Solar Power to make bio char

It is said that bio char is a good way of sequestering carbon and therefore is helpful in preventing climate change.

The thing is, in order to make bio char, we have to burn bio mass that releases carbon into the air.

What I have in mind is to use solar heat to make bio char. If we can make a solar cooker big enough to attain the temperature needed to turn bio mass into bio char, then we can avoid the part of burning fuel to make it.