Solar Panel > Battery and 12V Heat Tape

[Enviromant]

I've recently been handed the task of trying to design a stand-alone system to heat a 10 foot section of water pipe during the winter months.

Let me preface with the fact that I'm an environmental engineer and it's been a while since my Intro to Electrical classes.

I figure I'll need a 10-20W solar panel, a 12V battery (maybe 2?) and either acquire or create a section of 12V heat tape. I figure avoiding inverting into a 120V heat tape should conserve a considerable amount of power/help efficiency?

The site is very sunny. Perhaps a heat tape wouldn't be necessary if the section was insulated well with heat strips such as (

http://www.mcmaster.com/#heat-tape/=8g3q46)?

At this point the solution is very open ended, so I'd appreciate any different directions and/or OTC solutions or ideas you electrically adept folks may have. Thanks for your time!

 

[BJC]

Insulation on the pipe is critical. Over insulate and make it rugged and keep it dry.
Batteries drop off in efficiency when they get cold. If your batteries freeze so might your water pipe. I would put them in an insulated enclosure ( with a vent) and a heater of some kind. You may need a bigger solar panel.

 

[IRstuff]

How cold is is the cold, and how windy?
How hot is the water?

TTFN

FAQ731-376

 

[waross]

Is this for freeze protection or a warm shower?
Presumably the pipe is coming from somewhere and going somewhere. For freeze protection you may be better to consider constructing a duct between the "From" and the "To" and running the pipe in the duct.
BTW, what may be the consequence of a heating system failure?
Have you considered the possibility of installing monitoring and solenoid valves to close the flow and dump the pipe contents to prevent freeze up when the solar system fails. (I give it about 3 to 5 years max from my experience with solar. But batteries may be better now.)(Less if there is a an extended period of overcast skys.)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[IRstuff]

Assuming:
1 in OD pipe
40°C delta from water to air temp
25 W/m^2-K convection+radiative loss to air

Using a 35mm thick vacuum insulation with 0.003W/m-K thermal conductivity, the heat loss from the water is only about 2.25 W, which could be made up by your heater.

http://www.glacierbaytechnology.com/category/insulation/

TTFN

FAQ731-376

 

[Compositepro]

Freezing water pipe has been a problem for centuries. There are several possible solutions, but solar/electric is very rarely one of them. Burial is the most common solution. Maintaining a small flow of water at all times is also common.
A small drip is less expensive and more reliable than batteries. And, of course, insulate.

 

[itsmoked]

I totally agree with Compositepro. Batteries for heat tracing are a disaster. Solar for the batteries in heat tracing - a guaranteed disaster.

Standard scenario: In rolls the cold weather => overcast => solar cell output drops to 10% design value => freak snow storm => batteries die => pipe freezes and splits => batteries freeze and split shortly after.

Furthermore batteries have a life cycle. Without careful testing and monitoring after a time the end result will be insufficient battery capacity and spit pipe.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rbulsara]

Solar for heat tracing is a very bad idea, even more so if you are "environmentalist", as freezing the pipe would be guaranteed as stated above by some wiser folks. It wont be generating any heat when needed most, on a cloudy, cold, snowy day. And you probably won't need heating on a sunny day!

Only you would know the environmental impact of a pipe burst due to freezing. You should be the one opposing this idea.

Rafiq Bulsara

http://www.srengineersct.com

 

[rbulsara]

Consider other alternatives such as keeping the water flowing, if practicable.

Rafiq Bulsara

http://www.srengineersct.com

 

[Enviromant]

So as basically is sounds like the idea is untenable. At the time of this posting the problem had been on my desk for about 3 minutes. The solution to the problem of the flowing water had already been decided upon by my PM... the solar>batter>heat tape solution. I thought it sounded a bit suspect but am no expert on batteries and how well they'd be able to power heat tape, whether for hours, days, or weeks and so I thought I'd pose the question to some folks in the know. I certainly want to avoid spilling any water and your fervent responses will help me with my case lol

And while I hear a lot of naysaying, do we have any more suggestions on the constructive side?

I'll answer some of the questions first.

The system is for freeze protection. The pipe is 6" diam, flowing full, and flowing most of the time. It is fairly well insulated, but could be improved upon. Temps can get down to -20F. The site typically does not stay overcast for long, but it sounds like just 3 days would be enough to completely drain a battery. The water starts at ~55 deg.

I can certainly scale up if it'd make the difference... 5 batteries? 10? Deep Cells? 60W panel? Wind actually has a lot of potential.

The site has full time employees and it's not a problem to have the batteries regularly checked up on. Burial is not an option for grade and rock reasons.

So aside from using wind as well as solar and keeping the water running, who's got some other fresh ideas?

 

[IRstuff]

OK, given the new information, the exposed length of pipe, if insulated with VIP, would lose about 5 W, total. An 80Ah battery could keep a heater powered for about 6 days continuously at that draw.

Given that, you're probably looking at lots more batteries, and lots more solar panels. Have you considered a gas generator as an addition to the solar panels? I'm guessing that 5 panels is a bit of an overkill, but it would allow the batteries to be charged emough in a few hours to make it through the night and still have power to run the heaters during day.

If there are people around, then what are they using for power?

TTFN

FAQ731-376

 

[OperaHouse]

I have 6 panels totaling 480W and a lot of days I can't even get one amp total at 12V in the summer. Don't even get me started on batteries!

 

[itsmoked]

<grin>

Keith Cress
kcress -

http://www.flaminsystems.com