diy solar

diy solar

New to here have some questions for the more seasoned folks on here if you have the time.

satiricalsniper

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May 16, 2021
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Clearing off a new homestead, getting power ran was going to be expensive, came across a deal on some used panels I've got 16 250 watt panels on the way.
I'm building a skoolie with an addition, so around 400 sq ft. The skoolie will be mobile in about a year or so, but for now my wife has surgeries so it's going to be stationary for her recovery. I'm going to mount the panels on racks not on the bus for the time being (depends on her recovery when I'll be making the switch)
I need to run I think a 8k-10k btu air conditioner to cool during the summer (I'm in Alabama Central part). I've been looking at a 10cu ft Galanz fridge and for the
AC I've been looking at the Midea U shaped those will be the 2 biggest draws. My son (who is in an out due to work and college ) will just be using a fan, a desk lamp and charge a Dell gaming laptop ( I think the charger is 95 watts) and I'll have my and my wife's laptop.
A. Is 16 panels going to be enough to power all of that
B. Would it be smart to separate the system into 3 parts with the AC on it's on set and battery bank, Fridge and Kitchen (small marine water pump) on it's own and then the small draw on its own?
C. Battery bank size wise what would I need.
I've done a lot of research, and if it was just me I'd go on that , but with my family involved I'm trying to make the most informed decisions I can. Thanks for any help , advice, that you can give. Equipment recommends, setups, all of that will be welcome as I comb through all of this.
 
use some of the internet planning sites to get an early idea of the load you are designing to, such as:
The tricky part is not only WHAT the device load will be, but how often that load will be running per day.

the you can convert watthours per day into your needed battery bank size.
watt-hours = AH * volts

so lets play with some numbers:
If you are going to use up 4000watt-hours in a day and you have a 24V system that will be 167 AH of available power.
no system is remotely 100% efficient so you had better add in some nice headroom...maybe 25% for conversion losses.
167*1.25 = 209AH you will "use" in a day so you need to replenish at least that much

Your solar panels will need to recharge those batteries in the available sun light producing time which depends on your local area and position on the planet (and do not forget the angle of your panels unless you plan on using solar tracking panels)
daily watt hours from you panels is just their wattage * sunlight hours

16*250 = 4000
For lots of reasons this is NOT what you will really get!!!
conversion losses, cable losses, panel dirt/shading, birds and squirrels deciding to sit down for a bit, panels getting hot, etc. etc.

you will need to think about several side issues such as:
1)how long do you need to run on batteries? (think about the most cloudy days in a row you can recall in your area)
2)design to use no more than 75% of your battery capacity if lifepo4, less than 50% if lead acid
3)your inverter must be able to handle the PEAK demands, but you can control that to some extent (if AC is on nobody use the microwave oven)
4)solar panels will ALWAYS produce less than you think...and everybody consumes more power than they think; it just works out that way hehe

fyi, I have one of those small mideaU units... VERY cool air output while only consuming 600w!
 
use some of the internet planning sites to get an early idea of the load you are designing to, such as:
The tricky part is not only WHAT the device load will be, but how often that load will be running per day.

the you can convert watthours per day into your needed battery bank size.
watt-hours = AH * volts

so lets play with some numbers:
If you are going to use up 4000watt-hours in a day and you have a 24V system that will be 167 AH of available power.
no system is remotely 100% efficient so you had better add in some nice headroom...maybe 25% for conversion losses.
167*1.25 = 209AH you will "use" in a day so you need to replenish at least that much

Your solar panels will need to recharge those batteries in the available sun light producing time which depends on your local area and position on the planet (and do not forget the angle of your panels unless you plan on using solar tracking panels)
daily watt hours from you panels is just their wattage * sunlight hours

16*250 = 4000
For lots of reasons this is NOT what you will really get!!!
conversion losses, cable losses, panel dirt/shading, birds and squirrels deciding to sit down for a bit, panels getting hot, etc. etc.

you will need to think about several side issues such as:
1)how long do you need to run on batteries? (think about the most cloudy days in a row you can recall in your area)
2)design to use no more than 75% of your battery capacity if lifepo4, less than 50% if lead acid
3)your inverter must be able to handle the PEAK demands, but you can control that to some extent (if AC is on nobody use the microwave oven)
4)solar panels will ALWAYS produce less than you think...and everybody consumes more power than they think; it just works out that way hehe

fyi, I have one of those small mideaU units... VERY cool air output while only consuming 600w!
The Refrigerator says it uses around 292 kwh a year it'll obviously have to be on 24 hours a day with her insulin and such.
The AC I really looked into and the Midea seemed like the most efficient choice, it does hit the 90's quite a bit during the summertime
so it'll be on at least 8 hours.
I can offset the AC at night if need with a generator if need be. What are you thoughts about splitting the system up, I have a spare 750w inverter I thought I could throw the kid with a 12v battery and 2 of the panels for his needs. That'd leave me 14 to work with (I can add more) if needed.
I'm most concerned about the fridge to be honest, occasional microwave use (but I'll be smart about it) I'm just seeing about your thoughts on how many batteries 12v 100ah batteries I'd need to safely power that fridge overnight. I appreciate you taking the time to reply.
 
Perhaps build a carport for the bus. Mount panels on carport. The bus will be in the shade so that will help. One AC might struggle to cool bus in the summer sun. I would have a screed in patio with outside kitchen and a few fans. Just guessing here but 8 of the 302 amp cells would probably do it. Those would probably be around$1000. The problem is the time to get them delivered is 60 to 120 days. You need to order batteries ASAP if you are going that route.
 
Perhaps build a carport for the bus. Mount panels on carport. The bus will be in the shade so that will help. One AC might struggle to cool bus in the summer sun. I would have a screed in patio with outside kitchen and a few fans. Just guessing here but 8 of the 302 amp cells would probably do it. Those would probably be around$1000. The problem is the time to get them delivered is 60 to 120 days. You need to order batteries ASAP if you are going that route.
If you have a moment could you link me those batteries? Thanks so much.
 
The Refrigerator says it uses around 292 kwh a year it'll obviously have to be on 24 hours a day with her insulin and such.
no no no...
you have to think in terms of devices actively "using" power, not just that their switch is on.
No refrigerator runs 24x7, unless its broken or you left the door open.
most heating/cooling devices "cycle" thruout the day, they will be actively perfoirming their function and then, they will "sleep" for some time.

so be careful when computing your system load or you will end up with an insanely high number.
A computer or router is "always on"..heating and cooling devices are more like an automatic microwave, they will have multiple big events during the day and then draw very little power.
 
when it comes to AC, its about the cost to move heat from one space to another space.
The problem is that you have many sources of heat trying to get IN.
one small window unit will have zero chance to cool a sheet metal uninsulated small shed in the sun...too much heat coming IN.
You need to really think about overall heat flow, the sun beating down on an uninsulated structure is, well, a really powerful space HEATER hehe
also remember that other devices, such as a fridge, as also heat producers!!.

perhaps hit some of the "skoolie" sites to first get a feeling for how they insulated their vehicles or I think you are fighting a losing battle.
a typical school bus AC unit is something like a 50000-100000BTU unit!!!
 
Ok, I gotcha, so we are thinking in terms of idle and peak, the decision to go solar was more of a need to then what was anticipated. I used to build houses, any of that stuff, no issues, but the solar in terms of all the equipment and stuff I'm having to have more of a crash course than I'd like. When looking at appliances I'm trying to make sure (like the Midea) they seem to be the most efficient in our price range and adjusted accordingly.
 
when it comes to AC, its about the cost to move heat from one space to another space.
The problem is that you have many sources of heat trying to get IN.
one small window unit will have zero chance to cool a sheet metal uninsulated small shed in the sun...too much heat coming IN.
You need to really think about overall heat flow, the sun beating down on an uninsulated structure is, well, a really powerful space HEATER hehe
also remember that other devices, such as a fridge, as also heat producers!!.

perhaps hit some of the "skoolie" sites to first get a feeling for how they insulated their vehicles or I think you are fighting a losing battle.
a typical school bus AC unit is something like a 50000-100000BTU unit!!!
Insulation part is already being done, was prepared to do a shipping container home, but ended up with a bus on a deal, so I'm applying some of the lessons learned on that initial research on this one. I can shade it with a carport since I'm going with detached racks, i'll insulate the sides and floor as well as removing many of the windows and turning them into solid sides with insulation. Thanks for everything you are bringing up, so let's say if I can get it insulated and shaded. Would 10 panels of the 250w panels be enough to power the 10k btu Midea (in your opinion) Would 10 panels a 2000w inverter and applicable battery storage be enough to do that? (I've got no idea how many of the 12v100 ah I'd need. Just talking about for the AC. Like I said again, thanks for all the feedback.
 
lets do some back of envelope fun!!!!

so using that solar sizing site I linked and putting some random alabama zip code to get sunlight hours...
I added in a 12000BTU window AC unit (which will use a bit more power than the midae but its close)...
Then I figured in the summer it will be on 1/3 of the time so 8hrs per day...thats 9600Whours/day
9600Wh / 24V = 400Ah/day just for the AC unit... or in hourly terms you are consuming about 17AH on average all day (obviously more during day, less at night, but then solar is a bit weak at night hehe)

you have 16 *250W panels = 4000Wh and using a random AL zipcode it shows you will have around 4 "sun hours" per day.

4000 / 24v = your solar charger is outputting 160AH; you are "using" lets just call it 20AH during the day, so that leaves 140AH's into you battery pack for four hours which should "just" charge up your 400AH 24v bank

this is a really crude calculation that, well, ignores lots of things(solar panel angles, dirt, clouds) but it gives you some numbers to play with...

the good thing about AC calculations is that you get more sun hours per day in the summer which is when you will need it the most!
 
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