yep , can't beat the info given already !!! I would go the way of HM , no heat mat/lamps at all . Any pigs I have looked after never had anything other than plenty of straw in a dry arc/shed. Battery powered heat mat lamps would use a fair bit of electricity , and you would need a large bank of batteries to keep it all going . You would also need a good charging system , I doubt a trickle charge would do the job , ie trickle charger of 1 watt per hour (only during the day for solar !!) would only put in a max of 10 watts per day. I can't imagine any heat mat/lamp that would run on that ? So if you had a mat/lamp that was say 100 watts , that was running for only 10 hours a day . You would need god knows how many batteries to keep it going , an inverter would convert from 12v to 240v but it also uses power itself . So you have another loss to cope with ..ie you need even more power/batteries. I have lived with inverters and batteries and unless you have a really good charging system , it is a real pain . With a good charging system it is a good way to keep off the grid , but you always end up having to buy new batteries,and car even tractor batteries aren't the ones to buy for that system . The new led solar powered lights are great, but heat mats/lamps are a different matter. Good ole straw will do the job fine , pigs are really tuff little sods and get by with very basic stuff.
cheers
Russ