The Budding Energy Footprint of Indoor Agriculture

Indoor agriculture energy usage is projected to grow substantially over the next several years, driven in large part (but not entirely) by the legalization of medical and recreational cannabis. Seven U.S. states and the District of Columbia have legalized recreational cannabis already, with more states likely to follow. Twenty-nine states and the District of Columbia have legalized cannabis for medical use. This rapid shift in many parts of the United States is driving much of the nation’s energy load growth. The Northwest Power and Conservation Council projects that indoor cannabis growing operations alone will add as much as 300 average megawatts by 2030 in the Pacific Northwest. That is equivalent to 1.5% of total regional electricity demand. In Colorado, Xcel energy says 45% of its load growth is due to indoor cannabis cultivation operations.

Indoor agriculture operations not related to cannabis are expanding, too. The price of LEDs has fallen dramatically in the past few years and local food movements in cities are driving increased demand for fresh high-quality produce. More restaurants are interested in sourcing ingredients directly from the producer, and in dense urban areas a growing number of new indoor agriculture operations have begun to meet this demand.

In general, grow lights are completely exempt from building codes and efficiency standards. NBI drafted and proposed the first standard at the national model code level for the efficiency of grow lights in agriculture. But when we start talking about standards we have to consider metrics: how do we measure the energy efficiency of a light?

“Lumens are for Humans”

Lighting intended for human vision applications is properly measured by lumens and lumens per watt is the typical metric for fixture efficacy. However, lumens are defined using a spectral distribution (the spectral distribution defines the amount of light emitted at various wavelengths across the spectrum) whose weighting function is based on what human eyes can see. This is why we say that “lumens are for humans.” But plant growth and maintenance – aka photosynthesis – requires a different spectral distribution than we humans need for vision. This is why the indoor agriculture and greenhouse industries do not use lumens as a metric.

So what’s the right metric for indoor agriculture grow lights?

The light output of grow lights is often rated by the Photosynthetic Photon Flux (PPF). This is a measure of the total quantity, in micromoles per second, of Photosynthetically Active Radiation (PAR) photons (defined as the photons with wavelengths between 400 and 700 nm) emitted by the fixture. When we divide the fixture’s PPF by its total Wattage, we calculate the photonic efficacy of the fixture. The units of photonic efficacy are micromoles of photons emitted per Joule of energy input, abbreviated as µmol/J. Photonic efficacy appears to be the best way to compare the energy performance of various fixtures to one another. (That said, this is a complex topic and every potential metric, including this one, has its pros and cons. If you know of a perfect answer, let us know, because we’re looking for it!)

Now that we have a metric, where do we set the standard?

Based on our extensive research of the luminaire market, NBI has proposed a standard at 1.6 µmol/J for the photonic efficacy of luminaires used in agricultural application. We have documented more than 80 fixtures, from 19 different manufacturers, that meet or exceed this standard today. We are working with code stakeholders in Washington and Oregon, at the ICC, and at NEMA to establish applications for this standard.

We also think about these issues in contexts beyond lighting standards. We participate closely with the Resource Innovation Institute. Alexi Miller, NBI Senior Project Manager, serves on their Technical Advisory Committee, helping develop and implement energy and carbon metrics for indoor agriculture operations. We support our utility sponsors in accessing technical knowledge and leading-edge program innovation as their efficiency programs ramp up to meet this new industry. We work with other leaders and experts in the field to develop white papers, baseline information, and best practices guidance for this industry.

For more information about NBI’s Cannabis Sustainability Initiative, please contact Alexi Miller.

Jim Edelson, Director of Codes & Policy and Alexi Miller, Senior Project Manager