Heating Greenhouse Soil With Solar Air Heaters -- And Other Applications?

I ran across a paper from the University of Minnesota Extension that describes a simple way to heat the soil in a greenhouse through the winter using very simple solar air heating collectors.   In a nutshell, the air heated by the solar air heating collectors is blown through corrugated plastic pipe that is buried in the soil under the greenhouse.  A layer of insulation around the soil prevents the heat from being lost downward and outward.

The results in terms of keeping the greenhouse soil and air warmer well into the winter were impressive.

Burying the solar heated pipe in the greenhouse soil

The nice thing about this scheme is that efficient solar air heating collectors can be built for about $4 per sqft and they are very fast and easy to build.  The only other components to the system are a blower and a $10 thermal snap switch to turn the blower on when the collector is warm.  Really simple.

This all got me to wondering if this might not also be a good method to use with homes that use sand-bed heat stores for space heating.   Currently, these designs use more expensive and more complex solar water heating collectors to store heat in the sand-bed.   It seems like using simple, site built, solar air heating collectors would make the simple sand-bed solar heat storage system even simpler and more cost effective?

All the details on the solar ground heating scheme here...

Gary

Concentrating vs Flat Plate Collectors -- George's Tests

If you have ever puzzled over whether it would be better to make a regular flat plate collector or to make a tracked parabolic trough concentrating collector for your solar water or space heating project, George has done some really interesting side by side test comparisons of the two.

George's side by side test rig

The test setup George built allows two collectors to be mounted side by side.  Either or both collectors can be setup to track the sun through the day.  Each collector heats an identical insulated water reservoir, and the figure of merit is the water reservoir temperature over the day.

This is George's well written rundown on each of the tests and the results here...

Some of my thoughts on the test results...

Gary February 27, 2012

Solar Water Heating Kits or Packages

I've added a new section to Build-It-Solar that provides some info on solar water heating kits or packages.  These packages provide a full set of parts (collectors, tanks, pumps, controllers, ...) that allow you to install a solar water heating system yourself.

I've tried to aim at kit packages that are high quality, but still save s substantial amount of money over having a system professionally installed.    A typical solar water heating system for a family professionally installed runs about $8000.  These kits are in the $3000 to $5500 area.  You have to add a bit to that for a few things not generally included, but the savings can be of the order of half.   By comparison, a system that you build from scratch like our $1K system costs about (surprise) $1000.

The kits I've included vary quite a bit in design and come from large and small companies, and address warm and cold climates.  There may be something you are looking for.

I've also included some alternative approaches that are kind of between the  kit and and a full scratch build approaches.

The list is just a start -- I'm sure there are other good systems out there that I missed, so let me know if you know of a good one, or if you have installed any of these yourself, and how it went.

The full rundown on  Solar Water Heater kits...

The Solar Water Heating page with about 100 solar water heating projects...

Gary

Video -- A Home Built thermo-siphon solar air heater in Bozeman, Montana

Peter and Dana have finished the video on our themosyphon shop heating collector, and it looks great to me.

This is the link to the video on Peter's website...

Peter is a local builder and skilled video maker -- lots of interesting construction oriented videos on his site.

Paul, who you see in the video, runs http://www.bozemanbiofuels.com/  here in Bozeman will build one of these very fast payback solar collectors on your south wall.

Peter and Dana making moving pictures

For more on the details of building the collector...

Gary

Need help with sun simulator design

I've been doing a fair bit of solar thermal collector testing over the last couple years.  The way I do that is to wait for good steady sun, and then test the new collector design as well as a known baseline design side by side in the same sun conditions.  This works pretty well, but you have to wait for the sun, and you always have to test a baseline collector along with the new collector to account for sun variations.

To make the testing easier, I've been working on an inexpensive indoor sun simulator.  This gadget uses a few high wattage metal halide lamps (like street lights) to reproduce lighting levels similar to the sun on an up to 2 ft by 4 ft test collector.  This setup is looking pretty good, but I'm having trouble coming up with a reflector design  that puts enough of each lamps light output onto the collector.

So, if you have a minute and want to have a look at what the current sun simulator/reflector look like and pass on any ideas for improvements, I'd appreciate the help.

Details on the sun simulator and reflector ...

Gary

Mother Earth News Article on Our Solar Water and Space Heating System

The new (February 2012) issue of Mother Earth News has an article on our DIY solar system that heats water for domestic use AND also provides space heating.

The article provides a good and detailed overview of the system in about 5 pages--
So,

- If you want a good detailed overview of how the system works to see if it might be for you, go to the Mother Earth Article -- its available on the Mother Earth website here...

- If you decide you want a much more detailed version that covers the full design as well as design alternatives, and provides detailed build instructions, then go to the 100 page write up here...

The MEN article.

The emphasis for this system was to provide both solar space heating and solar domestic water heating while still keeping the system simple and easy to build.  All the lessons learned over the past five years by me and others who have built the system are included.

Gary

An Easy/Good DIY LED Can Light Retrofit

Home Depot is selling a nice and easy to install LED retrofit for can lights.  We decided to try one as we have lots of can lights that would benefit from an efficient retrofit.

It is equivalent to a 65 watt incandescent, and has a 2700K color temperature -- nice and warm.   Output is 575 lumen.  Power consumption 10.5 watts.
Price is $40 -- kind of pricey, but see the payback comments below.  Claimed life is 20 years.
It is said to be dimmable, but apparently not all dimmers are compatible with it.


The 117 reviews on the HD site show a nearly 5 out of 5 stars with very few unhappy people.  Lots of very favorable comments.


The installation was relatively easy.  You take out the old can light bezel and remove the stuff holding the old can socket in place.  You then rotate out the little metal wings on the new fixture and just push it up into the old can housing -- very simple.  They can be removed by rotating the fixture CCW.

The springy metal pieces wedge into the existing can
light housing to hold the new fixture in place.

We also sealed up the openings and cracks in the existing can housing to reduce infiltration.


If you are going from incandescent bulbs to this LED, the saving is 55 watts.  This adds up pretty quickly.  For our usage and power costs, the payback period on saved electricity is only about 3 years. 


The lighting is very nice.

Nice warm lighting.

All the details on the installation and the payback calculations here...


Hundreds more conservation projects...


Gary

Solar Cooking After Dark -- A DIY Stored Heat Solar Cooker

Mik has been working on a way to collect and store solar energy during the daytime so that it can be used after sunset to cook meals.   He is looking for ideas to solve some of the technical issues that still remain, so if you have any ideas.

Reflector from satellite dish heating the bundle of iron rods.

Mik's solar cooker uses a concentrating reflector to heat a bundle of iron rods to very high temperatures.  Once the rods are heated, they are stored away in an insulated container to retain heat.  Later in the day (after the sun has set), the stored heat is used for cooking.

Diagram showing the design of the heat storage unit.

Cooking on stored heat.

While this is not the first solar collector to use stored heat, it is a very simple design that can be built fairly easily and cheaply in a low tech environment.  It could potentially reduce the amount of fossil fuel use by allowing people to cook with solar at normal meal times without regard to whether the sun is present at that time or not.

Mik has run into some material and insulation challenges in this project, and is looking for advice.

All the details on Mik's stored energy solar cooker... 
There is a comment section at this link.

Lots more on solar cooker designs...

Gary

Large Thermosyphon Collector Updates and Developments

I've been using a very simple solar thermosyphon collector to heat my shop for several years.  It is large and puts out a lot of heat -- its also simple, cheap, and low maintenance.  Where we live it has a kind of amazing one year payback on the cost of materials to build it.

The large thermosyphon shop heating collector

The collector has been getting some attention lately and that coupled with some new testing and 9 years of accumulated experience makes me think its time to do an update.  This update covers a lot of territory:

• A new commercial version of the collector 
• A video featuring the collector
• Potential changes and refinements
• Maintenance and upkeep over 9 years
• Testing effect of reducing vent size to make construction easier
• More accurate collector efficiency measurements

A New Commercial Version 

Paul House  of Choice Energy here in Bozeman  is offering a commercial version of the collector.  He will build one on your wall for about $2000.  In our climate, the collector offers about a 5 year payback (rebates could make it even shorter).  This is the best rate of return I know of for commercially installed collectors by a wide margin.  For example, if you compare it to the popular SolarSheat commercial collector, it is about 5 times more cost effective on a dollars per BTU basis.

All the details here...

A New Video on the Collector

There is a new video in works on the collector being done by Peter and Dana.  This is the first in a series of videos they are doing that will feature renewable energy projects in the SW Montana area.  They were out capturing video and audio before Christmas, and the final product should be out in a month or two -- I'll post a notice when its available.   I think this series of videos is going to be very interesting as there is a lot going on the renewable energy front in this area.

Paul and Gary on video day

Potential Changes and Refinements

The collector has performed very well, but, as always, there are a few things I would do differently if starting over.  So, this section lists a few small changes and one large change I would make.

The small changes have to do with details of the absorber installation, flashing, glazing...   just small refinements.

Collector cross section (from Home Power article)
The absorber change has to do with the tilt of the screen layers.

The one big possible change would be to revise the design to allow the collector to pass more daylighting into the shop area.  On my other shop, I use this glazed door arrangement, and I have to say I just love the solar daylighting it provides -- it not only helps when doing work, but it also just gives the place a more pleasant feeling.  I'd like to incorporate some some glazed area in the back wall of the thermosyphon collector that would add this solar daylighting feature.   If you have any ideas on good ways to do this, please let me know.

All the details on potential changes and refinements ...

Testing Smaller Vents

Paul suggested the idea of using a large hole saw to cut the inlet and outlet vents for the collector.  This would save some work and look nicer.  The potential downside is that a 6 inch or even 8 inch hole saw results in a smaller vent size than the design guide lines for these collectors specify.  

The two adjacent bays of the collector used to test
effect of smaller vents.

In order to get an idea what the performance penalty for the smaller vents might be, I masked down the vents on one bay, and then compared the heat output from this bay to the adjacent bay with the full sized vents.  Unfortunately, there is a pretty big penalty for the 6 inch round vents, and even the 8 inch round vents show a drop in heat output.  It looks like a 9 inch circular vent would be about right.

All the details on small vent testing...

Efficiency and Flow Rate Testing

While doing the small vent testing, I also had another go at testing the efficiency of the collector.  I have somewhat improved instrumentation and accounted for more of the odds and ends that effect efficiency.  Its difficult to get good efficiency measurements on any solar air heating collector because measuring airflow accurately is hard.  Getting good airflow measurements on the thermosyphon collector is even more difficult due to the large vents with low vent velocities.    But, I do think these new measurements are pretty good.  

Bottom line is that for the full sun, moderate winter day I tested on, the efficiency comes out between 62 and 65%  -- this is really very good, especially considering how simple and inexpensive the collector design is.

Logger plot used for vent size and efficiency estimates.

There are also some test results on collector flow rate, dust filter effects on flow rate, and on using the back surface of the collector as a radiant room heater.

Details on collector efficiency measurements...

Maintenance 

Through the first 9 years, the collector maintenance has been very minimal.  

The poly back draft dampers have been replaced once at a cost of 2 cents per damper.

I painted the outside of the collector frame last year.

The fact that the collector does not have a fan or controller eliminates the two most maintenance prone items on solar air heating collectors. 

After 9 years, the polycarbonate glazing still looks very good.

All the details on maintenance over the last 9 years...

If you have any thoughts or suggestions on the collector, please let me know.

Collector parts diagram (from Home Power article)

All the details on  simple solar thermosyphon collector

Gary

January 6, 2012

Restoring an Elec-Trak Tractor and Integrating it With Our PV System

Last summer, we bought a used Elec-Trak tractor -- I suppose "used" is a bit redundant since the last Elec-Trak left the factory in the 80's.

Our "new" Elec-Trak after some TLC.

The Elec-Traks are all electric tractors powered by a set of on-board lead acid (golf cart) batteries.  They were made by GE for several years during the 70's, and were popular with more than 30,000 made.  They are very durable and functional machines with a wide range of all electric accessories.  The Elec-Traks have a strong following with an online owner forum and good parts support.   Many of these tractors have been rebuilt and are serving people well.  Being electric, these machines are cleaner, cheaper to run, and low maintenance than equivalent gasoline models.

The Elec-Trac with new charger/inverter supplying 120 VAC power out in the field.

In addition to the usual mowing and snow blowing tasks, we wanted to be able to use the Elec-Trak to power our home during power outages -- it has a large enough battery pack to power a few critical loads like the fridge and furnace for something in excess of a day.   This proved to be a relatively easy thing to do using a commercial charger/inverter from Tripplite.

In addition,  we wanted to work out a way to use our grid-tied PV array to charge the Elec-Trak battery pack during power outages.  This proved to be more of a challenge in that grid-tied PV arrays are designed to stop operating as soon as a power outage is detected, and to stay offline until the grid comes back.  After a bit of head scratching, we did work out a way that is fairly easy and effective if not terribly elegant.  The nice thing about our arrangement is that we get most of the benefits of a grid-tied with battery backup PV system, but without the considerable initial expense of these systems and without the need to maintain and replace a set of batteries that is almost never used.  See the link below for details.

Charging the Elec-Trak batteries during a simulated power outage using our PV array.

All the detail on our Elec-Trak project -- from scraping and painting to integrating it with our grid-tie PV system -- about 20 pages in all...

More Elec-Trak stuff:
For a rundown on the history of the Elec-Trak and a description of the various models, see Mark's article...

The Build-It-Solar section on Elec-Traks and similar electric machines...

One of my favorite Elec-Trac sites is George's My Elec-Traks site...  He has restored just about every model and also has lots of the Elec-Trak manuals and brochures.

The online Elec-Trak owners forum...

Just a bit of rust to clean up.

The new charger/inverter rides with the Elec-Trak when power is needed for 120VAC loads, or can stay back in the barn for charging.

The new charge controller that allows the grid-tie PV

array to temporarily be used as an off-grid PV array to charge

the Elec-Trak during power outages.

Gary

December 21, 2011