That is a bit like how long is a piece of string question.
The only answer I can give is... it depends.
On where it is (North, South?)
how warm do you like to be?
What type of winter are we going to have.
How well insulated is the static (walls, roof, floor).
Is the gas mains? LPG? How much is it per unit?
It sounds as if you are planning full time living, in which case are you getting a static for your own land, or on a park?
If on a park, then it will have to be a licensed residential park, which means a park home - modern park homes (built to BS3632) are as well insulated as bricks&mortar (better, in some cases) so heating should be the same, or less, as a bricks&mortar house.
If you are buying a static for your own land, do try and get one that has been built to BS3632, as this is considerably better than winterised (which is intended for comfortable holidays, not full time use).
If planning on solar, then you either need stand-alone panels, or a specially strengthened roof and frame (usually done at the manufacturing stage) plus extra supports underneath.
Linkback: https://staticforum.co.uk/index.php/topic,748.msg1966.html#msg1966