LPG (liquefied petroleum gas) is among the most important fuels for achieving clean cooking. Many countries are actively developing intervention programs. In a five year project starting in 2007, an Indonesian program converted over 50 million households cooking with kerosene to LPG. In 2016, India intensified their campaign providing free connections to LPG cylinders to “Below Poverty Line” homes. In China, gas and biomass fuels, the dominant energy fuels for cooking, are used by 44.8% and 32.1% of households, respectively. In 2014, 47.6% of rural cooks used biomass, whereas urban households were more likely to cook with gas (65.8%) (Applied Energy 2014, 136:692-703 Duan, et al.).

Even older LPG stoves burn cleanly. Five different LPG stoves were tested 89 times and described in a 2018 article. Two stoves were manufactured in China and obtained in a local market near Beijing. One was manufactured in Japan and purchased in Kampala, Uganda. Solgas Repsol Downstream Peru (an international LPG distributor) disseminated another stove. A worn-out appliance was obtained from a rural household in Cameroon  (Environ. Sci. Technol. 2018, 52, 904−915 Guofeng Shen, et al.).

• The average thermal efficiency for the LPG cook stoves was 51 ± 6%.
• Approximately 90% of the PM2.5 data was below the level of detection.
• The other 10% of the stoves had an average PM2.5 score of 0.20 ± 0.16 mg/minute. (The WHO Emission Rate target is 0.23mg/minute).

However, in a country like Rwanda the switch from wood and charcoal to LPG is slow. In 2019, only 2% of cooks were using LPG in the cities. 64% used a charcoal or wood stove and in rural areas “the use of clean fuels is negligible” (The World Bank, 2019). 93% of rural households use wood, 6% of charcoal, and 0.2% of gas (National Institute of Statistics Rwanda, 2019).

The cost of LPG is a big factor. “Prices are much higher in rural areas and upcountry towns as retail traders factor in transport logistics. Rising prices for cooking gas in the country have sparked concerns of likely reversing gains made in the push for a clean cooking solution as more households turn to wood and charcoal.”  

Marie-Jeanne Uwanyiringira, a businesswoman who sells LPG, says that the fluctuation in prices has caused frustration among consumers. “When someone buys gas from me at RWF 3,500 and the next month I tell them that it is RWF 5,500, ($5 USD) they don’t seem to understand that it is not the seller’s fault.” (Rwanda Today, April 9, 2021).

When I went to UC Berkeley, studying psychology as an undergrad, lots of people made fun of Freud, Jung, and Adler who wrote (a lot) about divergent theories of what makes people tick. UCB liked to think of itself as a scientific institution, and facts are proven by statistical validity. Why should we believe speculation from the dear departed? I eventually agreed and I was intrigued by the big question: How do we know the truth?

The paradigm that captured my thinking was the BLACK BOX. In black box theory facts are like an elephant in a box. Scientists poke sticks into small holes in the box and one stick hits a toenail. A scientist exclaims, “Why, what is in the box is hard and slippery!” Other sticks hit the softer belly or the trunk, resulting in very different observations. Hopefully, after many experiments an accurate description of the elephant can emerge. (Although, what the elephant is thinking may well remain private.)

I was really excited by statistics!

If you’re trying to know the effectiveness of something, calculating the statistical significance can help. It gives you a measured amount of confidence in the hypothetical conclusion. At UCB we did experiments and 95% confidence was the minimum that students had to achieve to get an “A.” To achieve 95%, the sample size and the size of the effect had to be big enough.

Here’s the application to stoves: 

When we try to use found wood sticks from the forest in our experiments, one stick, for example, has two inches of bark on it. Another stick has three inches of bark and the two sticks make very different amounts of smoke. So, the variable of using sticks that emit different amounts of smoke makes it more difficult to know the truth: Did changing the air/fuel ratio, for example, result in the stove making less smoke? Using wood with no bark, we can achieve confidence in five to seven tests. We have to do a lot more tests when the fuel has added variables.

When trying to understand heat transfer or combustion efficiency in the lab (not what happens in the field) limiting variables has a great appeal to lazy researchers like me at ARC. So, we do not design stoves in the lab!

We realized quite a long time ago that we could only investigate heat transfer and combustion efficiency in the lab, and then with great relief go to an amazing place, work with wonderful people in a new culture, eat incredible meals, etc. in order to help a local team evolve a stove using found everything (and testing/statistics).