Plant 600 trees in a grid 8 by 8 feet. After 2 years you cut the 120 trees closest to the south. This wood will be about 2" in diameter, good for kindling. Doing this will give extra sun light to the trees behind them. Next year (year 3) you cut the next 120 trees behind them. Year 4 you continue cutting your way back. By now you are cutting trees that are about 4 to 5 inches in diameter. Year 5 you have only 120 original trees left. They are 6 inches in diameter which means, no splitting. Cut them down and use them. You should get enough wood from those 120 trees to heat your house that winter.
Up to this point, you have been increasing the amount of wood you cut every year. You would say, now what?
Year 6 you will be cutting down the first lot of 120 trees you cut 5 years ago. They regenerate! Those trees you cut on year 6 will also be 6 inches in diameter. Year after year you will be cutting 120 trees that are 6 inches in diameter. Life expectancy of a poplar is 40 years.
Do you think your trees are getting old? Use some of the cuttings you get every year (you get thousands) to plant new trees.
You have heard that poplars do not give you the BTU that other woods do. That is correct, hybrid poplars will give you about .6 of the energy you can get from hard woods, such as hickory or maple but this shortcoming is offset by the amount of wood these trees generate.
black locust would give you more BTU's and are fast growing, nitrogen fixers.
Regards,
Mike