, it'd be better to get a large inverter so you can grow into it, instead of having to replace it. 1800 / 2500 = 72% load. That doesn't leave much room for expansion, aside from lights maybe (which should be ran on DC anyways, imho)

My house has 10 tons of ac on it, a 1 ton window ac will run non stop.

The math im looking for is non stop supplying 15 amps
I cant find any real amps per window ac the older they are the worse they are.

Just like korishan says 12 amps for his, i read 9-14
A mini split is way more efficient and hacking it to feed direct dc, but i get window acs for free.

I wont be buying anything to just power one ac but i want real world experience on what it takes to supply 15 amps non stop.

Nah, when I said 12A, that was pretty much the low end. And then there were the spikes of around 40A (but this was partially due to a bad start up capacitor)

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Actually, looking back at the influxdb, I'm showing about 16-17A continuous load.
Now the other window unit for the bedroom, must smaller, draws around 6-8A

Making 15 amps 24 hrs a day

1800 watts an hour
43200 watts total per day
30600 watts during night

19x 320w pannels
31kw battery bank
Not figuring in any losses

Why does this seem like a huge system just to run 1 ac?

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Something is messed up in my math.
My whole house uses 39,000 kw per day

1958 greyhound said:

Why does this seem like a huge system just to run 1 ac?

Click to expand...

Hahah, because it is

First you aren't going to be pulling for 24/7. It'll be closer to 16hrs/day. The A/C will run about 80% duty cycle during the day, and probably about 40% at night. This probably fluctuates a bit more depending on the humidity and how fast outside temps drop.

So, going with 1800W/h:
28,800Wh/24hrs

You'll only have sun about 14-16hrs, during the summer (which is great for the scenario as we need it to cool the house). If we have 320W panels, then we'd need 7 Panels for the A/C alone. If we go to 10 panels, we can charge the batteries up as well. I guess 10 panels because when the A/C cycles off for the 10mins (usual shut off time), you'll get a boost of current from the other 7 panels until the A/C kicks back on. This will decrease obviously as the day progresses and the A/C needs to run longer to hold temps.

So in total, a 31kWh battery would be a good target, gives some buffer room when there are clouds. 10 panels will hold things steady, but 12 would really get your batteries charged.

Now, let's figure in costs:
1.8kW * $0.13/kWh = $13.85 * 30 = $415.50 This is assuming 100% duty. Let's go with 50% duty averaging between day/night, which comes to $207.75. This is actually still a bit high overall, but could be considered worst case, or almost worst case.

If a panel costs $225 (assuming about $0.70/W), that'd be $2700 for 12 panels
Inverter would be about $300.
So that gives a grand total of about $3000.
ROI would be around $3000 / $208 = 14.42 months


(I think I got my math right there)
This is about what I'd be looking at if I were to install the solar/inverter to run an A/C here in Florida. Further north would be cooler and wouldn't need to run as long.

O i like that math way better.
My electric is 24 cents not 13
Panels are 35 cents a kw here local on auction, i have seen them down to .07 but that was back in the 09 crash.

Night temps in july only to to mid 90s, it never cools off.
Two 5 ton heat pumps cycle on and off, the run less than they are on. Thats why i was figuring 15 amps non stop but i dont think it would even use that.

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I guess my summer and winter power bills will tell me the dif in electricity usage for what is currently the ac only portion

ick 24cents, that sux.

I figured on 70/W on the panels as that's about what they are new. So, going with worst case on those costs as well
What makes heat pumps power hogs is that they have a compressor, a blower fan, and a cooling fan, so 3 induction motors to accomplish 1 task. To bad they can't make them things use only 1 motor, 2 at the most (like a window unit).

I noticed a huge decrease in power usage when I stopped using the A/C. Dropped by about 60% watt usage





On the left side is the cycling of the A/C with all those spikes. You can see where I switched it off and started using just a blower fan to pull cool air in with the constant current load. The peak on the right I think was when I turned on the oven to make some pizza

Under closer inspection of the data on the left, I think my A/C is about to die. It was cycling an awful lot that last week I used it. You can see it cycling about every 2 minutes, way to frequent.

There's still too much factors involved. You are right in that mini-splits are better, but it all comes down to efficiency. If your window A/C is old, let's say over 10 years old, then it probably has a SEER rating of less than 10. Newer units now are slightly more efficient at over 13. I have a mini-split and it has a SEER of 22. If your central A/C is relatively new, its probably in the 20 range. So it's roughly twice as efficient compared to a window A/C unit.

Then it comes down to how much sq ft are you cooling down. If it's too undersized then it will run all the time, probably around 13A. But again you said your total usage is only 39kwh a day. The math doesn't add up too much since you run two 5 ton units so your central air units could possibly be oversized. So if your room is not that large, your 1 ton A/C unit may not run all the time either. That's why placing a kill-a-watt will determine your actual usage. You're localizing the cooling so it's not efficient just to blast cold air in one spot and try to radiate the cooling to the rest of the house. It's not an efficient way to cool down the house. Efficiency is key here.

Korishan is right in the large draw from start-up of a pump. You probably need to find an inverter unit capable of handling at least 50% more than your rated max A/C. Also on hard start a/c, the inverter style mini-split does have a better advantage in this sense, as it is a variable speed pump so it slowly ramps up and no high spikes.

Your Arizona sun hours is probably in the 6-8 hours during the summers. I wouldn't expect more than that even though you may have over 12 hours of sun. The angles of the sun lowers the efficiency drastically and so does any shadows, etc. So morning and dusk suns don't really put out that much power. 12x320W= 3840W. 3840W*7hrs (avg)= 26880W. Minus 10% solar controller, minus 10% inverter efficiency = 21kwh. Add another 10% misc loss you're looking to get slightly less than 20kwh. It's still a decent amount to start with. I'd lower your expectation of ROI and enjoy the process more

Well dang, not2bme, you shot down our expectations

Im thinking i need to refigure lots of things.
Previous house was 2700 sq ft and twin 5 tons
This house is 1900 sq ft and one 5 ton.

I have a Neurio Home Electricity Monitor.
Moving usage around to off peek saved my a 100 a month in electric.

Ill hook it back up just on the heat pump portion.

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No calculator on the net says 2700 sq ft needs 10 tons.
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