Ratings (1 bad – 5 good) in pure carbon-cycle and physical terms
• Gas from grass clippings: 4. It uses an existing residual biomass stream, stays inside the biogenic carbon cycle, requires comparatively little exotic mining or complex infrastructure, and can return material to soil. Real limits are logistics energy, methane management, and absolute scale. It is a practical, low-complexity use of something already growing and being cut.
• Air-source heat pumps: 2.5–3. High end-use efficiency is real, but the full system demands continuous electricity plus large-scale mining and grid infrastructure whose material and energy costs are substantial and recurring. It shifts burdens upstream into extraction and power generation rather than eliminating them. Without assuming a particular electricity mix or political support, the carbon-cycle and resource footprint is heavier.
Guess who I buy my gas from?