Non-tracking Solar Thermal Technology and Its Applications Bruce Johnston UC Solar University of California, Merced

Objectives The objective was to develop a non- tracking solar thermal system that would: The objective was to develop a non- tracking solar thermal system that would: –Operate at relatively high temperatures –Be easily adapted for practical use –Have a fairly low manufacturing cost

Result XCPC design using MGVT XCPC design using MGVT Relies on non-imaging optics Relies on non-imaging optics 60 degree acceptance angle 60 degree acceptance angle Consistently operates at 200C Consistently operates at 200C Has the potential to operate at even higher temperatures (approaching 400C) Has the potential to operate at even higher temperatures (approaching 400C)

Significance of a Non-tracking System Cost Cost –Trackers are priced in the thousands of dollars –Each tracker requires a power supply Ease of Maintenance Ease of Maintenance –Few moving parts –Easier to keep clean Stability Stability –Sturdy, well anchored frame

5 slider R Collector Shape 2  R/sin

Tube Design Standard Tube-in-tube design Standard Tube-in-tube design –Commercially available –Reliable –Replacement rate is 2%-4% per year U-tube design U-tube design –Designed by our group –Slightly better performance than the tube-in- tube design

Tube-in-tube Configuration 1 Outer Glass 1 Outer Glass 2 Absorber 2 Absorber 3 Seal 3 Seal 4 Outlet Channel 4 Outlet Channel 5 Inlet Channel 5 Inlet Channel

U-tube Configuration

Collector Orientation East West East West –Collectors are arranged horizontally or left to right –Better performing than North South configuration at higher temperatures North South North South –Collectors are arranged vertically or up and down –Easy maintenance is a trade off for slightly lower performance

Efficiency with 60 degree Acceptance Angle

Parabolic Trough Improvements Angular tolerance could be increased from 0.5° to 2.0° Thermodynamic efficiency could improve significantly Overall system costs will be reduced

Vacuum Tube Improvements Improve tube design Improve tube design  Better flow path design  Better selective coatings  Better vacuum seals

Selective Coating Improvement Low Emissivity (< 0.07 at 400C) Low Emissivity (< 0.07 at 400C) High Absorptivity (> 0.96) High Absorptivity (> 0.96) Low reflectance (  ≈0) at wavelengths <= 2 microns Low reflectance (  ≈0) at wavelengths <= 2 microns High reflectance (  ≈1) and wavelengths > 2 microns High reflectance (  ≈1) and wavelengths > 2 microns Stability in a vacuum at 400C Stability in a vacuum at 400C

Applications Process heat (e.g. to dry fruit) Process heat (e.g. to dry fruit) Desalination processes Desalination processes Heating and cooling of structures Heating and cooling of structures –Absorption chillers  Single effect  Double effect

Solar Cooling Demonstration Project UC Solar Project UC Solar Project First of its kind in the USA First of its kind in the USA Student designed Student designed 23.5 KW system 23.5 KW system 6.5 ton double effect absorption chiller 6.5 ton double effect absorption chiller Cools a 700 sq. ft. structure Cools a 700 sq. ft. structure

UC Solar Absorption Chiller Broad 6.5 ton unit Broad 6.5 ton unit Hot water or gas driven Hot water or gas driven COP approx. 1.2 COP approx. 1.2 Made in China Made in China

Hot Water or Steam Absorption Chillers COP COP Single-effect chiller to 0.75 Single-effect chiller to 0.75 – 90C-150C Double-effect chiller to 1.35 Double-effect chiller to 1.35 – > 150C

23.5 KW Collector Array

Building and Array 12’x57’ Office (approx 700 sq. ft.) 12’x57’ Office (approx 700 sq. ft.) 23.5 KW array (52 sq. meters) 23.5 KW array (52 sq. meters)

Key Project Members Dr. Roland Winston Dr. Roland Winston Kevin Balkowski Kevin Balkowski Heather Poiry Heather Poiry

Questions Bruce Johnston Bruce Johnston