If you can't fit a heat pump, resistive heating should work fine, but it will be more expensive to run. It would obviously put more load on your renewable grid,

If you can't fit a heat pump, resistive heating should work fine, but it will be more expensive to run. It would obviously put more load on your renewable grid, so you'd want to put heatpumps wherever possible, but at least it's better than burning gas/oil/coal for heat.