Heating Polytunnel with Solar

[Susan BBPM]

We have an unheated polytunnel - I never considered heating it due to cost.

However, last year we installed solar generators for the house (a solar 'generator' is just a portable unit with an inverter, battery and slick interface). In April, May and June there's loads of sunlight but it's still cold at night especially. We'll have far more free electricity than we can use so it makes sense to use it for a) solar lamps for indoor growing and b) heating for the polytunnel.

How can that heat be best utilized?

I'm considering making heated 'mats' by burying heated wires in trays of sand. This would allow tomatoes, peppers and half hardy annuals to go outside much earlier than would otherwise be possible.

Is there any point trying to heat the whole polytunnel with an electric heater? Presumably it'd be too wasteful. Maybe heat a small portable greenhouse inside the polytunnel?

All suggestions welcome! Using 1kwh of electricity overnight is probably doable without any cost. More on the odd night when it's very cold. Fortunately, cold nights typically follow very sunny days so my batteries should be full.

 

[Tetters]

Hiya Susan, we also have a solar system with an inverter and batteries. Lord Awful, aka@Zigs knows much more about it than I do as it's his 'baby' I have a fairly large propagator which takes at least a dozen seed trays, and LA says there is sufficient power to run that.
I reckon if that is set up inside a smaller polythene ''tent'' inside your tunnel it would be great for propagation as well as helping to increase the temperature in the ''tent'' Zigs specialises in growing cactus in 'his' tunnel, and I usually let him get on with it. My gardening is mostly in fine weather, outside where I grow hardy perennials and grasses - I just call him in when I have heavy jobs to do.