Cheapest DIY options for a Closed Loop Solar Hot Water system for a hot tub?

Hi folks! First time post (and I assume it will show but here goes).
I recently picked up an old hot tub online. Got it running two weeks ago and in general it works ok but the heater struggles and I'm expecting a noticeable add-on to my electric bill.
I was hoping to put together a closed loop solar water heater. I live in New England and the winter will be bad, but I'd love to have a cheap-to-run hot tub to slip into in the (potential) snow.

I'm using this site (http://www.solartubs.com/solar-hot-tubs/) for reference on it, but I want to know if I can adapt cheap home made solar panels (even the tin can solar air heater) to these types of systems.

If anyone can point me to something helpful online, I'd appreciate it greatly. (Or if you've done something that would work that is as far under $1000 as possible, that would be amazing.)

Thanks in advance,
Nathan.

Howdy Nathan , welcome to permies.
Can you find some old sliding glass doors? I pick them up from craigslist now and then. How about some poly pipe? or even black PVC or copper? Then some old wood , plywood and 2X4's or 2X6's.
Some old tin roofing would work too. Build a box and pump the water through the collector and there you have it.
You will need to keep the tubes full of moving water as it might melt the tube if it gets to hot. It might also freeze in the winter.

There are lots of online plans to help. And lots of discusions here at permies if you take some time and look around.

http://www.ehow.com/how_6553432_diy_-solar-hot-panel.html

http://www.instructables.com/id/Solar-Thermosiphoning-Hot-Tub-Heater/

Hi Nathan welcome! No experience with that exact application but Ive always wondered about it. Dont temps usually run from 100-109F? Thats pretty hard to squeeze out of a typical New England winter day. On really sunny days I bet its possible but you would need a lot of really good collectors for a typical sized, very insulated tub. Guessing (4-15) 4x8 panels (collectors)? Probably best you could do is pre warm the water which is still not something to overlook for such a thirsty, expensive and usually destructive energy user.

In my area there used to be quite a few used panels around which are well worth the money compared to DIY. If you could get the collectors below the tub in elevation, you might be able to avoid pumps with thermosiphoning. Strongly avoid grid tied ac circulating pumps as they can compound the whole equation for the worse. One of my final projects in school was a solar water heater that was just a cheap poly pipe (insulated on both sides and glazed on one side) in a loop down hill with the tank at the top. Might be nice to have any assist possible.

Iam getting close to installing a compost water heater, which might be a better choice for your tub too. Compost would run 24/7 and you could probably do it without freeze measures because it lends itself to burial. Again, with a compost water heater downhill (or below) your hot tub, you could probably get it to siphon on its own with no pumps. So you could have solar AND/or compost (leaves and coffee grounds). That might get a pretty reasonable base temp to finish with the dirty fuel. Thanks Nate for the inspiration on the pumpless, compost hot tub. I want one and am building a deck at some point..

Wood is the most popular option to entirely heat the tub or finish heating the pre-warmed water from solar or compost. Where I grew up, there was a story about a certain river hippy that had found a hot springs up a mountain creek. I heard rumor about the particular creek, it was protected by remote national forests on one side and a tight mtn gorge highway with the mighty ocoee river on the other. It was a fun adventure exploring the seldom traveled creek bed and knew there were no hot springs in these parts. Lo and behold, on a gravel bank there lay a deflated kiddie pool and a fire ring with a coil of copper nearby. I couldnt believe I had found Frankie Hubbards secret hot springs!

I have zero experience in heating water with wood although I would if I could. I know its dangerous so everyone be careful about it please. Also be careful about trying to elevate hot tubs geez.

Checked out the site, pretty cool. Did you get pricing for the wood heater? Those evacuated tube panels are impressive. Last time I priced them they were around 1100. Its going to be tough to DIY cost effectively to match the BTUs you can get with those suckers. Not to mention take a lot of time, space and probably look like the s word. I think compost piles look better than solar panels (especially homemade) but I bet my neighbors would disagree. Maintenance on the other hand..

Thanks for the input guys!
I'm actually finding a few used collectors on Craigslist, that I hope would take the most expensive component that I was finding.

Not too sure about the compost pile solution. I think it wouldn't be very effective with the yard I have, but I'll keep reading.

Thanks, continued input welcome.

Nathan : I want you to think of the number of times you have picked the spot on the mall parking lot free from ice, and after a while being in the mall, coming out to a very warm car,
even though the outside temps were only 10 F ) F or lower !

Yes you can do this, you don't get to pick the days this happens , but it does happen ! you are the only one who can decide if you can be happy with this ! Hope this helps

For the Craft , Think like a fire ,flow like a Gas, Don't be the Marshmallow BIG AL !

Hey Nathtan,
This group started as a yahoo group, now has their own forum. They discuss all aspects of DIY solar hot water and solar air as well. Tons of info on DIY collectors. I like the PEX or CPVC myself.

Simply Solar

A simple wood box, insulated with some polyiso, and a run of CPVC, PEX, or copper (if you could afford that). A drainback design would work great for the cold. You could use a snap switch in the panel to run the pump. Good luck!
Sooner A