Totally uneconomic on crop fed. You might make it stack up on slurry + waste silage, but only if you use the electricity and the heat to good purpose. You will get more electricity per acre from your solar by a long way, and far less work, maintenance costs, haulage and the rest.
Anyone going seriously down this route is welcome to come to our farm and see how we have had to modify our AD to get it to work, and reduce maintenance costs.Been having similar thoughts, but small enough to cover our winter demand when solar is down (10kw/h Average)
Speaking to AD owners, if you think you can justify the upfront cost, just double it to cover maintenance and running costs.
rocketskills.in
I helped in the build of the gasholder in this one in Malawi in 1977. It made gas for cooking the farm workers food. Ran on cow manure (got a hyaena stuck in it after I left)3rd World biogas production... Saw these in the early 80s in action in India, but possibly not quite what the OP had in mind....
Gobar Gas Plant- Step by Step Basic Guide for 2020
Gobar gas will help change the game for farmers- it can increase their surplus and harvests, it can be used as an impressive domestic fuel, and will also help the farmers save money.
TBH, that is all most of us would want. Needs to be cheap and cheerful and simple to operate (and clean)
www.quberenewables.co.uk