Newby solar questions... Overwhelmed

Chris has given you a good start.

I suggest looking at your load requirements / power exceptions. Even though a lot of sites like to call these systems "Solar Generators"--They are not what most people expect, power/energy wise, from a genset. One gallon of gasoline and a Honda eu2200i, and you will get close to 10+ hours of power running a refrigerator, LED lighting, cell/laptop chargers, etc... Or upwards of ~3,000 to 4,000 WH of energy (power is a rate, like 400 Watts, and energy is an amount, like 400 Watts * 10 hours of use = 4,000 WH).

Since we don't have a "load" or expectations starting point, we can start with your hardware definition. I like to call the Battery Bank the "heart" of your system. As Chris suggestions, a pair of 6 volt golf cart batteries (6 volt @ ~210 AH in series for a 12 volt @ ~210 AH battery bank--We use the 20 hour discharge rate for battery AH capacity--Works for most of our designs) is a very good place to start.

You have a few things you need to do... 1) check the electrolyte level once a month--If you over charge/let the plates get exposed, the Flooded Cell Lead AC Batteries are quickly ruined.

And 2), make sure you do not run the battery bank "flat/dead". That also kills them quickly. If you run them between 50% and 100% state of charge, they will be very happy (and avoid going below 20% SoC ever--Again can kill battery cell(s)). (fixed--Thank you littleharbor2. -Bill)

For a full time off grid system, suggest that you use the batteries for 2 days without sun and 50% maximum discharge--That means your "stored energy" supply would be:

• 210 AH * 12 volts * 0.85 (AC inverter eff) * 1/2 days storage * 0.50 max discharge = 536 WH per night
• Assuming 5 hours per night for 2 nights: 536 WH / 5 hours = 107 Watt average AC load (for 5 hours)

Your loads are different that what I suggest above--But the math is easy for you to plug in your numbers. If most of your loads are DC, then you can avoid the 85% AC inverter Efficiency/losses.

Next, two sets of solar panel calculations. The first is based on charging current for the battery. Nominally 5% rate of charge works OK for a weekend/sunny weather system. 10%-13%+ rate of charge is better for a full time off grid daily use system (battery bank is "happier", and you don't have to watch the system nearly as closely):

• 210 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 198 Watt array minimum
• 210 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 395 Watt array nominal
• 210 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 514 Watt array "typical" cost effective maximum

And then we can also size the array based on your daily loads and where you live... For example, say your daily loads are 536 WH per day (battery loading), and you are around Mesa AZ, fixed array facing south:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Mesa
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.94	5.55	6.48	7.10	7.03	6.76
Jul	Aug	Sep	Oct	Nov	Dec
6.21	6.01	6.39	6.02	5.35	4.78

Lots of sun... Worst case average is December at 4.78 hours per day (long term average):

• 536 WH per day * 1/0.52 end to end AC off grid solar eff * 1/4.78 hours of sun per day = 216 Watt array "nominal" for December

Now--Realistically, you should only use around 50% to 65% of daily forecasted harvest (i.e., running a refrigerator and LED lights every day--Put off water pumping, cooling fan, etc. washing machine use during cloudy weather).... 

The math says that 198 to 514 Watt array would work. If you want to have a system that supports more energy (fan, working in the shed, etc. during non-Winter), a 10%+ system would be nice. A 395 Watt array with 5.55 hours of sun per day average (February though October) would produce:

• 395 Watts * 0.52 AC system eff * 5.55 hours of sun per day = 1,140 WH per day harvest
• 1,140 WH per day - 536 WH "night usage" = 604 WH for "day time usage" and 536 WH for night time.

A 40 Amp solar charge controller--The maximum array for PWM would be:

• 40 amps * 17.5 volts Vmp array * = 700 Watt array maximum for a "cheaper" PWM solar charge controller (or less-check manual)
• 40 amps * 14.5 volts Vbatt charging * 1/0.77 panel+controller deratings = 753 WH typical cost effective maximum

And there are always the "Tools of Trade"... For flooded cell lead acid batteries, a hydrometer is pretty much a requirement:

https://www.solar-electric.com/search/?q=hydrometer

And an AC+DC current clamp meter-DMM. Makes it very easy to understand and diagnose problems (both AC and DC side--There are AC only current clamp meters, work great, just not for DC):

https://www.amazon.com/UNI-T-Digital-Current-Capacitance-Multimeter/dp/B0772FYF5M (cheap "good enough")
https://www.amazon.com/gp/product/B019CY4FB4 (nice mid priced meter)

For solar panels--140 Watt "12 volt" panels (Vmp~17.5 to 18.x volts) are cheaper/easier to ship and move around. Work well with PWM type charge controllers. But these panels cost more $$$/Watt.

And there are >~200-350+ Watt panels that have to ship truck/pallet (shipping one or two panels can be very expensive). And their Vmp~30-38 volt or so) output needs a more expensive MPPT controller (take high voltage/low current from array and efficiently down converts to low voltage/high current for charging the battery bank). Ends up many times with "cheap" $/Watt panels and more expensive (and usually more capable) MPPT charge controllers.

If you need a little bit of AC power... A 300 Watt or smaller PSW/TSW AC inverter is nice. They don't waste much power. And some these days come with remote on/off, and even search mode (inverter runs in low power standby until >~8 Watts of AC power is needed--Then turns on to run AC loads).

MorningStar makes a nice/rugged 300 Watt PSW AC inverter with remote on/off and search mode... May be more than you want to spend, but at least you can see what other options are out there:

https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html

Our Host Northern Arizona Wind & Sun does have a bunch of reference articles if you want to do some more reading:

https://www.solar-electric.com/learning-center

And one of our members has some nice real world photos and evolution of his DIY solar power systems:

http://2manytoyz.com/

-Bill

Thank you Littleharbor2. I have fixed.

-Bill