In 2011, Irish Aid and Trinity College Dublin (TCD) came together to work on a novel project aimed at tackling the energy access crisis in developing countries. The objective was clear: use the heat produced during normal cooking practices to develop a low-cost technology capable of generating small amounts of electricity for use in off-grid communities in the developing world.
At this point the ‘μPower TEG-stove’ concept was truly born. The work is being permed open source and by December 2015, 100 prototype generator stoves will be manufactured and assembled in Malawi and deployed in the country's rural communities.
Context of the project
According to recent World Health Organisation estimates, more than 20 per cent of the world’s population currently lack access to a regular, reliable, safe source of electricity. Additionally, approximately three billion people worldwide rely upon biomass for cooking as well as light and heat. The data shows that a huge number of these people are rural inhabitants of developing countries.
One of the oldest, yet still one of the most common, cooking practices encountered in developing countries is the ‘three stone fire’ method. As the name suggests, this simple approach requires the operator to lay a cooking pot on top of three stones placed on the ground.
This cooking method is familiar, adaptable and easy to perform, but unfortunately it is also very fuel inefficient and produces a lot of pollutants and harmful emissions. Such cooking practices must change. Staggeringly, an estimated four million people die prematurely from illness attributable to the household air pollution from cooking with solid fuels, and sadly children under the age of five are at particular risk.
Smoke and soot inhalation are just the tip of the iceberg. Inefficient cooking practices can be linked to a vast range of undesirable subjects including deforestation, climate change, gender issues, health and personal safety and, almost unbelievably, even the spread of HIV. Despite the negative aspects surrounding the use of the three stone fire and other similar cooking methods, their ease of use and cultural acceptance make them difficult obstacles to overcome.
Thankfully, the issue is gaining more attention and there are now some stove-themed global initiatives confronting this problem. Nevertheless, convincing people to fully adopt new technologies is this area is a very difficult task.
When we assess a new technology, we generally need to see a clearly identifiable benefit, otherwise our natural inclination is to return to what we know best. When the TEG-stove project was conceived, one of the key considerations for us and Irish Aid was how we could engineer something to make a new cooking stove technology more appealing to rural off-grid communities. It is this point that perhaps separates our research from other electricity-generating methods such as solar PV. Power-generation, although important, is not the sole reason for the TEG-stove generator.
We came up with several plausible options to improve the attractiveness of a cleaner cooking stove: what if the stove could also charge your mobile phone? Or provide light so that your children could study in the evening? Or power a radio so you could listen to music and keep abreast of current affairs in your region? Or do all of the above and save you money at the same time? These are the challenges our TEG-stove research group have been working on for the past number of years.
How the μPower TEG-stove works
Cooking stoves generate a lot of energy in the form of heat and this energy can be converted to electricity directly by taking advantage of the thermoelectric principle. According to the Seebeck effect, a temperature difference between the junction of two dissimilar electrical conductors or semiconductors and their ends creates a voltage difference between the two substances. This is the operating principle of the thermocouple.
Thermoelectric generators, or TEGs, are electricity producing devices consisting of many thermocouples or pellets connected electrically in series and thermally in parallel to create hot and cold surfaces. If a TEG experiences a temperature difference between the two surfaces, it produces a DC voltage proportional to that temperature difference.
If the TEG is connected to an electrical circuit and sufficiently large temperature differences can be maintained, the TEG can act as a DC power source. The main drawback of using TEGs is their low efficiency, so they are typically employed in waste energy harvesting applications, where the energy would be otherwise dissipated to the environment.
The first major step in the project was to gain an understanding of how TEGs operate as power sources. Persuading a TEG to produce power in a lab scenario was easy. Using a power supply and a simple cooling loop we were able to study the TEGs output performance relatively quickly. The lab work only gets you so far, however - we needed to choose a cooking stove to integrate with the TEG. Several concepts were conceived and tested.
We experimented with several different cooking stoves from around the world. We even looked into developing our own stove. Suitably, the project began in humble beginnings with our initial experiments taking place in the TCD car park inside a (2m)
3 flat pack garden shed. After several months of testing, a clay cooking stove produced locally in Malawi was selected for integration with the TEG generator.
This portable biomass-fed stove, known locally as the
chitetezo mbaula, is becoming more commonplace in the country and has already somewhat overcome the acceptance barriers mentioned above. The stove is promoted by Irish Aid and other non-profit and development organisations as being a much cleaner, safer and more fuel-efficient alternative to the three stone fire. The Malawian government has recognised the need for improved cooking practices and is committed to introducing two million clean cooking stoves across the country by 2020.
Once the TEG and stove were selected, the next significant engineering hurdle was to design a heat collection and dissipation strategy. We needed a method of capturing a small amount of heat from the fire, delivering it safely through the TEG and then relieving this heat away from the stove. The first edition of the device was to be used as a proof-of-concept – could we produce meaningful electrical power from a cooking stove?
The first version consisted of three copper rods which protruded into the centre of the stove and collected heat primarily by radiation and conduction. The rods were connected to a copper plate to act as the heat collector for the TEG. To maintain the temperature difference across the TEG, an off-the-shelf CPU heat sink was used. A fan driven by a low power DC motor, which was powered by the TEG, completed the configuration. A very simple circuit was designed to manage the power generated by the TEG which could be delivered to connected devices, or stored in a rechargeable battery.
Into the field
Our initial experiments in TCD using the Malawian stove showed that we could produce sufficient power to charge mobile phones and LED lanterns. We were, however, very conscious that our methods of operating the stove could differ significantly to the people for whom it is designed (for example, I know that our PhD student burns wood at about twice the rate I do!). We needed to get some of these devices into the hands of the target communities.
Irish Aid firmly supported this notion too and, in November 2011, the first μPower TEG-stove generators boarded a plane destined for Malawi. In collaboration with Concern Universal, the objective was to deploy a small number of TEG-stoves into a rural off-grid community for six months and to monitor their performance as well as the users’ attitudes and behaviour. To this end, each of the TEG-stoves was fitted with data-logging equipment for the first 80 days of the field trial, and we took temperature, power generation and power consumption data every single minute of the trial.
We also data-logged a control group without TEGs because we were worried that the inclusion of the generator might cause people to burn more fuel than normal. Thankfully, our data showed this not to be the case. Although behavioural patterns may change from region to region due to fuel scarcity, it seems that prolonged stove usage is quite common.
The data we obtained showed that the TEG-stove users regularly charged their phones and LED lights. Some even manipulated their own connections to power radios. The feedback from the participant communities was extremely positive. One of the participants refused to let anybody else use the stove because she valued it so highly. Everybody was asking when we could bring more TEG-stoves to the communities.
The project from this point gained momentum. We knew it was technically feasible, but at this point our design certainly wasn’t realistic economically or sustainable from a development perspective. A second version of the generator soon followed. Based on experimental work carried out in TCD it was once more designed and constructed in-house.
Again employing a CPU fan-based cooler, this version reduced the cost and complexity of the cooling system in particular. In July 2012, 10 version two generators were deployed to two communities in Ntcheu, Malawi. Once more we monitored usage patterns and power generation and consumption. The results were vastly different compared with the first trial. It seemed that word had spread about the ‘electricity stove’.
Usage patterns showed intense burning periods, and our field facilitators discovered that some users had set up phone-charging businesses using the TEG-stove. Some of the stoves failed in the early weeks of the trial because the rechargeable battery was never able to recharge sufficiently to keep the fan running to cool the generator. We were concerned, and it took a lot of hard work and analysis from TCD and Concern Universal to figure out what had gone wrong.
Present study
Irish Aid was not perturbed. It returned to the table eager to fund the next stage of the TEG-stove project. Valuable lessons had been learnt during the first two field trials. The message was clear: if the TEG-stove was to become a viable and sustainable technology it had to be low-cost, low-maintenance, easily repairable and made close to market where possible. A new design approach was necessary.
The failures in the second field trial caused us to rethink the cooling strategy. We removed the fan (a moving part) and replaced it with a passive water cooler. We engaged local metal manufacturers and fabricators in Malawi to make the metal components for the generator. We spoke with the women’s group responsible for making the
chitetezo mbaula, and now they also make a modified stove with a pre-made hole for the inclusion of our generator.
The circuit has been completely redesigned. Since rechargeable batteries are not common in Malawi and our data showed that users preferred to charge during cooking times, the battery has been removed. The new circuit includes separate user-selectable modes for phone charging, lights, radios and batteries if required. Data logging is also in-built on our circuit board so that we can assess the generator’s performance without resorting to expensive third party equipment. We now employ a full-time Concern Universal field facilitator to manage our research in Malawi.
By December 2015 we plan to have 100 prototype TEG-stoves deployed to rural communities. The rollout has been under way since 2014, with user feedback informing successive iterations of the design and circuitry. In addition to the technology development, this project phase also involves the investigation of different business models working towards a sustainable approach. We hope that this field trial proves to be even more successful than those before it and that we can move towards developing the technology as a viable option for the people of Malawi, and indeed other countries in the developing world.
The TCD team is comprised of post-doctoral research fellow Dr Seamus O’Shaughnessy; PhD candidate Maurice Deasy; and principal investigator Dr Anthony Robinson - who together have been working on the μPower TEG-stove for almost five years