New Mexico team roasts green chillies with solar power

Energy researchers in New Mexico have used concentrated solar power to roast batches of green chilis, opening up the possibility of using the sun for high-temperature food preparation.

The pilot project was led by Kenneth Armijo, a Sandia National Laboratories engineer who grew up on a chilli farm in New Mexico. With the help of colleagues at Sandia, Armijo placed a traditional steel-drum tumbling chilli roaster to the top of the 200-foot tower at Sandia’s National Solar Thermal Test Facility, protecting the rotor mechanism from the intense solar heat. Using between 38 and 42 of the facility’s 212 heliostats, Armijo was able to achieve a temperature close to 500 degrees Celsius uniformly across the roasting drum, comparable to the temperature of a traditional propane chilli roaster.

“The principle behind this research was to see if high-temperature food roasting, not just peppers, could be done with solar and produce comparable results as traditional propane roasting, and the answer is yes,” Armijo said.

“We used green chilli to showcase the culture of New Mexico. Combining the state-of-the-art facilities and research at Sandia National Labs with the culture, food and people of New Mexico is just so special. What other national lab in the world would have done this?”

According to the team, not only is the technique more sustainable than using propane, it also has the potential to be quicker and produce better results. Armijo presented several green chilli connoisseurs with both solar-roasted chilli and traditional propane-roasted chilli and surveyed them on a variety of qualities. He found that on average, the respondents favoured the solar-roasted chiles by 18 per cent for flavour, 12 per cent for smell and 2 per cent for ease of peeling the inedible skin. However, the respondents preferred the texture of the propane-roasted peppers by 4 per cent.

Sandia National Laboratories engineer Ken Armijo installs a chilli roaster on top of the solar tower above a field of mirror heliostats - Randy Montoya

 “I did a survey and overall, the participants preferred the solar-roasted chilli to the propane-roasted chilli,” said Armijo. “That was shocking to me. They preferred the taste because it didn’t have as burnt a taste. They said it just tastes cleaner than green chilli.”

“With the solar roasting, we were actually able to achieve a more uniform distribution of heat. With propane roasting, you just get heat right where the burners are, but all the chilli piled on top isn’t really getting heated as efficiently. We saw with our infrared cameras that with solar, it’s more uniform. In essence, the heat is reaching all the chilli in the front of the roaster. In practice, this has a lot of potential for roasting chilli more quickly, with better quality, as well as greener.”

Swapping from propane to solar in New Mexico alone for chilli roasting could save around 7,800 metric tons of carbon dioxide each year – the equivalent of taking about 1,700 cars off the road. However, the team believes the technique could have much wider applications across other foodstuffs, including soybeans, nuts and coffee. Armijo and his colleagues are working on a portable version of the solar roaster that does not rely on a large array of heliostats to achieve the extreme roasting temperatures.

The results of the experiment will be shared at the American Society of Mechanical Engineers’ conference on energy and sustainability next week.