# easy, DIY solar powered AC for small room??

A

#### AA

Jan 1, 1970
0
I have a small 10x10 foot room I am considering cooling with a small 12000
btu AC, but I am wondering if it's possible to set this up to be powered by
solar? The AC would not be run continuously, just long enough to cool the
room off for sleeping, maybe 2 hours per day. I'm thinking a car battery
with an inverter and the battery charged by solar cells, but I don't know if
this would work or even how to begin. I also want to keep this as low cost
as possible and stick with a simple design that works.

Any suggestions would be appreciated.

Thanks,
AA

M

#### Michael Karas

Jan 1, 1970
0
[This followup was posted to sci.electronics.design and a copy was sent
to the cited author.]

I have a small 10x10 foot room I am considering cooling with a small 12000
btu AC, but I am wondering if it's possible to set this up to be powered by
solar? The AC would not be run continuously, just long enough to cool the
room off for sleeping, maybe 2 hours per day. I'm thinking a car battery
with an inverter and the battery charged by solar cells, but I don't know if
this would work or even how to begin. I also want to keep this as low cost
as possible and stick with a simple design that works.

Any suggestions would be appreciated.

Thanks,
AA

Some considerations, The 12000 BTU AC unit listed here:

http://www.lg.com/us/air-conditioners/lg-L1210ER-window-air-conditioner

...shows that it has a rating of 115VAC/60Hz with a draw of 10.2 Amps.
They also quote a rating of 1110 Watts.

If you were to use an inverter such as the following:

http://www.donrowe.com/inverters/sw1220.html

...the "optimum" efficiency is listed at ~90%. It would be more likely
that you may see 85% efficiency. That would take an input power of
1110 Watts / 0.85 = 1306 Watts.

Converting the wattage requirement to Amps at a nominal 12VDC would be
1306W / 12V ~= 110 Amps. This amperage delivered for the two hours that
you specified is 220 AmpHour.

A possible battery may be the Trojan model T-145 shown in this brochure
on page 11 of the PDF. The quoted 5-Hr rate is 215 AH.

http://www.trojanbatteryre.com/PDF/TRJN0159_RESeriesColl.pdf

To re-charge the battery from a solar array will require an array
capable of restoring the 220 AmpHour of energy during one summy day
period of time.

The solar panel showen here:

http://www.saferwholesale.com/High-Quality-280-Watt-Solar-Panel-p/dsp-
280_watt_panel.htm

...is good for 280 Watts on a good sunny day. One could estimate that you
have say 8 hours of sunlight on days when you would like the air
conditioner to function. Also let us guess at solar battery charger
efficiency of 85%. Some simple math shows that:

(1306W / 0.85) / 8 hr = 192

It looks like one of the above panels could keep your battery charged.
Two panels would give you a nice extra capacity in case you wanted to
swipe some system power for something else besides the AC unit.

W

#### Wond

Jan 1, 1970
0
I have a small 10x10 foot room I am considering cooling with a small
12000 btu AC, but I am wondering if it's possible to set this up to be
powered by solar? The AC would not be run continuously, just long
enough to cool the room off for sleeping, maybe 2 hours per day. I'm
thinking a car battery with an inverter and the battery charged by solar
cells, but I don't know if this would work or even how to begin. I also
want to keep this as low cost as possible and stick with a simple design
that works.

Any suggestions would be appreciated.

Thanks,
AA

I would look at direct solar absorption cooling, like the kerosene or
propane refrigerators use. The solar heat collector would supply the
energy.
There used to be a clever little 12V 'fridge available, "Norcold" I
think. It used a "vibrator compressor" and could be used on a small boat.
Perhaps something could be adapted from that.

H

#### hamilton

Jan 1, 1970
0
[This followup was posted to sci.electronics.design and a copy was sent
to the cited author.]

I have a small 10x10 foot room I am considering cooling with a small 12000
btu AC, but I am wondering if it's possible to set this up to be powered by
solar? The AC would not be run continuously, just long enough to cool the
room off for sleeping, maybe 2 hours per day. I'm thinking a car battery
with an inverter and the battery charged by solar cells, but I don't know if
this would work or even how to begin. I also want to keep this as low cost
as possible and stick with a simple design that works.

Any suggestions would be appreciated.

Thanks,
AA

Some considerations, The 12000 BTU AC unit listed here:

http://www.lg.com/us/air-conditioners/lg-L1210ER-window-air-conditioner

..shows that it has a rating of 115VAC/60Hz with a draw of 10.2 Amps.
They also quote a rating of 1110 Watts.

If you were to use an inverter such as the following:

http://www.donrowe.com/inverters/sw1220.html

..the "optimum" efficiency is listed at ~90%. It would be more likely
that you may see 85% efficiency. That would take an input power of
1110 Watts / 0.85 = 1306 Watts.

Converting the wattage requirement to Amps at a nominal 12VDC would be
1306W / 12V ~= 110 Amps. This amperage delivered for the two hours that
you specified is 220 AmpHour.

A possible battery may be the Trojan model T-145 shown in this brochure
on page 11 of the PDF. The quoted 5-Hr rate is 215 AH.

http://www.trojanbatteryre.com/PDF/TRJN0159_RESeriesColl.pdf

To re-charge the battery from a solar array will require an array
capable of restoring the 220 AmpHour of energy during one summy day
period of time.

The solar panel showen here:

http://www.saferwholesale.com/High-Quality-280-Watt-Solar-Panel-p/dsp-
280_watt_panel.htm

..is good for 280 Watts on a good sunny day. One could estimate that you
have say 8 hours of sunlight on days when you would like the air
conditioner to function. Also let us guess at solar battery charger
efficiency of 85%. Some simple math shows that:

(1306W / 0.85) / 8 hr = 192

It looks like one of the above panels could keep your battery charged.
Two panels would give you a nice extra capacity in case you wanted to
swipe some system power for something else besides the AC unit.

WOW, this looks doable.

What would be used to connect the solar panel too the battery ?

I would think there would be some sort of a protection circuit between
the solar panel and battery.

Thanks

A

#### AA

Jan 1, 1970
0
Thanks. Although this design looks interesting, it far exceeds the
budgetary amount I had in mind ($500 max, sorry I didn't specify initially). I thought maybe I could put something together quick, simply, and cheaply but doesn't really look that way. Unless someone else has some other suggestions. AA Michael Karas said: [This followup was posted to sci.electronics.design and a copy was sent to the cited author.] I have a small 10x10 foot room I am considering cooling with a small 12000 btu AC, but I am wondering if it's possible to set this up to be powered by solar? The AC would not be run continuously, just long enough to cool the room off for sleeping, maybe 2 hours per day. I'm thinking a car battery with an inverter and the battery charged by solar cells, but I don't know if this would work or even how to begin. I also want to keep this as low cost as possible and stick with a simple design that works. Any suggestions would be appreciated. Thanks, AA Some considerations, The 12000 BTU AC unit listed here: http://www.lg.com/us/air-conditioners/lg-L1210ER-window-air-conditioner ..shows that it has a rating of 115VAC/60Hz with a draw of 10.2 Amps. They also quote a rating of 1110 Watts. If you were to use an inverter such as the following: http://www.donrowe.com/inverters/sw1220.html ..the "optimum" efficiency is listed at ~90%. It would be more likely that you may see 85% efficiency. That would take an input power of 1110 Watts / 0.85 = 1306 Watts. Converting the wattage requirement to Amps at a nominal 12VDC would be 1306W / 12V ~= 110 Amps. This amperage delivered for the two hours that you specified is 220 AmpHour. A possible battery may be the Trojan model T-145 shown in this brochure on page 11 of the PDF. The quoted 5-Hr rate is 215 AH. http://www.trojanbatteryre.com/PDF/TRJN0159_RESeriesColl.pdf To re-charge the battery from a solar array will require an array capable of restoring the 220 AmpHour of energy during one summy day period of time. The solar panel showen here: http://www.saferwholesale.com/High-Quality-280-Watt-Solar-Panel-p/dsp- 280_watt_panel.htm ..is good for 280 Watts on a good sunny day. One could estimate that you have say 8 hours of sunlight on days when you would like the air conditioner to function. Also let us guess at solar battery charger efficiency of 85%. Some simple math shows that: (1306W / 0.85) / 8 hr = 192 It looks like one of the above panels could keep your battery charged. Two panels would give you a nice extra capacity in case you wanted to swipe some system power for something else besides the AC unit. -- Michael Karas Carousel Design Solutions http://www.carousel-design.com M #### Michael Karas Jan 1, 1970 0 [This followup was posted to sci.electronics.design and a copy was sent to the cited author.] [This followup was posted to sci.electronics.design and a copy was sent to the cited author.] I have a small 10x10 foot room I am considering cooling with a small 12000 btu AC, but I am wondering if it's possible to set this up to be powered by solar? The AC would not be run continuously, just long enough to cool the room off for sleeping, maybe 2 hours per day. I'm thinking a car battery with an inverter and the battery charged by solar cells, but I don't know if this would work or even how to begin. I also want to keep this as low cost as possible and stick with a simple design that works. Any suggestions would be appreciated. Thanks, AA Some considerations, The 12000 BTU AC unit listed here: http://www.lg.com/us/air-conditioners/lg-L1210ER-window-air-conditioner ..shows that it has a rating of 115VAC/60Hz with a draw of 10.2 Amps. They also quote a rating of 1110 Watts. If you were to use an inverter such as the following: http://www.donrowe.com/inverters/sw1220.html ..the "optimum" efficiency is listed at ~90%. It would be more likely that you may see 85% efficiency. That would take an input power of 1110 Watts / 0.85 = 1306 Watts. Converting the wattage requirement to Amps at a nominal 12VDC would be 1306W / 12V ~= 110 Amps. This amperage delivered for the two hours that you specified is 220 AmpHour. A possible battery may be the Trojan model T-145 shown in this brochure on page 11 of the PDF. The quoted 5-Hr rate is 215 AH. http://www.trojanbatteryre.com/PDF/TRJN0159_RESeriesColl.pdf To re-charge the battery from a solar array will require an array capable of restoring the 220 AmpHour of energy during one summy day period of time. The solar panel showen here: Adapting the solar panel to the battery requires the use of a high efficiency switch mode converter/charger unit. Those are available from various solar equipment suppliers. It may very well be more cost effective to find an integrated solution that combines the solar cell / battery management with the sine wave inverter to the 120 or 240 VAC. The OP's idea to try to support his 12000 btu AC unit for$500 is just
not in the game plan. There is a portable 1800 Watt solar power
gererator available at Northern Tool for ~$1800 that may be of interest for those that want a more turnkey solution. http://www.northerntool.com/shop/tools/product_200496999_200496999 Do check carefully as to your application with the above unit as it is not clear if it even produces a simulated sine wave output or a full sine wave output. Some loads will requre full sine output. N #### nospam Jan 1, 1970 0 hamilton said: WOW, this looks doable. Really? The first (discounted) price I find for a T-145 battery is$209 and it is
6v so you need 2 of them for $418. Cycled to 80% discharge they claim a life of around 700 cycles. Replacing around 2.2kWh of mains electricity with a cycle of these batteries gives a kWh life of around 1540kWh. Where I live 1540kWh of mains electricity costs around$300 (and that is
after political interference with the market to heavily subsidise eco green
bollocks power generation)..

Is constantly loosing money on just the batteries never mind the capital
expense and depreciation of the panels, control electronics and
installation doable?

Only if mains electricity is really expensive where you live or if you can
steal the equipment.

K

#### [email protected]

Jan 1, 1970
0
[This followup was posted to sci.electronics.design and a copy was sent
to the cited author.]

I have a small 10x10 foot room I am considering cooling with a small 12000
btu AC, but I am wondering if it's possible to set this up to be powered by
solar? The AC would not be run continuously, just long enough to cool the
room off for sleeping, maybe 2 hours per day. I'm thinking a car battery
with an inverter and the battery charged by solar cells, but I don't know if
this would work or even how to begin. I also want to keep this as low cost
as possible and stick with a simple design that works.

Any suggestions would be appreciated.

Thanks,
AA

Some considerations, The 12000 BTU AC unit listed here:

http://www.lg.com/us/air-conditioners/lg-L1210ER-window-air-conditioner

..shows that it has a rating of 115VAC/60Hz with a draw of 10.2 Amps.
They also quote a rating of 1110 Watts.

If you were to use an inverter such as the following:

http://www.donrowe.com/inverters/sw1220.html

..the "optimum" efficiency is listed at ~90%. It would be more likely
that you may see 85% efficiency. That would take an input power of
1110 Watts / 0.85 = 1306 Watts.

A *big* assumption here is that the inverter can supply the compressor
starting current.
Converting the wattage requirement to Amps at a nominal 12VDC would be
1306W / 12V ~= 110 Amps. This amperage delivered for the two hours that
you specified is 220 AmpHour.

Assuming PF=1.
A possible battery may be the Trojan model T-145 shown in this brochure
on page 11 of the PDF. The quoted 5-Hr rate is 215 AH.

http://www.trojanbatteryre.com/PDF/TRJN0159_RESeriesColl.pdf

To re-charge the battery from a solar array will require an array
capable of restoring the 220 AmpHour of energy during one summy day
period of time.

Double that for 2 hours per day.
The solar panel showen here:

http://www.saferwholesale.com/High-Quality-280-Watt-Solar-Panel-p/dsp-
280_watt_panel.htm

..is good for 280 Watts on a good sunny day. One could estimate that you
have say 8 hours of sunlight on days when you would like the air
conditioner to function. Also let us guess at solar battery charger
efficiency of 85%. Some simple math shows that:

(1306W / 0.85) / 8 hr = 192

It looks like one of the above panels could keep your battery charged.
Two panels would give you a nice extra capacity in case you wanted to
swipe some system power for something else besides the AC unit.

It's not going to work.

T

#### Tom Kupp

Jan 1, 1970
0
I have a small 10x10 foot room I am considering cooling with a small
12000 btu AC, but I am wondering if it's possible to set this up to be
powered by solar? The AC would not be run continuously, just long
enough to cool the room off for sleeping, maybe 2 hours per day. I'm
thinking a car battery with an inverter and the battery charged by solar
cells, but I don't know if this would work or even how to begin. I also
want to keep this as low cost as possible and stick with a simple design
that works.

Any suggestions would be appreciated.

Thanks,
AA
Are you sure you need 12,000 btu's for a 10x10 room? I'm pretty sure my
bedroom is bigger and uses only about 5,900.

D

#### Don Lancaster

Jan 1, 1970
0
Are you sure you need 12,000 btu's for a 10x10 room? I'm pretty sure my
bedroom is bigger and uses only about 5,900.

Not one net watthour of PV solar has ever been generated.
To date, pv anything remains a gasoline destroying net energy sink.

Net pv energy can be expected eight to ten years after the fully
burdened, subsidy free costs drop below twenty five cents per peak panel
watt.

more at < http://www.tinaja.com/etsamp1.shtml >

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552

Please visit my GURU's LAIR web site at http://www.tinaja.com

M

#### mike

Jan 1, 1970
0
I have a small 10x10 foot room I am considering cooling with a small
12000 btu AC, but I am wondering if it's possible to set this up to be
powered by solar? The AC would not be run continuously, just long enough
to cool the room off for sleeping, maybe 2 hours per day. I'm thinking a
car battery with an inverter and the battery charged by solar cells, but
I don't know if this would work or even how to begin. I also want to
keep this as low cost as possible and stick with a simple design that
works.

Any suggestions would be appreciated.

Thanks,
AA
Give it up.
If you have access to the power grid, there is no, zero, none, not any
cost-effective PV generation scheme.
Unless you can steal the components, that is.
There were schemes where the government stole money from me to subsidize
your PV scheme, but those programs are pretty much exposed and defunct.

PV is great for school crossing signs where the high cost of the solar
component
is still WAY less than the cost to dig up the street to get power from
100 feet away.

Put your budget into better insulation.
Needing a 12000 BTU unit to cool 100 square feet at night suggests that your
insulation is deficient.
Consider ground-source cooling.
Depends a lot on where you live.
Right now, it's 86F outside, 107F in the attic and 65F under the house.
Stays about that temperature under the house year-round.

I once had a fantasy about reworking an electric blanket to pipe
chilled water thru it. Never got past the concept stage. Maybe with a
heat exchanger under the house...
If you've ever tried to share a waterbed, you're aware how tiny differences
in water temperature make a huge difference in comfort level. Wouldn't
take much energy to keep the water cool enough.

RE the other suggestions... if you do attempt this, consider that it
can take a LOT more power to start an AC compressor than to run it.
Make sure your inverter can handle the surge.

M

#### miso

Jan 1, 1970
0
Nice, but the two panels are only 45 watts. Assuming an 1800 watt
draw for 1 hour, it would take:
1800 / 90 = 20 hrs
of continuous sunlight to recharge the battery (assuming perfect
weather and probably tracking the sun).

A few years ago, I built a spreadsheet to size the solar array and
battery pile needed to run a local ham radio repeater.
<http://802.11junk.com/jeffl/rf-calc/solar-repeater-207.xls>
Just replace the repeater drain characteristics with the A/C numbers
and see what happens. I'll try it when I get back from service calls.
Incidentally, the basic assumption is that the solar array must
recharge the batteries within a 24 hr period or the load will
eventually run the battery to zero.

I have some 95Ahr AGMs and they are ball busters. The biggest Odyssey
battery is 125Ahr. You can always put batteries in series like they do
in data centers, but that won't drive the repeater directly.

It isn't clear from your spreadsheet if you are taking into account both
the loss of the charger and the charge efficiency of the battery itself.

Based on an APU battery evaluation project for a company I can't name,
the Odyssey batteries were the best, with Dekka a close second. They
are selling APUs for military use, basically to remove generators from
sensitive locations. An additional product line is to replace APUs in
trucks with battery storage.

For example:

A

#### amdx

Jan 1, 1970
0
Thanks. Although this design looks interesting, it far exceeds the
budgetary amount I had in mind ($500 max, sorry I didn't specify initially). I thought maybe I could put something together quick, simply, and cheaply but doesn't really look that way. Unless someone else has some other suggestions. AA Ya, I did the calculations using my cost per KWh of 12.1 cents. We recently had a cost reduction of about 1 cent per KWh. Yea! I made the assumption you would use the air conditioner 2 hrs a day for 6 months of the year. I got a yearly expense of$48.89.
It's a shame electricity is so cheap, or not!
Mikek

A

#### amdx

Jan 1, 1970
0
Heat pumps (like an air conditioner uses) are a poor choice for power-stingy
applications. If your room has one or two occupants, you'll need to
pump at least a few hundred watts of heat (the metabolism of living
persons guarantees that) as well as dehumidifying...

So, consider a heat-storage unit (a big water tank?)
and some heat exchangers (like car radiators, with a fan)
so you can cool the water in the night, and use that reservoir
of cool material to relieve the hottest hours of the next day.

So-called swamp coolers (basically a big wick kept damp with water,
that evaporates outdoors) can also deal with a bit of heat, without
burning big motor-power.

Build your bedroom in the form of this fridge.

http://www.dailymail.co.uk/sciencet...ing-shed-helps-poverty-stricken-Africans.html

Mikek

J

#### John S

Jan 1, 1970
0
RE the other suggestions... if you do attempt this, consider that it
can take a LOT more power to start an AC compressor than to run it.
Make sure your inverter can handle the surge.

Are you sure? Do you mean "power", or do you mean VA? Lots of VA at low
RPM (except for losses), but less power. And, it doesn't last long. I
doubt it takes more power to start than to run.

M

#### mike

Jan 1, 1970
0
Are you sure? Do you mean "power", or do you mean VA? Lots of VA at low
RPM (except for losses), but less power. And, it doesn't last long. I
doubt it takes more power to start than to run.
Yes, you're right. Takes more amps to start a compressor than to run it.
I've never tried to measure the starting VA vs starting Power.
And we've not discussed the potentially significant (power) factor that
inverters are likely rated in power into a resistive load. Running
a motor ain't resistive.

But, your nitpicking is missing the point of the exercise.
It's gonna take an inverter (system) with a LOT more peak capability
to start a compressor than to run it. Matching what it says on the
air conditioner name plate is likely to result in failure.

An inverter that switches off to protect itself from the start transient
or worse, lets the smoke out, isn't gonna be very useful in this,
or any application.

D

#### Don Lancaster

Jan 1, 1970
0
Yes, you're right. Takes more amps to start a compressor than to run it.
I've never tried to measure the starting VA vs starting Power.
And we've not discussed the potentially significant (power) factor that
inverters are likely rated in power into a resistive load. Running
a motor ain't resistive.

But, your nitpicking is missing the point of the exercise.
It's gonna take an inverter (system) with a LOT more peak capability
to start a compressor than to run it. Matching what it says on the
air conditioner name plate is likely to result in failure.

An inverter that switches off to protect itself from the start transient
or worse, lets the smoke out, isn't gonna be very useful in this,
or any application.

Almost all home sized synchronous inverters consume at least 150 percent
of the value of the electricity sent through them.

More at < http://www.tinaja.com/etsamp1.shtml >

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552

Please visit my GURU's LAIR web site at http://www.tinaja.com

M

#### mike

Jan 1, 1970
0
Can you explain how this works?
I can understand how a breeze can cause evaporation cooling the contents
as low as the dew point.
But the article describes how the sun's rays cause the evaporation.
Can't see how the "rays" do anything helpful?????

W

#### Winston

Jan 1, 1970
0
I have a small 10x10 foot room I am considering cooling with a small
12000 btu AC, but I am wondering if it's possible to set this up to be
powered by solar? The AC would not be run continuously, just long
enough to cool the room off for sleeping, maybe 2 hours per day. I'm
thinking a car battery with an inverter and the battery charged by solar
cells, but I don't know if this would work or even how to begin. I also
want to keep this as low cost as possible and stick with a simple design
that works.

Any suggestions would be appreciated.

Consider an evaporative cooler.

--Winston

P

#### P E Schoen

Jan 1, 1970
0
"AA" wrote in message
I have a small 10x10 foot room I am considering cooling with a small
12000 btu AC, but I am wondering if it's possible to set this up to be
powered by solar? The AC would not be run continuously, just long
enough to cool the room off for sleeping, maybe 2 hours per day.
I'm thinking a car battery with an inverter and the battery charged
by solar cells, but I don't know if this would work or even how to begin.
I also want to keep this as low cost as possible and stick with a
simple design that works.
Any suggestions would be appreciated.

Check this out:
He says the small A/C uses just 500-600 watts, so the 280W solar panel could
produce about 1200-1500 W-Hr per day, and that's enough to run the A/C for
2-3 hours.
Or this:
There were some other ideas:
That's a 24VDC air conditioner running on about 20A, which is 480W. But 6000
BTU/hr is about 1800W. It was probably measured with the compressor off or
under minimum load. But it may be possible to replace the AC motor of an A/C
unit with an efficient DC motor, eliminating most of the conversion losses.

Here is a homemade swamp cooler:

Here's a complete off-grid cabin with 12V appliances:

You could use a Peltier effect cooler. Here is a 150 BTU/hr (12V 4A 48W)
unit for $30 plus$13 shipping. Get 10 of them for 1500 BTU/hr. You might be
able to combine these with a swamp cooler by thermally connecting the hot
plate to the water. You pay for the difference in temperature, so with cold
water you'll have a lot colder air (or better heat removal, actually) for
the same cost.
http://www.ebay.com/itm/12-Volt-The...841?pt=LH_DefaultDomain_0&hash=item1e62607299

Actually you might be able to use a dorm size refrigerator or a 12V camping
fridge and stick it in a window with the door open and a small fan running.

Finally, it might be possible to get a car or truck air conditioning unit
and drive the compressor with a DC motor.

Sometimes you just gotta think outside the (ice) box!

Paul

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