DIY Solar project - is this worthwhile, or a waste?

[PrivatePilot]

Hey all...I've been tinkering for the last few days with solar after managing to pickup most of the essentials here and there over the last few weeks at a pretty minimal cost. I got a nice pump (brand spanking new) for $20 from a garage sale (1/2 horse, so I'm not running my 1 HP main pump just for the solar), and the rest amounted to a DIY project...one which is so embarassing in some regards that I don't even want to post the details at the moment.

I've got probably $80 invested in it all, though...so if the experiment fails, well, I've still got a $200 pump that I paid $20 for and all the other plumbing etc to use with a better system.

I've plumbed the system in so that it's drawing off my skimmer and returns to a dedicated return line which is temporarily just draped across the deck at the moment at the opposite side of the pool.

Can someone crunch my numbers and tell me if my numbers make this worthwhile, or a waste?

Current input temperature of the system (measured electronically right at the input) is 82F.
Current output of the system (measured electronically right at the output pipe) is 86F.
GPH through the system measured at roughly 360 GPH.
This is with the collector in almost direct sun at pretty much the perfect angle.

I've been watching the temp probes for about an hour and those figures have been pretty constant.

So...wise solar guys, school me please.

(Edit: Adjusted in/out readings, figures just changed in the last 10 minutes, solar blanket is also doing it's thing, but both temps went up exactly 1 degree so it's still consistent with the solar collection..)

 

[Isaac-1]

Well it sounds like you are getting near optimal flow, you generally want to keep water output temperature as close as possible to input temperature, having said that at retail pricing, and often even below retail pricing the economics just are not there for home built collectors. When it comes to solar collectors surface area and minimal flow resistance is everything. When mail order 2x20 ft (40 sq ft) panel kits are available for $150 or less (eco saver on amazon at $139 w free shipping) it gets very hard to build any type of collector of equal size for anything close to equal money. I am not saying these bargain panels are the best quality, but will likely hold up as well as anything home built.

Ike

 

[PrivatePilot]

When mail order 2x20 ft (40 sq ft) panel kits are available for $150 or less (eco saver on amazon at $139 w free shipping)

Plumbing to and from the collector aside, I have a total investment of about $40 involved in the collector itself and have roughly about the same collection area, although my efficiency is probably a lot less than a proper collector.

My question remains though, with those hard numbers and my measured temperature rise should I expect much out of what I've setup?

Forgot to mention it's about a 5000Gal 12x16 if those numbers are helpful to anyone doing the math.

Although the nice cheap solar collectors from Amazon look good, keep in mind I'm in Canada and much Amazon stuff won't ship here. Costco is the cheapest option I found for a low-end solar system and I'm still looking at about $250 by the time I'm done. That's the route I'll go if this system turns out to be a failure (and I'm resigned to that possibility), but for the price, I had to give it a shot.

 

[mas985]

What is the collector area?

Also, a 4 degree rise with only 6 GPM means, that you will probably only gain a few degrees per day in the pool which isn't much.

 

[PrivatePilot]

What is the collector area?

Also, a 4 degree rise with only 6 GPM means, that you will probably only gain a few degrees per day in the pool which isn't much.

I figure roughly 30-40 square feet.

A few degrees per day would be great. Pool is at 81 currently (having reached that with the solar blanket only, basically) which just isn't doing it for most of my family - I'd like to see about 85/86.

 

[mas985]

You would probably get a lot more net heat gain with just a pool cover. Most of the time I don't need solar when I am using the cover.

 

[PrivatePilot]

I've peaked at about 82 with the cover alone. The weather hasn't been conducive to getting past that - I hit 84 a few weeks back but a few chilly evenings and I lost it all.

 

[JasonLion]

You can probably get twice as much heat out of that, or more, if you can split the plumbing runs into four or more parallel runs for each run you have now. That requires many more joints, which can be a leak risk, but it can significantly improve efficiency. The more parallel runs you have, the higher you can get the overall flow rate, the lower the temperature gain through the system, the higher the total efficiency. (I know, lower temperature gain is better overall isn't what you might expect, but that is the way it works, more water run through more than makes up for less temperature gain for any given packet of water.)

 

[waterfall]

I just set up and have running 5 collectors 4' x 10' each and built a wifi solar pump controller. Living in Michigan where the weather is not always great. coming off a few 65 degree days it raised my pool from 77 to 88 degrees and I had to turn down the temp to bypass the collectors.

With this system it will bypass the solar if it is not hot enough to generate heat. So far I am extremely happy with my results. 15000 gallon vinyl

 

[PrivatePilot]

You can probably get twice as much heat out of that, or more, if you can split the plumbing runs into four or more parallel runs

There are two parrallels already. With the size of plumbing I used anything less would have built in inordinate amount of backpressure.

I'll get a decent test on the system all day tomorrow as it's (finally!) supposed to be bright and sunny all day...and I'll be home to actually run/test the system constantly all day.

 

[mike1975]

Can someone crunch my numbers and tell me if my numbers make this worthwhile, or a waste?

If your pool is warmer with the collector and you didn't spend much money, it's not a waste. Just make sure you didn't use any UV-blocking materials for the front of your panels, you want to let the UV in.

You can probably get twice as much heat out of that, or more, if you can split the plumbing runs into four or more parallel runs

There are two parrallels already. With the size of plumbing I used anything less would have built in inordinate amount of backpressure.

He's saying to add more parallel paths, i.e. 8 paths instead of 2. Back pressure will go down, flow in each path will go down but total flow will go up slightly because you have more flow paths. More flow = lower average fluid temperature = greater temperature differential driving heat into the water.

On the other hand, higher flow equals more turbulance, and turbulant flow is better for heat transfer from the pipe walls to the fluid.

 

[mas985]

Just make sure you didn't use any UV-blocking materials for the front of your panels, you want to let the UV in.

Most commercial solar panels are made of UV resistant materials which means they partially block UV. Otherwise the material would fall apart in a very short time period. So you really don't want the plastic to absorb UV.

But UV really doesn't add much heat anyway and is a small part of the total solar spectrum. There is much more energy in visible and infra-red parts of the spectrum.