Reflectors to Improve the Performance of Solar Collectors (and Windows)

This is a section that looks into using reflectors to improve the performance of solar thermal collectors (including windows). The section covers:

- Reflector design information (tables)

- A mechanical earth-sun simulator for reflector studies

- Some tests of reflectors on actual collectors

- Links to projects using reflectors for performance improvement

- Some thoughts on using reflectors

This section deals with using flat reflectors to improve the performance of flat collectors or windows -- it does not deal concentrating reflectors such as parabolic dishes or troughs etc. -- see this page for more on concentrating collectors and reflectors...

Table of Contents -- Reflector Section

Reflector Design Tables from The Passive Solar Energy Book

Benefit of a Horizontal Reflector for a Vertical Solar Collector -- a lookup table...

Reflector design for vertical collectors and for skylights...

Earth-Sun simulator for modeling collector performance.

Building it

Using it

Seasonal Benefit of a Reflector on a South Facing Vertical Solar Collector

A reflector to fix a problem with our $2K space and water heating project...

Links to other projects involving flat reflectors with flat plate collectors and windows:

Solar Today -- Low-tech reflector to boost collector efficiency

Solar Panel Heating Project -- Reflectors

Reflector/Shades -- A great Steve Baer paper about reflector/shades and life...

Some projects from the Book "Low Cost Solar Heating -- 100 Daring Schemes Tried and Untred", William Shurcliff

Three -Mode Reflecting and insulatiing plates for use the Bier's Absorber and Storage Walls...

Set of Absorber and Storage Walls Each of Which Consists of Sided by Side pair of Vertical, Water Filled Cylinders with Two Mode, Reflecting and Insulating Plates...

Outdoor Near-Horizontal Reflector Mounted at Base of South window...

Outdoor Vertical Reflector Mounted Adjacent to North Edge of East or West Window...

Is a 45 deg Orientation as Good as A Straight South Orientation for a Passively Solar Heated Building if Use of External Vertical Reflectors is Permitted?...

System Employing Water Filled Bags on Two Level Roof Equipped with Hinged Plates that Reflect, Insulate, and Also Shed Snow...

Multi Purpose, Window Seat Type, Passive Collection and Storage System that Includes Three Mode, Hinged, Reflecting and Insulating Plates...

System that includes Indoor and Outdoor Plates and a Group of Overhead Water Filled Tanks...

Passive System that Employs Upward Traveling Radiation and Total Internal Reflection Within Tall, Water Filled Glass Tanks and Can Achieve Very High Temperature with Very Small Losses...

System Employing an Outdoor, Below Window Level, Concave Reflector and a Canopy Enclosed Water Type Black Absorber...

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THIS STUFF PROBABLY NEEDS ITS OWN PAGE

Gary's Reflections on Reflectors

Things learned about reflectors:

This is a by no means complete list of some of the features and benefits and characteristics of reflectors:

- Reflectors add to solar gain without (substantialy) adding to collector heat losses. This is a key point. A typical collector operating with a modest sun level of 500 watt/sm under winter conditions might have an efficiency around 30%, but if you can boost the sun intensity to 1000 watts/sm with a reflector, the efficiency jumps up to more than 50%. The heat output goes from (500 w/sm)(0.3) = 150 watts up to (1000 w/sm)(0.5) = 500 watts -- a 3.3 times increase in heat output! You would have to more than triple the area of the collector to get this increase. Granted, this takes a VERY well designed reflector, but you get the idea.

- Application of reflectors to solar passive homes:

- Think about the south windows on a passive gain solar home - they gain a lot of heat during a sunny the day, but they lose a lot of heat at night. Adding a reflector in front of that window increases the day gain substantially but does not increase the night loss at all.

- William Shurcliff shows several schemes for using reflectors to increase the gain for windows facing east or west and also for windows facing SW and SE.

- Steve Baer shows several ways of using combination reflector and shading devices to both increase winter gain through either windows or skylights and with the same device, decrease unwanted summer heat gain.

- I am very much interested in expanding this area on reflectors, so if you have or see any good reflector designs, builds, or ideas, please let me know.

Gary June 4, 2011