Solar in Winter

[bzeller]

We are considering building a pool and looking at various heating options. We were originally looking at a pool and spa combination with NG heater. Now, I'm considering removing the gunite spa and heater to the tune of $14K and adding a Dimension 1 spa for about half that. The problem is of still like year round access to the pool. How does solar do in the winter in TX, specifically Austin? I'm wondering if I can expect to get decent increase in temps on a sunny 45-50 degree day? Anyone have any experience?

Thanks,
Benjie

 

[JohnT]

The large delta between pool water temperature and air temperature is going to be a problem with pool solar.

My guess is that at 45-50 degrees with a breeze you'd do well not to lose heat through the panels since they will act as radiators as well as collectors. The heat demand of the pool will be enormous as well, since heat loss is proportional to the delta between water temperature and the air above it.

With a 20,000 gallon pool, you'd have to add hundreds of thousands of BTU per day to make up for loss, and extra capacity to recover from cloudy weather. That would mean you'd need the equivalent of 10-20 panels in summer sun, which would not be practical in the winter.

Glazed panels may be able to help, but they are substantially more expensive.

 

[bzeller]

Is there a product you can use on top of the water to help mitigate the water to air heat transfer?

 

[duraleigh]

Well, a solar cover is essential to the performance of ANY solar heat system but I don't think it will be enough to solve what you are trying to do.

 

[bzeller]

Bummer. I guess the next question would be given how inexpensive NG is right now, what would be the advantages of adding solar? I'm not afraid to spend money up front if it saves me money on the backend.

 

[JasonLion]

You could use evacuated collectors, which have the water flowing through vacuum tubes, kind of like a good thermos but one that lets the sun through. They are significantly more expensive than regular panels and aren't as effective in the late spring, summer, early fall, but are dramatically more effective in the winter.

Whatever kind of heater you get, it will need to be significantly larger than is usually used to have any hope of maintaining the water temperature in those conditions.

Are you sure you will actually want to swim when the air is that cold?

 

[Isaac-1]

I would say don't give up yet, Solar could certainly extend your swim season in central TX, how much depends on the number of panels you install, with a solar cover and enough conventional unglazed panels you could probably extend your swim season to 10+ months per year on the average year.

 

[bzeller]

Are you sure you will actually want to swim when the air is that cold?

Well, if you're going to state the obvious, then maybe not!

The weather here in Austin can vary greatly from December through March. One day we might have a low of 40 and a high of 55, but then the next day a low of 55 and a high of 75 - 80. More realistically, we might watch the 10 day forecast and heat the pool in anticipation of a 70 - 80 degree day.

If I got solar, would this allow me to maintain my hot tub at higher temps reducing the time to heat or maybe even the size heater? This would make it similar to a stand alone spa that is always "ready". I want solar if there's a cost and/or convenience factor such as Issac-1 stated.

Is solar one of those items easily added later or better to do upfront? In looking at it briefly, it looks like its mostly a matter of installing on my roof (which faces south) and plumbing into an existing system if added at a later date.

 

[Isaac-1]

Solar can be easy to add on later, particularly if you plan ahead for it when it comes to things like pump location and plumbing to access intended collector mounting points, etc.