Solar Concentrator Reviews

Review of cost predictions by Gang Xiao and Response by Marcin

   Hi,

   This computation is not quite correct. I am doing a better calculation; I will let you know when it is OK.

   Here I would like to give you my opinion on the cost analysis. I don't expect you to believe me right now; I only hope that you remember my estimations when you've learned it the hard way via a prototype whose efficiency falls short of your expectations.

   Your cost computation on the linear fresnel concentrator is fundamentally flawed. It is a general understanding within the solar concentrator industry that the main cost of a concentrator is not the raw materials but the manufacturing cost meeting the high optical precision requirement.

Yes, but how many industrial players are working with flat arrays? That coudl be the secret to low cost - via DIY - as the intelligence is taken out of the manufacturing process and put into the advanced electronic controls. Isn't it true that field adjustment of alignment, slat by slat, will be a foolproof way to obain the required alignment?

The only trick is - a properly stiff mounting structure for the slats. That does not appear to be an intractable problem, and these guys from the UK claim to have done it at low cost -

http://openfarmtech.org/weblog/?p=446

   If you put a value of zero for the manufacturing cost in your cost analysis, it does not make much sense.

We are allowing for 50 cent per watt labor costs.

   To my knowledge, my trough design is the only method that can avoid this fatal correlation between cost and precision. 

Tell me more about your key to success.

   That's the reason why my cost is low. If your design is based on known technology, you can only reduce cost by sacrifying precision and hence efficiency, and you will end by getting a product with worse performance/cost ratio.

   In fact, the cost to pay by using flat slat mirrors is exactly that the precision requirement is several times higher for a given concentration ratio. I've told you that you need a precision of plus minus 2 mrad, or 0.1 degree. At this level, everything is non-negligeable: manufacturing (fixation) error, deformations by gravity, wind, aging, etc. Your design should take all this into account, and calculate carefully incorporationg error margins. Of course, the cost will inevitably grow.

   For example, using a simple screw to fix the mirror on the rod is much too coarse. The screws will get loose over time, and it is impossible to refasten on the field towards a precision of 2 mrad.

   Such a precision requirement needs precision manufacturing (fixation) equipments and trained personnel, so you cannot put labor cost to 0 by counting on unexperienced volonteers. And I have made a preliminary cost analysis for you, according to the industrial standard. My estimation is about 200$/m^2 plus installation cost, in line with commercial products. What I am not sure is whether you will be able to get the same quality standard as a commercial product.

   On the other hand, the steam engine net electricity output will be single digit if you use direct steam. 

Are you saying that oil heat exchange is the answer?

   My next precise calculation will show that it is around 8%. So the overall efficiency is less than 4%, so the net electricity cost is more than that of optimally tilted photovoltaic panels, if you add shade loss, end loss, cosine effect, as well as the miss of diffuse light. Your claim of 1$/W is much too exaggerated.

   In fact, electricity-only solar thermal technology is only viable for large scale power plants, with high quality concentrators and sophisticated turbines 

The electronically valved steam engine is reportedly superior to turbines in the sub 500 hp power scale.

   and so on. But this market is for the time being neither for you nor for me: it is not a technical problem but a social one. It is big money affair and political lobbying, we have no access to it.

   We can only look at small scale applications. But even with my trough design that is much cheaper and of much higher performance, I don't dare advocate for small scale electricity-only applications. This is not economically competitive.  At small scale, CHP is the only competitive solution.

   It is here that the compactness of my design shows its great advantage. CHP means that it must be installed near heat users, because long hot water pipes mean huge heat losses. Ideally, installations for individual homes. For this, linear fresnel is downright impossible, because of its minimal practical size. You need a minimal field size of tens of square meters to minimize endlosses. H

Agreed.

   ow can a family do to consume the huge quantity of collected heat? In most places, the only real "market" is winter home heating. However, linear fresnel collectors simply don't work during winter due to a too low sun angle. The cosine effect is too high for flat north-south installations, and shade loss

Shade loss fraction may increase, but can be potentially mitigated by sufficient inter-slat spacing. This may work in winter - and it can definitely work under the assumption of an optimally-matched steam engine. At the very worst, there may be a limited range of performance in winter. At the very least, winter operation could afford space heating.

What do you think of the potential of a system like Nolaris? (http://nolaris.ch/17-0-Our-Technology.html)

   is too important for flat east-west installation. The incoming energy will even not make up for heat losses. I call this phenomenon "solar hibernation". The only solution is to make tilted installations, but that's explosion in cost. In most residential areas, the height of a tilted linear fresnel collector would simply exceed what is allowed by the legislation. And you will have hard time fighting wind load and so on.

   Best regards,

Marcin