The pyrolysis of wood, also called "charcoal making" is a very old technique. Traditionally, a part of the wood sample is burnt in order to provide the heat for the pyrolysis of the rest of the wood sample (this is well described in wikipedia).
The amount of wood burnt is given by the amount of air (oxygen) allowed to enter the pyrolysis volume.

If instead one admits a correspondingly larger amount of air to enter in a controlled way, the wood gets gasified. During the second world war, many cars in Italy and Germany were operated with wood gasifiers.

This way of producing charcoal or wood gas has three major disadvantages:

1) a part of the biomass is consumed for providing heat, limiting the efficiency of the process
2) the burning of the wood is difficult to control, as a consequence these processes are difficult to industrialize.
3) only high quality wood can be used, "cheap biomass" like straw or waste cannot be used

Quoting wikipedia:

Charcoal production at a sub-industrial level is one of the causes of deforestation. Charcoal production is now usually illegal and nearly always unregulated as in Brazil where charcoal production is a large illegal industry for making pig iron.[18][19][20] Massive forest destruction has been documented in areas such as Virunga National Park in the Democratic Republic of Congo, where it is considered a primary threat to the survival of the mountain gorillas. [21] Similar threats are found in Zambia.[22] In Malawi, illegal charcoal trade employs 92,800 workers and is the main source of heat and cooking fuel for 90 percent of the nation's population.[23] Some experts, such as Duncan MacQueen, Principal Researcher-Forest Team, International Institute for Environment and Development (IIED), argue that while illegal charcoal production causes deforestation, a regulated charcoal industry that required replanting and sustainable use of the forests would give their people clean efficient energy - and their energy industries a strong competitive advantage.

If instead one heats the pyrolysis volume from outside, all of these problems are solved:

1) 100% of the biomass is used
2) the process is easy to industrialize since no internal combustion occurs
3) all kinds of biomass can be used

If this external heat is provided by solar heat, we get what is called "solar pyrolysis".
This was described the first time by Isomorph H. Grassmann et al., First Measurements with a Linear Mirror device of second generation, Smart Grid and Renewable Energy, 2013, 4,253-258 and in more detail in Solar pyrolysis is also a way to store solar energy for long periods of time, without losses. Bio char made from solar pyrolysis, we call it "solar carbon" can substitue fossil coal in all applications, solar carbon can be used for firing in conventional power plants, it can be gasified to produce "town gas" and it can be transformed to liquid fuel for operating traditional car engines.