Excess power from solar panel to fridge / heater

[paulpw]

I have an old campervan and want to install a solar panel system. I’m a bit technically minded but this is all new to me.
What I have :- 180 watt monocrystalline panel..
A 30 Amp Solar30 regulator.
Flat on top of a campervan mounted with rubber clamps around the edge, one underneath centrally, for support with a 3 cm gap to the roof.
Two batteries 125 AH leisure and 72AH car battery in parallel at moment, though I understand this is not the best way to do things. Eventually I should go for one single leisure battery maybe an AGM type of higher capacity when I can afford it.
Question / Objective: - How to keep my batteries charged as full as possible and automatically use any excess power to either run the fridge / cool box or to heat water.
If I understand correctly with both MPPT and PWM technologies as the battery reaches its maximum, a very small amount of power goes to the battery and the rest is wasted or blocked. I’ve been trying to think of a way to then switch this.
What if I got a voltage controlled switch / relay like you get between the vehicle battery and the leisure battery that has little potentiometers to adjust the switch on / off point. Perhaps ‘ on’ at 13.4 and ‘off’ at 13.2. This relay would then operate another relay(s) arranged so that the power from the output of the controller that was going to the battery now goes to the fridge, until the battery voltage naturally seeps to the lower set point voltage. Do you think this would work ?
Along the same lines, could I switch the output of the panel directly to a water heating element of 12v rating say skipping the controller?

[Sunking]

All you need is a controller with a Dump Load option.

[paulpw]

Controler with dump load .

Yes, thankyou. The thing is, at least here in England I have not yet found one. I did a search on Ebay and the only references to 'dump load' seem to be for dual solar and wind turbine controllers and only related to the turbine output, and are a bit too expensive for my mini system. For the water heating bit, redgardless of how the power is re-routed, does it matter what heating element I use ? ie:- Would a mains kettle element work? Thanks for looking.

[Sunking]

Yes, thankyou. The thing is, at least here in England I have not yet found one. I did a search on Ebay and the only references to 'dump load' seem to be for dual solar and wind turbine controllers and only related to the turbine output, and are a bit too expensive for my mini system. For the water heating bit, redgardless of how the power is re-routed, does it matter what heating element I use ? ie:- Would a mains kettle element work? Thanks for looking.

The heating element would need to be matched to the voltage. Using 12 volts on a 240 volt element is not going to work as the resistance of the higher voltage element will be to high to load up 12 volt power.