One of the greatest attributes of biogas is the flexible nature of the resource. It can be generated from a variety of organic feedstocks such as food waste, livestock manure, crop residues, biosolids, or solid waste in a landfill. It is also flexible in the utilization of the gas. Biogas can be burned for electrical generation or heat, cleaned and used as a replacement for natural gas or compressed for use as a vehicle fuel. There is even early stage research to figure out how biogas can be a feedstock for biobased chemical production to displace petroleum in materials and products we use every day. The flexibility of biogas offers many advantages, but the flexibility of the resource also presents several challenges.
Given the multiple project configurations for biogas projects, it can be difficult to design policy initiatives aimed at taking advantage of biogas utilization. Biogas is much more than a low carbon energy resource. It can be a more effective tool in managing organic waste feedstocks because biogas generation relies on anaerobic digestion to produce the gas. Biogas projects can also result in other positive environmental benefits such as reduced greenhouse gas emissions and improved air and water quality. Often to make biogas projects economical, monetization of additional environmental benefits is required. Not all U.S. markets offer the ability to monetize non-energy benefits.
Given the multiple biogas project configurations and the need to bundle various economic benefits to make projects pencil out, squeezing the most value out of projects all along the supply and production chain is critical. Many biogas projects are feasible when focusing on on-site energy production and use. This can also make a project more efficient – using the same amount of feedstock to produce multiple outputs.
Combined heat and power (CHP) projects using biogas as the primary fuel source can achieve efficiencies of up to 80 percent when compared with electricity generated at central station facilities with no heat capture and reuse. Livestock-based biogas projects have been able to achieve greater project efficiencies by capturing waste heat from the engine generator and using the heat in the barn or parlor. There are also technologies that provide cooling options for recovered thermal energy. Recovered energy is an opportunity to improve project economics and efficiency by avoiding energy purchases.
Biogas projects that clean or upgrade raw biogas to make a product that is chemically identical to conventional natural gas also have the opportunity to integrate CHP into the project configuration. A portion of biogas can be used to generate electricity which can then be used on-site to power gas clean up equipment. Projects can also recover thermal energy for utilization elsewhere in the production process. These project configurations can have multiple energy end-uses for biogas and are a combination of on-site utilization and off-site distribution.
For as long as I have worked on biogas projects, the ultimate project configuration has been to co-locate a biogas project next to a greenhouse. A greenhouse has large thermal (heating) and electrical (lighting) needs. A greenhouse also presents the opportunity to have a closed-loop system where food scraps could be a part of the feedstock mix in a digester and the digested material would be an excellent fertilizer for food grown inside. There are examples of landfill gas projects that have partially demonstrated this model, but as the anaerobic digestion system costs decline, we could see more of this model implemented across the country.
Although biogas projects have multiple project configurations that present some challenges in resource scale-up, the flexible feedstock sources and end-use utilization make biogas projects a worthwhile pursuit. The key will be to put together all the different financial benefits to get the most value out of each biogas project.
This post originally appeared in Biomass Magazine.
