By "biomass" you must include whale oil which is what was used for lighting before petroleum or gas was used for lighting.

Not that I think we would slip back that far either, but there were practices back then which we couldn't revert to today.

Solar panels, batteries and CF lamps are far better than whale oil.  If you couldn't manage that, I suspect that properly ventilated mantle lamps fed by biogas or wood gas would serve reasonably well even if much less conveniently.
And that is key.  That is why after a "catabolic collapse," society may take hundreds of years to recover, or never recover.  All the resources are converted to waste, making it much harder to support a society than it was before.  
Exept at least metals. There a millions of tons of steel, copper, aluminium, etc for any post collapse society to pick up from the ruins.
I have always thought that Savinar, with his "the metals are all gone" line, has ignored the scrap market which could end up being a big deal far past peak.