If you can find a way to heat your hot tub with solar power think of all the money you would save. Unfortunately, you cannot go down to your local hot tub store to buy a solar powered hot tub because they don't make them. That's right, there is no hot tub manufacturer that is currently making solar hot tubs.
If you want to heat your hot tub with solar power you are going to have to find a way to harness the sun's rays to heat your hot tub. You are going to have to either build something on your own to do this or get something like a solar blanket.
Putting a solar blanket on your hot tub, jacuzzi, or pool with help greatly in keeping the water warm and depending on the time of year, it may even heat the water some on its own. However, to do a real job of heating your hot tub with solar power, you are going to have to use a solar panel of some sort and hook it up to your hot tub.
Building your own makeshift solar powered hot tub is too hard for most people and probably not worth the time. In addition, you have to live in a place that is hot and sunny most of the year to be able to benefit from something like a solar hot tub. Again though, you can't just go out and get a solar unit that is made for heating hot tubs. This is because they just don't make them.
You can buy parts on Ebay and other such websites to start making a unit to harness solar energy but solar pannels are rather expensive. Once you have your solar panel and battery built, you will still need to find a way to heat the water using that energy. For most people, the difficulty of all this is too much and just getting a solar blanket to help keep the water warm is recommended.