The Dairy Farm That Sells Gas Instead of Milk
Manure produces methane, and capturing it produces a fuel that qualifies for environmental credits worth far more than the energy itself. That has made digesters attractive and created some uncomfortable incentives.
The Basic Process
An anaerobic digester is a sealed vessel in which bacteria break down organic material without oxygen, producing biogas that is roughly half methane, and a residual digestate used as fertiliser or bedding.
On a dairy farm the feedstock is manure, which would otherwise be stored in a lagoon where it decomposes anaerobically anyway and releases methane directly to the atmosphere.
Capturing that methane and using it as fuel achieves two things: it produces energy, and it prevents a potent greenhouse gas from being released.
Where the Money Actually Comes From
The energy is worth relatively little. Biogas competes against natural gas, which is cheap, and a farm scale digester produces a modest quantity.
The economics work because of environmental credits, and the credit value can exceed the energy value by a large multiple.
| Revenue Source | Relative Contribution |
|---|---|
| Energy sold as gas or electricity | Small |
| Renewable fuel credits | Large |
| Low carbon fuel standard credits | Frequently the largest |
| Digestate and bedding value | Modest, mostly avoided cost |
The reason credits are so valuable is the carbon intensity calculation. Fuel programmes score fuels by lifecycle emissions, and dairy manure biogas receives an extremely favourable score because the baseline against which it is measured is methane venting from a lagoon.
Avoiding that release is credited, which can produce a carbon intensity score that is deeply negative, meaning the fuel is treated as removing emissions rather than merely producing few.
A deeply negative carbon intensity score means one unit of this fuel generates the credits of several units of an ordinary low carbon alternative. The value comes from what would have happened to the manure, not from the gas.
The Baseline Problem
That mechanism is where the criticism concentrates, and it is the same additionality question that appears in carbon offsets.
The credit assumes the counterfactual is open lagoon storage releasing methane. If a farm would have adopted a different manure management practice anyway, or if the operation was not previously using a lagoon, the avoided emissions are smaller than credited.
The sharper concern is directional. If manure from a large lagoon based operation generates far more credit value than manure from a pasture based one, the credit structure rewards the more emissions intensive baseline.
Taken further, the value of the credits could in principle support expanding herd size or maintaining lagoon systems, because the waste stream has become a revenue centre. Whether that has actually occurred is contested, and the incentive is present in the design regardless.
The Scale Problem
Digesters have substantial capital cost and the economics improve sharply with herd size.
The result is that adoption concentrates on large operations, and small dairies cannot justify the investment individually.
Two responses have emerged. Cluster projects connect several nearby farms to a central digester through pipelines, spreading the capital cost. And third party developers finance, build, and operate digesters on farms in exchange for the credit revenue, paying the farmer a fee or a share.
That last structure is now dominant, which means the farmer frequently receives a modest payment while the developer captures the credit value, and the farmer has entered a long term agreement over their own waste stream.
The Policy Fragility
The entire economics depend on credit prices set by regulation, and those prices have been volatile.
Low carbon fuel programme credit prices have fallen substantially at points when credit generation exceeded programme demand, which happens when the mandated reduction schedule is met more easily than expected.
Projects financed on credit price assumptions from a strong period have found the revenue substantially lower, and the energy value alone does not support the capital.
Regulatory changes to the carbon intensity methodology present a further risk. Any revision reducing the credit for avoided manure methane would remove most of the project revenue directly, and such revisions have been proposed.
How to Read a Project
For anyone assessing one, the questions are what share of revenue comes from credits rather than energy, which is nearly always most of it; what carbon intensity score is assumed and whether it has been certified; what the credit price assumption is and how it compares against recent trading; the contract term with the farm and who owns the credits; and the exposure to methodology revision, which is the risk least likely to be disclosed.
The Bottom Line
Farm digesters capture methane that would otherwise reach the atmosphere, which is a genuine environmental benefit, and they are financed almost entirely by credits reflecting that avoidance rather than by the value of the gas. The credit depends on a baseline assumption about what would have happened to the manure, which rewards the operations with the worst existing practice and creates an incentive structure nobody would design deliberately. The revenue rests on a regulated credit price and a methodology that can be revised, which makes it a policy exposure dressed as an energy project.