Help for beginner with small cabin solar

I hope I'm putting this question in the right place! As a novice, I need advice from folks who aren't trying to sell me something.
In our cabin, we have a small harbor freight solar system running a few lights/stereo/phone charger with no problem. However, we want to stay up there more regularly so will need more power. We estimate we'll use about 400 amp hours a day. We're located in northern Idaho so temp gets into the teens and lots of gray winter days.
Does anyone have suggestions for what type of battery (acid v lithium), size of charge controller, and how many panel we should get. We're on a budget but don't want something that's not going to last a while. I've done a ton of research but I'm still not sure I'm getting it! 😑
Also, any thoughts on solar generators? Would that be a better way to go?
Thanks for any input!!
In our cabin, we have a small harbor freight solar system running a few lights/stereo/phone charger with no problem. However, we want to stay up there more regularly so will need more power. We estimate we'll use about 400 amp hours a day. We're located in northern Idaho so temp gets into the teens and lots of gray winter days.
Does anyone have suggestions for what type of battery (acid v lithium), size of charge controller, and how many panel we should get. We're on a budget but don't want something that's not going to last a while. I've done a ton of research but I'm still not sure I'm getting it! 😑
Also, any thoughts on solar generators? Would that be a better way to go?
Thanks for any input!!
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- 400 AH * 12 volts = 4,800 Watt*Hours per day (combination of 12 VDC and 120 VAC loads?)
4,800 WH per day is a lot of energy for a "cabin"... I suggest that a very efficient cabin/small home can be a "near normal" electrical existence (LED lightning, energy star refrigerator, RV or small well pump, clothes washer, laptop, cell charger)... But lets go with your numbers (this is your cabin, not mine- 4,800 WH per day * 1/0.85 inverter eff (drop if all DC) * 2 days storage * 1/0.50 max planned discharge 1/12 volt battery bus = 1,882 AH @ 12 volt battery bank
That is a lot of battery bank @ 12 volts... I would either look more at 3,300 WH per day and a 24 (or 48 volt battery bank) or at a pure 48 volt battery bank and run everything from a 120 VAC inverter:Coeur d'Alene
Measured in kWh/m2/day onto a solar panel set at a 42° angle from vertical:Average Solar Insolation figures
(For best year-round performance)
-Bill
One of these things is not like the other. How much open space do you have to install solar panels? What's your budget? And, "amp hours" is pretty meaningless unless you also mention a voltage, because Ah doesn't measure energy..
I worry about your expected energy use, 500 amp hours, I'll assume at 12 volts, is only 6000 Watts (watts is a measure of power). That is a large load for a solar electric system during winter. See Bill's calculations above.
I live on about 3-4000 watts in the winter months and it's difficult with long periods of overcast weather to maintain battery health without a generator. So let us look at your loads and see if we can suggest alternative energy or systems to cut those down before suggesting a large system with a generator.
I appreciate all y'all's knowledge...it is impressive!
Thanks for your help!!
I'm not sure what you are saying here?
So you added a battery and a couple more panels?
Did you also add a charge controller? If so what did you add?
Do you know what the energy star rating is for your fridge?
Most fridges will use 1000 watt hours or more each day, even small ones. If you look at your regional daily solar insolation (Bill looked this up for you) You are only averaging 2 hours of direct sunlight a day. So if you wanted to run an efficient fridge you would want enough array(solar panels) to produce 1000 watts of energy each day to break even. I could do the math, but losses for energy use from stored lead acid batteries in a solar electric system is roughly 50% efficient, losses include the inverter conversion, the battery efficiency and the solar panels derating. So figure 2000 watt hours needed from the 2 hours of direct sunlight, so about 1000 watts of array.
Now understand that the sun doesn't shine everyday! So you need storage to get you through the overcast days. So a 2000 watt load converts too about 2000watthrs/12volts=166 amphours of storage for each overcast day you need to supply energy from your battery bank. A pair of golf cart batteries store about 210 amp hours of energy at 12 volts.
A solar electric system MUST be inefficient! You need to produce enough wattage so that the batteries are fully charged a couple times a week.
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Now things that may be a problem, inexpensive inverters are typically modified sine wave and will use more wattage with motors like a compressor. 12 volt inverter with higher wattage tend to need large cables to prevent voltage drop. They may also use more energy idling than quality inverters.
You don't want to add new batteries to old, and want batteries to be the same size so they share the load and charging equally.
The nice thing about charge controllers, is they are amperage based, so a 60 amp charge controller can handle roughly a 1000-1200 watt array at 12 volts, and 2000-2400 watt array at 24 volts...
More later, feel free to ad info on system and loads...
I'm sorry I dont understand this better. I am trying and we'd like to stop paying rent by moving out to our cabin.
- 100 watts * 5 hours = 500 Watt*Hours
- 100 mph * 5 hours = 500 miles driven
Amps and Amp*Hours is like Watts and Watt*Hours... The difference is we are "missing" the voltage for Amps and Amp*Hours to know about your loads/etc...- 100 amps is a rate--But it could be at 12 Volts DC (like your battery bank) or at 120 VAC (like the output of your AC inverter/utility power)
- Watts = Volts * Amps
- Watt*Hours = Volts * Amps * Hours (time)
For example, 1.4 amps for your refrigerator (I know it is 120 VAC--just an example of the confusion just working with Amps and multiple voltages in an off grid Battery+AC Inverter system):- 12 VDC * 1.4 Amps = 16.8 Watts
- 120 VAC * 1.4 Amps = 168 Watts
And there gets to be more confusion in AC power (Watts vs VA, power factor, cosine, inverter losses, etc.)... But we can skip most of that for now.- 110 Watts * 0.50 duty cycle * 24 hours per day = 1,320 Watt*Hours per day (assuming warm weather, average usage--A realistic number for a relatively efficient refrigerator/freezer)
And the battery bank:- 1,320 WH per day * 1/0.52 off grid solar eff for AC power * 1/1.88 hours of sun per average December day = 1,350 Watt array "break even"
And, to account for some bad weather, you should only plan on using 50-65% of your predicted harvest for your "base loads" (i.e., refrigerator--You cannot turn it off for a few days of bad weather).- 1,350 Watt array (Dec Break Even) / 0.65 bad weather "fudge factor" = 2,077 Watt array to run fridge "full time" in December and some other loads when it is sunny (washer, vacuum, TV, laptop, etc.).
Or--You can go with a smaller solar array and battery bank, and run a (for example) Honda eu2200i "inverter-generator"---It will take about 2 gallons of gasoline per day to run your fridge and other (relatively light) loads (something like a 300-400 Watt average load, upwards of 1,800 Watts at full power when needed (microwave, etc.). And pay something like $2-$4 per gallon for gasoline/diesel/propane/etc.- 30 Watts * 10 hours per day = 300 WH per day
- 300 Watts * 10 hours per day = 3,000 WH per day
Smaller loads that run for many hours per day can really hit your solar usage... A microwave running 15 minutes per day at 1,400 Watts:- 1,400 Watts * 1/4 hour = 350 WH per day
Or a small laptop and microwave can use the same amount of energy per day... And a desktop could use 2x more than your refrigerator.I suspect you are heating with wood or gas, as well as water heating/cooking. I recently proposed a bare minimum system for a fridge, laptops and lights for a someone with a better year round solar insolation, roughly 3 hours a day average in winter.
They wanted to start as inexpensively as possible and grow a system, so It would sort of work for you. Remember that growing a system will be somewhat more expensive than starting with one to size, but an idea of the rough costs now would likely help.
Samlex makes a nice 1200 watt inverter/charger in 24 volt. This would allow you to charge the battery bank with a generator through the inverter/charger. It runs $600, Northern Arizona Wind and Sun doesn't carry it, but might price match if you talk with them (They sponsor this forum)
https://www.donrowe.com/samlex-evo-1212f-hw-pure-sine-inverter-charger-p/evo-1212f-hw.htm
You will likely want a 2000 watt array or larger to minimize winter generator run time, but if you can charge with the generator you can look for deal on solar panels in your area or online. Shipping is often very expensive for large solar panels. I would suggest a minimum array of 600watts so you could just run the generator for a couple hours in the morning and the solar would likely top off on sunny days. BUT I would go ahead and get a larger charge controller so you wouldn't need to replace it for a larger array. The FM80 has a reasonable price now at under $500 and should be able to handle an array of 2000 watts. ;
Outback FM80 Charge Controller | Northern Arizona Wind & Sun (solar-electric.com)
I'm a fan of Midnite's Solar classic 150, which Would be fine for a bit larger array but runs a tad over $600 for the solar only version;
MidNite Solar Classic 150-SL Controller | Northern Arizona Wind & Sun (solar-electric.com)
Since you are in northern Idaho, I seriously suggest stopping in at Backwoods solar. They are located in Northern Idaho at;
1589 Rapid Lightning Rd, Sandpoint, ID 83864. They won't have great deals other than their bargain basement, but are local and will have knowledge in your area, which will make a big difference in suggesting systems for your environment. Ask for their catalog/learning manual! I has helped a lot of people figure out things, I think I got one 25 years ago, maybe longer!!!
Off-Grid Solar Electric Systems | Solar Panels | Solar Energy Shop (backwoodssolar.com)
So with a inverter/charger and a controller and a small array, you could work on your battery bank. You could likely get by with 4 golf cart batteries for the next 4-5 years... remember they age together, so you won't want to upgrade until they are near dead.(To be cost effective) You can add solar panels to your array too reduce run time on your generator...
Sam's club and Costco have golf cart batteries for around $90 each. They are very generous on cores! I've used lawn tractor batteries as exchange/cores!
Here is my current build, costs from about 2012, I got good deals and costs will be roughly the same other than solar panels.
It's going to be close to cost effective! or Off grid at 26 cents a KWh! — northernarizona-windandsun (solar-electric.com)
The usual suspects for cheap solar panels are;
SunElectronics
Sun Electronics – World's Lowest Solar Panel Prices
and Santan Solar
Wholesale Solar Panels in Phoenix, Arizona (santansolar.com)
Also there is a 26% federal tax credit (against any tax liability) for the next 3 years. But read carefully when looking at these solar discounters. used panels should not qualify (I've never heard that said directly, but IRS frowns on double dipping)
I’ve been scraping on these panels for a hour or so ☹️ Yesterday
If it warmed up to 20o today I may of cleared 3 or 6 panels and had some charging , but I got 12” of snow today ☹️ Chances are I won’t see these panels till sometime in March .
Since I have Limited electrical experience This was the easiest route I bought the system from AWS
my panels 15 295 watt panels and mounting iron ridge 1000 came from my local supply house .
The 3600 watt inverter draws a lot of power just being on but I can charge thru it at 17/2000 watts .
so I bring water up in a 275 gallon tote or collect it off my deck roof .