receiver for parabolic dish solar concentrator

[russ]

So with one 2.5 m dish (area = 4.9 m2), an installation efficiency of 0.7, in a sunny winter day (sun power = 1000 W/m2) and 5-6 hours of sun (very optimistic), you can hope to produce 17-20 kWh per day. You see that 3 winter months, all of them sunny, would provide at best 1800 kWh. If your house is 160 m2, it needs from 6400 kWh (minergie) to 32000 kWh (standard) per year !

Better to get the insolation numbers for your area off the web - You will never see 1000 watts/m2 in the winter - maybe with enough reflectors.

[ReggieThe Dog]

Heating a house only with renewable energy is extremely difficult, unless your house is up to the best insulation standards. Let me explain why: Energy needs for heating can vary from 30-40 kWh/m2 (for the best insulated houses) to 200 kWh/m2 for "standard" houses from the 1970, when nobody cared about energy efficiency. These numbers are per year. Keep in mind that heating is the main source of energy consumption (roughly 80% of your total energy need). Check out the swiss Minergie standard for more specific info (http://www.minergie.ch/minergie_fr.html). For instance to attain 40 kWh/m2, your walls and roof need to be insulated with ~20-25 cm of the best insulating material with lambda around 0.035 W/mK to attain U=0.2 W/m2K, your windows need to be triple glass with Argon gas (U = 0.5-0.7 W/m2K), etc...

So with one 2.5 m dish (area = 4.9 m2), an installation efficiency of 0.7, in a sunny winter day (sun power = 1000 W/m2) and 5-6 hours of sun (very optimistic), you can hope to produce 17-20 kWh per day. You see that 3 winter months, all of them sunny, would provide at best 1800 kWh. If your house is 160 m2, it needs from 6400 kWh (minergie) to 32000 kWh (standard) per year !

Therfore you need to 1) insulate your house and change the windows, if not already done, and 2) install more antenna or solar panels. Nonetheless, going solar is in any case a good idea since it's clean energy, but you need to make careful calculations, to see where is best to invest your money (insulation, windows or panels).

A nice solution if you have a heat pump (with COP = 3) is to go for photovoltaic panels: the electricity produced at 20% efficiency, with a COP of 3, "becomes" 60% efficiency in thermal energy thanks to the heat pump, almost as good as thermal solar panels, but with the gain that during summer, photovoltaic still produce a lot of useful energy (electricity that you can sell throughout the grid), as opposed to the useless hot water produced by solar thermal panel in the summer (I'm only talking of hot water for heating, since hot water for the shower is only 15% of your energy needs).

Nic

[ATTACH=CONFIG]2582[/ATTACH]

Nic, Wise words indeed. I have looked into this also but not quite at the same depth and understanding you have. Thankfully we have a south facing house with large double glazed panoramic windows so the whole of the first floor requires no heating during the day whatsoever. When the sun is out, like today, it raises the main living area from 3-5C easily keeping it a steady 18C. Fair to say though if the sun is not shining it does get a little cold. Coupled with the fact we do have really good insulation installed about 3 years ago the house keeps that heat in very well so we only need a small fire at night to maintain a reasonable temperature.
To clarify my need - The only level that requires heating is in fact the lower level where my workshop is, which is about 50m2.
I'm loathed to put central heating on just to heat the workshop but I was toying with a having the dish, which will be a square dish of about 6.25m2,http://www.solarpaneltalk.com/images/attach/jpg.gif to perhaps heat a thermostore, using water stratification to store the heat, but that may have to be phase II of the project. I do like the sound of the heat pump, I'll have to look into it, though the cost of PV and all the associated equipment is a concern. I have an electric capability in mind for my Solar Dish too but not by way of anything like a Stirling engine, moreover a CPV or HCPV. Just waiting to see what the next gen PV cells will offer. In the meantime, I'm looking into a really nice heatsink solution that could work very nicely for both heat and light and hopefully give a really good percentage of efficiency for HCPV.
Besides heating, which as you say is the lions share of power consumption in the home during the winter, I would also like to utilise the heat produced for distillation/pasteurisation and to help drive a solar kiln for drying wood be that fire wood or furniture quality timber where temperatures of 80C++ are required and indeed not uncommon. Again, all future phases but am constructing/designing with these in mind. Arh so many things and so little time. Can I ask what you plan to do with the output of your dish once this project is complete?
Just discovered that a commercially available system of similar scale to the one I am designing would cost around 7000 euro. The ROI on that alone would be something like 10 years. Not very appetising

[nic]

Better to get the insolation numbers for your area off the web - You will never see 1000 watts/m2 in the winter - maybe with enough reflectors.

what I meant is that the theoretical maximum energy from the sun, the solar flux, is 1000 watt/m2: it does not depend on the number of reflectors installed.
It is true that in winter, when the sun is "lower" in the sky, the solar light crosses more of the Earth atmosphere, and this number goes down.

If you want to compare with reflectors surface, you have to take into account the angle of incidence (which can be perpendicular (max) only around noon) and the
efficiency of your thermal panel (around 70-80% for the best vacuum tubes solar collectors). Note that with a 2 axis-tracking system (e.g. dish), you are always perpendicular to the sun, contrary to fixed panels. Compared to fixed panels, tracking systems produce 20-30% more energy (see attachments).

A useful rule of thumb calculation shows that, at least for the latitude of Switzerland and for south facing installations, 1 kW installed translates into 1000 kWh per year, taking into account all of the above.

Picture 2.jpgtracking_vs_fixed.jpg

[nic]

Nic, Wise words indeed. I have looked into this also but not quite at the same depth and understanding you have. Thankfully we have a south facing house with large double glazed panoramic windows so the whole of the first floor requires no heating during the day whatsoever. When the sun is out, like today, it raises the main living area from 3-5C easily keeping it a steady 18C. Fair to say though if the sun is not shining it does get a little cold. Coupled with the fact we do have really good insulation installed about 3 years ago the house keeps that heat in very well so we only need a small fire at night to maintain a reasonable temperature.
To clarify my need - The only level that requires heating is in fact the lower level where my workshop is, which is about 50m2.
I'm loathed to put central heating on just to heat the workshop but I was toying with a having the dish, which will be a square dish of about 6.25m2,http://www.solarpaneltalk.com/images/attach/jpg.gif to perhaps heat a thermostore, using water stratification to store the heat, but that may have to be phase II of the project. I do like the sound of the heat pump, I'll have to look into it, though the cost of PV and all the associated equipment is a concern. I have an electric capability in mind for my Solar Dish too but not by way of anything like a Stirling engine, moreover a CPV or HCPV. Just waiting to see what the next gen PV cells will offer. In the meantime, I'm looking into a really nice heatsink solution that could work very nicely for both heat and light and hopefully give a really good percentage of efficiency for HCPV.
Besides heating, which as you say is the lions share of power consumption in the home during the winter, I would also like to utilise the heat produced for distillation/pasteurisation and to help drive a solar kiln for drying wood be that fire wood or furniture quality timber where temperatures of 80C++ are required and indeed not uncommon. Again, all future phases but am constructing/designing with these in mind. Arh so many things and so little time. Can I ask what you plan to do with the output of your dish once this project is complete?
Just discovered that a commercially available system of similar scale to the one I am designing would cost around 7000 euro. The ROI on that alone would be something like 10 years. Not very appetising

I also considered a Stirling engine to convert the heat into electricity in the summer, given that I have too much hot water. Due to costs and low efficiency of such systems (around 10% because of the rather low water temperature (60-80 deg)), I gave up and decided to install efficient PV panels, which work all year round. The best I found are the Sunpower (too expensive) and the Sanyo around 20% efficiency. High efficiency is important if your roof has limited space.
Otherwise, if you have enough space on the roof, you can go for lower efficiency PV that are quite a bit cheaper.

To answer your question: I'm planing to warm up water for heating purposes with the tracking dish. It will be complementary to a fixed vacuum tubes installation that I have already. In the summer, I will cover the dish and not use it (sigh). By the way, this is also what I do with half of my fixed thermal collectors, otherwise the water tank
goes above 90 deg (not good). Besides the showers, I also use solar hot water for the dish washer and the washing machine.

[russ]

what I meant is that the theoretical maximum energy from the sun, the solar flux, is 1000 watt/m2: it does not depend on the number of reflectors installed.wrong - without reflectors you would never get close to 1000 watts/m2 in the winter
It is true that in winter, when the sun is "lower" in the sky, the solar light crosses more of the Earth atmosphere, and this number goes down.

The number goes way down and heating is all about winter months - from PV Watts

The only way you will have a space close to 1000 watts/m2 is by reflecting outside light on to it.

"Station Identification"
"City:","Geneva"
"State:","CHE"
"Lat (deg N):", 46.25
"Long (deg W):", 6.13
"Elev (m): ", 416
"Weather Data:","IWEC"

"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 0.8 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 46.2"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 0.2 franc/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (franc)"
1, 1.27, 26, 0.05
2, 2.52, 51, 0.09
3, 3.92, 89, 0.16
4, 4.49, 98, 0.17
5, 4.94, 108, 0.19
6, 4.98, 105, 0.19
7, 5.46, 114, 0.20
8, 5.26, 112, 0.20
9, 4.49, 95, 0.17
10, 2.82, 62, 0.11
11, 1.61, 33, 0.06
12, 0.98, 19, 0.03
"Year", 3.57, 913, 1.62

[russ]

For a neat installation that can be adapted take a look at George's Workshop http://ffwdm.com/

He has parabolic collectors for heating a swomming pool but the same can be used for home heat.

[nic]

The number goes way down and heating is all about winter months - from PV Watts

The only way you will have a space close to 1000 watts/m2 is by reflecting outside light on to it.

"Station Identification"
"City:","Geneva"
"State:","CHE"
"Lat (deg N):", 46.25
"Long (deg W):", 6.13
"Elev (m): ", 416
"Weather Data:","IWEC"

"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 0.8 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 46.2"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 0.2 franc/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (franc)"
1, 1.27, 26, 0.05
2, 2.52, 51, 0.09
3, 3.92, 89, 0.16
4, 4.49, 98, 0.17
5, 4.94, 108, 0.19
6, 4.98, 105, 0.19
7, 5.46, 114, 0.20
8, 5.26, 112, 0.20
9, 4.49, 95, 0.17
10, 2.82, 62, 0.11
11, 1.61, 33, 0.06
12, 0.98, 19, 0.03
"Year", 3.57, 913, 1.62

yes, thanks. I realised that there was a misunderstanding from my side, sorry. By "reflectors" I thought you meant
"collectors" or "panels". Of course the solar flux (W/m2) does not depend the number of m2 of solar panels you installed.
I thought there was a confusion with the number of Watt your panel can produce per m2. Sorry again.

[nic]

For a neat installation that can be adapted take a look at George's Workshop http://ffwdm.com/

He has parabolic collectors for heating a swomming pool but the same can be used for home heat.

Indeed, with another group of students, we are also constructing troughs (see attachments), taking George as an model to follow. His brochure is great and was very useful to us. The difference with respect to Georges original model (for the swimming pool) is that we are using vacuum tubes for the winter. In the meantime and in parallel, Georges also tested vacuum tubes: convergent evolution! It is a more difficult case, since the weight of the trough can not hang on the tube at the focus: it is made out of glass and is therefore too fragile. We came up with a neat system of bearings.


pic3.jpgpic2.jpgpic1.jpg

[ReggieThe Dog]

For a neat installation that can be adapted take a look at George's Workshop http://ffwdm.com/

He has parabolic collectors for heating a swomming pool but the same can be used for home heat.

A swomming pool eh. Sadly I only have a 45,000 litre reservoir but I think I might rename it to a swomming pool. Sounds some much more up market!
Seriously, Nic has some great advice and sound figures, some of which I have. I'm more than happy to continue discussion with this obviously well-informed man.
I have thought about bouncing sunlight into the workshop but would be a little tricky and perhaps dangerous too.
By the way my design is for a dish and not a trough and if it works well I might even make it a double dish array. Finances depending! but if I can get this heat-sink idea off the ground a HCPV might be the answer for extra power. Watch this space. For me winter is the key. If I can sustain a good heat for water etc then I'll be happy. If I can help power my solar kiln and thus have a longer annual operation then I'll be thrilled.

Nic, I have plenty of space for PV panels www.naplanini.si but my pockets are simply nowhere deep enough and even if they were I would still think twice about it. The price would have to come down seriously before I opened my wallet, although this is an interesting site and one worth a watch for anyone in EU http://www.distribuzionesolare.com/web/

[ReggieThe Dog]

Indeed, with another group of students, we are also constructing troughs (see attachments), taking George as an model to follow. His brochure is great and was very useful to us. The difference with respect to Georges original model (for the swimming pool) is that we are using vacuum tubes for the winter. In the meantime and in parallel, Georges also tested vacuum tubes: convergent evolution! It is a more difficult case, since the weight of the trough can not hang on the tube at the focus: it is made out of glass and is therefore too fragile. We came up with a neat system of bearings.


[ATTACH=CONFIG]2586[/ATTACH][ATTACH=CONFIG]2587[/ATTACH][ATTACH=CONFIG]2588[/ATTACH]

Nic that looks great. There has been the same sort of problem in aeronautics for moving items passing through pressurised bulkheads with a myriad of different and sometimes entertaining solutions. Vacuum tubes are quite expensive I understand so I hope your solution works well. Can I ask if you intend to have a mirror-like reflective coating on your trough or will you simply polish what is already there? Are they compound parabolic or straightforward parabola's and will they track or not? Seems a shame not to put all that Arduino experience to use..

[nic]

Nic that looks great. There has been the same sort of problem in aeronautics for moving items passing through pressurised bulkheads with a myriad of different and sometimes entertaining solutions. Vacuum tubes are quite expensive I understand so I hope your solution works well. Can I ask if you intend to have a mirror-like reflective coating on your trough or will you simply polish what is already there? Are they compound parabolic or straightforward parabola's and will they track or not? Seems a shame not to put all that Arduino experience to use..

coating? yes! in the pics of my previous answer, the through is made out of aluminium (0.5 mm thick, more than that, they don't bend well enough), but we coated them
with mylar paper: we used http://www.wallliner.com/contactpaper.html
We tested the light paths in the lab with a small pointer laser and it works perfectly fine.

They are straightforward parabola, see georges phlak document http://www.ffwdm.com/solar/solar-index.htm

They will track by rotating around the focal line. So it is a 1 axis tracking, see the nice videos on Georges page.
and we ARE using Arduino for the tracking

I just got (after a 1 year procedure, long live Switzerland) the permit for the construction of 15 troughs in my garden.

[russ]

Comments within the text

A swomming pool eh. Sounds some much more up market! For the peasant class a swoming pool is a very luxurious item indeed - either that or someone that types poorly and doesn't proofread well enough.

Seriously, Nic has some great advice and sound figures, some of which I have. I'm more than happy to continue discussion with this obviously well-informed man. Take a look at George's calculations too - a few errors but the right direction

[russ]

Nic - I thought George had really laid things out nicely for the average person with shop skills to follow.

Looking forward to seeing more of your work.

[nic]

Nic - I thought George had really laid things out nicely for the average person with shop skills to follow.

Looking forward to seeing more of your work.

yes, true. George's model was immensely useful for us and I would recommend his brochure to everybody. I bought his brochure, but we had to make a few modifications, since his intent was for the summer (for the swimming pool). We wanted to use the troughs in the winter for house heating purposes, so we chose vacuum glass tubes, much more fragile than Georges original design (about 1.5 years ago). Hence all the "trouble" with the bearings and weight support.

On our side, I will post our final document on my webpage. Unfortunately, since we are in an Italian-speaking region, the diploma of my students will be written in Italian, as required by the high school regulation. More later.

[ReggieThe Dog]

Comments within the text

Nicely put Russ... I'll invest in one of those upmarket things if ever I become a millionaire. Until then I'll settle with our reservoir, despite having to share it with the ducks... hee hee
I have looked at Georges stuff before and to be fair about thirty other websites. George, as you say lays things out quite nicely and his set up is nicely arranged Though for tracking I believe he's using a redRok kit if my eyes don't deceive me.