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RFClark
Super Nomad
Posts: 2410
Registered: 8-27-2015
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Air Conditioning off the Grid
I thought a update on our adventures in off the grid AC might be of interest here (or not!)
We like to come down in the Summer but San Felipe can be hot and humid this time of year. Over the last 30 years we have tried a variety of things.
Generators to run AC units, but they are noisy and expensive.
After mini split AC units were available we could run an AC in the day off of solar and at night in one of the bedrooms.
Now with more efficient mini splits and Li Ion batteries we can cool the whole house from 7:00 to 19:00 and the bedroom all night when necessary. We
could cool the whole house all night but it only takes an hour or so to cool down in the morning.
What it takes to do it.
The most important thing is to keep out the heat and humidity in the first place.
1) A white or reflective roof.
2) An as air tight as possible house
3) insulation
4) double pane windows
5) eves that shade the walls.
Having done the above we have about 3KW of solar and 300AH of 24V Li Batteries plus a 9KW propane inverter generator.
We can generate more than 20KW of power per day and keeping the 1200 sq ft house at 76F plus refrigerator and recharging the batteries requires about
16KW per day.
We have a 24K & 18K btu Heat Pump. The 24K unit is on the East side where all the windows are. That and a retractable sun shade cool in the
morning. 90F outside 76F inside load 2.2KW by about 10:00 the load drops off to 1.2KW and we start the 18K unit on the West side. By 19:00 we are
only running the 18K unit and the load is down to 700W.
As it gets hotter at night we probably will need to run the AC longer requiring the generator (9KW inverter) to recharge the batteries. Li Batteries
charge much faster than Lead batteries. They also like the heat.
More as the weather gets hotter!
Feel free to ask questions or make suggestions!
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RFClark
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The house is on the 2nd level so we depend on wide eves. We have some trees but not that tall. We water trees and plants with our gray water plus the
AC generates 5-7 gal of water per day
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mtgoat666
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Quote: Originally posted by RFClark  | I thought a update on our adventures in off the grid AC might be of interest here (or not!)
We like to come down in the Summer but San Felipe can be hot and humid this time of year. Over the last 30 years we have tried a variety of things.
…
More as the weather gets hotter!
Feel free to ask questions or make suggestions!
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Suggestion: Leave town in hot period!
Oh, god! Summer in San Felipe! Sounds miserable. Too hot to go outside in daylight. Too hot to go outside at night. Life is confined to AC indoors,
pinching Pennies to afford the electric bill
Woke!
“...ask not what your country can do for you – ask what you can do for your country.” “My fellow citizens of the world: ask not what America
will do for you, but what together we can do for the freedom of man.”
Prefered gender pronoun: the royal we
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John Harper
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Registered: 3-9-2017
Location: SoCal
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Any particular reason for going 24V? Less wiring expense due to lower amp load?
John
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Russ
Elite Nomad
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Location: Punta Chivato
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This guy has lots of videos and covers solar really well.
https://www.youtube.com/c/WillProwse
Bahia Concepcion where life starts...given a chance!
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larryC
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Registered: 8-11-2008
Location: BoLA
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You answered your own question and 48v is even better. Then there is the savings of less charge controllers. I find that everything seems to just run
smoother at the higher battery voltages.
Off grid, 12-190 watt evergreen solar panels on solar trackers, 2-3648 stacked Outback inverters, 610ah LiFePo4 48v battery bank, FM 60 and MX60
Outback charge controllers, X-240 Outback transformer for 240v from inverters, 6500 watt Kubota diesel generator.
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JDCanuck
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RFClark: I am surprised you get that much daily solar power from only 3kw of panels. Works out to 6.66 hours at full rating per day in winter. I would
have predicted more like 5.5 hours at full rating in winter. I'm impressed to say the least! How many hours per day average does the generator run?
It appears we may have even more surplus solar available with our system than I had thought, but we are still adding in loads and want to have some
excess left over for timed charging of an EV in late afternoons.
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JDCanuck
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RFClark: I have another question I was pondering. Had you looked into water sourced heat pumps for hot water preheating? We find our largest single
load is the hot water demand, almost all of it through electric tank water heaters, 3 in total supplying 60 gal due to the way hot water pipes are run
in cement homes, with a lot of hot water lost to the supply pipes to the demand points.
Even with the shorter supply runs from the 3 hot water tanks, it takes about 1/2 minute to get hot water at sinks and showers. I hate this wasted
energy and was wondering how you handled it.
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RFClark
Super Nomad
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Registered: 8-27-2015
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Goat,
Let’s compare notes over the next few months!
1) Gas prices
2) Water prices
3) Electricity Prices
4) Food Prices
5) Availability of the above
It’s 81F here, the AC is running off the Solar! The cost “0”! The looks on people’s faces when they open their utility bills or fill up
“Priceless”!
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RFClark
Super Nomad
Posts: 2410
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Mood: Looking forward to 2024
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John,
The system here is old. 48V wasn’t a real choice 14 years ago.
JD,
We have 2.4KW mounted on trackers which doubles the output. Hot water is not a problem here! We have on demand hot water and our propane bill
including fuel for the water truck and generator is about $350/year.
We just sold this house, the new place we’re building next door is 48V with 4K of fixed panels and point of use demand hot water. It generates
20KW/day and the solar cost less than 40% of the original system. It’s way simpler too. Should run 4 years with little maintenance!
Generally we don’t run the generator except when cloudy or when running the AC at night.
With point of use demand hot water the runs are all under 6’!
[Edited on 6-8-2022 by RFClark]
[Edited on 6-8-2022 by RFClark]
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TMW
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Location: Bakersfield, CA
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I have a lady friend who wanted to buy an RV and wanted a solar system to run the AC in the summer. I helped her look at several RVs and my conclusion
was that RV salesmen don't know crap about solar systems.
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Bob and Susan
Elite Nomad
Posts: 8809
Registered: 8-20-2003
Location: Mulege BCS on the BAY
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ive been living "off the grid" for 16 yrs
i've never seen anyone air condition their house
using ONLY solar and batteries without the assist of a generator
i have a "million miles" on my diesel generator
mini splits work great
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RFClark
Super Nomad
Posts: 2410
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Come and visit us.
Humidity is our big problem. Right next to the beach the temperature runs mid 80s to 90 degrees daytime going down to 74 around 2:00 to 3:00 in the
early morning currently. Humidity runs 70-90% (we collect around 8 gal of water per day)
Currently we run the AC from 7:00 to 19:30. We hold the temperature around 75F. After sunset it takes 700W to hold that temperature (1200sq ft house).
That would be around 7KW of battery overnight. We have 15KW of Li Ion batteries available to use. When necessary we have a 9KW propane inverter
generator that can charge the batteries at 100A (5KW) and carry the electrical load. So we can generate a nights worth of electricity in under 2 Hrs.
To generate 100% of the 20KW we use a day would require running 5hrs!
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mtgoat666
Select Nomad
Posts: 17549
Registered: 9-16-2006
Location: San Diego
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| Quote: Originally posted by Bob and Susan | ive been living "off the grid" for 16 yrs
i've never seen anyone air condition their house
using ONLY solar and batteries without the assist of a generator
i have a "million miles" on my diesel generator
mini splits work great |
Bobby,
Just need to build bigger, more panels, more batteries.
Also helps to build houses designed for hot environs, large eaves, shade, insulation. The typical gringo box is not good design for desert. Have you
ever been to Middle East and seen pre-AC building design?
Plant some trees! Best thing for a house is shade trees! And a garden w/out trees is undesireable barren wasteland
[Edited on 6-9-2022 by mtgoat666]
Woke!
“...ask not what your country can do for you – ask what you can do for your country.” “My fellow citizens of the world: ask not what America
will do for you, but what together we can do for the freedom of man.”
Prefered gender pronoun: the royal we
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pacificobob
Super Nomad
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Registered: 4-23-2006
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Trees planted today and well cared for can provide significant shade in 5 years.
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RFClark
Super Nomad
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Goat,
You’re right eaves that shade in summer and let the sun shine on the walls in winter are very important, how much your house leaks air matters too.
Solar heating and humid air leaking in are the two big items on your cooling budget that you can reduce. Doing so makes a big difference in how much
energy you need to cool your home.
Batteries are equally important! Most off the grid operations have run generators in the past cause lead acid batteries suck! Li batteries are a game
changer.
Consider how Hyundai gets 60 mpg from a car. They use a gasoline generator operating at an efficient power level to run the car and ether charge or
draw from an Li battery for the difference. The motor can be off quite a bit of the time because the car runs on electricity.
The same idea will work with off the grid systems.
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pacificobob
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In our construction I included a whole house exhaust fan. It's capable of a complete air swap in 5 minutes of use. If the house is warmer than desired
and the outside air temp is several degrees cooler I turn it on .
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RFClark
Super Nomad
Posts: 2410
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We have a solar whole house fan for the big house. We have a 40W exhaust fan in the small house’s garage. We run it at night after it cools down. It
makes a big difference,
Notes on Solar powered AC.
After 2 weeks of warm to hot weather I notice the following:
You can have AC on Solar only.
Air leakage makes a big difference. Wind makes it (the leakage) worse.
Keeping the heat out in the first place is very important.
Tracker solar panels deliver a more constant amount of power for more of the day. 1400 - 1900 watts from 7:30 - 18:00 currently. larger Fixed Solar
arrays deliver more power midday and need more batteries to average out the power as they start and stop sooner.
It takes twice as many fixed panels to equal the power output of a tracker.
Currently we’re averaging 35-40KW of solar per day. We AC the whole house from 8:00 - 20:00 and the bedroom 24 hrs. We have enough extra power to AC
600 sq ft we are building into living space in the garage from 9:00 to 17:30.
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Hook
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Location: Sonora
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Do you REALLY need to try and keep the house at 76F during the day?
When we used to live in San Carlos Sonora during the summer (just as humid, maybe not as hot as SF), we discovered that we were perfectly comfortable
in our house by putting our mini-splits on the de-humidify setting and putting the temp at the max: 84F. This, in combination with ceiling fans,
worked just fine for us.
Try it. It may take a week or so of acclimation, but you might be surprised.
The de-humidify setting seems to run the fan and the compressor much less than the true cooling setting.
It's really all about removing as much of that humidity out of the air.
Think about it. Are you ever uncomfortable in 82-84 degree DRY air in the spring or late fall?
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RFClark
Super Nomad
Posts: 2410
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We generally run around 24-26 C during the day and 25C in the bedroom at night. The humidity runs in the mid 40s. As you point out with lower humidity
at night up to 28C is fine. We open the house to air it out when it’s like that.
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