I suspect that it might not work.
Why not use the solar energy to warm a very well insulated tank, giving warm rather than hot water,

How about a propane tankless instant water heater;
I’ve no experience of them, but here’s one example from Amazon.
Some are designed for outdoor/camping use, so likely work off a 12v pump and bottle gas.

Other sources and models are available.

Bill

To answer the orginial question, No a instant hot water tap like the Pudin will not work on a gravity water feed. Assuming the wter thank is about 50 ft above the tap thst is. The taps rely on pressure differential to operate the heater. Additionally the heater will be less efficent at lower voltage and if the tap uses electrically operated valves these will also have issues.

As others have indicated it might be better to look at solutions designed for campers and caravans.

Robert.

As model engineers surely you can make something simple to supply warm water, the boiler inspector can check it, or a heat exchanger from the base of the urinal even ? Noel.

Having got over yesterdays sillyness, one thought is that catering supply spares offer heating elements from about 800W for the likes of bain maries Etc. One of these and a stat and your there ! Noel.

On 25 December 2023 at 11:26 malcolm hollins Said:

Our club Site does not have Mains Electric or running water.

( our Solar Panel and Inverter will no support a 3000Watt load )

What 12V Inverter could be used as a stand alone power supply? (Not an expensive one )

Does your solar system charge a battery?

Ebay has 2ndhand Truma 10L water heaters 

They run on 12V, gas or mains If you only use it at weekends it should recharge in time

As a start I would go for solar hot water. That solves most of the warmer sunnier months. Now you need something to act as a fill in boost when the feed is too cold.
regards Martin