few questions about solar power....

Welcome to the forum CC. No problem with English... My only language--And I do it poorly.

Lots of questions that have deep/detailed answers. I will just answer the questions simply--But we can dive deeply into each subject as you ask.

Batteries are the "heart" of your system. They supply current (power) when the sun is not shining, and/or when your loads exceed your solar power input (I.e., you have 300 Watts of solar at high noon, and 500 Watts of DC/AC inverter loads).

A couple of good rules of thumbs (at least get you somewhere on target), the 12 volt battery (battery bank) should be rated at least for 400 AH per 1,000 Watt of AC inverter rating. This is assuming you want to draw 1,000 Watts at night (no sun) for loads--Which may be longer term (vacuuming the home, running a microwave, etc.) or short term such as starting a water pump, power saw, etc. (most AC inverters are rated roughly 2x the name plate Wattage for a few seconds to a minute of heavy surge loads). The battery bank needs to be able to reliably support those loads.

Lead Acid battery banks are (roughly) fully charged when measuring around 12.8 volts after batteries have "rested" for a 3+ hours. And are near dead when 11.8 volts or less (resting). For lead acid batteries, you really do not want to draw them below 50% state of charge for daily loads. You can discharge down to 20% SoC as long as you quickly recharge the next sunny day.

That your batteries are at 18-20 VDC when the sun is shining--That would normally indicate that there is a problem with the charge controller... Normally, the battery bank should not exceed 14.75 Volts (normal charging) or much over 15-16 VDC when "Equalize Charging" (slightly over charging once a month or so for Flooded Cell Lead Acid Batteries).

The ideal method to measure FLA battery state of charge is with a Hydrometer (density of the Electrolyte).

Electrons do flow either direction in wiring... And in batteries. One direction when discharging, another when charging (in AC wiring, the current flow reverses 50-60 times a second--Alternating Current).

Adding a UPS to your system does add more loads (to run the UPS+loads+battery charging). Not a great idea. I would suggest an inexpensive laptop computer instead--Includes batteries and, for example, my Chrome Book only averages a 5-10 Watt load (can draw more when recharging its internal battery).

There are lots of details to discuss--And I suggest that we address (in detail) one or two questions at a time.

In general... Choose your most energy efficient loads (a desktop computer plus monitor can take upwards of 200-300 Watts vs the 10 Watts for my little laptop). That defines the size of the battery bank (voltage and AH ratings). Then design the solar array to run your loads and charge your battery bank (keep the batteries "happy"). Then start picking components for your solar system that work well together.

Got to go now--

-Bill

Generally, a "Solar Battery" = "Deep Cycle" battery (really for flooded cell/lead acid type batteries).

The general purpose lead acid battery is an SLI type (starting, lights, ignition). Designed for high current (starter), and really not to be discharged below 85% or so Stage of Charge for longer service life. Usually charging voltage is around 14.0-14.4 volts.

Deep cycle batteries typically have a bit less starting current rating (maybe 25% less???), and can require higher charging voltage (for flooded cell type) of ~14.78 volts or so.

And you have batteries that are compounded to use "less water or zero added water" during normal life (call it around 3 years for typical automotive batteries. These typically are not "deep cycle" type.

Marine batteries--Should be "deep cycle" but are usually either a hybrid of SLI and DC, or just a marketing branded SLI battery--Typically used with "trolling motors".

Any of the low/zero water batteries typically use the lower DC charging voltages (to reduce water usage). If your charger runs at a higher voltage (even "cheap" trickle chargers) will still "boil" the water out (gassing) over time (a year or two in my experience).

"Sealed" lead acid batteries are typically "zero water usage" types (and usually not a great deep cycle battery).

The other types of Lead Acid Batteries are the AGM (absorb gas mat)--A very nice "solar/deep cycle" Lead Acid battery, not refillable. VRLA (valve regulated lead acid)--Another type of FLA (there are both float and deep cycle types available--need to read the specifications). And GEL type (electrolyte is treated to turn into a GEL)--Typically not preferred for Solar/fast charging applications.

Most lead acid batteries can be connected in parallel without major issues (same type, roughly same age, keep wiring "the same" to each battery, etc.).

Then there are the Lithium Ion and the Lithium Iron Phosphate batteries. LIP type batteries are what are usually recommended for solar/off grid usage. Long life, long cycle life, generally "safer"--Less chances of fire--Than other types of Li Ion batteries.

Lithium batteries are more prone to early life failures with over voltage/under voltage/out of temperature range, etc. than FLA type batteries... And usually have a BMS (battery management system) connected to monitor the "health of each cell" and the overall operational state of battery (max current, min/max temperature, etc.)...

With Lithiuim batteries, they are "more complicated" to interconnect (BMS, wiring safety issues, etc.) and should be addressed specifically to what brand/models you have.

And for everyone, you can click on this link and setup email notifications:

https://forum.solar-electric.com/profile/preferences/

For Corporal_Canada, you should be receiving emails on your "threads"... You might double check your email address here and your spam folder.

-Bill

You can find less expensive cable crimpers (these are US suppliers--Not sure what you can find locally):

https://www.solar-electric.com/hacrtoforlal.html (hammer crimping tool)

https://www.harborfreight.com/electrical/electrician-s-tools/wire-strippers-crimpers/crimpers/hydraulic-wire-crimping-tool-64044.html

One person here took an old pair of cable cutters, heated and slowly cooled the cutters, drilled the appropriate sized hole, and reheated/quenched to harden again and made his own crimper.

If you have a battery or welding shop nearby, they can crimp/build some cables for you...

-Bill

I was saying that DC Current Clamp Meters can drift over time (minutes) and may need to be re-zeroed ever so often to keep them accurate (one of mine will drift by a few 1/10's of an amp over a few minutes). NOT that you need to measure the current for 1 minute to get an accurate/useful reading.

Your meter appears to be an AC only current clamp meter. They are very nice for measuring AC current (household 120/240/etc. VAC 50/60 Hz. They have a small internal transformer to measure the 100's of amps and down convert that to a fraction of amp for the meter to read.

Transformers do not accurately/reliably transfer DC magnetic fields.

Question about smart phone cable current measurement... If you are clamping the "whole" USB cable (power+data wires), then 1) it will read zero current because the + current flow cancels the - current flow and the sum of the currents are zero (+1.00 amps -1.00 amps = 0 zero amp magnetic field). And 2) your meter cannot measure DC current (it may read non-zero/not accurate for fluctuating DC current).

Doing a quick search, your meter appears to be an AC only current clamp DMM (notice the tilda "~" sign under the current and some voltage range settings)... Note that it can measure DC Voltages (the solid line over the dashed line is a common "DC" symbol):

An AC+DC current clamp meter can measure Either AC or DC current (need to select the correct "major function of voltage vs current" and then the "sub function of AC vs DC, etc.).

https://www.amazon.com/UNI-T-Digital-Handheld-Resistance-Capacitance/dp/B0188WD1NE
r

Quick example of using a current clamp meter:

https://www.youtube.com/watch?v=Ncr7Pz_-Alg

Note that AC power has "no polarity" on AC current measurements. For DC current measurements, you will see a "+/-" polarity depending on DC current flow direction.

-Bill

Ummm.... This is an engineering/physics after school discussion with lots of beer available. 

In math, there are lots of assumptions and simplifications that are made so that the math and physics can be simplified to make "good enough" equations to solve for the needed information.

Could you argue that a battery is actually AC (alternating current) with a frequency of hours (i.e, 5 hours charging, change current flow direction and 19 hours of discharge) and time variable current changes (switches turn on/off, 60 Hz single phase AC inverter with a 120 Hz "sine squared" current wave form). Sort of yes... But assuming this would work with an AC transformer--Not really useful in the "real world" (would need a huge "low frequency" transformer to work at 1/24 hour or 0.0000115740740741 Hz (cycles per second).

Go give you a quick idea of the scope of "AC" power... Thomas Edison was a "practical" experimental engineer. He did not have a background in Calculus and other high level math. So, he was enamored with DC (direct current) power distributi

Tesla, on the other had, was very much immersed in high level math and physics that would make your head spin.

The end result was that Edison and his "DC power plants" could only send "useful amount" of energy for a few miles, and could not use high voltage distribution and transformers--Very limiting. And he had to use DC motors with brushes (brushes that had to be changed every few years for 24x7 operation), the electrical noise of brushes arcing, Ozone generation, vs the "simplicity" and reliability of transformers, induction motors, and such.

The history is very interesting and has its own "title"--War of the Currents.

https://www.history.com/news/what-was-the-war-of-the-currents
https://en.wikipedia.org/wiki/War_of_the_currents

For "our needs", we do differentiate between AC and DC voltages/currents because our measuring instruments are (typically) designed for one or the other model of operation. And the "loads" have certain assumptions too (a filament lamp can run on AC or DC power--The standard Florescent Tube system needs AC power because it uses a "ballast" to limit current once the "arc inside the tube" is running.

There are times that "fluctuating DC current" has some "AC" current characteristics and we have to take those into account--And more than happy to have a discussion about these issues, but at this point, I would be concerned that this would cause more confusion than clarity until with have the "basics" down.

https://www.khanacademy.org/science/physics/circuits-topic/circuits-resistance/a/ee-voltage-and-current

Khan Academy has a lot of (as far as I know) free courses that could be a good start. For electrical, there is some basic math that is required to understand and implement electrical circuits. But you can get pretty fare with just the basics for day to day home/car/solar/etc. work.

Jumping into electrical applications without a bit of background can be pretty daunting.

-Bill