Electricity needs when the grids down.

[Lightspeed]

Pete, I get what you're saying. Even though the CH control and pumps only consume a few watts, its a few watts 24hours a day. To keep it running in winter would need around 1kW of solar generation power + scaled battery storage to see the system through the night.

Here's a useful tool to calculate PV output from you location, orientation and pitch of solar array: https://pvwatts.nrel.gov/pvwatts.php