24v,

Welcome to the forum Seedguy,

Generally, the place to start is to understand how much energy (amps, volts, just running clock, cycling/holding water valves, etc.).

For example, if you needed 1.8 amps @ 24 volts for 24 hours per day:

• 1.8 amps * 24 volts * 24 hours per day = 1,037 Watt*Hours per day

That is a fair amount of energy... My guess is that the timer (if LCD, not LED which would draw more power), would only pull a fraction of that power (24 hour a day load). And if you only run the solenoids are few hours a day (at perhaps 0.25 to 0.50 amps or so), the actual WH/AH per day is much less than would be suggested from my above "dumb" equation with 100% power draw assumption.

Then the other is how much current the solenoid takes... There are those, full size, that pull current whenever they are "on"... And there are others that are a small solenoid that channels water pressure to the main valve and pull much less current, or possibly only pull current when cycling off to on and on to off.

Here is an example of a single solar valve that uses almost no energy (solar panel only several inches in size):

https://www.dripworks.com/dig-leit-solar-timer-with-1-valve

To full blown commercial timers (not cheap):

https://www.ewingirrigation.com/products/controllers/solar/leit-x-20-station-solar-irrigation-controller.html

And latching valves (only take energy to change state--I think):

https://www.digcorp.com/professional-irrigation-products/lema-1600he-dc-solenoid-actuator-adapters

If you have a known sprinkler system and want to compare setting up a solar power system to run them, tell us how much energy per day (Watt*Hours or Amp*Hours @ 24 volts) you need.

Note--Check the power output from the 24 volt power cube... Is it 24 VDC or 24 VAC -- Many times, running an AC coil on DC can cause them to draw too much current and overheat. Also, the switching controls is usually different between AC vs DC loads.

-Bill

Just to say there are a lot of pretty cost effective solar powered irrigation systems out there (many are 1 circuit systems--4x may not be cheap, or meet your needs for ease of programming):

https://www.amazon.com/s?k=solar+powered+irrigation+system+controllers

However, I am more than happy to give you an idea of what full sized AC solar power system may look like.

For a better estimate, get a Kill-a-Watt meter to figure out what the "real loads" are per day:

https://www.amazon.com/s?k=kill+a+watt+meter

First, lets assume worst case of 1,037 WH per day (this will actually give you more than enough power for some LED lighting, cell phone charging, laptop power, etc... -- My guess). So this is a good sized off grid power system for a cabin (no refrigerator).

First size the battery:

• 1,037 WH per day * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days storage * 0.50 max discharge = 406 AH @ 12 volts

That is the equivalent of 2x 6 volt @ ~220 AH golf cart batteries in series (12 volts) by 2x parallel = ~440 AH battery bank for a total of 4x $100 golf cart batteries (flooded cell, AGM will be more expensive).

The first choice you need to make... For base load design (24 hours per day x 7 days per week), I would make the battery bank (and supported load) 2x larger--But lets not bother now--I believe that would be terribly oversized for your needs and make this proposed system way too expensive... To continue

Next size the solar array to the size of the battery bank... 5% to 13% rate of charge suggested. 5% for weekend/summer usage, 10%+ for full time off grid:

• 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 207 Watt solar array minimum
• 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 414 Watt array nominal
  
• 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 539 Watt array "cost effective" maximum
  

And then there is sizing for the amount of sun you get in a day for your area (and is this 3 or 4 season irrigation system). Say fixed array near St. George Utah:

Saint George
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.34	4.65	5.96	6.36	6.49	6.64
Jul	Aug	Sep	Oct	Nov	Dec
6.20	6.12	6.17	5.81	4.82	4.32

Assuming worst case (through winter), a December "break even" array (you may need a genset during bad weather to keep battery bank >50% state of charge):

• 1,037 WH per day * 1/0.52 AC inverter off grid system eff * 1/4.32 hours of sun = 462 Watt array (Dec break even)

And, in reality, I would be suggesting 2x that amount to reliably supply a 1,037 Watt*Hour per day Base Load 12 months a year (minimal genset usage).

• 2 * 462 Watt array = 924 Watt array

Hardware wise, you would need an MPPT controller of:

• 924 Watt array * 0.77 panel+controller derarings * 1/14.5 volt charging = 49 Amp minimum MPPT controller

https://www.solar-electric.com/motr60ampmps.html (nice controller, not cheap)

AC inverter:

https://www.solar-electric.com/samlex-pst-120-12-inverter.html
https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html

Solar panels (3x in parallel):

https://www.solar-electric.com/axitec-ac-330p-156-72s-polycrystalline-solar-panel.html

The above is a very capable AC off grid power system, probably 3x larger than you would need (after you measure your irrigation controller energy usage)--But gives you the math behind the design, and some samples of good quality hardware and what questions you have to answer vs my guesstimates.

-Bill