,Lidle do an air compressor about the size of a cordless hand drill comes in a pack with a tyre inflator for very little money, the battery packs fit their drills and various other cordless tools they do. seems a good option to me. Having had discussions on this with various people if you could run a barrel cooler of a compressor with a air tank on it, as the compressed air expands it would get very cold. ( if you have ever used air tools you will know how cold they get ), it would need a moisture trap on it but that would be the ultimate.