With regards to burning rice hulls: because they do not have high caloric values, they can be a challenge to burn efficiently and completely. If the combustion unit isn't well engineered, then it's a nearly impossible challenge.
On of the 'new' technologies that allows biomass to be combusted...
Hi Jake:
Here are a few biomass property databases which should help you with an approximate energy content for your local sources:
http://www.ecn.nl/phyllis/
http://www.vt.tuwien.ac.at/biobib/oxford.html
Often the best local sources of biomass waste in the absence of devoted energy crops...