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
   1. Reflectech film, according to Doug, lasts 7 years according to accelerated degradation testing
   2. Reflectech is marketing its own reflection system - but it has no track record of performance yet
   3. Apparently, 3M marketed this technology earlier, but went out of business with this product
4. 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
5. Using flat mirrors avoids any issues with defocusing of a parabola at low incidence angles
6. Losses from shading in this regime are about 1'/x, where x is the total width of the reflectors (about 16 reflector strips)
7. Utilizing a steam engine is the only proven formula for a system with water as a working medium
8. We are aiming at temperatures of about 300 Celsius (600K)
9. We are aiming at steam generation rates of about 3 lbs/min
10. Cost of $3/watt in the 5% overall efficiency scenario, and $1.5/watt in the 10% overall efficiency scenario
    1. 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