Solar Hot Water Panel

Pipe spacing is a function of panel efficiency -- e.g. temperature differential between incoming and outgoing heat transfer fluid. Also know that heat sinks become heat radiators. NASA and Sandia Labs have done extensive research in fluid heat exchange solar panels, and they have come up with some really exotic designs, coatings, etc., which, in my opinion, kinda misses the point. If the cost of solar panels is too high, the dang things will not pay for themselves in an ordinary lifetime.

Is that the reason why 90 % of the city of Athens, Greece has solar hot water? And why 17 million systems are in use world wide? The inclination of the panel towards the son (taking the breaking index of the glass into account) counts for a lot more difference in efficiency than the pipe array.

At the equator, about horizontal and further inclined more to the poles to. A a rule you can use your local coordinates.

I agree when you consider a once through system that the balance is pretty critical, but I politely but completely disagree with your theory in thermo siphon application. 2000 Watts/m2 heat from the sun is a great gift.

Israel is one of the pioneers on this matter. The pool heating systems of Heliocol are according your ideas. Plenty black PP or ABS tubes (1/4"- 6 mm) that cut into 2 feeders of 2 inch. No tank - all the heat is conveyed to the pool. It is applied with a pump,(1-2Hp) that also eats power. .

For one section or for 10 sections. They are one pass through.

Same diameter.

A far better approach however, is a PP circular tube in 1 roll flattened out behind glass. without any fins.

One disadvantage is emptying for freezing problems in regular areas. The things do not need to be expensive at all ( a DIY'er can make a good panel for $200 or 150 euro or less - you can even use a plat one plate black heating radiator) - and clever combinations can be set up with the local electric water heater tank, almost in each house. (I only wish they were a little more efficient) Respectfully

Is that the reason why 90 % of the city of Athens, Greece has solar hot water? And why 17 million systems are in use world wide?

I believe the point Bill was making is NOT to over engineer or design.

p911

I think I see your points. First and foremost, it is a factor of cost vs output. If I am collecting all the heat I need, why add piping. Seems to me that I am going to have to test and see just how much heat I can collect and go with that. Looks like modular panels that you could add to would be attractive. Kind of like grow as your needs grow.

I have been pioneering for 35 years with solar panels. If there is something with a fast payback - it is your solar water heater. The system lasts 15 years plus and pays back in 2- 3 years here. Subtropics. (power cost is between 30-40 $ cents per kWh.) We have installed 395 Megasun systems with thermo siphon (Helioakmi) and people like it. The size of the transfer pipes between feeder and receiver is only a matter of cost. (copper) For a 3/8 pipe you go with 3 inch fin - a 1/2 pipe takes 4 to 5 a 3/4 - a 3/4 pipe 5-7. Some manufacturers solder, others press them together. (Omega- shape) It is more important that you create one big black area under wind- free glass. We have done lots of tests during research when we had our factory and whatever of these pipes with fin combination makes less than 0.3 % difference. Within the same Glass frame box and combined with a top tank. It is just economics and maintenance that might help you make up your mind. If you build it yourself, your tank will be the most expensive part. Solar is simple: on a hot day your tank is always far too small, and on a cloudy day always far too big. (almost boiling water to look warm) I only have a supplementary heater in a second (very small) tank as backup. (Average 20 days in use per year)

GA from me dvmdsc. Do you have an idea of the payback time, when the system is installed in the Benelux countries, if cost of energie is about 0.22 Euro / khW ?

What system has the fastest pay back time : Photo voltage cells or Solar hot water panel ?

Solar thermal (hot water) hands down - plus it is much simpler.

Please elaborate who what which stainless steel tanks and where corrosion was appearing due to what ? Incompatible metals? poor grade stainless?

Thanks

As promised, more about PV solar payback.

Now we are into politics - the government's and the local power companies'.

Both differ from country to country.

Austria, I heard is searching for each good situated roof, even in bad condition and the power company there proposes to replace it when they can cover it with PV panels.

Austria has been very progressive and they understand what the eco solution is and adapt the economics to the grid.

PV panel farming is not that efficient, because of the loss of space on the ground. PV needs 15 to 25 times more surface for the same output.

(with black arrays) When using free space on clients' roofs, they bring down the cost of wires too. They divide and distribute on grid voltage level this way. = thinner cables. Each system is delivering to the grid. Fronius (AU)is also one of the world's leader in inverters. Countries like yours have incentives for investors, you get some government's money, however I also heard they give it one hand and take it back later with the other, by re appraising the house afterwards and raising the cadastral (house) tax. A grid -tied system (no batteries) is doable if you count on a payback period of 10-15 years in a good scenario. You can try with a part and expand it at your ease (read pocket assets) The power companies mostly pay less for what you deliver as for what you get. This can be a little tricky for your payback calculations. But on the other hand, they still have to supply the peak loads, when your panels are "sleepy". The "battery" inverter situation is different and more expensive.

Batteries are not that eco friendly, expensive and don't live that long.

They present a serious cut in the budget and the don't last in your payback scheme. Count 1 or 2 replacements in the 20 years plus payback time.

I have the impression that the USA is getting prepared for solar too, however implementation is still ample. It has a lot to do with culture and kWh costs.

Florida, the Sunshine State is far behind everyone else when it comes to solar on private buildings. They use a lot more energy for everything - resources are "cheap"? And politics behind it have been different for decades.

On the Islands of the Bahamas the story is completely different: here the first "offenders" start to provoke law suits to get Solar Legalized. According the law, it its not allowed. The Power company is monopolist and has attempted to close down solar businesses - with some help - and successfully. At the end I predict they will loose the "battle".

If you need more specifics the link of Lynlynch provides a calculation method, slightly to adapt for Europe.

thanks for the detailed answer.

dvmdsc

Yes Dear,

Your question itself has partly answered your query. I quote your statement "Seems to me that the closer the better unless you are using the finned tubing" That is exactly the answer. Here I may add that it is OK that closer is better but there come two considerations, more pipes add to:

1. Cost of the solar collector/panel

2. Weight of the panel

Selective coating takes care of the radiation and by virtue of its properties it does not allow the pipes to re-radiate the incoming radiation, hence most of the radiation 95-98% is converted to heat and transferred to water in pipes.

Answer to your question:

As far as the size of the fins is concerned, as a rule of thumb optimally each side of the fin should be three times the diameter of the pipe for proper heat transfer. That makes :- 3+3+ diameter of the pipe=7 times of the diameter of the pipe is optimum spacing between the pipes in a solar panel

Regards

Dr N P Singh

I'm surprised Del hasn't been here.

http://cr4.globalspec.com/blogentry/4969

I would like to share your opinions on replies to this question since I am also trying to find a solution. Please contact boragroup@yahoo.com thanks

I have read Del's posts and found them very informative. I think I am going to scale down the size of my panels and add more tubing. One will offset the other as far as weight is concerned. I thank you all for your input it has been helpful.