Modern Solar Heat Collectors, What Happens If the Energy is Not Used?

The situation is similiar to what is happening to the earth.With so much of solar energy incident on it and all this energy is not used nowadays(earlier it was the trees ,vegetation which converted this energy to useful work) it is leading to global warming.So will the solar collector will start heating up till the heat radiated from it is in balance with the heat received.This will place additional stress on the equipment and reduces its life.

This is also happening to the earth!!So plant more trees!!use less wood,paper...

With so much of solar energy incident on it and all this energy is not used nowadays

Not used nowadays? Nonsense. We are using more solar energy all the time.

(earlier it was the trees ,vegetation which converted this energy to useful work)

Useful work? Like what, waving their branched around to make a nice breeze for us humans? (A little hint, the wind is actually moving the branches, not the other way round).

Yes, we are using more solar energy all the time. However the vast majority of the available energy is doing un-controlled work such as creating hurricanes, tornadoes, huge snow and rain storms, etc. Not to mention massive cold and heat waves as different air masses are driven further from thier traditional haunts by the excess heat-energy in the global system. I've been telling people for thirty years not to mess with Mother Nature but I'm just a dumb-assed electrician. What do I know?

You wrote, "The situation is similiar to what is happening to the earth.With so much of solar energy incident on it and all this energy is not used nowadays(earlier it was the trees ,vegetation which converted this energy to useful work) it is leading to global warming."

I have no idea where you are getting such "facts". US forests have only declined slightly since 1630. In 1907 we hit a low going from 46% of total land area in 1630 to 34% in 1907.

Post 1907 forest area has remained flat until recently where it has started an upward trend.

However, even that data is misleading. The vast bulk of the land that was lost forest since 1630 has been converted to agricultural use, so still remains "green" and produces useful work.

As for the net equation of solar radiation and heat, solar heat transferred to produce hot water or other forms of energy ultimately returns most of that energy as heat anyway. In the case of hot water solar heat, 100% of that solar energy is still given off as heat somewhere. So how can you claim a loss given the law of conservation of energy?

"Here's a good paper:"

I agree, a very good explanation. This is a good read for anybody interested in solar heat collectors.

Milo - Thanks for the paper on solar panel heating.

I think around here (California, USA) the plumbing codes require pressure relief valves on hot water thermal systems regardless of the type of system. Just like a hot water heater. This to me would be a logical choice whether the fluid in the panels was the potable hot water or a heat transfer mix with propylene glycol. Which I think should be able to handle temperatures well into the range of 175C, as long as the mix is below its boiling point, without chemical degradation.

I don't know much about electrical panels. I honestly don't think a solar electric panel would be a viable product unless it could withstand continuous direct exposure to overhead sunlight at zero power output, 40C air temperature, a maximum altitude around 4000 meters, still air and an infinite area array(no way for air to move from below to above except for vent spaces in the individual panel).

I should ask my son, David, about this. He's in the biz. Might be some solar panel technologies are more sensitive to high temperatures than others and have to be limited in their environmental applications.

Ed Weldon

Great paper, many thanks. Now I have to study it!!

Get a bigger battery pack, so that you can store and use as much energy as feasible.

Here in Bangalore at 13ºN latitude, there is virtually no winter to speak about. We keep the collectors (Vacuum tube or otherwise) covered with a white cloth if we are away for more than two days. The system does have a vent pipe open to the atmosphere. So there is no bursting issue. However, there could be other heat damage. Hence the precaution.

Bioramani

Good answer, thanks! (Even though I'm not the OP.)

A followup though, partly because I'm not awake and ready to think yet--what happens in freezing conditions--must the water system be set up to drain the outdoor portions containing water? (I guess they must.)

Are there provisions for doing that, or is that something that must be built into the system (like a pump up / draindown system, that if the pump stops pumping, no water gets out to the collector)?

If freezing is likely, the absorber circuit is run using anti-freeze and an exchanger in the hot water tank. This is also the preferred approach if the water is 'hard'.

Typical snow latitude setup

^{_{(which I stole, so don't blame me if the tubes are tilted the wrong way off horizontal)}}

GA for a good comprehensive answer 34...

Usually, a small amount of MEK is used in the heat pipe due to it's boiling, evaporative and heat transfer properties. That's what I'm using in the heat pipes for my evacuated tubes that I'm fabricating presently.

Some sources recommend that you cover a portion of your solar tubes during the summer months if there is a lesser demand for heat, unless you're using the generated heat for air conditioning purposes. There have been reported collector tube failures in closed-loop systems resulting over heating due to failed or malfunctioning pressure relief valves, temperature relief valves, and thermocouples which control the circulating pump functions. Best to play it safe and conservatively I guess!

The effect you describe does happen and can cause overheating problems. One solution is to incorporate a thermal "waste gate" into the system. These function much like the waste-gate on a supercharger or turbocharger to vent excess pressure (in your case, heat) back into the environment.

Thanks to you all for replying, I now have some studying to do, particularly Milo's pdf..

hi ,

Solar system is designed considering avg. solar insolation available throughout year and considering period of max. during day time [4-6 hrs.]

So. whatever the case winter or summer does not effect designed solar capacity.

Also, collection tank is well designed [insulated ] to take care of winter season.

Here in india we provide air relief valve and safety valve for tank safety.

In summer or when there is no use [holydays]. The water in the tank gets heated and evaporated through ARF. In case pressure increased it gets released by safety valve.

When all water in the system comes to end. The heated air gets circulated.

there will be no damage to solar system. So there is no shade system reqd.

Some users take precaution to shade/ cover the collecters. Only precaution is to protect it from external damage.

Please supply some weblinks that support your comments, because I simply cannot believe you witout that.......I need more infos. Thanks in advance.