A DIY Solar Expert Shares His Wisdom

From a low-cost thermosyphon solar space heater to a $1,000 solar water heating system, Gary Reysa has built a variety of unique solar projects. Learn what inspires him and how you can follow in his footsteps.
Interview by Troy Griepentrog
November 13, 2009

Gary Reysa, DIY solar expert, with the first solar project he built.
GARY REYSA


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Gary Reysa is a DIY solar expert and regular contributor to MOTHER EARTH NEWS. He’s been tinkering with solar projects for nine years, and he gathers data for every project he builds. We thought you’d like to learn more about the person MOTHER EARTH NEWS turns to when we have questions about home solar projects.

How did you become interested in solar power projects?

I’ve been interested in solar heating projects for quite a while — a lot of people were experimenting with solar in the ’80s, and I always found that interesting but didn’t take on any projects at the time. When we retired to Montana in 2000 — and faced the prospect of bills for 1,800 gallons of propane for a heating season — I thought it was time to get busy on some solar heating!

I’ve found solar thermal projects to be not only helpful on energy bills, but also interesting from a technical and design point of view. There are lots of opportunities for innovation in this field. It’s a great area for “garage inventors,” and I encourage people with an interest to give it a go.

What was your first homemade solar project?

The first real solar project was the thermosyphon solar heating collector for my barn. (Read about it in Build a Simple Solar Heater.) The simplicity, effectiveness and short payback of this heater got me hooked on doing more.

Whenever you build a solar project, you record data and analyze efficiency. How did you develop the knowledge required to do that?

I guess this comes out of a long career in engineering at Boeing. If you can’t measure how well version A of a design does, you don’t know where to go with version B — measuring results is the real key to improving a design. The physics and measurements of solar thermal applications tend to be pretty simple and easy to understand, which is nice.

You have tons of information about solar projects on your website,  Build It Solar . What’s your favorite project?  

I guess if I had to pick a single project, it would be the solar shop heater. It’s just a set of glazed doors outside of my shop’s overhead door. To let solar heat and light in, you raise the overhead door, and to keep this from being a huge night heat drain, you lower the insulated overhead door — nothing could be simpler.

The combination of solar heating and outstanding lighting that you get from this simple design transforms the shop into a great place to spend time. People look at me strangely when I pick this project as my favorite, but I really appreciate simple things that work well.

What do you think is the most important material on your website?

I have a program called The Half Plan, which is an easy and cost effective way to cut one’s energy consumption and carbon emissions in half (or more). When I read about trillion dollar programs to implement carbon sequestration for coal-fired power plants, I realized that simply not using the energy in the first place is less costly, is less technically risky, and pays a big dividend in saved fuel costs. And, it’s easy to do — we just all need to get busy and do it!

Have you ever built something that didn’t work? 

Oh, if I had a nickel for every failure!

Prototypes that don’t work are the way you get to designs that do work. But, you have to set them up so that you learn from each try — this goes back to measuring results.

Do you also experiment with photovoltaic (PV) or wind-generated electricity?

I’m putting in a PV system right now. I’m doing all the work myself and learning a lot — it’s a fascinating technology. From my perspective, the negatives are that there is not much room for innovation and the payback is still not very good.

Why do you prefer to work with solar-heated air and water projects?

I’m a backyard innovator, and solar thermal is an area in which garage inventors can make significant contributions. I can’t really build a better silicon wafer fabricator, but I can work on a better solar air collector. Space conditioning and water heating make up the bulk of home energy use, so solar thermal improvements are the real key to our energy problem — and there is still lots of room for improvement.

For anyone interested in getting involved in solar thermal, I recommend William Shurcliff’s book, Low-Cost Solar Heating — 100 Daring Schemes Tried and Untried. Shurcliff was a fine physicist and author, and this book is a great source of ideas and clear thinking. The book is out of print, but (thanks to Shurcliff) can be downloaded from my website.

What advice do you have for people who are just starting to experiment with solar DIY projects?

Start by doing some small, simple projects or experiments to get a feel for how solar heating works. Try a simple solar cooker, or something such as the MOTHER EARTH NEWS Solar Heat Grabber, or do some of the Educational Page projects on my website. These kinds of things can be built in half a day, and you learn a lot from them. They’re also great projects to do with the kids.

Learn the physics of solar collectors — this is simple stuff, but important. And some things are not intuitive. After you understand what is happening in a collector, it’s a lot easier to know what will work and what won’t.

When you set out to do a serious project that you expect to last for many years, there are a few basic rules about collector design and materials that will hold up in collectors. You can learn about these by reading the projects that others have built and that have performed well and are durable.


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Post a comment below.

 

Gary Reysa
1/14/2010 3:17:23 PM
Hi David, Yes --that should be fine. The Atlas R-Board polyiso is nice to work with in that it has face sheets on each side that are fairly durable, but any brand should be fine. Gary

David_131
1/13/2010 4:58:04 PM
Didn't notice the spelling's slightly different.

David_131
1/13/2010 4:54:08 PM
Hello, The Holidays and some illness has delayed the project... Will Polyisocyanurate Insulation work okay?

David_131
1/13/2010 4:53:11 PM
Hello, The Holidays and some illness has delayed the project... Will Polyisocyanurate Insulation work okay?

Gary Reysa
11/23/2009 10:04:09 AM
Hi David, I think that the airflow passages should be deeper. It looks like the original plan calls for a 7 inch deep box, so the airflow passages are about 3 inches deep. This seems about right to me -- the rule-of-thumb for thermosyphon collectors is that the depth should be about 1/15th of the height, and since the heat grabber has a down and an up, it would be twice that. Its not that it would not work at all with the shallow passages, it just won't be as efficient. I would make the two passages deeper if you can. Be sure that the insulation you have will stand up to the heat in the collector. Polystyrene (the white, pink, or blue sheets) will not. You want to get polyisocyanurate insulation board (some call it polyiso). Many lumber yards carry it, but may not know it by that name. It will say polyisocyanurate somewhere on the sheet. Steep angles right up to vertical work well for space heating collectors because the sun is low in the winter. Performance does not change rapidly with tilt angle. If you get snow on the ground, the reflection off the snow will make vertical work very well. For climates that have snow on the ground most of the winter, I think vertical is the best angle for heating collectors. Gary

David_131
11/23/2009 8:47:39 AM
Also, since I have goats - so I will have to mount it almost vertical so they don't use it as a "mountain to climb". So I wonder how much that will reduce efficiency?

David_131
11/23/2009 8:31:52 AM
Design question... I appreciate your comment on air resistance - that is concern with my design... I re-read through the article and design pictures, I have a "air flow" question. For my particular design -- for supplies, I have a 80" skid (1/2" sheet plywood back, with 2x4 runners - 36" wide) that I wanted to use as the "box" -- I need it to be sturdy because I have goats that would easily tear up just a "foam box". It has not been cut down yet to make the window insert section. I have 1/2" insulation board, and 10" wide sheet aluminum. I was planning to use the insulation board line the skid to make the separator and "cold air return". But when I planned out the cutting, it looks like I would have 2 'boxes' (since there is 2x4 runner down the center) that the open area would be 1.5" deep x 15" wide for the air to flow down, and 1" area for the air to heat up and rise (from my design, the sheet aluminum would be mounted to the have the air flow on both sides as the air rose). Do you think 1" would be enough of an open area for it to work? Should I redesign and have two 2x4 mounted together (edge to edge) for a larger air flow thickness? Or would adding a small computer CPU fan at the exit to draw the air through? I really appreciate your time, expertise, and willingness to help me work through this project

Gary Reysa
11/21/2009 8:28:44 AM
Hi David, 62.5 degs is what I get -- you might just check it with a couple pieces of scrap to be sure, but I think 62.5 is correct. Making the collector longer will get you more heat. Technically, for a thermosyphon collector it should also get a little deeper (thicker) when it gets longer, but for such a small change, you could just keep the same depth. On adding the screen, the good side of adding it would be that it increases the surface area for heat transfer from the absorber (the screen) to the air, and on air collectors good heat transfer from absorber to air is really the key to good performance. Anything dark in color will do a good job of absorbing the heat, but getting the heat efficiently transferred to the air is the real trick. On the negative side, it adds some air resistance, and thermosyphon collectors are sensitive to air resistance. But, I think its very likely that adding the screen would improve performance. let us know how it turns out. Gary

David_131
11/19/2009 10:05:43 AM
Thanks! So to have it sit at a 55 degree incline - If I am looking at the Step 3 picture - I need to cut two 62.5 degree cuts to separate the top end from the foot. Correct? That would allow the top end sit flat / flush with the window opening when placed and mounted. If the "foot" is longer than the 61", that would allow more heat to created, right? Also, I saw a very similar design with a wire screen (a screen door screen) mounted halfway from the glazing to the foam board to create another heat source... Do you think that would be more efficient or more heat output?

Gary Reysa
11/18/2009 7:19:42 PM
Hi David, The heat grabber will make a great first solar project. It looks like the drawing shows a tilt angle of 45 degrees, but you would get somewhat better performance during the winter if you tilted it a bit more steeply. The usual rule to get the best winter performance, is to tilt the collector at your latitude plus 15 degrees. That would be about 55 degrees for you. This is the angle from the ground (horizontal) up to the collector glazing plane. Its not critical to get it just right -- a few degrees either way will not make a lot of difference. As you say, the reason that the steeper tilt will work better in the winter is that the sun is lower, and by tilting more steeply, the sun's rays will be closer to perpendicular to the collector, where they are most effective. A tilt of latitude + 15 degrees is a pretty good compromise for the full heating season. For areas that have snow on the ground in the winter, very steep tilt angles, including vertical also work very well because you get some additional benefit from the sun reflected off the snow. Good luck on your project! Gary

David_131
11/18/2009 11:32:41 AM
I really appreciate your article. I have been looking into making a Solar Heat Grabber for some time, and currently have the materials. I am posting for a discussion on the installation. I want to confirm the optimum angle... My latitude is 39.6750561 (Northern Hemisphere). From the formula mentioned, I would cut 65.17 degree angles from the top of the frame. So when it is in the window, it would sit (roughly) at 50 degrees (with 90 degrees being straight up and down). Am I correct on my thinking? Now the question I am wondering is... During the Fall/Winter/Spring months the Sun will be at a lower angle -- closer to the Horizon. Should the angle of the S.H.G. be more vertical to be more efficient -- like sitting 60 degrees instead (from my example)? I had read some time ago - to add 10 more degree's would be helpful during this time of year. Also, for a non-engineer... How do I measure the BTU output if I am to test a few different designs? Thank You again for your contribution of your expertise and experience!

David_131
11/18/2009 11:32:37 AM
I really appreciate your article. I have been looking into making a Solar Heat Grabber for some time, and currently have the materials. I am posting for a discussion on the installation. I want to confirm the optimum angle... My latitude is 39.6750561 (Northern Hemisphere). From the formula mentioned, I would cut 65.17 degree angles from the top of the frame. So when it is in the window, it would sit (roughly) at 50 degrees (with 90 degrees being straight up and down). Am I correct on my thinking? Now the question I am wondering is... During the Fall/Winter/Spring months the Sun will be at a lower angle -- closer to the Horizon. Should the angle of the S.H.G. be more vertical to be more efficient -- like sitting 60 degrees instead (from my example)? I had read some time ago - to add 10 more degree's would be helpful during this time of year. Also, for a non-engineer... How do I measure the BTU output if I am to test a few different designs? Thank You again for your contribution of your expertise and experience!








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