New Solar Calculator I wrote just now. Come size up your Solar Array!

[nikitis]

I wrote a solar calculator web app because I was wanting to play around with certain solar configurations and needed quick answers.

I was amazed that there seemed to be ZERO free online solar calculators. All of them seem to be behind companies trying to sell solar and a paywall. This kind of information should be free, so I grabbed algorithms and added it to the calculator. I used Grok A.I. to help me with the quick formatting of the HTML since I couldn't be bothered with remembering all the syntax right now.

It calculates your panel setup in series + parallel,
You add the Voltage of your panels,
You add the Amperage of your panels,
You add the Voltage of your battery array, (12v, 24v, 48v only for now as these are common for skoolies.)
You add the Amphours of your battery array,
You add the Peak Average Sun hours/day. Link in the ? box to find your value if you don't know it.
You add how many "Panels in Series" (per parallel string, not total panels).
You add how many "Parallel Strings" Combine into the MPPT Controller.
You add MPPT Max Voltage
You add the operating temperatures you want to test with to see if your MPPT Controller voltage will be exceeded due to temperature change as voltage rises with colder temps.

It then gives you:

Your voltage to the MPPT Controller
Your amperage to the MPPT Controller
Total Power in Wattage you'll produce
Time to full Charge (Assuming Lithium batteries, roughly cut in half for AGM)
Recommended Wire Size for your selection from the Panels to your MPPT (Considers rough voltage drop)

It then tells you at the bottom if you have sized your solar right for your battery setup, and if not it will tell you WHY it's not sized correctly.

Try it out and tell me what you think, or if there are any bugs:
Nikitis' Ultimate Solar Calculator – Solar, Battery, and Wire Size Guide

Site: Nikitis' Ultimate Solar Calculator – Solar, Battery, and Wire Size Guide

Screenshot:

This is running on my personal web server so it may go down at times, but I'll work to keep it up. Enjoy!

 

[TaliaDPerkins]

Hi! Please include a temperature coefficient and ambient min/max entry -- so no one cooks their MPPT/charger input on a cold day.

The approx. cable distance will maybe better be the 2X average of the closest connection and the farthest connection, that X 1.1.

Suggestions.

 

[nikitis]

Hi! Please include a temperature coefficient and ambient min/max entry -- so no one cooks their MPPT/charger input on a cold day.

Interesting, are there pretty set universal values for this? Or does that differ between MPPT brands? If it's universal I can add it. If it's different per brand, there's no real way to code for that without knowing every brand including chinese knock-off MPPT chargers.

 

[TaliaDPerkins]

Interesting, are there pretty set universal values for this? Or does that differ between MPPT brands? If it's universal I can add it. If it's different per brand, there's no real way to code for that without knowing every brand including chinese knock-off MPPT chargers.

All MPPTs will have a manufacturer spec maximum voltage they can accept. Temperature coeffs tend to be roughly similar, the point is the voltage will rise maybe dramatically on cold days -- the panel array may need to short out and free wheel a panel (usually harmless to do) on a very cold day.

There would be 3 numeric entries to add (maybe 4?):
- an MPPT max allowed V from that manufacturer
- a panel temp coefficient from that manufacturer
- and an ambient min ( and max?) to be evaluated from the person evaluating the array performance.

 

[TaliaDPerkins]

Tcoeff is usually written as a negative value in percent per degree C with 25 or 20 degrees C as the datum point. So my Jinko panel array on cold day in Alaska can be generating ~53 more volts than it does on a warm day in Florida! It's something like VOC-((Tdatum-Tambient)*Tcoeff). Long day, I'm fried -- if the voltage goes up in proportion to the decrease in temperature you've got the equation correct. Tcoeff is negative so the VOC goes up when you subtract the result.

A quick Google search says Tcoeff's range usually from -.2 to - .5 .

 

[nikitis]

Added MPPT Max Allowed voltage by user.
Added Ambient min max to be evaluated by user.

Test it out.

 

[TaliaDPerkins]

Test it out.

Looks golden to me! Thank you!

The Forum should feature/host this in an electrical area!

 

[nikitis]

You're very welcome!

I wrote this because I'm about to do my own solar, and wanted to play around a lot with values. I got a bunch of chinese solar products from 8 years ago, never used. When you go Chinese with this stuff, you gotta be pretty exacting with your figures.

Victron tends to add a bit of room for growth and mistakes in sizing, I'm going the cheap route with this build so I gotta be pretty exact. When I got the stuff back then, I didn't know much at all about solar, but ran my chinese equipment through the numbers just now on my calculator and the equipment fits well with some error of margin so I must of known a little something about it back then, or got extremely lucky.

I know you did electrical stuff @TaliaDPerkins so I'm glad you tested this out.

 

[TaliaDPerkins]

This is what it looks like:

And that warning is the kind of thing which has me having a way to manually and automatically short out a panel in cold weather. I like my EG4 6000xp's, I want them to last.

One thing that seemed odd but doesn't matter per this, each string feeds a separate EG4's MPPT but the input max V for the MPPTs are the same so it doesn't matter, each MPPT is set for each string which is half of 19.2A.

 

[TheHubbardBus]

Great work, nikitis.

Constructive criticism: A) not sure if your wire runs assume round-trip distance, but they need to if they don't, and the wire insulation temp rating (70, 90, 105, etc) is an important metric. Without this information either assumed and documented for the user to see, and/or an input for them to select such, you can't accurately determine the wire size for a given application.

 

[TaliaDPerkins]

Great work, nikitis.

Constructive criticism: A) not sure if your wire runs assume round-trip distance, but they need to if they don't, and the wire insulation temp rating (70, 90, 105, etc) is an important metric. Without this information either assumed and documented for the user to see, and/or an input for them to select such, you can't accurately determine the wire size for a given application.

The 3% drop presumed assures the temperature rating of the conductor is not exceeded almost regardless of type. It would be sufficient to exclude the unusual TW and UF insulation types while specifying Copper stranded ( and if well supported copper solid should be fine).

Home Depot doesn't apparently sell TW wire, and the closest they come to UF is UF-B specified for being buried in a trench.

 

[TaliaDPerkins]

Apparently, vehicular wiring near the engine/exhaust/drive train is silicone insulated and terribly expensive and generally only used for ignition wiring -- or -- XLPE in other engine/exhaust related applications (good for up to 125dC). [I've never rewired an engine compartment.]

For all house applications THHN should be fine, and DLO where used is overkill.

Solar wiring exposed to direct UV should be XHHW-2, RHW-2USE-2, or THHN/THWN-2 labeled UV resistant.

 

[nikitis]

I just bought some CE TUV IP68 solar wiring, 10 AWG. It's a German rating for Solar PV usage. Has a code on it for H1Z2Z2-K rated 1500v .

10 AWG is near the limit for my 1920 watts. 64v/30amp solar system, The 10 AWG cable is actually rated for up to 40 amps, my system will be at 30 amps. NEC goes even safer and would say to recommend using 125% over what you're system is. 10 awg is up to 40 amps, so it's pretty exact to what I need to use. No room for growth though.

If I add 2 extra panels down the road I'm gonna have to also buy all 8 AWG wiring though and use a PV Combiner. I'm at the max for a 3 wire Y adapter/combiner.