By David Landolfi, DGA 2021 Winter Intern
Commercial greenhouses are critical to the food system, generating $200 billion of produce sales annually in the United States. This agricultural method can minimize inputs, such as land and water, while catalyzing plant growth and protecting against severe weather. Commercial greenhouses offer a sustainable opportunity to feed a growing population, but energy inputs needed for operation remain high. These facilities often require sufficient thermal energy and electricity to replicate ideal growing conditions. Combined heat and power (CHP) systems can provide heat, cooling, and electricity to greenhouses, cutting energy costs and reducing emissions. CHP units can also support CO2 fertilization, a common method for inducing plant growth.
Thermal energy represents a significant portion of energy consumption in commercial greenhouses. The optimal temperature for indoor plant growth ranges from 80-85°F, with heat and cooling demands constantly adjusting to maintain this level. Commercial greenhouses also require thermal energy to preheat water and control humidity levels. CHP systems have a high capacity factor, meaning they can supply heat and cooling nearly continuously, meeting the constant energy demand of indoor growing facilities. They also have the potential to run on biomass and renewable natural gas (RNG), fuels that the agriculture sector produces in high quantities.
CHP systems effectively meet the power needs of commercial greenhouses as well, which represent a significant share of expenses. Lighting alone can account for up to 30% of a commercial greenhouse’s operating costs. Electricity may also be used to meet thermal energy demand, such as through air conditioners and space heaters. CHP units can cut energy expenditures as a result of efficient fuel consumption. By producing power on site, facilities also decrease the impact of utility rates.
Commercial greenhouses may use CO2 enrichment to accelerate plant growth and facilities can integrate CHP systems to support this process. Studies have found that supplying an elevated level of CO2 to crops can increase photosynthesis by as much as 50%. Carbon enrichment has also been shown to reduce water consumption by limiting evaporative losses. Commercial greenhouses that utilize the emissions from CHP fuel combustion can raise produce yields while reducing their overall carbon footprint.
While indoor growing facilities can protect against harsh natural disasters, utility grid outages threaten crop production. During the recent power crisis in Texas, one farmer lost 80% of her microgreens after temperatures plunged overnight and she couldn’t maintain adequate growing conditions in her greenhouse. CHP systems decrease reliance on the electric grid by allowing facilities to produce their energy on-site. This added layer of resiliency is critical for commercial greenhouses, which require uninterrupted electric and thermal energy to preserve their output.
Greenhouses are already integrating CHP units into their facilities. According to a DOE database, 11 greenhouses nationwide have installed cogeneration units for a combined output of 684 megawatts (MW). Houweling’s Tomatoes launched the first CHP system that captures carbon for plant fertilization in 2012. The 13 MW system covers 128 acres of greenhouse space and boasts a total efficiency of 88%. Houweling’s carbon footprint has roughly halved since decreasing its reliance on grid power, and by 2016 the installation had already paid for itself.
As global food consumption rises, commercial greenhouses offer a sustainable opportunity to meet this growing demand. CHP systems can address the diverse energy inputs required by commercial greenhouses while lowering energy costs, improving fuel efficiency, and decreasing emissions. CHP also adds an extra layer of energy resilience to commercial greenhouse operations, which is especially critical as climate change amplifies severe weather events and threatens the electric grid.