Over half the people on earth (3 billion people) rely on fire wood directly for essentially all their daily energy needs such as cooking and heating. Though burning wood is sustainable in small quantities within a sustainable relationship with the ecosystem, burning in too much quantity degrades the land. Moreover, with the increase in the price of fossil fuel, more and more people will turn to fire wood for energy, causing further pressure on our trees and ecosystems precisely when we need our trees and ecosystems to heal the damage caused by fossil fuel burning.
Also, for the over 3 billion people that rely on fire wood for cooking, often this is done indoors and the smoke causes serious health problems for the (usually) women that keep the hearth as well as accompanying children. In some places plastic and tires are also burned for cooking which causes even more diseases.
However, when 1 kg of wood is turned into 400 grams of charcoal, 50 % or more energy is extracted from the 400 grams of charcoal than if we burn the 1 kg of wood in the average fire .
This means by using charcoal instead of wood 50 % less wood can be consumed right away.
What is more, since charcoal is pure carbon it burns cleaner than wood, there is no smoke (no tarballs and other semi burned particles), and so is safer to use indoors with proper ventilation and causes less pollution in the neighborhood.
(Though it should be noted that there is no smoke but there are gases: burning charcoal produces carbon dioxide and carbon monoxide, both of which can be fatal in large concentrations that can easily accumulate indoors without ventilation. Carbon monoxide is of particular concern as it is can be fatal at very low concentrations. However, a wood fire will also produce carbon monoxide and dioxide as well as a lot of smoke which lodge in the lungs. So charcoal is preferable than burning wood, but using solar to cook is far better than both, which is the point of this exercise is to create a transition fuel towards solar energy. )
Also, since charcoal is much more energy dense, it requires a far smaller metal stove compared to a wood fire (whether charcoal can be burned safely indoors with a stone stove should be investigated) 
Charcoal also has other incredible uses, such as in the ancient Amazonian indigenous technique of Terra Preta (Portuguese for “black earth”) to grow humus (more on this below). In the process of making charcoal produces a liquid bi-product of organic tar with a myriad of ancient and new uses, from water-proofing roofs to medicine.
With all these advantages it may seem puzzling why all firewood is not already turned into charcaol. The problem with making charcoal is that it takes energy to heat the airtight container to evaporate all the liquid in the wood (destructive distilling). If we burn wood to power our charcoal oven, then in the end we either don’t save any energy and/or have gone through a lot of time and trouble to make the charcoal (some high-tech charcoal machines are extremely energy efficient, but far too expensive for the people that have little energy access). However, today the technology exists to heat the charcoal oven with solar energy, which is a completely free fuel.
Solar charcoal can be made with simple solar concentrators in villages locally all around the world, providing all the benefits of using charcoal and creating a new income of organic tar. In time, after increased familiarity and skill with solar concentration, the solar concentrators can be easily used directly for the majority of energy tasks and charcoal only burned when there is no sun.
For this, a Helios Peanut Roaster produced by Tinytech can be brought and adapted to produce charcoal. How to and how much charcoal can produced can be determined, and with a community effort of running the oven, a significant amount of the tree trunk (which is mostly carbon) can be transformed into charcoal (the leaves and branches can be shredded and turned into compost). Some charcoal can then be burned by the participants mixed or non-mixed with regular fire wood, and the experience of using charcoal can be discussed and recorded.
Another part of the charcoal can be mixed with earth and compost to help the development of humus and plants called Terra preta, that was grown by ancient Amazonians between 450 bc and 950 ad, a thick rich black earth often up to 2 m deep that dots the Amazonian (and is known to regenerate itself up to 1 cm per year). Why and how Terra preta works is not yet understood by modern science, but there are patches of ancient Mayan gardens cultivated over thousands of years with a humus layer of over 2 meters in tropical rain forests that usually have a very thin humus layer. It is thought that the charcoal in the soil allows the humus to conserve the nutrients far better, rather than being washed out, resulting in a rapid increase of the humus year by year, compared to the slow natural increase without charcoal or the rapid decline in conventional agriculture. Though the details are not known, this nature-charcoal relationship is unsurprising since we know that forest fires play a vital role in ecosystems 
The participants can also use this solar charcoal in their gardens and record and discuss the experience.
Organic tar will also be produced but has so many uses it is beyond the scope of this introduction.
With the documentation of the experience of everyone involved people everywhere and far away can both benefit from and continue the experience, which may very well be one among many of the practices needed to stop using fossil fuels, without chaos and famine, and start living sustainably in a relationship with nature.
The experience will also allow the participation in, directly or indirectly, here and there, creating solar centers to develop and train in low-tech solar energy.
*** Thank you Ray Menke for contributing ideas to this piece.