Choose solar collectors: plans or vacuum tubes?

Solar thermal energy in all its forms: solar heating, hot water, choosing a solar collector, solar concentration, ovens and solar cookers, solar energy storage by heat buffer, solar pool, air conditioning and solar cold ..
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gfgh31
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Registration: 25/09/13, 11:20




by gfgh31 » 25/09/13, 11:44

Hi everybody
5 years after the beginning of the post does someone have a more decisive result?
I do not want to blame you and thank you and congratulate your forum then once for any planar or tubular sensor?
(according to your tests of course)
maybe the answer escaped me in which case I apologize to you of course
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I Citro
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by I Citro » 25/09/13, 14:12

We can not answer categorically. :?
We must choose according to the use that we will make.

In all cases, I wanted tubular sensors for performance. I finally opted for flat sensors for a question of aesthetic integration.

My sensors are on a roof visible on the street side and I installed at the same time photovoltaic sensors.
I found a manufacturer who proposed universal modules.

I was able to integrate my thermal sensors in the middle of my PV sensors.
The aesthetic rendering is excellent, it would have been deplorable with tubular sensors.
Image
Soon 4 years and more of 15 MWh of hot water produced (yes, 15 MegaWatt.hour) is close to 4000kWh per year.
Of course, this represents only 400 € of saving per year compared to an electric water heater but in 2ans, it will be economically depreciated.

For me, the greatest satisfaction is to no longer consume the slightest gas m3 (to top up when the sun is out) for more than 6 months a year.
Formerly, I was forced to leave the boiler with its night light on 365 days a year, today, I cut the boiler from April to October and relaunch it only for the heating season. It then completes the solar water heater IF NEED EAST.
: Mrgreen:
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by Cuicui » 26/09/13, 00:12

I find that planar sensors of larger surface render the same service as tubular sensors more efficient but more fragile.
Your photo: Google Earth or drone?
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I Citro
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by I Citro » 26/09/13, 00:33

: Lol: You would not need glasses ...
The photo is from google, and I did not do anything to hide it ... :P

When I see all these tiles around the panels and that are useless ...
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of
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Solar panels




by of » 08/10/13, 14:15

I am not convinced by the solar although all the sites where I inform myself support the solar with 100%!
On this site for example: http://www.climamaison.com/demontrons-les-economies-par-l-exemple.htm we give as return on investment 6 years! But after 6 years, flat or tubular sensors will be fouled and what about performance?
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by I Citro » 08/10/13, 15:15

Dirty. :?:
Depending on where the sensors are placed, they can indeed get dirty (car polution, proximity of trees, factory chimneys, storm rains, laterite, pollen, bird droppings ...), but that Nothing is irreversible and has little impact on performance.

We are talking about thermal sensors that heat water. The yield is exceptional because in principle higher than 80%.
That is more than 1400Watt / m².
Yesterday again (we are at the beginning of October), my solar water heater has garnered 26kWh of energy thermal in his 300L balloon.
Even if Bordeaux is not the Arctic Circle, it says a lot about the merits of a solar water heater ...
: Mrgreen:

My gas boiler that provides extra in case of absence of sun has been disconnected since May. since I am equipped with this material (already 3 years) the sun provides 100% my hot water needs for more than 6 months and 80% the rest of the year.

My flat collectors are located in the center of the photovoltaic collectors (see picture a little higher). Usually I clean them several times a year (a throw of a jet and a large squeegee window cleaner), I have not done this year, but the production does not show a significant decline ...

If the investment does not exceed 3500 € and if the material is designed to last and assembled in the rules of art, do not hesitate.

Despite a deplorable assembly, my solar water heater (Schuco) paid 3300 € gives me complete satisfaction.
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Isma10
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Calculation of the performance of a water sensor




by Isma10 » 19/08/14, 10:22

Hello,

I have trouble doing a renewable energy exercise. I do not know where I'm wrong in the calculations but the result I find is inconsistent.

I will begin by stating the exercise:

Exercise:

"
Calculate the performance of a water sensor operating under the following conditions:
- h = 20 Wm-2 ° C-1
- L = 2m; l = 1m
- Absorber: steel sheet thickness 1mm, tubes diameters 15 / 21mm, distance tube / tube = 10cm.
- Absorption factor = 0,9 across the spectrum
- Water flow = 0,0035 kg.s-1, inlet temperature = 32 ° C
- Fluid / Tube Exchange Coefficient = 1500 Wm-2. ° C-1
- Weather conditions: Ta = 35 ° C; HRa = 40%; V = 2m.s-1; G * = 750W.m-2
- Glass: tau (ci) = 0; alpha (ci) = 0,88; tau (cs) = 0,85; alpha (cs) = 0,08 distant from 3cm of the absorber

Resume the calculation with a glazed sensor with a selective absorber: tau (ps) = 0,9; tau (pi) = 0,1.

The details of the calculations and the intermediate numerical results (values ​​of all transfer coefficients and thermal resistances) will be given. "

solution:

The formula I used is:

r = B- (K x (Tm-Text)) / G

with: r represents the yield in%.

B is the optical factor (%), it varies between 50% and 80% depending on the nature of the sensor. The optical factor corresponds to the maximum efficiency, ie when Tm-Text = 0. In this case, B = alpha (ps) * tau (cs) = 0.9 * 0.85 (alpha (ps) is the absorption factor)

K is the coefficient of loss in W / m².K, it is equal to h = 20 W / m².K
Tm is the average value of the fluid temperatures at the sensor input in degrees Celsius, it is equal to 32 ° C.

G is solar irradiation in W / m², G * = 750 W / m².

hence the result is:
r = 0.9 * 0.85 - (20 * (32-35) / 750) = 0.845 = 84.5%

I am waiting for your comments for the different calculations, and to know if what I did is right or not, because I think why I have more data in the statement if I do not use them. So, I thought it would be better to have some advice on the formula used and if I took the trouble to solve the problem in order to calculate the yield, since the 2th question I could not do because I do not know how to do it.

Thank you in advance.
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Re: Choosing solar collectors: planes or vacuum tubes?




by Christophe » 12/03/16, 18:08

I put a diagram that explains the geometric interest of vacuum tube solar collectors:

performance-sensor-solar-in-function-from-orientation-pic426.jpg
efficiency-solar-sensor-in-function-of-the-orientation-pic426.jpg (24.62 KIO) Accessed 10576 times


sensor-solar-a-tube-vacuum-pic425.jpg
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