Growing large scale pharmaceutical cannabis within a closed environment, such as a greenhouse or indoor facility, requires an intense amount of energy and a high power load capability. In a high-tech facility design, most systems operate using some form of energy converted into electricity.
According to energy statistics from data recorded in US states with established large-scale cannabis production, HVAC systems account for up to 51% of energy use, while artificial lighting contributes to approximately 38% of consumption . Citywide energy consumption in Denver, Colorado increased by 1.2% annually between 2012 and 2014, with 45% of that growth attributed to indoor cannabis cultivation .
The rising awareness in the dangers of fossil fuels, and the need to produce energy without toxic emissions, must be applied to the emerging medical cannabis industry in Europe. Many various sources of alternative energy can be harnessed to power cultivation sites. With forethought, and planned project phasing, producers can reach sustainable, carbon-neutral, and even carbon-negative goals.
Here, we will focus on integrating photovoltaic energy sources into pharmaceutical cultivation systems, exploring the most practical and efficient options. Photovoltaics can be understood through the theory of photons. In this case, photons are energy “packets” from the sun (without mass!), which strike loosely bound outer electrons contained in the photovoltaic semiconductor material, and knock them free via the photoelectric effect. This phenomenon can be envisioned as a white cue ball striking a striped or solid coloured ball on a pool table, and transferring its energy to this ball. Once the electron is free, it must be directed into an electric current to provide harnessable energy.
To create a current with these electrons, a semiconductor material, such as silicon, is “doped” with small amounts of other elements. Introducing these elemental impurities into the silicon crystal structure causes changes in electron positions within that structure, and an electric field forms across the cell. This electric field “catches” the electrons that are smashed off the silicon atoms, directing them into a current, thus generating power.
There are two ways to implement solar power into a pharmaceutical operation: 1) by choosing or designing equipment with built-in photovoltaic cells generating electrical energy used to directly run the system, and 2) through storing the harvested solar energy in a battery bank for future use in whatever system requires it most.
Direct Utilisation of Solar Produced Energy
The most energy and cost efficient method of direct utilisation for a greenhouse or indoor cultivator is to adapt HVAC systems such as industrial extraction and circulation fans, dehumidifiers, and chillers to run straight off solar power being produced by photovoltaics. Hot and sunny summer months, when the photovoltaic cells generate close to their peak capacities of energy and power (rate of energy consumption), are precisely when cooling systems will need to utilise the greatest amount of energy. This creates a highly efficient self-regulating feedback loop. More energy and a higher power capacity will be available to the fan or chiller systems exactly when it is required. On cooler, cloudy days, there will be less energy and power available, and the systems will also not require as much of either to keep the appropriate environmental conditions.
Solar energy obtained by photovoltaics can also be directly converted into thermal energy. This thermal energy can be used for heating purposes in refrigerant compression-expansion cycles, featured in chillers and some dehumidifiers, or for heating the reactivation air in desiccant wheel dehumidifiers. In the winter, solar generated thermal energy has valuable heating applications in the cultivation area; using this source of heat can save an operation significant amounts of spending on grid or natural gas energy.
Lithium Ion Battery Storage
A limiting factor in the functionality of photovoltaic systems is inefficient energy storage. Once the sun energy is harvested, if not utilized immediately, some energy is irretrievably lost, even with the most current battery technology. If a system has no battery storage capacity, excess energy captured is simply wasted or flows to the main grid if connected. Lithium ion batteries represent the most practical choice for a large scale storage system. These batteries can hold up to six times the amount of energy per kilogram compared to traditional lead-acid batteries, and 40% more energy can be drawn from the battery before it must be recharged (a characteristic called Depth of Discharge) . Lithium ion units can also retain energy for longer without degradation, and have an overall longer life-span compared to other technologies.
Storage banks with capacities of 1-5 Megawatt-hours (MWh), are already commonly used in industrial applications. A one hectare pharmaceutical operation can consume from 5-8 MWh of energy per day. Larger storage banks are available, however their extremely high cost inhibits them from being a practical option for cultivators. With a more affordable 0,5 -2 MWh storage bank, for example, the greenhouse grower can power artificial lights to keep plants in the vegetative phase, or add supplemental light on cloudy days, and an indoor grower can significantly reduce the amount of energy consumed from traditional grid sources for their lighting and other machinery.
Battery stored energy can essentially be used in whatever system the cultivator wishes, offsetting costs of grid power and reducing emissions. The inherent loss of energy associated with battery storage, is mitigated by the ability to use the energy in a way customised to one’s production needs.
Although expensive, lithium ion battery banks are undeniably crucial in providing energy efficiency to private solar cell systems. Used along with HVAC and other cultivation systems designed to run off solar energy sources connected to their circuitry, lithium ion storage can save the the pharmaceutical cultivator significant cost and reduce facility emissions drastically. Environmentally responsible, sustainable cultivation requires the widespread application of photovoltaic technology.
By J.R. Tremblay
 Northwest Power and Conservation Council; “Electrical Load Impacts of Indoor Cannabis Production”, 3 September, 2014; https://www.nwcouncil.org/sites/default/files/p7.pdf
 Denver Environmental Health Cannabis Sustainability Work Group; “The Cannabis Environmental Best Practices Management Guide”, 1 August, 2017; https://www.denvergov.org/content/dam/denvergov/Portals/771/documents/EQ/MJ%20Sustainability/Draft%20Cannabis%20Environmental%20BMP%20Guide.pdf