It should work very well as the temperature is very stable and the low temps needed for tropical systems would mean you only need a relatively small surface area of land...unless you wanted a bore hole, but that may prove too expensive, depending on where you are and what companies are about. . You would need a few large tanks to make it worthwhile as I would guess buying/installing a small system would be around £1000. If I was going to put on in for the tanks, I'd do a bigger one for the whole house too...
If your handy though this would be the ideal application to try making your own, theres not much too them. And if it stopped working youd know as your in tank heaters would start again, so not much risk.