Cable AWG Help!!

I would first get Kill-a-Watt type energy meter and see how much power your TV uses:

https://www.amazon.com/s?k=kill+a+watt&ref=nb_sb_noss_2

Then define how many hours per day (or over two days, if you want to "battery through" 2 days of no-sun).

How long do you plan on recharging the GEL battery... At least in the USA, GEL Batteries are rated for C/20 rate of charge (100 AH * 1/20 hour charge rate = 5 amp charging).

You discharge the battery over 2 days to 50 AH, it will take (100AH/5amps= ) >10 hours of sun per day (most places do well at 5 hours of sun or better during summer, and down to 3 or 2 hours per day during winter).

AGM may be a better choice---Or flooded cell lead acid would be good for a first try (FLA is cheaper battery, AGM charges faster).

As always look at the specifications for "your planned" battery to see it charging specifications.

And roughly where the system will be used (nearest major city)--And what season(s) will the system be used... Obviously, Winter has less sun, generates less power and/or need more solar panels.

Do your load estimates and paper designs first, before you plan and by the hardware.

Solar Power Systems generate less energy than most people assume, and their loads are higher than understood.

Say your TV takes 24 Watts...:

• 24 Watts * 1/0.85 AC inverter eff * 1/12 volts = 2.4 Amps @ 12 volt nominal draw

If you use 50% of battery capacity:

• 100 AH * 0.50 discharge = 50 AH
• 50 AH / 2.4 amps draw = 20.8 hour runtime

And a 500 Watt AC inverter may be "overkill" for this application... Generally suggest a PSW/TSW type inverter (pure/true sine wave). MSW (modified square/sine wave) inverters can by "hard" on some electronic (and induction motor/transformer) based loads (cause overheating, shortened life).

Current wise, a 100 Watt panel will produce, in full sun:

• 100 Watts / 17.5 Volts Vmp (voltage maximum power) = 5.71 Amps

14 AWG house wiring will work nicely here... Good for 12-15 amps very easily, keep wiring short (lower voltage drop)--Do you have the distance from your panel to the charge controller (long wire runs, need heavier wiring to keep voltage drop down).

Where you may need heavier wiring, is from the battery to the AC Inverter... A 500 Watt inverter:

• 500 Watt inverter * 1/0.85 inverter eff * 1/10.5 inverter cutoff = 56 Amps (worst case)
• 56 Amps * 1.25 NEC derating = 70 Amp rated branch circuit wiring and fuse/breaker

Using the NEC wire table (pretty conservative):

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

Recommend 4 AWG wiring (optimum). Always keep AC inverter wiring relatively short (low voltage drop)...

Or use a 100 Watt inverter which will be around:

• 100 Watts * 1/0.85 * 1/10.5 volts cutoff = 11 Amps

A much more "reasonable" draw for your TV usage and size of battery bank--500 Watts is a bit on the "overkill side" (too large of AC inverters can "waste" energy too--Upwards of 1/2 of your battery draw would be just to "keep the oversized inverter" running).

Amount of sun for your area. Fixed array facing south:

http://www.solarelectricityhandbook.com/solar-irradiance.html
The energy harvest for an average April day:

Frederick
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 51° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.05	3.62	4.27	4.72	4.79	4.94
Jul	Aug	Sep	Oct	Nov	Dec
4.98	4.76	4.66	4.52	3.25	2.73

The math looks like:

• 100 Watts * 0.52 end to end off grid system eff * 4.72 hours of sun per day = 254 WH per day (April average)
• 254 WH per day / 24 Watt TV load = 10 hours of TV runtime...

Or roughly 5-10 hours of TV run time per day of energy harvest for April. All things being equal (which they rarely are).

And based on a pure guess of 24 Watts for your TV. And probably using a much smaller AC inverter--The 500 Watt AC inverter Tare losses are probably significant.

Anyway, some really quick answers... The above are based are relatively conservative rules of thumb. And how you use the system, how/where you mount the solar array. Do you use the TV a lot, or just run it for a few hours every other day, etc...

Your thoughts/corrections/questions?

-Bill

Your panek Imp (current maximum power) should be round 5.71 amps. Let's try 15 feet with 14 AWG cable:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=17.5&phase=dc&noofconductor=1&distance=15&distanceunit=feet&amperes=5.71&x=41&y=18

Voltage drop: 0.43
Voltage drop percentage: 2.47%
Voltage at the end: 17.07

That is about the maximum drop I would suggest... Generally, we try for 1-3% voltage drop.

For the charge controller to battery bank connection, you want around 0.05 to 0.10 volts maximum drop... The charge controller needs to "accurately" measure the battery voltage. If there is too much drop, the battery will charge slower (more wasted sun). We can plug in some numbers and see what works. 5.71 amps, 0.10 volts drop max, 3 foot cable run (one way for this calculator):
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=17.5&phase=dc&noofconductor=1&distance=3&distanceunit=feet&amperes=5.71&x=61&y=24

14 AWG works here:
Voltage drop: 0.087
Voltage drop percentage: 0.49%
Voltage at the end: 17.413

Regarding the inverters... I don't know if the TV is sensitive to MSW or not. And that is the problem, it is difficult to tell without trying, and you won't know until the TV power supply gets hot or fails. A TSW/PSW AC inverter just bypasses that problem. It is the old 80/20 rule of thumb... 80% of your loads will probably work fine--And 20% may have issues/fail.

If you plan on other loads (LED lighting, battery chargers, cell phone chargers, etc...) I would suggest that you bite the bullet and get the PSW/TSW type inverter.

For TARE losses, many specification sheets will list the loss for AC inverters... 6-8 Watts is typical for that class of AC inverter. Probably not going to find many that are lower (even with smaller AC inverters).

Just remember to turn off the inverter (DC input) when you are done... More that a few battery banks have been "killed" by forgetting to turn off all loads when done:

• 45 Watts * 3 hours per day = 135 Watt*Hours of energy used per day
• 6 Watt inverter Tare * 24 hours per day = 144 WH of energy per day "inverter just turned on"

Many times, it is the small loads that run 24 hours per day that really use a lot of solar energy.

-Bill

Heavier cable will be fine. It does let you harvest more power... But copper is expensive too, so going for less than 1% drop is usually not cost effective--Just get a second solar panel and parallel it--You get 2x more harvest.

One other issue is the cable that goes to the solar panel. The UV Radiation from the sun will cause most insulation to fail over time (months or longer). Using UV rated insulation (or Outdoor rated cable) is suggested if this is "permanent" install.

Take care,
-Bill

Let us know how it all works out.

-Bill