DIY Solar Air Heating Collectors: Pop Can vs Screen Absorbers

DIY solar air heating collectors are one of the better solar projects. They are easy to build, cheap to build, and offer a very quick payback on the cost of the materials to build them. They also offer a huge saving over equivalent commercially made collectors.

Two of the more popular designs are the pop can collector and screen absorber collector. 

The pop can and screen collectors being tested side by side

The pop can collector uses columns of black painted pop cans for the absorber with the air pumped through the columns.  The screen collector use 2 or 3 layers of ordinary black insect screening for the absorber.  The air flows through the layers of screen to pick up the solar heat.

In this test, a pop can collector and a screen absorber collector are run side by side with the temperature rise and airflow being noted for each.

There are also details on building each of the collectors and on the cost of materials.

Building the pop can collector.

In addition to measuring temperature rise and flow, thermal images were taken of the collector glazing and absorber.

Thermal image of glazing on the two collectors.

For all the details on how each collector did go here...

Gary

Two new resources on the web for the DIY solar crowd

A couple brand new resources available on the web for the DIY solar and renewable energy crowd:

Ask the Renewable Engineer

This is Nick Pine's new blog site.  Nick is a long time solar and renewable energy analyst, designer and innovator.  He is posting solar and renewable energy questions along with answers that include a full analysis.

Nick in his new, 3 story, Low Thermal Mass Sunspace

Hot and Cold TV

For several years, Tom Gocze hosted a TV show in Maine called Hot and Cold TV. 

In each show, Tom goes into a project of interest to DIYers.  Often the topics are renewable energy related.

The shows are factual, down to earth, practical, DIY oriented, innovative, and often funny -- a hard to beat combination.  The unfortunate thing was that if you did not live in Maine the shows were not available.  Now that has changed -- Tom has started a Youtube channel for Hot and Cold TV and has put up a number of the past shows with more to come.

Tom re-plumbs his shop using the Manablok system 

Tom covers the ins and outs of picking a good used pellet stove.

Lots more on the Hot and Cold TV Youtube channel...

Gary

A Test of Reflective Surfaces In Front of Vertical Solar Collectors to Improve Performance

I like my 100 sqft vertical collector that is integrated with the south wall of the house.  It provides our solar water heating and also some solar space heating. It provides excellent performance all winter, and does not have any tendency to overheat in the summer.  The boss says it looks nice.

The one downside of this collector is that in the late spring, the sun is getting up higher in the sky, which reduces the effective area of the collector, and there is still some need for space heating.  So, it would be nice if it could put out a bit more heat in the late spring.

This test looks at adding several types of reflective material on the ground in front of the collector to improve late spring and summer output.  A near horizontal ground reflector works well under these circumstance because the sun is hitting the collector nearly straight on.

The reflective materials include bright white rocks, a white painted reflector board, and at a flat board covered with highly reflective aluminized Mylar.  The results for each of these was measured -- the chart at the end shows how the did.

White reflective rocks

The radiation intensity was measured at each of the blue tape squares on the collector.

White painted board as reflector

The aluminized Mylar reflector was made by just applying the Mylar film over the white board.

This chart shows how the materials compared.

How each of the materials compared as reflectors

The first black bar is a baseline and was done with black weed fabric on the ground in front of the collector.

As expected, the aluminized Mylar does the best, but the white board also does well, and even the white rocks provide some useful gain.

For all the details on using these materials and actual percentage improvements...

Gary

Using Reflectors to Improve Collector/Window Solar Gain

I've added a new section that covers using reflectors to improve the performance of solar collector  or passive solar gain windows.

The section covers:

• Design tables that allow you determine the benefit of reflectors of various sizes and to optimize the placement of the reflector.
• An easy to build earth-sun simulator that allows you to see how a reflector of a given size and shape will perform for any location at any time of the year at any hour of the day.
• Examples of the use of reflectors to improve collector performance.

Reflectors offer a uniquely effective way to increase the energy produced by a collector in that they increase the solar energy incident on the collector without increasing the heat losses from the collector -- so, you get both an increase in solar input and an increase in collector efficiency -- see the new section for more on this.

This earth-simulator allows reflector performance to be seen  for
any location and for any time of year and for any time of day.
A quick spin of the turntable shows the reflector light pattern for a full day.
Can also be used for shading and lighting studies.
Lots of fun!

Example of reflector performance table.

The new section on reflectors is here...

Gary

A Design Challenge: Help ClubRust with Solar Heating Low Income Homes

ClubRust builds several low cost homes for families in northern Mexico each year. They would like to work out a way to insulate and solar heat these homes. The very small budget for these homes makes this a difficult design challenge.

So, here is your chance to help out with some ideas for solar heating and insulating these homes on a tight budget.

The ClubRust crew and one of their homes 

What's Needed:

Most cost effective means to insulate and heat small houses in mild winter climate with little or no electricity.

Ideally the solution would provide heat thru a few cloudy days and cost less than $700.

Typical house is 320sf wood-frame construction on concrete slab -- see the link below for full details.

ClubRust home under construction.

Full details on the the home construction, heating goals, climate, etc. are provided here...

Take some time to think over this solar heating and insulation challenge, and contribute your ideas and  comments at the link just above.

Gary

Building a Solar Heated Well House

This is a very nice and well documented project on the Alt. Build Blog that covers building a freeze resistant well house.  The idea is to keep the well plumbing and tanks above freezing with a passive solar heating system.

The well house and Trombe wall solar heater.

The well house is built from dry stack concrete blocks that are insulated with rigid foam insulation on the outside and then stucco for the outer weather surface.

A Trombe wall solar collector covers most of the south face of the structure -- the south wall concrete blocks are used for the mass of the Trombe wall, and twinwall polycarbonate is used for the Trombe wall glazing.

The advantage of using a Trombe wall for this situation is that the wall absorbs heat when the sun is on it, and this stored heat is released over the night time period to keep the structure above freezing for the full day.  The mass of the other wall concrete block walls should also help in maintaining a more even temperature -- putting the insulation on the outside of the block allows the wall mass to be effective in regulating the temperature of the space.  The mass of the water in the tanks should also help to even out temperature variations.

Trombe wall opening surrounded by stucco walls.

The entire project is described in 9 blog entries covering the whole build in a great deal of detail.  To my eye, the overall design and details are well thought out and executed -- a really nice job.

For colder climates, some changes that might be considered -- 1) use thicker insulation to reduce the heat loss out the roof and walls (possibly polyiso), 2) add insulation under the floor to reduce heat loss to the ground.  For really challenging climates, you  could consider going to a drain back solar collector on the outside that heats water in a relatively large unvented water tank on the inside that stores heat.  The heat loss from the heat storage tank would then heat the well house so that it stays above freezing.  The tank insulation could be set at a level such that the tank loses heat at a rate that keeps the inside of the structure above freezing all day -- even with some cloudy days.   The drain back circulation pump could be something like a PV powered TopsFlo pump, so that no separate differential controller would be needed.  While the drain back solution is more complicated and more expensive than the Trombe wall, the advantage is that its about twice as efficient as the Trombe wall collector -- so, it may payoff for cold climates.

All the details on the solar heated well house here...

Lots of interesting article on the  Alt. Build Blog -- have a look.

For hundreds more solar space and water heating ideas and projects...

Inside the well house.

Gary

A Simple and Inexpensive High Lift Solar Pumping Setup

Stan was faced with a difficult garden watering problem in which he had to get water from a spring to a greenhouse that was located several hundred feet away and 50 ft uphill from the spring. The flow requirement was relatively small at about 3 gpm for for an hour and half a day about 3 times a week.

Using a conventional AC powered pump would have meant running a lot of wire, and the 800ft distance would have meant a larger than normal wire gage to keep the voltage drop from being excessive.

Using one of the submersible well pumps that are made to run directly from solar PV panels is a nice solution, but the pumps are expensive and they require quite a bit of PV panel area to drive. So, this would have been an expensive solution for the relatively low flow required.

PV panel at spring -- green bucket covers pump and battery.

Stan's solution was to use a relatively inexpensive 12 VDC Shurflo pump that is intended for spraying and RV applications. The pump draws about 8 amps, so, to drive it directly with PV panels would have required at least 100 watts of PV array, and perhaps a linear current booster for startup. Instead of direct PV drive, Stan incorporates a deep cycle 12 volt battery to drive the pump, and then uses a small (30 watt) PV panel to charge the battery over the course of the day. This works well because the run time for the pump is not very long and can be handled by the battery, and the PV panel has all day to recharge the battery.

Pump, battery and charge controller under PV panel.

All the details on building and sizing this system...

More on solar water pumping...

Gary

Waterbag Solar Water Heating Collector Using Inflatable Film Cover and Soap Bubble Insulation

This is an innovative new wrinkle on the Integral Collector Storage (ICS) design from Nick Pine.

With ICS solar water heaters, the collector and the storage are combined into a single unit. Basically they consist of a water container that typically sits inside of of a glazed enclosure. Solar radiation heats the water container during the day. This is an example of a commercial ICS design.

One of the downsides of the nice simple ICS design is that it tends to lose quite a bit of heat at night through the glazing. Nick has addressed this problem by filling the area between the water container and the glazing with soap bubbles at night. The soap bubbles are good insulators and greatly reduce the night heat loss.

The design has several other innovations:

• A film bag is used to hold the water, which reduces the cost of the water container.
• A greenhouse polyethylene film cylinder is used for the glazing and is inflated to hold its shape -- a significant cost saving over conventional glazing. Similar to a hoop style greenhouse.
• The north half of the glazing cylinder is reflectorized to reflect more solar onto the water bag.

One upshot of the inexpensive materials used in Nick's design is that it is not expensive to build a solar water heater with a large collection area and a large storage capacity -- this increases the solar fraction.

Thanks to Jay Burch for this diagram.

To transfer the heat stored in the bag to the domestic water, a large coil of PEX pipe is immersed in the bag, and the cold water from the house takes ones pass through this large coil of PEX and is heated by the water in the bag. This heat exchanger scheme has been used quite successfully on the $1K solar water heater.

Be the first on your block to build one!

All the details here....

If you have any thoughts or ideas on this design, please leave them at the link above.

Gary

Dave's £900 Homemade Solar Water Heating System

David lives at 52 degree North latitude in the UK -- a pretty tough location for solar water heating, but his homemade system works quite well.

This is a really nice build with lots of good ideas and details to learn from.

The system is loosely modeled after our $1K system, but has a number of noteworthy features:

• Very nice workmanship and details.
  
• Solar heat is stored in the existing house thermal storage tank (which is used for both space and domestic water heating).
  
• An aesthetically pleasing collector and mounting arrangement.
  
• A pumping station that is mounted in a weather protected box on the back of the collector.
  
• A freeze protection system that takes into account his unique circumstances.

Dave is a professional plumber who now teaches plumbing, and this shows in the attention to detail in the design and the careful workmanship.

Thanks very much to David for sending this in!

All the details in a 25 page pdf...

The copper riser, aluminum fin collector under construction.

The pump was located at the collector in the box as there was no
space near the tank.

This is the existing thermal storage tank for the house that
is used for space and water heating and now stores solar heat as well.

Gary April 26, 2013

Elektra One Solar Airplane

Being an old airplane guy, I though this development in solar airplanes was really interesting.

The Elektra One Solar from PC-Aero is a single place, electric airplane with a maximum range of 1000 km.  While flying, it is about half powered by solar cells mounted on the wings and tail.

The empty weight is only 100 kg -- it is constructed mostly from carbon fiber.

There is also a 2 place version.

Seems like solar powered airplanes may be coming out of the extreme experimenter class into something more interesting to regular small airplane users?

Makes you wonder what an electric, aerodynamic, 100 kg car with solar cells could do?

All the details...

Gary