HOW TO BUILD A

Solar Thermal Roof

John Canivan

July 2004
Sunny Future Press, Wantagh , NY
Copyright © John Canivan 2003
$20.00

All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means electronic or mechanical without the express permission of the publisher. On line support is available from www.JC-SolarHomes.com. If you have any questions or comments about this book feel free to post them on the JC Solar Collector Forum or join the Solar Energy group or send email to canivan@optonline.net. If you find this book helpful you may also appreciate my other books: How to Build a Solar Hot Water System, Solar Thermal Energy, Energy Independent Housing, Do-it-Yourself-Solar

"This is a small book with a large concept."

How to Build a Solar Thermal Roof is based on the concepts developed in the Solar Thermal Energy Workshops at Farmingdale University , NY and my book, How to Build a Solar Hot Water System. Rooftops are perhaps the best place to collect the suns energy. All we need to do is find a cost effective method of heat collection. This book is about that cost effective method. Photovoltaic systems only collect about 10% of the energy available while solar thermal systems harvest heat energy at the same heat transfer efficiency as oil burners. Without rebate incentives installed solar thermal roofs systems can pay for themselves in less time than photo voltaic systems. They can supply a cold climate household with all or most of it’s hot water and heating needs.

If you build and install your own solar thermal roof you could be saving thousands of dollars each year with a system that pays for itself in several years. How to Build a Solar Thermal Roof is a down to earth, easy to understand, step by step cutting edge book designed to help you become energy independent. Over 50 color illustrations are used to clarify construction details and facilitate the learning of basic solar thermal energy concepts. A glossary is included along with a list of suggested materials for your convenience.

CONTENTS

I. Basic Concept 5

II. Absorber Plate Jig 8

III. Making an Absorber Plate 11

IV. Installing insulation 14

V. Installing Absorber Plates 15

VI. Installing the Flow Pipes 16

VII. Energy Independence 18

VIII. Radiant Heating 22

IX. Spinning Sunlight Into Gold 26

X. Glossary 41

PROLOG

It is now possible to build a practical renewable energy system that everyone can afford by using the entire surface area of a roof for collecting the sun’s energy. Why mess around with a few pitiful eyesores when the entire roof can be used to harvest energy. Every dwelling needs a roof. With a little planning that roof could become an asset rather than a liability. Did you know that most roofs have a life expectancy of 20 years or less? A solar roof could easily outlast conventional roof and keep your house cool in the summer and warm in the winter.

Of course not all roofs are suitable for a solar thermal application. The best orientation and pitch of a roof will depend on its global position as well local climatic conditions. If you live in the Adirondacks and all you have to work with is a North facing roof you might consider growing mushroom. East and West facing roofs are capable of harvesting some heat energy during those short winter days but if you’re serious about heating and cooling your house with the sun your roof should face south if you live in the North. Of course the reverse will be true if you live on the other side of the equator. If you live on or close to the equator you’re in the twilight zone of solar thermal roof application and you’ll probably have more sunlight than you know what to do with so this book was not written for you. How to Build a Solar Thermal Roof was written for you cold climate people who live between the latitudes of 30 and 60 degrees. Since I live North of the equator at a latitude of 41 degrees my references with respect to roof orientation will be made with respect to this latitude.

How expensive is a solar thermal roof?
An installed solar thermal roof system complete with heat storage vault and radiant floor heating could easily pay for itself in less than eight years without government, state or local incentives. With these incentives a solar thermal roof might easily pay for itself in less than four years. The initial cost of a system will depend on the size of the roof, the size of the heat storage vault and the size of the radiant floor heating system.

I. Basic Concept

A rooftop is an ideal place for harvesting the suns energy if it’s oriented and pitched properly. For a northern climate the best orientation is normally south and the best pitch would be about 13 degrees plus latitude for winter heat gain. If you read How to Build a Solar Hot Water System and built a few serpentine collectors you’ll have an experience that that should make the solar thermal roof project more comprehensive.

People around the world have built and installed serpentine collectors. These collectors are the same kind we build at my all day Solar Thermal Energy Workshops at Farmingdale University in NY. They’re cost effective and at least as good as any expensive commercial units that I’ve seen. Building and installing a serpentine solar hot water system gives a person the practical experience needed to understand the value and dynamics of a heat gain, heat transfer and heat storage, but I believe we can go one better when it comes to a practical solar thermal energy project.

We have become so dependent on energy concentrates that the transformation to energy independence based on diffuse renewable energy resources will be difficult. Most homes aren’t oriented with the sun in mind, and some new housing design embellish poorly insulated cathedral ceilings with gable roofs that waste, materials, space and heat. New, cost effective, attractive, energy independent houses are possible but the traditions of wasteful spending and energy inefficient designs make the process of change difficult. We’re stuck with a lot environmentally unfriendly houses with roofs unsuitable for this kind of application, but if we look hard enough I’m sure we’ll be able to find a few that could benefit from a solar thermal roof.

An 800 sq. ft. solar thermal roof with a 3,000 gallon multi tank heat storage vault, radiant floor heating system and total hot water system would of course be more expensive than two commercial, 20 sq. ft. collectors with a 60 gallon SHW tank, but the pay back would be less. Instead of saving $200/yr on a commercially installed system costing $5,000 with a payback of 25 years you could save $2,000/yr on a do-it-yourself project that costs $6,000 and has a payback of 3 years.

The main problems with solar thermal roofs have to do with size and orientation. Not all roofs are suitable. The roof below has a pitch of 45 degrees. 54 degrees would be ideal for winter heat gain in the Long Island area where I live, but a roof with a 45 degree pitch like the one below could still put a serious dent in the heating and hot water bills. Let’s focus on what we can do rather than what we can’t.

BEFORE

Here’s a good candidate for a solar thermal roof. Notice the steeply pitched south facing roof. If the sewer vent could be moved the entire surface area of the roof could be used for making hot water all year long. Home heating needs could also be supplemented in the winter.

AFTER

This 600 square foot solar thermal roof is capable of a 190,000 BTU harvest per hour in direct sunlight which is the fuel oil equivalent of 1.26 gallons. In a location like Long Island a solar energy harvest equal to the fuel oil equivalent of 1260 gallons of #2 fuel oil are available to a roof like this. As long as your neighbors don’t go crazy and run you out of town on a rail you’ll be saving lots of money that would normally go down the fuel oil drain.

If you’re not turned off by the appearance of a roof like this and you’d like to have a go at it I’ll do what I can to guide you through the processes, but before we go on this solar thermal roof adventure we’ll have to make some absorber plates. To do this we’ll need to construct an absorber plate jig.

II. ABSORBER PLATE JIG

Absorber plates provide an inexpensive method of transferring the sun’s heat to the flow tubes of the solar thermal roof. Absorber plates increase the surface area exposed to sunlight. More than 700 linear feet of copper tubing would be required to cover the same surface area that could be covered with 60 linear feet bonded to a well-constructed absorber plate.

Copper absorber plates facilitate the soldering of copper tubes, but they’re expensive, heavy, difficult to fabricate and unnecessary. Aluminum absorber plates are less expensive, lighter, easy to fabricate and also the best conductor of heat per pound known. You should be relieved to know that we’ll be using aluminum absorber plates. Individual absorber plates can be as long and as wide as you wish. The ones that I use to make serpentine collectors are 20 inches wide and 100 inches long. The jig plans of for this size absorber plate are the ones detailed in the book but you may decide to make absorber plates 24 inches wide since the lower bonding strips on the roof will be 24 inches on center.

The starting length of the plate should be about a foot longer than the distance between the peak of your roof and the edge of your roof. After pounding the aluminum flashing, the length of the aluminum should shrink to fit on your roof. If it’s a little too long you could always trim it to fit.

These jig plans are for 20” wide absorber plates made from 20” wide sheets of aluminum flashing with a thickness of about .01”. Be sure to alter the construction dimensions if you decide to make 24 inch wide absorber plates.

Are we ready? Let’s build the absorber plate jig.

1. Cut four 1X6 boards 4 feet long.

2. Cut seven 1X6 boards to a precise length of 20+1/8 inches. The extra 1/8 inch allows the 20” aluminum to slid through the jig without binding.

3. Rip one ½” strip of wood 2’ long and rip two 1X3’s 24 inches long.

4. On a flat concrete floor place two 1x6x4 boards parallel to each other as depicted in illustration below.

5. Attach the 20+1/8 inch boards to the 48 inch boards. They should be perpendicular to the 48 inch boards, parallel to each other and separated by a ½ inch gap between. Use the ½ reference spacers to adjust the gap so that the boards will be centered six inches apart.

After screwing the boards together in this manner with the ½ inch gap between them, a third 1x6x4 board may be joined to the bottom of the jig for additional support. My original absorber plate jig looked like the one above, but the aluminum flashing is difficult to align so I added guides.

GUIDES

Guides make all the difference. They’ll save time and labor. They automatically align the aluminum flashing and also position the steel rods.

Temporarily screw the 1x3 guide supports into the sides of the absorber plate jig. Translate the location of the slots onto the guide boards with a pencil. Remove the guide boards to cut out the ½ inch steel rod guides in the guide board. Now screw the guide boards back into position.

The finished absorber plate bending jig is a little different than the one above. It has more slots for bending but the design principles are the same.

Without the guides pounding grooves into the aluminum is a bit tedious.

See what I mean? Guides are good.

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