Solar Thermal Electrical Generation

=Introduction=

We are building a solar thermal concentrator electrical generation system prototype at Factor e Farm, starting in mid August. We have a Google group organized around this, and a development wiki here. Some of the highlights are shown in the description below.

=Summary of Learnings to Date= (updated 9.12.08)

Our learnings to date are as follows. We have 'concluded':
 * 1) Using glass mirror is the only proven solar thermal generation medium known to humankind
 * 2) High-iron glass mirrors, according to Doug Wood (he is mentioned in this artcle) are an option with a 50-year proven track record of durability
 * 3) According to Doug Wood, reflective film of any sort has at most a 7 year proven track record
 * 4) Reflectech film, according to Doug, lasts 7 years according to accelerated degradation testing
 * 5) Reflectech is marketing its own reflection system - but it has no track record of performance yet
 * 6) Apparently, 3M marketed this technology earlier, but went out of business with this product
 * 7) We are aiming at flat glass, with 1' wide strips, and a secondary parabolic collector, to focus a 1' wide reflection onto a 2" collector tube - for 6-fold concentration of about 16 mirrors - or total of about 100 concentration ratio
 * 8) Using flat mirrors avoids any issues with defocusing of a parabola at low incidence angles
 * 9) Losses from shading in this regime are about 1'/x, where x is the total width of the reflectors (about 16 reflector strips)
 * 10) Utilizing a steam engine is the only proven formula for a system with water as a working medium
 * 11) We are aiming at temperatures of about 300 Celsius (600K)
 * 12) We are aiming at steam generation rates of about 3 lbs/min
 * 13) Cost of $3/watt in the 5% overall efficiency scenario, and $1.5/watt in the 10% overall efficiency scenario
 * 14) Calculations forthcoming

=Research Areas=

Key developments involve:


 * Reflector structure optimization - lighweight, low-cost support structure is needed
 * Tracking system - accurate daily tracking is needed - RedRok tracker may need improvement
 * Collector structure optimization - minimize reflective, conductive, emissivity losses
 * Steam engine development - digital fabrication molding, casting, and machining of modern steam engine
 * Steam cycle optimization of temperature, pressure, cooling, preheating, and energy regeneration regimes

Based on the outcomes of the August prototype, we will continue. Presently, we need to procure a heat engine and test the fabrication procedure of collector/reflector structure to verify cost predictions of $1950 for a 30kW solar intercept system that generates between 500 and 3500 watts of electrical power.

=Email Group=

Join the Solar Turbine email group

=Introduction=

We are building a replicable solar thermal concentrator electric power system - on the kW scale. The closest system that we found to our design is:



Source. We should identify and contact the designers.

=Design Drawings=

The site will be prepared by leveling with a tractor and blade. We are building on the conceptual drawings in Solar Concentrators and Solar_Concentrator_Technical_Drawings:


 * 1) Solar Concentrator Foundation - CEB posts are presently our first choice, but we may revert to lumber if technical difficulties arise
 * 2) Concentrator Structure - collector tube mounting, slat mounting, connecting posts together
 * 3) Mirror Slats - rotation support bearing, bearing mounts, rod, slats, mechanical fasteners
 * 4) Tracking - sensor, actuator, gearing
 * 5) Solar Concentrator Tube - glazing, insulation and cover, tubing connection, attachment to support structure, alignment mechanism

=Reflectors, Collector, and Data Acquisition=



Overview. Steam is our preferred choice due to its simplicity. I am not sure whether steam will yield the highest efficiency, but we can optimize this point by going to higher temperatures. Advantage: a sustainable resource. Disadvantage: freezes in winter

=Updated Designs=

Here is an updated proposition from Ben, end of July, 2008:







Marcin proposes the following implementation:



=Additional Information=

See Solar_Turbine