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Old 05-01-2018, 11:01 PM   #1
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Solar powered A/C

Hey Everyone,

I see the question from time to time of running air conditioning from solar. The consensus is that it is, for the most part, impractical.

I have, however, seen a few interesting exceptions. Here is one that I found interesting :http://forum.solar-electric.com/discussion/350889/automatic-control-of-off-grid-mini-split-a-c#latest
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Old 05-02-2018, 05:04 AM   #2
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Hey Everyone,

I see the question from time to time of running air conditioning from solar. The consensus is that it is, for the most part, impractical.

I have, however, seen a few interesting exceptions. Here is one that I found interesting :Automatic control of off grid mini split A/C ‚ÄĒ northernarizona-windandsun
I intend to run a mini split off solar, like my mentor Juan:
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Old 05-02-2018, 07:52 AM   #3
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Not practical compared to most noobie expectations.

If you know what you're getting into, have the roof space and are willing to both live within limitations and spend a lot up front, no problem.
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Old 05-02-2018, 09:08 PM   #4
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Most would say a generator running an ac is cheaper, in the long run, even with the cost of fuel, at least at the moment.

I suppose if one wanted to spend $10k plus on a solar powered electrical system, one could run an ac unit most of the time.

How many watts of panels do you envision?
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Old 05-02-2018, 10:34 PM   #5
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In clear sunny climate 800W is just enough to run (some, small) aircon from panel output directly.

1200 would give your bank some recharging.

Doubling that would help with cloudy days and ensure you can get your bank to true Full.

But even with 1000's of bank AH, running the aircon **off the batteries** for more than a few minutes, is just time-shifting when you have to start the genny.

So may as well run aircon directly off the genny.
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Old 05-03-2018, 07:00 AM   #6
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How many watts does a bus sized mini split use when running?
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Old 05-03-2018, 08:54 AM   #7
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How many watts does a bus sized mini split use when running?
I am considering this 12K BTU mini split.

The spec sheet for this and other Pioneer mini splits is here. For the 12K 120V mini split the spec sheet says between ~500-1600W (~1100-1200W nominal).
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Old 05-03-2018, 10:33 AM   #8
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2000W of solar panels would correspond to the 800W outlined above as a minimum starting point for 5k BTU, for running off the panels only during peak solar conditions.

Call it 3kW panels to cover suboptimal insolation, and (some) concurrent bank recharging.

And sophisticated soft-start add-ons would likely be required for startup load levels.

And forget about running from batteries, even just a few hours' worth would weigh like a ton.
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Old 05-03-2018, 11:17 AM   #9
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2000W of solar panels would correspond to the 800W outlined above as a minimum starting point for 5k BTU, for running off the panels only during peak solar conditions.

Call it 3kW panels to cover suboptimal insolation, and (some) concurrent bank recharging.

And sophisticated soft-start add-ons would likely be required for startup load levels.

And forget about running from batteries, even just a few hours' worth would weigh like a ton.
FWIW, some, many (most?) mini splits have inverters to modulate outdoor unit fan speed. This feature also enables a soft start or ramp up of current draw.

Skip ahead to the 10 minute mark of this video more on this ramp up. Of course my hero Juan will be running his mini split off ~24kWh of lithium, a 5kW Victron inverter and a butt load (~3600W?) of solar...
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Old 05-03-2018, 05:25 PM   #10
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As above, If you know what you're getting into, have the roof space and are willing to both live within limitations and **spend a lot up front**, no problem.
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Old 05-06-2018, 03:36 PM   #11
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Ac off battery is easily obtainable. I bought a wrecked Tesla and salvaged the batteries for 3k. I can run my two minisplits on just two Tesla modules for 12 hours. With my 3kw of solar you canít touch the batteries. My two 9k btu minis only pull 350w a piece. My fridge uses more electric than my acs do.
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Old 05-06-2018, 05:42 PM   #12
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Ac off battery is easily obtainable. I bought a wrecked Tesla and salvaged the batteries for 3k. I can run my two minisplits on just two Tesla modules for 12 hours. With my 3kw of solar you canít touch the batteries. My two 9k btu minis only pull 350w a piece. My fridge uses more electric than my acs do.
No doubt that is a workable setup.

For some of us, 3kw of solar and two Tesla modules is not "easily obtainable". I am working on resolving that one lotto ticket at a time....
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Old 05-06-2018, 05:47 PM   #13
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Yes that's not a normal definition of "easy".

Many people start off thinking a few panels and a couple hundred AH bank will do.

I would not use a fridge that pulled more than 6A @12V myself.

And no way would I use any LI chemistry DIY system in a mobile context other than LFP. Maybe after open-hardware BMS+fire safety systems have proven themselves in a few years.
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Old 05-06-2018, 06:40 PM   #14
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Yes that's not a normal definition of "easy".

Many people start off thinking a few panels and a couple hundred AH bank will do.

I would not use a fridge that pulled more than 6A @12V myself.

And no way would I use any LI chemistry DIY system in a mobile context other than LFP. Maybe after open-hardware BMS+fire safety systems have proven themselves in a few years.
What happened to "If you know what you're getting into, have the roof space and are willing to both live within limitations and spend a lot up front, no problem"?

And I agree, using "DIY systems" on a skoolie is just crazy talk...
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Old 05-06-2018, 08:48 PM   #15
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3kw of solar covers the roof entirely it would seem. 30, 100 watt panels. This plus batteries, charge controller, wire ,etc. Is close to $10,000 or so. Not in my budget for now. Must say if it were i would really think about it though. I just do not like running a genny when boondocking
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Old 05-06-2018, 10:52 PM   #16
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What happened to "If you know what you're getting into, have the roof space and are willing to both live within limitations and spend a lot up front, no problem"?

And I agree, using "DIY systems" on a skoolie is just crazy talk...
I've got no problem with DIY LFP for those know what they're doing and willing to spend the money.

Trying to assure safety with EV packs is not just "far from easy" but IMHO a fool's errand to bother trying at this point in time.

Obviously you and others may feel differently, but don't try to say it's easy for regular folk.
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Old 05-07-2018, 12:23 AM   #17
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Ha itís all perspective, I guess what I meant is itís easy to see that lithium is the only way to go for ac off grid and a decent amount of solar as well. Also as far as buying an rv well you can easily spend 300k on a prefabíd nice rv but still not have a decent power setup. For 10-20k you can have an off grid system thatís reliable and maintaince free for 10-15 years and even then youíll only lose 10% of original potential.
5.4kw 24.9v Tesla batteries are 444 18650 cells fused on 6 bus bars in series and disconnect themselves from the rest of the pack if any cell has an issue. Truly a genius design for safety. 18650 cells as far as energy density, safety and cost go well nothing scales near their performance.
Itís about 200$ per kw right now. 400$ for 48v system.
I scaled my system to never need to charge my batteries above 80% which if you charge lithium regularly over 80% itís determental to them. Also if you donít drain them to 20 -30% the cycle count is changed from 2000 to a much higher number. You basically cycle them every month or two to maintain proper life to the cells.
In all honestly it is very easy to design a system such as I have and never have to worry about power and as cost goes compared to retail is nominal. Inverter, charge controller, panels, wires, fuses, batteries and of course $. With Victron software I can make addons to do anything automatically as far as maintaince goes.
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Old 05-07-2018, 01:25 AM   #18
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I'm half of mind to say most people converting school busses into homes aren't regular folk, but I know there's a bell curve to all this too.

Here's about how far I am into converting EV batteries into a storage array. I won't lie, it's been a lot of work. I wouldn't expect "normal" people to build these things.

We also don't expect normal people to build RVs, but here we are talking about doing it. I think it has more to do with the comfort level and experience of something that has more immediate feedback to doing things badly.

When you build a bus badly, it doesn't manifest right away.






Quote:
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I've got no problem with DIY LFP for those know what they're doing and willing to spend the money.

Trying to assure safety with EV packs is not just "far from easy" but IMHO a fool's errand to bother trying at this point in time.

Obviously you and others may feel differently, but don't try to say it's easy for regular folk.
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Old 05-07-2018, 07:21 AM   #19
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Originally Posted by john61ct View Post
I've got no problem with DIY LFP for those know what they're doing and willing to spend the money.

Trying to assure safety with EV packs is not just "far from easy" but IMHO a fool's errand to bother trying at this point in time.

Obviously you and others may feel differently, but don't try to say it's easy for regular folk.
John, your fellow forum member are providing actual examples of what they and others are actually doing or have already done. But you ask no questions and acknowledge nothing, providing only negative and inflamatory (humble??) "opinions".

By calling those of us who are integrating (or have already integrated) EV batteries into our skoolie electrical systems "fools", you insult and alienate me and likely many others.

If that was your goal: mission accomplished...
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Old 05-07-2018, 07:53 AM   #20
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I am considering this 12K BTU mini split.

The spec sheet for this and other Pioneer mini splits is here. For the 12K 120V mini split the spec sheet says between ~500-1600W (~1100-1200W nominal).
I have 3 minisplits in a custom c onfiguration in my house (custo menclousres and completely revamped controls to be able to operate them from a computer vs the crappy remote they ship with)..

my 2 12000 BTU Units when maxxed out run somewhere in the 1200 watt range in cool mode.. in heat mode ive seen them maxx out higher someplace in the 1350-1400 watt range.. (wattage is measured using CT's on a GreenEye Monitor )...

there are minisplits made that delete the first part of the power supply and accept DC directly.. 12v or 24 volt depending on the unit. from what I understand there is a bit of added efficiency in the power circuitry of those mini splits but ive not used them..

one thing to keep in mind with mini splits is size them such that you dont run them over 80% very often.. and your heat pump efficiency drops quickly as you go below 36 degrees f outside temp (if you plan to use them for heat / cool)..

the efficiency levels of the units drop if they are running on max.. quite a bit.. so size them such that they arent being run hard or you will be using a lot more power for not much more gain ..

I never flow-hooded mine and did the calculations to get the exact numbers but ive watched my wattage meeter jump pretty quickly and only see a little gain in cooling (measuring rise on the condensor and drop in the evaporator) when im at the top of the band..

Oversizing a mini split is not detrimental like oversizing a standard AC unit.. minisplits will simply slow down their fans and compressor to still maintain a dehumidifying air temp without the constant cycling when they are over-sized..

in my 1400 sq ft house i have a collective ability with my zoned / ducted system to go from 5000 btu all the way up to to about 50,000 btu if I maxx the blower and all the units... my lifestyle is such that I like the windows open till I cant stand it anymore then i close up and kick the AC on.. of course i want to cool down quickly and then pull humidity and maintain it cool until i repeat the cycle at some point.. my house had a 2 ton standard Home A/C in it (2004) when I then built the custom system (2009).. and my overall HVAC energy usage is 25% less with the custom system than it was with the standard AC.. (which would run for hours and hours if I got the house hot)... the comfort level is 200% better

probably more than you wanted to know but information is power..
-Christopher
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