Booster at thermodynamic limit - use of CPC and other innovative designs

[al2cand]

Be it to reach higher temperature for water purification, for CPV or for new LSC, using fixed booster mirrors is an interesting avenue.
The CPC patent was released to public and have been used by many solar cooker and other projects.
Compound Parabolic Concentrator reaches the thermodynamic limit so one would be rapidly criticized by introducing ideas trying to do better... The CPC is a 1 aperture and 1 absorber surface system which can be proven to be the best by different methods such as hedge ray, flow lines and radiation transfer equilibrium. Other modern techniques such as SMS Simultaneous Multiple Surface allow more freedom in the design and has potential to beat CPC on daily sun collection % (your opinion?).
For fun I have simulated daily energy collection for PV panel VS CPC VS other methods.
The CPC collects 18% more daily energy than non-boosted PV. (I would be interested to compare with existing publication?suggestions?)
The interesting part (if proven true) is that other systems I designed offer from 20% to 31% more daily collected energy depending on complexity.
I am new to the forum and I know many experienced seniors will shed more light on this, thanks!
Jean-Philippe Bédard

[J.P.M.]

Be it to reach higher temperature for water purification, for CPV or for new LSC, using fixed booster mirrors is an interesting avenue.
The CPC patent was released to public and have been used by many solar cooker and other projects.
Compound Parabolic Concentrator reaches the thermodynamic limit so one would be rapidly criticized by introducing ideas trying to do better... The CPC is a 1 aperture and 1 absorber surface system which can be proven to be the best by different methods such as hedge ray, flow lines and radiation transfer equilibrium. Other modern techniques such as SMS Simultaneous Multiple Surface allow more freedom in the design and has potential to beat CPC on daily sun collection % (your opinion?).
For fun I have simulated daily energy collection for PV panel VS CPC VS other methods.
The CPC collects 18% more daily energy than non-boosted PV. (I would be interested to compare with existing publication?suggestions?)
The interesting part (if proven true) is that other systems I designed offer from 20% to 31% more daily collected energy depending on complexity.
I am new to the forum and I know many experienced seniors will shed more light on this, thanks!
Jean-Philippe Bédard

The CPC has been around for a long time. It has some limited application. It is not unlike a lot of schemes that use reflectors to boost output and make claims of higher efficiency while downplaying the logistical and practical limitations and drawbacks. For domestic use and experiment, running the trough E-W with about a 20 deg. half acceptance angle may be a good start for minimal seasonal adjustment .

Interesting use of the term Thermodynamic limit.

For one source for comparison: " Solar Energy", Elsevier Press, has many papers dealing with the particulars.

[al2cand]

Hey JPM,
''logistical and practical limitations and drawbacks.''
Comparative enumeration I can think of at the moment:

Boosted-PV vs standard PV:
-higher installation cost
-higher maintenance cost for mirrors than standard panel
+pay for 100%/1.31 area of PV but pay for mirror surface (key criteria in favor) line focus case
(pay for 100%/~1.6 for point focus case)
-lower packing factor (even if panels have about 90% effective area)
-faster cell degradation with temperature
+possible to reduce cost of mounting structure by compensating with mirror configuration

A detailed analysis would be needed, at which point one would know what boosting factor is required to break even.

[J.P.M.]

Hey JPM,
''logistical and practical limitations and drawbacks.''
Comparative enumeration I can think of at the moment:

Boosted-PV vs standard PV:
-higher installation cost
-higher maintenance cost for mirrors than standard panel
+pay for 100%/1.31 area of PV but pay for mirror surface (key criteria in favor) line focus case
(pay for 100%/~1.6 for point focus case)
-lower packing factor (even if panels have about 90% effective area)
-faster cell degradation with temperature
+possible to reduce cost of mounting structure by compensating with mirror configuration

A detailed analysis would be needed, at which point one would know what boosting factor is required to break even.

Indeed !

(Note: For readers unfamiliar w/ the "CPC" concept, briefly and incompletely, it's similar to a "V" though concentrator w/ two truncated parabolas replacing the side reflectors. The side mirrors then relax some of the strict tracking requirements of true parabolic troughs, but do so by practical limits on the concentration ratios attainable, but still higher than planar side reflectors. So these CPC's are one of the class known as "non-imaging" concentrators". The concept has been around since the mid '60's and was somewhat simultaneously "invented" or discovered in the U.S.S.R, Germany and the U.S.)

If by "boosting factor" you are referring to what is more commonly called a "concentration ratio" (C.R.), as with other concentration schemes, you can often wind up chasing your tail. Added complexity as f(C.R.) seems to increase to a power > 1. How much greater is the stuff of engineering design. Once a C.R. > ~ 6 or so is achieved, for all the added complexity, it may be just as well to go to a full parabolic trough and be done with it. That's often where the process economics get serious.

Higher C.R.'s require more and more complex and precise (even though 1 axis) tracking, more robust support, probably more land, different PV considerations (if PV) etc. CPC's seem least complicated and perhaps more, or most workable, at lower C.R.'s of ~1.3 to <~2 or 3, depending on something called the "acceptance half angle", and then often in passive solar applications w/ half the reflecting surface for example, as part of the building envelope and the other half (side)eliminated.

Maybe an interesting factoid, and perhaps an example of science reinventing something that's been around for a long time: It was later discovered that the retinal receptors of horseshoe crabs have the same shape as a CPC, evolving quite a while back, perhaps, it is thought, to see better in dim light - Proving once again that there's not much new under the sun. Or, maybe proving that scientists can steal ideas from Mother Nature and then try to claim victory in a priority dispute.

[al2cand]

For PV panels it is questionable if CPCs are really worth the extra cost, but many applications require them to reach their critical process temperature:

The problem with CPC is that it is as perfect as a concentrator can be, BUT for its acceptance angle only.

As daily sun trajectory averages to 180deg so this means alot of light is lost on the CPC sides.

The interesting part is when a creative person asks himself how to create a concentrator that would collect slightly less energy within the acceptance angle, but recoup more than these losses outside the said acceptance angle. Then a special booster would be created, beating the CPC daily collected energy.

How important is it to create a say +15% efficiency concentrator than a standard CPC? This means a solar cooker could cook ~15% faster, this means purified water treated for E.coli at 65deg(?) would be produced ~15% faster, this means drying ~15% more food, and so on... at no additional costs.

I think it's possible, someone else have investigated such designs?

[russ]

Look at Arontis or Solar8 out of Sweden - they have been producing this for years.

http://www.arontis.se/solar/arontis_skule.php

They have an English section to the site I have seen before.

[al2cand]

Look at Arontis or Solar8 out of Sweden - they have been producing this for years.

Even their 'advertised' system seems bad:
-Production (Madrid) 6kWh/m2/day*365=2.19MWh/annum
Electricity: 120 kWh/m2/annum
Hot water (50°C): 750 kWh/m2/annum

Assuming hot water is worth half carnot maximum conversion: (1-350/300)/2=8.3%

(8.3%*750+120)/2190

global efficiency: 8.3%

Who wants to buy this...

[russ]

Even their 'advertised' system seems bad: Who wants to buy this...

That is a real system with real numbers - not dream land BS

[al2cand]

That is a real system with real numbers - not dream land BS

I'm just saying it's really hard to prove you product in this industry with theoretical numbers, often there is no way to know what is considered in the calculation (yearly or best day? storage included? $/kwh? etc)

I believe the only good way for long term progression is by putting on the table what projects you have done, for example, reference Iàinstallations and on-going projects:

http://www.absolicon.com/about-absolicon/

http://www.absolicon.com/about-absolicon/on-going-projects/

Some companies unveil dream numbers as you stated, then one can only assume it is the absolute best day numbers to which to add all possible losses.
At the opposite, if a company publishes sub-average numbers, they should clearly state all the of what is taken into account.

[J.P.M.]

Even their 'advertised' system seems bad:
-Production (Madrid) 6kWh/m2/day*365=2.19MWh/annum
Electricity: 120 kWh/m2/annum
Hot water (50°C): 750 kWh/m2/annum

Assuming hot water is worth half carnot maximum conversion: (1-350/300)/2=8.3%

(8.3%*750+120)/2190

global efficiency: 8.3%

Who wants to buy this...

I'd be careful about confusing efficiencies - 1st law vs. 2d law.
A common start is to match the method of production to the task. For example, don't design a device to produce 100 deg. C process water if the task only requires 50 deg. C. That's probably an unnecessary entropy increase and may be a more appropriate context for a discussion of Carnot efficiencies.

[al2cand]

I'd be careful about confusing efficiencies - 1st law vs. 2d law.

Indeed, for decentralized systems, a heat and power combo as so deserves its full energy output to be considered. So it's not possible to compare electric-only systems with CHP systems on the basis of efficiency alone.

Let's do a quick calculation on cost:
let's say we would hope to have a payback better than 5 years with utility rate at $0.1/kWh.
If small house system requires ~20kWhe/day * 365d/y / 120kWhe/m2/y = 60m2 would be the minimum required (assuming no loss in storage/reconversion)
20kWhe/day * 365d/y * $0.1/kWe = $730 saved for electricity
750kWht/year / 0.33 electric efficiency to heat tank * $0.1/kWe = $228 saved for heating domestic water (corresponds well to 1 tank/day * $0.70/tank * 365 = 256$)
($730+$228)*5y=4790$ maximal system cost with battery storage included
Since 20kWe / 0,5kWhe/battery * $100/battery = 4000$ (maybe this is wrong?)
We can appreciate the fact that storage is the main barrier to entry of renewables for off-grid installations. If a more reasonable (?) 10years payback is accepted it gets possible to break even, which is good enough for me. Any errors or additions?

[russ]

Like I pointed out - that system is on the market - not the back of an envelope.