Running AC from solar

bgu1982 · July 2022

I was thinking about getting a all AC unit and use it only during the extremely how part of the day.3-4 hours around there. I came across this chart. Does anyone think it's accurate?

Run time	Est. Energy Consumption in Watt-hours (Wh)	Est. Solar Power Needed (Watts)
1 hour	500-700 Wh	100 Watts
2 hours	1000-1400 Wh	200-250 Watts
4 hours	2000-2600 Wh	400-500 Watts
6 hours	3000-4000 Wh	600-700 Watts
8 hours	4000-5000 Wh	700-900 Watts
10 hours	5000-6500 Wh	1000-1300 Watts
12 hour	6000-7500 Wh	1200-1500 Watts

If this is accurate I could run a AC unit a few hours a day no problem. Like between noon and 5 pm. Any help appreciated.

P.S. It's 102° outside and it's getting hotter.

BB. · July 2022

The chart may be roughly accurate for a smaller A/C unit... There are newer "inverter powered" units that use variable frequency "inverter" to run the compressor motor--This can be more efficient when running at lower cooling levels--And does a nice job of reducing surge current to (typically) the maximum operating current/power (i.e., no "surge" current over running current). This allows you to use a smaller AC inverter and battery bank (i.e., supply 1,200 Watts max instead of needing to supply >2,400 Watts for starting loads).

And you did not say if you were looking for "off grid power" (solar->charge controller->battery bank->AC inverter->AC loads) or use a GT inverter (grid tied... solar->GT inverter->home electrical panel-AC loads).

GT solar is usually much less expensive and less maintenance--But usually require approval from your electrical utility and local building department--And not all utilities will allow GT Solar, or may have less than "customer friendly" billing/rate plans.

Also, the above chart really is an optimistic set of assumptions--Basically 5 hours a day of solar harvest and no losses. Sunny summer weather in good locations may be true--But for many other locations (and shading from trees/buildings/mountains/etc.) may have less harvest.

A 3,000 to 4,000 WH per day (3-4 kWH per day) system is not small... It will run an energy efficient home with LED Lighting, full size refrigerator, washing machine, LED TV, solar friendly well pump, laptop computer, etc... A/C systems take a fair amount of energy.

An Off grid power system for your A/C system will be $10,000 to $20,000 for parts and installation to power the A/C system. A GT Inveter system may take 1/4 the off grid system cost (Batteries are not cheap and have a limited lifetime).

You can estimate the amount of power you can harvest with a simple solar calculator based on your location and season of usage:

http://www.solarelectricityhandbook.com/solar-irradiance.html

Take the hours of sun and use this equation to figure out the "harvest" from, for example, 2,000 Watts of solar panels:

Off Grid: 2,000 Watts solar panels * 0.52 off grid system eff * x.x hours of sun per day = yyyy WH per day
GT Solar: 2,000 Watts solar panels * 0.77 GT solar eff * x.x hours of sun per day = yyyy WH per day

Say you do have 5 hours of solar energy a day of summer harvest. That would work out to:

OG: 2,000 Watt Array * 0.52 off grid system eff * 5.0 hours of sun per day = 5,200 WH per day
GT: 2,000 Watt array * 0.77 GT system eff * 5.0 hours of sun per day = 7,700 WH per day

Add batteries and AC inverter and solar charge controller--And the prices are not cheap (and complying with building codes, permits, etc. add costs too.

-Bill

bgu1982 · July 2022

I have no issues with any HOA. I'm in a rural off grid area. I was planning on powering the AC unit with my ecoflow delta pro. 3.6kw. I have panels hooked up but when the unit is low I use a gas generator to power it up at 1000 watts AC input to the unit. Takes an hour or so. I could go as high as 1600 watts but don't want to tax my generator to much.

My inverter in the delta pro is 3600 watts

Photowhit · July 2022

Could you describe your system, perhaps write a 'footer' for your ID here so we can refer to it.
Watts of solar panels,
Charge controller,
Inverter

Where you live is important in anything like the "Run Time" Estimated Solar power".

That said, I think you have the right idea! Running the air condition while you have a charged system and using the power being generated from the sun through your array, is MUCH more efficient than running off batteries at night, even with the highly efficient lithium batteries.

So I've done this for a long time. I built my second home system around air conditioning in 2004. I'm going to walk through the whole build and expansion so you can get an idea of how this worked.

A small efficient window air conditioner while the compressor is running, uses 400-460watts. This would be true of the 5200 watt I used in my cabin in 2004 and my current 6000btu in my bedroom now. I had a battery bank of about 5 kWhs (4 golf cart batteries) an looked at roughly 4 hours of duty cycle (compressor on) to run the batteries down to 40-50% (I had some other nominal loads laptop, lights, fan mp3 player)

While the math looks wrong, understand that the inverter also uses about 10% energy to convert the battery power from DC to AC. Also with lead acid batteries when running the air conditioner represent a discharge of about 1/10th of my battery, so it reduced the capacity of the battery a bit more.(something you won't have to worry about with your Lithium battery!)

So I had a 1000 watt array to start and I worked a 2nd shift so usually wasn't around when the battery bank reached Float so I could run the air conditioner with the solar support, remember I was running it down to 40% or so every night. So I set the air condition to come on about 10 so it would be cool when i came home about midnite. Duty cycle was something like 100% the first hour and a half, then 80 reducing to 60 over the next hour and a half, I usually turned it off or set it to turn off about 3am.

This allowed me to sleep pretty well. The prices of solar went down in the next couple years and I added another 650 watts. Now the batteries reach absorb around 11-noon and I could run the air conditioner in the afternoon once they reached this point as the energy needed to run the air conditioner came from energy that would be wasted from the array. I also added a fridge, about a 1kWh load. This worked fine for a couple years and the now 4.5 year old battery bank(a year old when starting this) showed reduced capacity going into the 4th summer, I shut down the fridge and used the one at work.

Lots of little things to be aware of, a 100 watt solar panel is rated with a Flash test, or Standard Test Conditions (STC). In reality they heat up and have a reduced output when hot. This is the Normal Operating Cell Temperature or NOCT value. This is usually about 75% of the Panel rating or STC or about 75 watts. Here's a picture of a couple solar panel labels that show the NOCT as well as the STC number;

So to run a 500 watt load directly from the array you would want something like 800 watts or array (allowing a little for the losses in wire and charge controller)

Hope this helps. May cabin with original 1000 watt array and outside battery box/power center, Circa 2005;

bgu1982 · July 2022

Everything is included in the ecoflow delta pro. Inverter,mppt controller, lithium iron phosphate battery's 3.6 kw capacity. Only 600 watts solar right now but the small Yamaha generator is quiet and quite efficient. The generator is used daily,not a problem at the moment but we will be adding more panels soon. At least 4 more for 1000 watts.

I was just hoping to find a really efficient small window unit to run for a few hours in the afternoon while it's extremely hot. perhaps only 3-5 hours tops and only on certain days when the temperature is brutally hot.
So that AC unit you said running around 400-450 or so I think would be terrific. My laptop alone can run almost 200watts plus all the fans and everything else.
Cool. My inverter is capable of up to 3600 watts so any surge during starting will be no problem

littleharbor2 · July 2022

I have a 5,000 btu window unit I run at night in my bedroom. I run a 2,000 watt Firman inverter generator which holds .9 gallon of gas. Running this combination in ECO mode gives me about 8 hours of runtime which I only would need 6 hours at night so about 3/4 gallon. Works great and I don't have to draw down my batteries at all.

Photowhit · July 2022

Compare the EER or CEER ratings, I think mine is 12 for a 6000 btu, pretty good.

I would buy the air conditioner properly sized to fit your area/room.
The new Midea is worth checking out, has a CEER rating of 15 and Energy Star "Most Efficient" rating! Come in 8000, 10,000 and 12000btu versions. There's a thread here about them I believe;

Amazon.com: Midea 8,000 BTU U-Shaped Smart Inverter Window Air Conditioner–Cools up to 350 Sq. Ft., Ultra Quiet with Open Window Flexibility, Works with Alexa/Google Assistant, 35% Energy Savings, Remote Control : Home & Kitchen

littleharbor2 · July 2022

Photowhit said:

Compare the EER or CEER ratings, I think mine is 12 for a 6000 btu, pretty good.

I would buy the air conditioner properly sized to fit your area/room.
The new Midea is worth checking out, has a CEER rating of 15 and Energy Star "Most Efficient" rating! Come in 8000, 10,000 and 12000btu versions. There's a thread here about them I believe;

Amazon.com: Midea 8,000 BTU U-Shaped Smart Inverter Window Air Conditioner–Cools up to 350 Sq. Ft., Ultra Quiet with Open Window Flexibility, Works with Alexa/Google Assistant, 35% Energy Savings, Remote Control : Home & Kitchen

I'd buy one in a heartbeat if I had double hung windows. Wonder if they make one for sliding windows.

Running AC from solar

Comments

Categories