Carbon Footprint Summary
Note: Using mostly EPA and California Department of Energy links/documents, this document compares the rough carbon footprint of a grid powered, controlled environment cultivation facility (CECF) to one powered by ‘combined heat and power’ (cogen) system.
Here is the close mix of power generation sources provided to us by Liberty Power – the utility supplier to the AV. The (nearly) ‘zero carbon’ supplies come mostly from geothermal and solar. This stated 30% is slightly less than the number Liberty gives for “renewables”, but a small percentage of those renewables are from combustion of biomass, etc. which produces Green House Gas. The ‘zero carbon’ number is thus slightly less. With the tiny exception of these consumed biomass products, the overwhelming percentage of the ‘carbon power’ side comes from natural gas (NG) generation in Nevada.
This mix is reasonably similar statewide as there are state ‘carbon reduction’ requirements driving them.
As almost 100% of the ‘carbon power’ side of the above chart is NG power plant produced, here is the base efficiency number for such fossil fuel power plants. This number comes from the EPA.gov and references for these numbers can be found in the footnotes [1] at the end of this document.
After the power leaves the generation facility, line losses across CA come to an average of 9.2%. Since the AV is a rural area, the losses are higher. We’ve rounded up to 10 which is very conservative for our area%. Data from EIA.gov [footnote: 2]
If you combine the power plant losses on the ‘carbon power’ side of the equation and the transmission/distribution line losses for both sides of the equation, you arrive at a close number for the overall Liberty grid efficiency. Again this number is reasonably similar across CA due to state mandates.
While the details of CHP will not be delved into here, combined heat and power (also called ‘cogen’) is more efficient than the grid in cases where heat is needed in addition to the electricity. Where a normal power plant is only 33% efficient, CHP systems are regularly measured approaching 80% – and close to 90% if exhaust gas heat is recovered, as we will. [footnote: 3] Remember how the power plant throws two-thirds of the energy it consumes away in the form of heat? Well, if you generate on-site you can put that heat to use rather than throw it away.
Here is how the Canadian industry magazine “Greenhouse Canada” describes it: [footnote: 4]
“Greenhouse cogen units now supply 10 to 15 percent of electricity generation in the Netherlands. Growers harness the CO2 and the heat, meaning their systems are operating at 90 per cent efficiency … substantially higher than stand-alone electricity generating plants in which the heat and CO2 are wasted … [saving] Europe about 200 million tonnes of CO2 each year. … CHP and greenhouses are a perfect fit.”
The more heating hours your facility requires per year, the better the heat utilization. Our needs fit perfectly. The ideal temperature for indoor cannabis is on average ~78f. Anytime it is below ~75f, we have to add heat to our intake air. The cool desert climate of our valley, with our large day/night deltas means that nearly 80% of our hours are heating hours (as recorded by the Federal RAWS station on Eastside Lane).
Read the full California Energy Commission Camarillo case study [footnote: 5). You’ll see that in this real world installation, they measured the efficiency at 87.8% (page 64, table 16). You’ll also understand why in that study they say “Modern greenhouses, because they need temperature control and enriched CO2 levels, represent a good application for combined heat and power technology. A natural gas fueled engine-generator produces hot water to warm the greenhouse and electricity to power the grow lights, plus carbon dioxide from the engine exhaust to accelerate photosynthesis.”
Footnote 1: The average efficiency of fossil-fueled power plants in the United States is 36 percent. This means that two-thirds of the energy used to produce electricity at most power plants in the United States is wasted in the form of heat discharged to the atmosphere."
https://www.epa.gov/chp/chp-benefits
Footnote 2: https://www.eia.gov/tools/faqs/faq.php?id=105&t=3
Footnote 3: "By recovering this wasted heat, CHP systems typically achieve total system efficiencies of 60 to 80 percent for producing electricity and useful thermal energy. Some systems achieve efficiencies approaching 90 percent." https://www.epa.gov/chp/chp-benefits
Footnote 4: https://www.greenhousecanada.com/energy/management/editorial-3943
Footnote 5: https://drive.google.com/file/d/10XIWj1CIx9dtlvKqReL6220QuIpilFg2/view?usp=sharing
