Reddit mentions of 25 Watts Monocrystalline Newpowa 12v Mono Solar Panel Module 20W < 25W < 30W Rv Marine Boat Off Grid

I got this one on Amazon. You'll also need the adapter and some connectors

So the 5 gallon water tank lasts you all day?

So, let's shave that 4 hour run time down to a mere 1 hour, and you'll have plenty forever. Building it smaller (since you're only building ONE of these systems) doesn't save you a whole lot:

Loads per day: 32.5 Watt-hours.
Days without sun: 3
Hours of sun per day: 4

Panel needed: ~25 Watts. (You only need ~8 watts for your load, but I figure you'd want to recover from a cloudy day or three with only one day of full sun, so that's where the extra wattage comes in!)

Battery Storage Needed: ~100 Watt-hours; a 35 amp-hour, 12-volt battery would be fine, and keep you above 75% SoC most of the time. Long as the cart's outside and in the sun every day, the battery will last a long time!

Charge Controller: Cheap 10 amp PWM still works.

A specific shopping list because I'm waiting on a video to render before I can get on with my night:

Solar Panel:

https://www.amazon.com/Monocrystalline-Newpowa-Quality-Module-Marine/dp/B01M9B6RQI/

Charge Controller:

www.amazon.com/PowerEZ-Controller-Battery-Intelligent-Regulator/dp/B074TB6FS8/

Battery:

https://www.amazon.com/Powersonic-PS-12350NB-Battery-Nut-Bolt-Connector/dp/B0010AI3LM/

Water Pump:

https://www.amazon.com/Seaflo-Diaphragm-Pressure-Caravan-Marine/dp/B00DLKT4OO/ref=sr_1_1_sspa?ie=UTF8&amp;amp;qid=1522996286&amp;amp;sr=8-1-spons&amp;amp;keywords=SeaFlo+water+pump&amp;amp;psc=1&amp;amp;smid=A3EBZ5HHZPL73

Wire:

https://www.amazon.com/gp/product/B01M0YDC6K/

This isn't copper, it's CCA, but for this amount of current really... :/ You're talking only a few amps at only a few feet, so it should be fine. (I mean, you're gonna get max less than 2 amps from that panel down to the controller, so really, you're not going to be pushing anything.

You can also use landscaping wire, if your hardware store carries 12 AWG landscaping wire. It's good for random small solar projects, or cut apart an old 12 AWG extension cord. (Or even 14 AWG if it's pure copper.)

Not this one specifically but my coop with about 35 chickens uses this timer design.

Automated Chicken Coop Door

I added a 12V LED light bar to give them some light at night during the winter. It definitely re-started their egg production then. It's all run off a 25W solar panel and 10Ah battery. Only thing I may change would be to add more battery capacity so on the sunny days during winter it can bank the additional power for the not so sunny days.

For reference, I'm in Northern California zone 9a/b and we get lots of sun here.