Switching high-current motor (relay vs. SSR vs. mechanical switch)

Question

I'm working on automating an irrigation system which has a large well pump that uses 24-32 V, directly from a solar array.

This was previously switched manually by a light switch, but after my uncle's death, I'm managing it remotely from four hours away, so I'm looking for a reliable solution.

I'm hoping to manage it remotely via a Raspberry Pi or Sonoff (ESP8266) controller. The pump will pull up to 24 A, but typically uses about 12 A. The power is nominally 24 V, but is unregulated and can peak at 32 V.

I've previously used a 60 A rated SSR, but this failed closed, likely due to being in an enclosure, and lacking thermal paste/padding between it and the heatsink. An emergency replacement also fried a Sonoff with three 10 A relays in parallel (specifically the PCB traces).

So I'm now weighing three options:

1. Use a mechanical relay, rated for 40+ A, which might require a smaller relay to activate from the 3.3 V Pi GPIO. My concern is with a high-current inductive load burning it out due to break-arcing. Should I consider contactors instead of relays for high-current DC?
2. Use another SSR, but keep it outside. This would need to handle 110°F (43°C) ambient conditions and not burn out like the previous one.
3. Use a linear actuator to mechanically switch the good old light switch. This is a bit hacky, but could work reliably. The advantage of a switch over relays is that the pump is "on" for 8 hours at a time, typically switching on/off once a day.

Is there a such thing as a digitally controlled discrete switch that doesn't have the energy waste associated with a relay or SSR during high duty cycles?

The pump will run all day except on cloudy/rainy days, in which the battery bank needs full solar power, hence the long duty cycles, to which a switch seems better suited than a relay.

Any advice about the choice between relay/contactor, SSR, or actuated switching would be very helpful, including factors I haven't considered.

As a reward for your reading this, here are some pictures of my previous attempts, minus missing magic smoke!

Answer 1

Mechanical Contactor in my opinion will be cheaper, try getting motor starting grade 24vdc and then you can drive it with a WebRelay output (24V). I haven't used it for well pumps but assuming your motor is a DC pump with conventional features, you will also want to withstand inrush current being high, You did not specify motor features or duty so it might be hard to size contractor with out. WebRelay also has inputs so you can use them on the aux contacts to monitor. You can power webrelay form separate 9v source, 24V or even PoE.