Solar Concentrators in the Earth W2014



This is the webpage for the Winter 2014 Solar Concentrator Group.

To see the Solar Concentrator from 2011 please go to:
Original Solar Concentrator


Throughout the world, the demand for new methods of cooking and heating grows as natural resources such as wood and natural gas become more scarce and the health risks of smoke related diseases have been recognized in developing countries. Free of emissions and air pollution, solar cooking can, if appropriately design, be an inexpensive and safe alternative to commonly used methods of burning wood or some other kind of biomass.

The aim of this project is to make a mold in the ground for a parabolic mirror and evaluate the appropriateness of this method. This is a part of a concept developed by professor Peter Schwartz, to use a flat tracking mirror in order to reflect sunlight onto a secondary parabolic mirror in the ground, that concentrates the light to a focal point, where it gets hot enough to cook (see figure below).

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Concept of the concentration. (Alberti, Simo; Murphy,Tyler & Schwartz, Pete)

The advantage of this design is that it can possibly be made cheaper than other designs, both single axis tracking of a flat mirror, and a stationary concentration mirror can be made inexpensively. Furthermore, the seasonal declination only needs to be adjusted occasionally by hand. (Alberti, Simo; Murphy,Tyler & Schwartz, Pete)


Our main goal for the quarter is to develop and try out an easier step-by-step process to facilitate building the concentrating collector directly in the ground.


Important constraints for successful implementation of appropriate technologies in developing communities are reduced complexity, which affects the skills needed to construct, operate and maintain the design as well as cost and local availability of materials. The facts that the design we are working on might be relatively easy to construct and maintain, and inexpensive compared to other solutions, make it especially appealing for implementation in developing countries.


With potential to fulfill all of the eight of the United Nations Millennium Development goals, solar cooking solutions have been recognized to have to potential to be appropriate solutions with large impact in many developing countries.

(Health Poverty Action, 2014)
(Health Poverty Action, 2014)

Goal 1: Eradicate extreme poverty and hunger.Solar cookers in general reduce the fuel needs by one third and many households in extreme poverty, spend one third of the less than a dollar a day they are living on per person, on fuel. This often equals less food.
Goal 2: Achieve universal primary education.Wood is a scarce resource for over 2 billion people, of around half living in regions rich of the sun as a resource. Taking advantage of the sun as a resource for cooking will free time from the many girls that start helping collecting wood from a young age, increasing the possibility for them to attend school.
Goal 3: Promote gender equality and empower women.With hours spent on collecting fuel and cooking food, many women suffer from health hazards from the smoke as well as have reduced time to generate income, increase food production and pursue education. In some areas, fuel gathering furthermore exposes women to violent assaults.
Goal 4: Reduce child mortality.
The primary causes for child mortality is waterborne and smoke related diseases. Solar cooking is smoke free and enables pasteurizing of water and milk.

Goal 5: Improve maternal health.
In developing countries, smoke from cooking fires is also a major cause of death of young women, closely linked to low birth weight and infant mortality.

Goal 6: Combat HIV/AIDS, malaria and other diseases.
Solar cookers can be left unattended and are user friendly for children and the sick, which is valuable when caring for sick family members and orphans take time from ordinary livelihood activities. Water pasteurization protects from diseases. Larger solar cookers reaching up to 300 F can be used for sanitizing dry materials in rural clinics.

Goal 7: Ensure environmental sustainability.
One third of the world’s population cooks their daily meals with food, charcoal or poor substitutes. A solar cooker can save around a ton of wood per year, reducing the CO2 emissions by 1.8 tons per year.

Goal 8: Develop a global partnership for development.
Governments as well as commercial and humanitarian sectors are involved with mutually beneficial participation when creating widespread access to solar cookers. (Solar Cookers International, 2014).


One of the possible locations for implementing the design cold be Congo. The Democratic Republic of Congo, in central Africa, is a large country with an area slightly less than one forth of the US. The population is 75.5 million, with 44 % of the population under 14 years old. After centuries of corruption, instability, and conflicts between different rebel groups, the country’s economic conditions have slowly begun to improve.

Location of the Democratic Republic of Congo (African Metals, 2014)
Location of the Democratic Republic of Congo (African Metals, 2014)

As seen in the graphs below, the life expectancy is one of the lowest in the world, and so is the average income and energy use per person. Looking at the world through these graphs, we can draw the conclusion that energy use and income is highly correlated to life expectancy for the countries lowest on the scale. Establishing an energy infrastructure and enabling people to engage in income generating activities can be thought of as means of development in order to achieve goals such as improved health situation. As mentioned, solar cooking may have many possible impacts in various dimensions of the development in a community. With many communities in Congo being in great need of energy as well as increased income, we believe that the solar concentrator has the potential to be implemented with many positive outcomes.

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Life Expectancy versus Income per Person (Gapminder, 2014)

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Life Expectancy versus Energy Use per Person (Gapminder, 2014)

We got in contact with Alexander Petroff who works for the organization Working Villages International in the Ruzizi valley in the eastern part of Congo. Through him we tried to get a picture of the conditions of the people living in the villages. We got the impression that the solar concentrator could be a solution that might work there, but Mr. Petroff mentioned that the farmers are very conservative and would only buy a product if it is extensively proven to work. They will have to see how it will substantially improve their lives over the existing methods, which will not be an easy job according to Mr. Petroff.

Location of Ruzizi Valley (Ekimondo, 2014)
Location of Ruzizi Valley (Ekimondo, 2014)

Us not being able to directly get to know the people of these communities, and learn about their life, habits, values, concerns, etc. definitely makes it hard, if not impossible to develop a fully appropriate technology. However we did give it a try that we hope resulted in some learnings that can be used in further development the concept of a stationary concentrating mirror in the ground.

Pictures from the Ruzizi Valley (Working Villages, 2014)


Introduction – in short what we are doing



Mold type Ease of Construction Appropriate-ness Cost Aesthetics Durability Sum
John’s idea (Semi-circles) 2 3 4 3 12
Scaffolding 3 3 3 2 11
Mold Material
Adobe 3 5 5 4 17
Cob? 0
latex/canvas 4 4 4 4 16
Reflective Material
Aluminized Mylar 5 3 2 1 11
Reflective tape 5 3 2 1 11
Cut up mirrors 3 4 4 5 16
aluminum foil* 5 4 4 1 14
beer cans* 1 5 5 5 16

*Scale of 1-5*
5 is best, 1 is worst
*Even though we rated beer cans and aluminum foil highly in the decision matrix, we ultimately decided to not use them. We cut up a beer can a while back but found that the inside was not very reflective and would not be very useful for a solar concentrator. Also, aluminum foil was not as durable as we would have liked.


Lab # Date Plan
1 Jan 28 Make a Solar Tyre Oven (
Create semicircle skeleton for in-ground mold.
2 Feb 4 Lab Write Up 2
3 Feb 11 Lab Write-Up 3
4 Feb 18 Lab Write-Up 4
5 Feb 25 Lab Write-Up 5
6 March 4 Lab Write-Up 6
7 March 11 Lab Write-Up 7


Lab 1:

We started by making a small scale solar concentrator using a discarded tire, newspaper, and aluminum foil. For the short time period we had it turned out to be ineffective but according to the video that inspired us to try it out if food is left in the tire all day it will be sufficiently cooked.

Next, we experimented with a type of scaffolding structure to use as a potential mold in the ground. Using cardboard a series of ‘ribs’ were slotted together to create a shape similar to that of the parabolic dish needed. With time, the shape can be improved but overall we concluded that there are easier methods of getting the shape needed.

Lab 2:

The prototype parabolic ‘scythe’ takes shape! Using plywood and pvc piping, we cut out a relatively parabolic shape for the scythe (to be improved at a later date). We mostly wanted to get a feel for how effective the scythe would be at excavating the correct surface in the ground. It worked wonderfully! And we started working at the experimental farm! By digging out a patch of dirt and then filling it back up with loose sand, dirt, and mud while sweeping the scythe back and forth around the PVC axis we were able to obtain the desired surface. Now the questions remain: How durable is the mud? Are other materials more effective? What is the appropriate shape to use? How can a reflective layer be installed?


Lab 3: Mud and Mylar.

For lab today we experimented with different materials for the foundation of the concentrator. The regular dirt and mud from last lab held up reasonably well but there are definitely better options with greater structural integrity and endurance. We started out by using the scythe on a pile of sand. Overall, the sand had the correct shape but didn’t retain it very well, especially if any pressure is applied to any point. The grains are simply too individual to stick together like we need them to. Next we mixed a bucket of adobe clay and dirt. This was a much thicker and more adhesive substance (also incredibly messy). By pouring the clay into the already dug out surface in the ground and using the scythe again to smooth it over we were able to create a promising foundation for the reflective material.

With the mylar (think material inside of potato chip bags), we lined the original surface in the dirt with strips about 4″ wide going across the surface. Even without anything holding them in place, the mylar strips reflected the sunlight rather well. There was a noticeable warm spot around the point where the focus should be. For the clay surface, we decided to see if the strips would adhere to the wet clay. We used the same method as with the dirt foundation and lightly pressed each strip into the clay foundation. The strips seemed to stick better than expected so we decided to leave them for a week and let the clay dry.

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Lab 4: Staples, Screws, and Dirty Shoes

We wanted more data on how to get the mylar strips to adhere to the foundation of the concentrator. Observing the effects from the previous week, the strips stuck to the clay foundation reasonably well. We decided that any sort of abuse probably wouldn’t help much though as a light tug of the fingers was sufficient to remove each strip. Additionally, we discovered another interesting result. Despite us leaving the clay to sit for a week, the clay covered up by the mylar hadn’t dried. The clay at the edges had dried in the sun but the mylar had prevented the rest of the foundation from setting properly.

We also wanted to look at a couple other methods of keeping the reflective material in place. Screws were terrible, about as expected. They went in well enough but without a super dense material to thread in to the screws were very easily pulled out and broke up the foundation doing so.

Staples worked much better. While they had similar problems to the screws with the wet clay, for the dry clay, we could staple a piece of mylar into the material and it was much more durable than before.

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Lab 5: The Turning Tripod

This is the lab where the final design for the mold really came together. After getting a large scale parabola printed out, we cut out the shape in plywood to use as the ‘scythe’ part of the apparatus. Cheap pvc piping and joints were used to hold the 3-axis together. In theory, the long leg of the tripod would be planted in the ground at the appropriate angle (approximately 37 degrees for our latitude) and the other two legs are used for support. Zip-ties and C-clamps were used to attach the parabolic scythe to the rotational axis. The rotation was allowed by having two seperate pvc pipes, with the scythe attached to the larger diameter outer pipe which was slipped over a smaller diameter inner pipe. Finally, the same method was used to create adjustable support legs. We put thumbscrews into the outer pipes which, when tightened onto the inner pipes would lock each leg in place.


Lab 6: Applying the Design

Digging in the dirt! The scythe works!
Things learned and improvements that should be made to make scythe better:
1. The pvc pipe isn’t the strongest material. Consider reinforcing with rebar or use different material altogether.
2. The angles are difficult to judge properly. Before digging, perhaps a stake should be driven into the ground at the correct angle for the rotational axis. Then the legs could be adjusted to maintain the appropriate angle of elevation.
3. The scythe itself is not good for digging/moving earth. A hole needs to be dug out and then refilled with loose dirt/mud/clay that the scythe can scrape and smooth out. Once the appropriate shape is created, then it can be packed down.


The next step was to place the reflective surfaces (broken mirrors) into the shape. As shown in the above photos, the mirrors work very well at focussing the light coming into the shape along the incident axis to the focal point (observe Curtis’ face in every mirror in the third picture). Once we confirmed that the shapes worked, Austin (from the other SC group) assisted us in making a combination of latex cement. We used the latex cement as the base and glue for our design and once we poured it into the hole, we placed the mirror pieces into the wet cement so that when it dried they would adhere to the surface. We will come back net week to see how well…

Lab 7: Blinded by the Light

After arriving at the experimental farm, we determined that the mirrors and latex cement had maintained its structural integrity throughout the past week. Some issues we noticed: there was an accumulated layer of dirt and weeds that had been blown into the hole over the mirrors. It was somewhat easy to sweep it out but if the entire mirror surface were removable, the cleaning process would be expedited tremendously. However, the mirror pieces set into the latex cement extremely well, meaning there are definitive merits to the structural integrity of the system.

Conclusions, Learnings, & Observations

We had a lot of fun and learned a lot throughout the course of this project. Our overall conclusions and tidbits that we learned are below.

1. It is very difficult to smoothly place mylar into a hole in the ground.
2. Staples and screws do not work as well as hoped when attempting to join mylar with clay/cement base. (Staples > Screws, however)
3. This design could be better utilized if it were made in adobe aboveground. This way, a hose or piping could be channelled underneath the dish shape.
4. While PVC pipe is good for prototypes, a model to be used for manufacturing purposes should be reinforced with something stronger or made of a different material.
5. The ‘scythe’ isn’t a great tool for digging. It is much easier to dig a bigger than necessary hole, and then fill it in with loose dirt/mud that the scythe can smooth over into the correct shape gradually.
6. Mirrors > Mylar as far as overall effectiveness is concerned.


  • Don’t continue this technique – it just makes a better shaped hole.
  • With the correct dish shape, a better hole isn’t necessary – focus on making dish with better/easier/cheaper materials.
  • Not as much benefit as hoped, for effort put in.


Left to right: Mike, Johanna, John & Curtis

Mike Kim: 5th Year Physics.
Johanna Eklund: 4th Year Industrial Engineering,
John Sekerak: 4th Year Physics,
Curtis Li: 3rd Year Math,


Working Villages International,
Solar Cookers International,
Parabolic Solar Reflectors (Solar Cookers International),
DIY – How to Make your own Parabolic Mirror:
Wood design (Arba Minch Solar Initiative):
Fascinating tire design:


Ekimondo (2014). Ruzizi Ecovillage.—ruzizi-ecovillage.html
Gapminder (2014). Gapminder World. (2014). The Democratic Republic of Congo.
Health Poverty Action (2014). Millenium Development Goals.
Solar Cookers International (2014). United Nations Millenium Development Goals.
Working Villages (2014). Photos.


(, 2014)
(, 2014)

In order to reflect about change we all had different interventions we performed during the quarter. This was to better understand the process of change in our lives, making us reflect and be humble about resistance to change of other people, possibly the people we are trying to design appropriate technologies for.

Johanna: My intervention was to get up at 5 in the morning every day for a week. I am not a morning person, and I do prefer to sleep for longer in the mornings and being productive later in the evenings. Not having morning classes this quarter made being awake late at night a routine. Waiting with starting my intervention until late in the quarter, where I got really busy studying for finals, which I do the best later at night, I realized this intervention was more difficult then a thought it would be. I only managed to get up early for 3 days, and then I felt like it was more important for me to be able to focus on studying. I do however plan to try this intervention again, and put more commitment into it. Maybe I can find ways to make it work, and be as productive in the mornings as in the evenings? However, effectively changing a habit like this will require more time than a week. Even though I did not completely succeed with the intervention, it made me reflect on how difficult change can be and that time and commitment is key, as well on how easy it is to rationalize reasons not to change (this homework is important, I will do it better when I am on top later at night etc..)

Mike: Vow of silence

John: Have gone without shampoo and body wash when showering since February 8th. Still going. Girlfriend said I smelled on Valentine’s day. Cool. I have decided that I no longer need shampoo. Additionally, I added not urinating in toilets (going outside to pee) for the last week to see exactly how much water I can save by not having toilet flushes for pee. Our flowers are looking good.

Final Update: Over the course of the week, I needed to pee ~ 4.5 times/day. My home toilet uses 1.2 gallons/flush, the school urinals use 0.25 gallons/flush. Average of 0.75 gallons/flush * 31 times/week = 23.25 gallons/week saved for a month ~ 100 gallons of water saved. Or, to put things in perspective, 50 minutes in a shower. Final conclusion: cutting showers is more effective, but nature peeing feels great.

Curtis: Washing my clothes in the shower. Started a while ago and it’s been going well and I haven’t had to go to the laundromat since. I also ripped off the sleeves of my shirts to make them easier to wash. My intervention was partly out of necessity since I live too far from a laundromat and biking is my only means of transportation.