A PPA is one of many necessary steps in the process, but more importantly it probably helped secure financing and potential grants.
If there are major private power user(s) nearby, Biogas, steam or electricity could be sold to client(s) individually without a PPA. In the case of electricity, if local utility lines were used then only a carrying (rolling) charge would be needed for use of the lines. The other choice is installing fluid or electric feeders from the plant to the client. It is financially feasible to run Biogas or steam lines up to about 5 miles from the plant to a major "take or pay" client.
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".....According to the Great Pumpkin, ...you're in .....iHub....., Charlie Brown....."!!