Crude oil is ancient sunlight captured by algae and trapped underground. Firewood is much newer sunlight snagged by trees and released in campfire flames. Veggies harvest fresh sunlight and convert it to health food.
The newer the sunlight, the cleaner and more renewable the energy. At camp we use three kinds of fuel to cook our meals. We burn dirty antique sunshine hundreds of millions of years old, rays that fell to Earth when granny was born, and zero-emission light produced by fusion in the sun just eight minutes ago.
fossil fuel- Modern cook stoves burn propane, natural gas, or electricity (most often generated from coal). The camp stove is propane. Although most convenient, fossil fuels are costly, polluting, and completely non-renewable.
biomass- We have a traditional wood cook stove, a large horno, and a rocket stove. It takes some time to make a tree, but biomass is a renewable fuel if the forest is sustainably harvested. Cooking with wood takes more preparation and attention, and does release carbon to the atmosphere.
solar- The sun is a massive furnace located 93 million miles away. It is reliable, quiet, clean burning, virtually inexhaustible, requires no maintenance, and costs nothing. Every hour, the sun radiates more energy onto the surface of the Earth than the entire human population uses in one year. The trick is catching it.
If you lie out in the sun, your skin feels warm, right? Now imagine all the sunshine that hits 63 square feet being focused on your face- ouch! The solar death ray collects about 17,500 watts of light and focuses it on one small area (like burning ants with a magnifying glass). The cooker is made from a recycled nine-foot satellite dish. Instead of focusing infomercial signals, it harnesses heat energy.
Rocket stove was invented for use in developing countries where firewood is scarce, and respiratory health suffers from smoky cook fires. An insulated chamber preheats the wood, and burns all of the combustible gasses. The efficient blue flame produces no visible smoke, and requires less fuel per BTU (combating deforestation).
The Sun- It Really Cooks