Newbie needs help with Solar Panel System Setup!

chim · June 2023

Greeting everyone!

I am completely new and learning power electronics right now and wanting to setup a solar panel system.
I will be using one solar panel (a 12V, 200W solar panel), one 20A solar charge controller, and one battery (12V, 100amphr).
All links are below.

I have found a fuse for between the solar panel and controller (again, linked below). However, I am having trouble finding an appropriate fuse for between the solar charge controller and the battery. I keep reading a mixture of using a 20A fuse or a 25A fuse with the 20A controller. I am very confused. I found a manual for the controller and it does say 25A; however, the product webpage says to use a 20A controller.

I would appreciate any insight! Thank you!

1. https://www.renogy.com/200-watt-12-volt-monocrystalline-solar-panel/
2. https://www.renogy.com/rover-li-20-amp-mppt-solar-charge-controller/
3. https://www.renogy.com/deep-cycle-agm-battery-12-volt-100ah/
4. 15A Fuse for between panel and controller: https://www.renogy.com/solar-connector-waterproof-in-line-fuse-holder-w-fuse/?srsltid=AR57-fDarZd1uHMw6wPE--KL6AvE9tc9CvJns0C_kG3Q1RSeUS3v4HVIspo

The ultimate goal is to connect a microcontroller to the battery to install sensors.

BB. · June 2023

Fusing (and circuit breakers) are really there to protect your wiring from overheating/catching fire if there is a short circuit. If you use USA NEC (national electric code), then 14 AWG = 15 fuse; 12 AWG = 20 amp vuse; and 10 AWG = 30 amp fuse.

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

With a single solar panel, there is not really any need for a fuse between it and the charge controller... Your specs:

SPECIFICATIONS

Max Power at STC: 200W

Open Circuit Voltage: 23V

Short Circuit Current: 11.05A

Optimum Operating Voltage: 19.2 V

Optimum Operating Current: 10.42 A

Operating Temperature: -40°F~194°F / -40℃~90℃

Maximum System Voltage: 600 VDC UL

Maximum Series Fuse Rating: 20A

Output Cable: 13 AWG (2.6 ft long)

Your specs say 20 Amp fuse maximum... And the short circuit max current is 11.05 amps--So a 15 amp minimum fuse (if you want to use one) is fine (15-20 amps). You want your fuse or breaker to be at lease 1.25x the max continuous current you want to draw--To prevent popping a fuse or breaker on clear sunny days (in USA, fuses and breakers are generally designed to not pop at 80% or less current, and will pop >100% of rated current--could take minutes or hours or longer).

Your MPPT controller is designed to not output any more than 20 amps... So 1.25 NEC factor * 20 amps = 25 amp fuse/breaker recommended (assuming at least 12 AWG thick cable).

You want the to mount the charge controller in a cool area with good air circulation (heat is the enemy of electronics). Also, you don't want very much voltage drop between the controller and the battery bank--So mount near battery bank with short cables. Note if lead acid battery bank, keep battery fumes and gasses vented away from charge controller (fumes can have electrolyte/acid and will corrode metal; and hydrogen+oxygen gasses can create an explosion hazard when charging).

As always, check the manual for their installation instructions.

You don't say what your loads are--But remember that the battery is usually the source of high current (100's of amperes into a short circuit with even one full size battery) into a short circuit. Pick your wiring to carry the needed/rated current. and use fuse(s)/breker(s) on any positive wiring leaving the battery to your loads. Ideally, fuses and breakers should be mounted close to the battery (less wire that can get cut/shorted if kept short and protected from sharp metal edges).

Many times circuit breakers are a nice solution... They not only protect against shorts, they can be reset (no spare fuses needed), and are handy for on/off switches (working on devices, turning off loads when system is not used, etc.).

-Bill

chim · June 2023

BB. said:

Fusing (and circuit breakers) are really there to protect your wiring from overheating/catching fire if there is a short circuit. If you use USA NEC (national electric code), then 14 AWG = 15 fuse; 12 AWG = 20 amp vuse; and 10 AWG = 30 amp fuse.

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

With a single solar panel, there is not really any need for a fuse between it and the charge controller... Your specs:

SPECIFICATIONS
Max Power at STC: 200W
Open Circuit Voltage: 23V
Short Circuit Current: 11.05A
Optimum Operating Voltage: 19.2 V
Optimum Operating Current: 10.42 A
Operating Temperature: -40°F~194°F / -40℃~90℃
Maximum System Voltage: 600 VDC UL
Maximum Series Fuse Rating: 20A
Output Cable: 13 AWG (2.6 ft long)
Your specs say 20 Amp fuse maximum... And the short circuit max current is 11.05 amps--So a 15 amp minimum fuse (if you want to use one) is fine (15-20 amps). You want your fuse or breaker to be at lease 1.25x the max continuous current you want to draw--To prevent popping a fuse or breaker on clear sunny days (in USA, fuses and breakers are generally designed to not pop at 80% or less current, and will pop >100% of rated current--could take minutes or hours or longer).
Your MPPT controller is designed to not output any more than 20 amps... So 1.25 NEC factor * 20 amps = 25 amp fuse/breaker recommended (assuming at least 12 AWG thick cable).
You want the to mount the charge controller in a cool area with good air circulation (heat is the enemy of electronics). Also, you don't want very much voltage drop between the controller and the battery bank--So mount near battery bank with short cables. Note if lead acid battery bank, keep battery fumes and gasses vented away from charge controller (fumes can have electrolyte/acid and will corrode metal; and hydrogen+oxygen gasses can create an explosion hazard when charging).
As always, check the manual for their installation instructions.
You don't say what your loads are--But remember that the battery is usually the source of high current (100's of amperes into a short circuit with even one full size battery) into a short circuit. Pick your wiring to carry the needed/rated current. and use fuse(s)/breker(s) on any positive wiring leaving the battery to your loads. Ideally, fuses and breakers should be mounted close to the battery (less wire that can get cut/shorted if kept short and protected from sharp metal edges).
Many times circuit breakers are a nice solution... They not only protect against shorts, they can be reset (no spare fuses needed), and are handy for on/off switches (working on devices, turning off loads when system is not used, etc.).
-Bill

Thank you so much for your response. I really appreciate it!

For the battery, the load is really small at around 78.51 milliamps total current consumption of the sensors that will be used along with a 5V Arduino. I am planning on connecting a dc-dc converter (12v to 5v converter) in between the battery and the load.
battery -> fuse/circuit breaker -> dc-dc converter -> Arduino

I am leaning towards circuit breakers because, as you mentioned, should be mounted close to the battery and will help to turn off the power to the Arduino when desired.

BB. · June 2023

You are very welcome Chim,

We are kind of jumping into the middle of the project... Backing up a moment, we need to define the loads, where the system will be used (hours of sun per day, location, seasonal usage, etc.). Just to show how the math works.

0.08 amps of current * 24 hours per day (guess) = 1.92 Amp*Hours per day
1.92 AH per day * 12 volt battery bus = 23 WH per day power usage (losses from converters, etc.?)

The battery at 100 AH is really an "overkill" capacity... For example, if you assume to use 50% of capacity (dark weather, other unplanned power needs):

100 AH * 0.50 max planned discharge * 12 volts = 600 WH of "planned capacity" of battery
600 WH battery capacity / 23 WH per day = 26 days of storage (no solar charging). Helpful if winter shading? (solar panels need full sun to generate "useful amounts of energy"

Note that Lead Acid batteries typically want to be kept above ~75% state of charge to reduce the rate of sulfation of the plates (longer battery life). Can discharge further to 50% (or deeper discharge) if cycling (i.e., discharging at night, charging during day). "Storing" Lead Acid batteries below ~75% SoC (no cycling) will accelerate battery sulfation (and earlier battery failure). Deeply discharge batteries (taken near dead) can, for example, be badly sulfated in days or weeks.

Generally, plan on 5% rate of charge for battery bank (minimum). or 10%-13%+ rate of charge for larger daily loads. Call 5% minimum (for minimum health of battery):

100 AH * 12 volts * 0.05 rate of charge * 1/0.77 typical panel+controller deratings = 80 Watt of solar panel minimum suggested

Or, looking at possible daily solar harvest in winter... Can run from 3 hours per day (sunny regions) to 1 hour of sun (poor winter sun location):

200 Watt panel * 0.61 DC off grid solar system eff * 3 hours of sun per day = 366 Watts per day (typical "not bad solar" location in winter)
200 Watt panel * 0.61 DC off grid solar system eff * 1 hour of sun per day = 122 Watts per day (typical "poor solar" location in winter)

Vs your estimated 23 WH per day loads--Your system should easily supply the daily power needs unless you have some very non-optimal solar conditions (lots of trees, shade from mountains in winter, etc.).

Anyway, hardly guesses vs just examples of the (relatively simple) math you can do to model/plan your system requirements before spending the money.

-Bill

Newbie needs help with Solar Panel System Setup!

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