Help with a basic solar lighting and water pump system
justjonesin
Registered Users Posts: 5 ✭✭
Hi,
I am hoping to wire a very simple 12 volt dc system for a tiny one room off grid guest cabin I just built. I have some questions I hoped could be answered. I’ want to run 4-5 small 5 watt led lights and a small dc water pump for teeth brushing and water bottle filling, etc. I have a single 75 watt solar panel of which I was planning on connecting to a charge controller then to a battery (battery to controller first) and then a fuse block and from there to the lights and pump. I also want to be able to completely unplug the battery to take it to my main house (on grid) where I can trickle charge the battery with a charger if the solar isn’t keeping up with the demand in the guest cabin.
My question are:
1) where in the circuit should I put fuses, what kind of fuses, and what size?
2) what size wire is appropriate from battery to charger, charger to fuse block, fuse block to lights and pump?
3) can I install a circuit breaker or shutoff switch to easily remove battery if it needs charged?
4) how do I ground the system if that is needed?
I am hoping to wire a very simple 12 volt dc system for a tiny one room off grid guest cabin I just built. I have some questions I hoped could be answered. I’ want to run 4-5 small 5 watt led lights and a small dc water pump for teeth brushing and water bottle filling, etc. I have a single 75 watt solar panel of which I was planning on connecting to a charge controller then to a battery (battery to controller first) and then a fuse block and from there to the lights and pump. I also want to be able to completely unplug the battery to take it to my main house (on grid) where I can trickle charge the battery with a charger if the solar isn’t keeping up with the demand in the guest cabin.
My question are:
1) where in the circuit should I put fuses, what kind of fuses, and what size?
2) what size wire is appropriate from battery to charger, charger to fuse block, fuse block to lights and pump?
3) can I install a circuit breaker or shutoff switch to easily remove battery if it needs charged?
4) how do I ground the system if that is needed?
Comments
Copper wire is expensive, so you don't buy larger than needed.
Wire size is related to length of run, and size of load ( how far will the pump be from the battery, and how much power does it consume)
Same for lights
same for charging circuit
Fuses are sized to protect the wire. Need wire calculations first
There are some automotive quick connects for batteries, I've not used any of them
Grounding is a touchy subject, someone else can address it.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
To take a stab at your system...
- 5 watt lights * 5 hours per night = 25 Watt*Hours
- 1.7 amp pump * 12 volts * 1/4 hour per day (15 minutes) = 5.1 WH per day
- 3 AH * 5 volts (12 volt cell phone charger) = 15 WH per day
- total = 25+5+5= 35 wH per day
Typically, a nice system has 2 days of storage (works out well for solar charging and supplying load currents) and 50% max planned discharge (better battery life) for a battery bank:- 35 WH per day * 1/12 volts * 2 days storage * 1/0.50 max discharge = 15 AH @ 12 volt battery bank
To charge such a battery--5% rate of charge for weekend/summer/sunny weather usage... 10%-13% for full time off grid/year round use:- 15 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 14 Watt array minimum
- 15 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 28 Watt array nominal
- 15 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 37 Watt array "typical" cost effective maximum
And then there is sizing the array for your daily loads and amount of sun (and season of usage). Guess around Helena Montana, fixed array facing south:http://www.solarelectricityhandbook.com/solar-irradiance.html
Helena
Measured in kWh/m2/day onto a solar panel set at a 43° angle from vertical:Average Solar Insolation figures
(For best year-round performance)
- 35 WH per day * 1/0.61 off grid DC solar system eff * 1/2.94 hours of sun per day = 20 Watt array for "November break even"
Your 75 Watt panel (assuming good quality, glass panel for permanent outdoor mounting) could easily support 2-3x larger AH battery bank than 15 AH @ 12 volts.You could also save powering the water pump with a "foot pump" system (how is water getting to the cabin? A 5 gallon container, cistern, etc.?):
https://www.amazon.com/Whale-Marine-BABYFOOT-OPERATED-GP4618/dp/B003ELUZHK
Before we get into the details of sizing the battery/charge controller/wiring--Are my guesses for your location and usage correct?
-Bill
Cheers,
Jason
Lead Acid batteries really need a lot of time "on charge" to properly and fully charge. 1/2 of day blocked sun--It does make it much more difficult.
Li Ion (LiFePO4) batteries do well in those conditions--But do not like cold--Anything below (roughly) 40F and they have lots of restrictions on charging and discharging (below freezing, the batteries are basically "in storage"). Lead Acid batteries work pretty well in subfreezing conditions (yes, temporary loss of capacity in 0F weather, but they do not freeze as long as they are kept relatively well charged). Also just cycling an FLA battery (flooded cell lead acid) in an insulated box keeps them warmer.
You really need to nail down your power/energy needs. The solutions for a small system vs a large(r) system are different. Like what kind of vehicle do you need--Motorcycle, small car, pickup, or Mac Truck. 200 feet of a small 75 watt array worth of cable--May not be a good idea (voltage drop, lots of copper, $$$). However a few 1,000 Watts of array and a 100 Vmp or even 400 Vmp array (there are high voltage solar charge controllers--They just are expensive and usually larger capacity)--And 200 feet can be done reliably.
Using a Kill-a-Watt type meter (if you end up using an AC inverter--Highly recommended for anything more than just a small 12 volt system) to measure your AC loads... And there are DC AH/WH meters too that are pretty cheap these days:
https://www.amazon.com/s?k=kill+a+watt+meter&ref=nb_sb_noss_2
https://www.amazon.com/s?k=dc+AH+meter&ref=nb_sb_noss_2
You do have to keep track of costs and complexity... Solar power is not cheap--So getting high efficiency appliances, LED lighting, Small Laptop computer, "solar friendly" water pumping, etc. all help to save energy and costs.
-Bill
So...per day...this should be my total consumption roughly:
Lights - 25wh
water pump ~5 wh
cell charger ~15wh
composting fan 20.16wh
Roughly 65 watt hours/day when the cabin is used. And 20.16 wh per day when not in use.
Since I have partial shade I was thinking about using the victron mppt 75/15 and a Dakota Lithium 23ah battery. And the 6 circuit blue sea fuse block. I used a wire size calculator for the wiring coming out of the fuse block and it spit out 16/2 wire for the pump, lights, and usb charger when I entered the wire length and current of each appliance.
What I’m still confused about is
-what guage wire should I use between the charge controller and the battery?
-do I need a fuse between the panel and the charger, or between the charger and the fuse block, if so what kind and what size?
-since I have a fair amount of shade and may not be able to get the battery recharged, what kind of shut off can I install (and where) for safely unhooking the battery to swap a discharged battery with a freshly charged (charged on the grid at my home with a charger) battery?
-will the bms actually stop the battery from charging if it gets below freezing or is that something I manually need to control?
Thanks again for all the help!
> Since I have partial shade I was thinking...
NO. STOP . Panels do not produce power in partial shade. They are solar panels. You need to go the the store and get shade panels. Those will be made in 2086, if I recall correctly.......
Do not fall for the lies sales droids tell you. A panel with shade actually produces little usable power.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
You fuse/breaker circuits based on the wiring ratings (example, 14 AWG is typically 15 Amps max)--You can use smaller fuses/breakers if you wish (especially if the load/fixtures at the end of the run are smaller AWG wiring). Fuses and breakers are there to prevent wiring from overheating/starting a fire.
The other thing to check, especially for low voltage 12 VDC wiring... You (typically) would want no more than ~0.5 volt drop from the battery bank to the load... Say you run 4 amps for 12 feet @ 12 volts and want a max 0.5 volt drop. Using a simple voltage drop calculator:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=12&phase=dc&noofconductor=1&distance=12&distanceunit=feet&eres=4&x=0&y=0
Result for 14 AWG
Voltage drop: 0.24
If you did the same calculation with 16 AWG wiring:Voltage drop percentage: 2.02%
Voltage at the end: 11.76
Result for 16 AWG
Voltage drop: 0.39
As you can see--It does not take much current/length to get "excessive" voltage drop on 12 volt circuits.Voltage drop percentage: 3.21%
Voltage at the end: 11.61
And that leads us to what AWG for the Charge controller to battery bank... Say you have a 75 Watt panel with Vmp~17.5 volts:
- 75 Watts / 17.5 volts Vmp = 4.3 amps Imp
- Use a 1.25x "safety factor" for solar wiring: 4.3 amps * 1.25 NEC derating = 5.4 amps
Using a simplified NEC wiring capacity chart:https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
Using 14 AWG is more than large enough... You can use smaller wiring--But heavier AWG will not hurt. Fusing/breaker for 14 AWG wiring (controller to battery bank) 15 amps or less, but at least 5.4 amps * 1.25 NEC derate = 6.75a ~ 7 amp minimum (to prevent false trips during normal operation of solar charging).
The other thing to look at is the voltage drop from controller to battery bank... Suggest a max of 0.05 to 0.10 volts drop for a 12 volt charge controller (you want the controller to have "accurate" battery voltage"). Using a voltage drop calculator for 14 AWG / 4.3 amps / 3 feet one way wire run for this calculator:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=12&phase=dc&noofconductor=1&distance=3&distanceunit=feet&eres=4.3&x=45&y=25
Result
Voltage drop: 0.065
Again, keeping wiring length short and "heavy" from battery charger to battery bank is critical for good operation (quick/accurate charging).Voltage drop percentage: 0.54%
Voltage at the end: 11.935
You typically only need fuses/breakers (combiner box) for solar arrays when you have 3 or more parallel panel connections. The fuse protects a shorted solar panel/wiring from the other 2 or more solar panels feeding the short (check panel specs for series protection fuse rating).
To "swap" the battery--You would want two switches (at least)... One for the solar array, and the other for the solar charger to the battery bus. Always turn the solar array off first, and the controller->battery bank second. And reconnecting, controller->battery on first, and solar array second. The Charger->Battery bank you can use a switched circuit breaker to both "protect" and switch with the same single device (the array side could be a breaker or a simple switch--Your choice if you don't need a combiner box).
There are lots of different BMS designs out there--Some shutdown the battery connection if the voltage/current/temperature is out of spec... Others do less.
Li Ion batteries are relatively new to the solar world--And older controllers may not shutdown charging (or loads if they have LVD--low voltage disconnect--connection).
Foir example, the newer Morningstar MPPT controllers will shutdown charging in cold weather:
https://www.solar-electric.com/morningstar-prostar-mppt-controller-ps-mppt-25.html
https://www.solar-electric.com/lib/wind-sun/MSC_Data_Sheet_ProStar_MPPT.pdf
- Detailed battery
programming options allow for advanced battery support for the
latest Lithium, Nickel Cadmium, and Lead Acid battery types.
I am certainly no expert in what is out there that supports Li Ion batteries and their BMS modules... You can call our host (NAWS--Link above for controller) or look around for other controllers/suppliers and they can probably give you some options (that controller I found for Morningstar is not a small/cheap unit).We did not talk about mounting an array farther from the cabin (200 feet away) for better sun--We can go into those details if you want--But basically similar calcustions. Usually an MPPT controller (can take "higher voltage" array) and send the power longer distances with something like 1% to 3% max drop... Just as an example... The above MorningStar controller can take 120 VDC max input voltage. Say we pick 4x 75 watt panels in series with Vmp~17.5 volts and 4.3 amps Imp:
- 4 * 75 Watts = 300 Watt array
- 4 * 17.5 volts Vmp = 70 Volts Vmp-array
- 70 volts * 0.03 max voltage drop = 2.1 volts max "ideal" (can allow larger drop to save copper costs at expense of more wiring losses
- 200 Foot one way wire run... Play with voltage drop calculator:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=70&phase=dc&noofconductor=1&distance=200&distanceunit=feet&eres=4.3&x=61&y=14Result @ 10 AWG / 200 feet / 4.3 amps (3x 75 watt panels in series)
Voltage drop: 1.72
Voltage drop percentage: 2.45%
Voltage at the end: 68.28
Result @ 12 AWG
Voltage drop: 2.73
So, 10-12 AWG cable and 4x 75 watt panels in series with a (not cheap) MPPT controller...Voltage drop percentage: 3.90%
Voltage at the end: 67.27
-Bill