Solar powered A/C

[john61ct]

No, I'm saying **drop-ins** are sub-par.

Ideal is to buy quality bare cells and figure out how to care for them, with the BMS **functionality** that suits your use case and priorities.

Many do without balancers, just basic monitoring and LVC, but it does take knowledge, research, basically a new hobby.

Other way is the packaged system, handholding, training, but it gets way pricey.

In the US market where all this is 10x the price of a decent lead bank, to me that's hard to justify, need to get decades of longevity and ROI thst far out is very risky.

[Grinn and Bare it]

I see what you're saying. However, this Skoolie project is going to be my hobby for a while. I won't have time for another sub-hobby. LOL

[kazetsukai]

Going for an off-grid A/C system myself, the way I calculated it- you should look at the splits first, and go for maximum efficiency. Whatever that efficiency costs you will save you money in $$$ and panels.


I was on the fence for a long while between a 29 SEER 12k BTU and a 37.5 SEER 9k BTU unit. Efficiency versus capacity. After speaking with an engineer from the manufacturer I was looking at, I concluded the 9000 would be enough for the time being and went that route.


Heating to 75 in 20 degree weather, the split I purchased draws ~1300W at the maximum. Average energy use was 7kWh/night. I never intended to run heat off solar, those numbers make it possible with some upgrades. Pay for the efficiency if you want to run off of solar, as chances are you will save 10x whatever you paid for that efficiency in batteries and panels needed to run a less costly unit.


And almost needless to say, your efficiency will only go as far as your insulation. I'm currently testing my split setup/insulation and intend to keep the bus heated the whole duration of winter while I make adjustments.

[Grinn and Bare it]

Originally Posted by kazetsukai

Going for an off-grid A/C system myself, the way I calculated it- you should look at the splits first, and go for maximum efficiency. Whatever that efficiency costs you will save you money in $$$ and panels.


I was on the fence for a long while between a 29 SEER 12k BTU and a 37.5 SEER 9k BTU unit. Efficiency versus capacity. After speaking with an engineer from the manufacturer I was looking at, I concluded the 9000 would be enough for the time being and went that route.

.

37.5 SEER!? I thought 22 was the max. A Google search didn't render any results over that. Please explain.


Also, you mention the AC unit but not the solar panel/ battery bank. What's "under the hood" to power your unit?

[kazetsukai]

Originally Posted by Grinn and Bare it

37.5 SEER!? I thought 22 was the max. A Google search didn't render any results over that. Please explain.

Its a company out of Florida called InnovAIR. The units I was looking at (the 9000BTU won):

12000 BTU, 29 SEER

https://www.ebay.com/itm/12000-BTU-M...sAAOSwyNxcWaWv


9000 BTU 37.5 SEER

https://www.ebay.com/itm/9000-BTU-Mi...cAAOSwxHlcWaYh

Originally Posted by Grinn and Bare it

Also, you mention the AC unit but not the solar panel/ battery bank. What's "under the hood" to power your unit?

Not enough as it is. The bus is staying plugged in over the winter.


I currently have 3x 5.3kWh 24V Tesla battery modules, 700W in panels, and an 8kW split phase inverter. Victron Energy 150V/100A charge controller. My panels can't keep up with my desired loads (obviously) but I don't have the budget to upgrade right now. Going for that spring/tax season, probably 2000W-3000W in panels. I'll also double the battery bank, which should leave me quite comfortable to run AC. I'll spend the time between now and then improving insulation and measuring energy usage.



I put some thermal images up on my build page a couple days ago, as well as pics of the split setup. I have some more updates on that front I'll probably post tomorrow.

[Grinn and Bare it]

Originally Posted by kazetsukai

Its a company out of Florida called InnovAIR. The units I was looking at (the 9000BTU won):

12000 BTU, 29 SEER

https://www.ebay.com/itm/12000-BTU-M...sAAOSwyNxcWaWv


9000 BTU 37.5 SEER

https://www.ebay.com/itm/9000-BTU-Mi...cAAOSwxHlcWaYh
.

Ah-hmm, You realize Miami is No.1 in terms of fraud in all of Florida and probably high up there in the US. While I see your pages. The US Energy Dept. has set minimums of 12 SEERS and the maximum SEERS is 22. So, it's not that I don't believe You, I don't trust Miami. And I live a few miles north of Miami. Buyer beware!! Definitely monitor that system. I don't know how to determine that you're getting more than 22 SEER

[Grinn and Bare it]

Originally Posted by kazetsukai

I currently have 3x 5.3kWh 24V Tesla battery modules, 700W in panels, and an 8kW split phase inverter. Victron Energy 150V/100A charge controller. My panels can't keep up with my desired loads (obviously) but I don't have the budget to upgrade right now. Going for that spring/tax season, probably 2000W-3000W in panels. I'll also double the battery bank, which should leave me quite comfortable to run AC. I'll spend the time between now and then improving insulation and measuring energy usage.



I put some thermal images up on my build page a couple days ago, as well as pics of the split setup. I have some more updates on that front I'll probably post tomorrow.

For such an efficient unit, I would think your 15+kw battery bank could run it for a while. Obviously the panels need some bolstering. So you're saying that you run your ultra efficient unit off house electric, through your battery bank?? Or just direct from your house?

[kazetsukai]

Originally Posted by Grinn and Bare it

Ah-hmm, You realize Miami is No.1 in terms of fraud in all of Florida and probably high up there in the US.

I'm not sure this is entirely relevant.

Originally Posted by Grinn and Bare it

So, it's not that I don't believe You, I don't trust Miami. And I live a few miles north of Miami. Buyer beware!!

I don't care if you live in Pleasantville: Buyer still beware. I think its a good idea to recommend people vet who they purchase through regardless.

Originally Posted by Grinn and Bare it

The US Energy Dept. has set minimums of 12 SEERS and the maximum SEERS is 22.

Fujitsu has a 33 SEER 9k unit and a 29.3 SEER 12k unit. I doubt 22 is the "maximum" in 2019. The InnovAirs are also AHRI Certified, and I've heard of up to 40 SEER 9ks (by a "Carrier Midea" brand). The premium, low capacity end of the lines tend to have some especially efficient units, seems like the tradeoff is a larger interior unit.

Originally Posted by Grinn and Bare it

Definitely monitor that system. I don't know how to determine that you're getting more than 22 SEER

I'm not certain either. I don't have a controlled environment where I know the precise R values to measure. What I do know is that this thing is doing something I'd have considered impossible a week ago. I am monitoring electrical usage closely as well as temperature deltas. All indications thusfar say to me its the real deal.

And again I'd refer you back to the AHRI certifications. Efficient units are out there.

[john61ct]

BTU rating vs

**actually measured** Wh/Ah per 24hrs

is a good metric to compare systems IRL

[kazetsukai]

Originally Posted by Grinn and Bare it

For such an efficient unit, I would think your 15+kw battery bank could run it for a while. Obviously the panels need some bolstering.

There are a couple factors to this. One, The voltage range of the Tesla packs is 19V-25V, roughly. Most 24V inverters, including mine, will not work below 20V as the "normal" 24V range is 21V-28V. So about 20%-30% of my bank is not usable through my inverter.



Whatever, I don't care. The less deep my discharges the more cycles I get. And most of my system runs DC, so when the inverter shuts off my lights / automation doesn't go out.


Second, I would like to be able to run the AC through 2 or 3 days of overcast, with little to no solar input. On those days its likely to cool down, so not a big deal, but I have other appliances like an electric clothes dryer I'd like to be able to spin up without worrying too much about capacity. 30kWh seems to me like a good starting point, given I plan to full time and don't ever want to run a generator.



That and if something goes wrong with my generation capabilities I have a good buffer to resolve the issue before the lights go out.

Originally Posted by Grinn and Bare it

So you're saying that you run your ultra efficient unit off house electric, through your battery bank?? Or just direct from your house?

I have a bunch of stuff in the bus now that cannot be allowed to freeze. Knowing this I quickly disconnected the inverter from my main panel last week and ran a 30A cord out to the bus from my garage. Thus everything AC is currently powered directly from my house. I intend to do a load test on my inverter by backfeeding its output into my home the same way at some point. DC stuff still uses the batteries.

[ComfortEagle]

Originally Posted by kazetsukai

...voltage range of the Tesla packs is 19V-25V, roughly. Most 24V inverters, including mine, will not work below 20V as the "normal" 24V range is 21V-28V. So about 20%-30% of my bank is not usable through my inverter.

A Tesla pack...? Shhh.... Don't tell John...

I am in a similar situation in that my "48V" battery pack is more like a nominal 45V, and I have the low voltage cut out set to ~40V.

For what it's worth, my 48V (4kW) Magnum Energy inverter is good down to 36V. It's a pretty nice piece of gear. I see their 24V inverters (2kW and 4kW) have a range of 18V to 33V.

https://www.solar-electric.com/lib/w...-Inverters.pdf

[john61ct]

Yes those are just crazy expectations, modern-life mod cons on solar-only, with a 3-day buffer.

Not to mention very dangerous.

Of course "can" be done, but to do it **right**, will need $10,000+, maybe 40x8' of panels, and likely still need a lot of genset runtime anyway.

[john61ct]

Yes Magnum's a top choice for inverter/chargers.

IMO got an edge over Victron's

[Dem0072]

Originally Posted by Grinn and Bare it

That's for the optimism and info. I probably wouldn't be using it all day everyday. But it would be nice to have on humid nights.


My bus shopping day is quickly approaching. The excitement is palpable! I've still got some time to research the AC / Solar array issue. I'm a Noob so I will not feel silly asking this question. How many lithium batteries = 10kw? I'm used to seeing amp hours on batteries. I'm looking at buying 4 or 6 Battle Born 100 amp hour batteries. Is that enough? Would I need more to accommodate the AC along with the usual daily uses?? As always Cheers and Thanks!

4 battleborns would be very generous. Any more and I'd question what you're trying to run with it. Here's a quick tool to help you with the math: https://www.inchcalculator.com/ah-to-kwh-calculator/

So your 100ah batteries, if run at 24v give you 2.4kWh, so yes 4 of them would get you to the 10kWh mark.

I'd stay away from 12v battery systems and the low cost of isolated modules unless you become adept at wiring in parallel/series arrays with quality bus bars and get neurotic about checking for voltage inconsistencies, and balancing the battery bank. Also forget about 12v solar systems (PWM controllers). Just go straight for MPPT (24v). You'll save money on the wiring, the batteries will charge faster, and more safely. Your battery bank will look a lot more civil. And far less of the energy from the roof will go to waste.

I know I mentioned 3000w, which is overkill in a lot of ways. 3000w is you trying to be a desert summertime warrior for the lore of it. Using a mesh sun screen to keep some of the heat off the side of the rig, and shooting for 2400w is probably a lot more practical, and on a full sized bus means you might have room for a roof deck. If spending time outside with a view and accepting the climate is of importance and an ice box isn't the goal, you can regain a lot of comfort on a couple thousand watts.

With the mini split, just remember - the highest efficiency you could possibly attain happens when you step up to 230v instead of 110v. That's where you exceed 21 SEERs, and get more cooling power per watt while having the smallest duration duty cycle possible. So your average wattage can be set at a budget of about 300w, if it runs only the 10 hottest hours of the day, that's 3kWh. If it runs 20 hours a day, that's 6kWh, or just over half of your banks budget. But the MPPT charge controller and having enough panels are important to replenish it, not every day is perfectly sunny. So you're building to some extent for less than sunny days. It sounds like a lot for a little comfort, but also consider the big guys with $50k RV's with dual roof mounted units are pulling over 4,000 watts continuously when those systems are on. You're going for a commercial/residential grade setup that offers a lot more efficiency, and does the job adequately on 1/4 of the power.

[kazetsukai]

Originally Posted by john61ct

Of course "can" be done, but to do it **right**, will need $10,000+, maybe 40x8' of panels, and likely still need a lot of genset runtime anyway.

With that much panel area I think you'd have plenty of panels. I'm starting to see daily yields of 11kWh from my similarly sized PV array, although I'm limited by storage capacity at this point. It really comes down to batteries if you have over around 2400W in PV, I think. (My 9000 BTU split tops out at around 1.2kW, averages around 700W draw over the day, bigger splits would require more).

If lets say you had a 50kWh bank you could probably get away with 24/7 given you didn't have a week of solid overcast. At 10kWh I am scraping the bottom of the bucket keeping the inside heated, its not enough. One contributing factor is that my cabin is not (yet) separated from the driver's area, so I do experience huge losses up front, but the rest of the bus is pretty well insulated.

I'm going for off-grid climate control and I will invest what it takes to get there. Rooting for anyone else who tries the same, but one does need realistic expectations. 2kW of PV is enough to power AC during sun, perhaps that's enough for some people. Its the no-sun part that is hard to get right.

[sproutroot]

Originally Posted by Grinn and Bare it

37.5 SEER!? I thought 22 was the max. A Google search didn't render any results over that. Please explain.

smaller units get more efficient. when you say the highest is 22, you're probably talking about central air in a house (2 ton units) - even then Lennox makes a 26 SEER.

there are a lot of 9k units over 30 SEER. 37.5 is damn high for such an affordable little kit, but it's probably not a ridiculous exaggeration.

[TheArgobus]

kazetsukai, you ever consider putting the panels on two motors to tilt and spin, and having them track the sun across the sky based on latitude and date/time? That would bump up your solar output by quite a bit, I'd imagine.

[kazetsukai]

Originally Posted by TheArgobus

kazetsukai, you ever consider putting the panels on two motors to tilt and spin, and having them track the sun across the sky based on latitude and date/time? That would bump up your solar output by quite a bit, I'd imagine.

I think I can say conclusively, its not worth the effort. At least not to me- the roof is filled with panels and I'd have to do all or most of them that way. And keep in mind, I have a 3050W array, and I see days with 2400W-2700W input for several hours just lying flat any time there's sun.



Now if you have a few hundred watts up top that is easy to add a _simplistic_ tilting system, you might even double your yield doing so. Complex sun tracking is more expensive than just putting more PV up.



My current problem isn't solar output, its storage. I need 2-4x the battery capacity to do what I want, 80% of the sun I could be capturing I cannot store. Most of the time I see any significant solar input, its either early morning charging the batteries back up to full or someone is running the microwave/coffee maker/AC. Imagine having 3000W up panels up top and getting only 50W-100W input in full sun. That's a good portion of my every day at this point, and I'm almost empty on batteries early morning if I run the heat overnight...

[john61ct]

Originally Posted by kazetsukai

one does need realistic expectations. 2kW of PV is enough to power AC during sun, perhaps that's enough for some people. Its the no-sun part that is hard to get right.

Yes an impractical demonstration is one thing, but actually running enough aircon to keep a 40' x 8' space cool in Arizona say 16 hours a day is another.

The realistic goal is reducing genset runtime by X%, save some fuel, and not annoy the neighbors as much late at night.

[dzl_]

Originally Posted by Grinn and Bare it

Hey John, I'm going through this thread and I notice that you come across as a Debbie Downer. LOL. I totally get your point of view though. Since I'm just a Noob, I appreciate your attempt to bring everyone down to earth and add a bit of perspective. I think I get it, it's very expensive to run AC from solar due to the up front costs, space and weight restrictions, etc.. But some of us like to think outside of the box, have high hopes and take advantage of all the solar energy we can to make up for years of paying the power companies

John might come across as overly negative here, but the argument he is making, is logical and worth stating, and for the most part he is the only person in this thread stating it.

To you it may seem like he is being a debbie downer, maybe an element of truth to that, but he is also doing a lot to keep this conversation grounded. While I agree with y'all that A/C can be done on solar alone if you have the money, the roof space, and possibly tempered expectations, I agree with him on several points that I think deserve to be highlighted.

1. Non LFP battery chemistries, used EV cells etc, are definitely not for beginners. They are inherently more risky than Lifepo4, and less beginner friendly, I don't doubt that many of you use them safely, and that systems can be designed in a way that significantly mitigates the risk. BUT y'all are not beginners, consider how often here, people confuse amps and amp-hours, amp-hours and watt-hours, etc. So BMS, thermal runaway, LVD, HVD, C-rate, charge curve, discharge curve, SOC, etc, is another language. I think its important when we talk about more advanced systems, especially potentially explode-y battery types that require a lot of DIY work and deeper electrical knowledge, to underscore that these systems are not for beginners, the risk averse, or anyone expecting a plug-and-play system.
2. Consistent A/C off of solar+batteries alone, is doable in some cases, and there are some good reasons to do so, but economics is probably not one of the reasons. It will increase the cost of your system substantially in most or all situations, and even then your expectations might need to be tempered. I think this is John's main point, people are confusing this with him being a 'debbie downer' or saying it can't be done, but if you read his comments closely, he has repeatedly acknowledged that it can be done, just at a high cost. As a general rule, I think we would all concede this is true.
3. Newbies often have an idea that solar is 'free energy' (it is), but overlook the cost of the system needed to generate and store that energy. Storage is the big issue, solar panels are relatively cheap, but storing electricity in batteries is still pretty damn expensive (Kazetsukai, you might be interested to know the person that really hammered this point home for me was Dacian 'electrodacus'). I think people (myself included) often overlook the cost of scaling up a system to handle a high draw appliance off solar/batteries alone. If you are willing to use a generator occasionally, or forego some of the creature comforts your used to in a grid tied home, or even just adjust to only using the A/C during peak solar hours, you can get by with a smaller system.
4. I agree with John that its probably useful to underscore to newbies that they likely will need to temper their expectations. Many of y'all are proving that A/C on solar+battery power is doable, but most of y'all have arrays measured in multiple kWh, have above average electrical knowledge (or paid someone who does), have battery banks well above average and way bigger than you would need without A/C, and have devoted a lot of time and money to achieving your goals. Your systems are great examples of what can be done, but are also much larger, and in some cases much more sophisticated than the average system.

All this said, I don't plan on having a generator (or A/C for that matter), and do connect with the idea of sustainably powering as much as possible via PV and love to see people pushing the limits of this. The above are just my opinions based on the little bit I've learned and I'm far from an expert, especially when it comes to A/C.

I just wanted to stand up for John, as I think he is adding a lot of value to this thread (as are most of you). I've disagreed with John on a number of issues, and think that sometimes he can be a little overly dogmatic, but I also usually see the logic of his position even when I disagree with him, and value his opinion.

Powering A/C off solar+batteries is doable but should be carefully considered, you should run the numbers (Watts & Dollars & maybe sq. ft.), and think carefully about your priorities and the trade-offs you are making. If you can make it work in your situation that is awesome, and at the end of the day, not every decision we make is purely economic or based on efficiency. There are some things that are worth the tradeoff

And on a semi-related note, I'm very impressed with some of your systems! Kazetsukai, I'm looking at you specifically, and love seeing someone using the SBMS0, I'd love to learn more about how your system is configured.

I've rambled on long enough.. carry on


edit: I hope, this didn't come across as grumpy or critical or otherwise negative, it certainly isn't meant to, and I think this has been a good discussion so far, the differing opinions have been constructive