by Seinergy LLC
Calculating defensible energy savings from efficient grow lights does not need to be complicated. Utility program planners, evaluators and regulators and policymakers – please read on.
Most utilities are aware of the increased electric loads from indoor agriculture and cannabis legalization. Many may want to guide customers towards efficient technology through incentives or other policies, yet become stalled in the multiple layers of decision making. The good news is that most utility programs have the guidelines and tools already at their disposal, and do not need to create a separate program in order to start addressing this massive conservation opportunity. The summary below is an abbreviated version of the longer, slightly more technical Horticulture Lighting Rebate Program Planning Document available for free to electric utilities, from Seinergy. This article is a refresh of–and deeper dive into–a blog post dating back to 2017.
Seinergy has estimated over 1,200 grow-light projects and completed over 130 horticultural lighting rebate applications with 28 utilities in 18 states, representing over $14 M in utility or carbon incentives. In this document, Seinergy shares some utility best practices, shortcuts and rules of thumb that may assist utilities with moving forward with offering horticulture lighting incentives today.
Leverage Custom Commercial
Horticultural lighting is an industrial process, and energy savings should be analyzed through the lens of custom commercial utility programs. Most utility programs already have custom incentive rates in terms of $/kWh, $/kW, incremental cost caps, payback ranges, etc. To incentivize horticultural lighting through the custom commercial track, all that is required is to establish methods for defining the following: proposed level of performance, proposed system efficiency, baseline system efficiency, HVAC (or other) interactive effects, equipment qualifying criteria, and persistence of savings. These are all addressed below.
And remember that horticulture lighting is not lighting. While legacy lighting calculators can be useful templates for reference, everything we know from standard lighting (watts/SF installed, energy codes, lumens, color rendering index) is irrelevant for horticulture lighting from a baseline and quality of output standpoint. Because, “lumens are for humans”, using lights to grow plants should not adhere to the same standards.
How to Measure Efficiency
The best available metric for measuring horticulture lighting efficacy is micromoles/joule (umol/j). This represents how efficiently an LED turns power into useful radiation within the primary lighting spectrum that is used by plants for photosynthesis. Legitimate grow-lamp manufacturers should prominently mark umol/j values on their technical and marketing materials.These claims should be based on an “LM79 test” from a qualified third-party lab. PPE, or Photosynthetic Photon Efficiency, is shorthand for umol/j. Modern LEDs will have a PPE range of 1.8 – 3.1, the higher being more efficient.
It is worth noting that umol/j is simply one measure of electric efficiency of turning energy into photons. While umol/j is a useful metric for comparing relative efficiencies of similarly qualified fixtures, it provides no value in assessing light spectrum, quality, effect on plant growth or effect on system production efficiency. Thus, Seinergy questions any regulation that uses umol/ (or watts-per-square foot) as a proxy for quality or energy efficiency without holistically assessing system performance, energy take-back, production output and system level energy productivity.
Due to the subjectivity of PPFD charts (particularly for baselines) Seinergy proposed relying on PPF based approach to establishing parity, and trusting that the grower will always try to maximize uniformity and PPF delivery to their canopy. PPFD maps are not useful for energy calculations. PPFD means “photosynthetic photon flux density”, and is a measure of how well LED radiation is delivered to a defined plant canopy area. PPFD charts are computer generated and are a function of the light throw angle, the height of the installed grow-lights, the table area, reflectivity of walls and other surfaces. While PPFD charts are useful for a grower to determine how high to hang their lights, for example, they are easily manipulated by the lighting engineer to best support their sales case. Some utilities ask for PPFD charts for a proposed lighting system and a baseline configuration. While well intended, these data requests are extraneous and unreliable basis for establishing parity as they are based on proprietary IES files and they cannot be objectively recreated by others.
Establishing Baseline
Seinergy recommends using a single-ended HID (“high intensity discharge” fixtures) with a 1.02 PPE as baseline for new construction. It is frustrating to establish a baseline without a recent and statically significant study, however no such study exists as of this writing December, 2020. Due to the dramatically lower cost, widespread availability, and proven viability, utilities should assume all growers are ready to install single-ended HIDs. Double-ended HIDs (primarily high-pressure-sodium fixtures) are 40-70% more efficient than single-ended HPS fixtures and cost about twice as much. Double-ended HIDs typically have an efficiency of 1.7 PPE (see Nelson and Bugbee report from 2014, table 3). Seinergy calls these the “prius of grow-lights” – while utilities tend to not pay incentives for them, growers know that for some additional upfront investment they are receiving more photometric output and achieving increased production, thus achieving energy efficiencies.
Seinergy discourages the automatic assumption of double-ended HIDs as the assumed baseline without primary data to substantiate market saturations first. If any utility insists on incorporating double-ended into a baseline based on their increasing prevalence in the market, Seinergy proposes a fixed 1.36 PPE as an alternative, which is the simple average of single-ended (1.02 PPE) and double-ended HIDs (1.70 PPE).
Calculating Savings 101
Once you know how to measure umol/j it is easy to compare efficient fixtures to baseline fixtures and articulate energy savings. First calculate the total umol or PPF proposed in the layout. This is calculated based on the proposed fixture quantity or total watts to be installed multiplied by the proposed fixture efficacy in terms of PPE or umol/j. This PPF value is the total radiation provided into the space. Now divide this value by the assumed baseline fixture efficacy (PPE or umol/j) and then by the baseline watts per fixture to arrive at the number of baseline fixtures that would provide the same level of radiant output into the grow space. We now have proposed wattage versus baseline wattage, and have established PPF parity (aka: an “apples-to-apples” analysis). Summary equations below.
Proposed PPF =proposed wattage installedproposed fixture efficacy in umol/j or PPE
Baseline Wattage = Proposed PPFBaseline fixture efficacy in umol/j or PPE
From here, calculating annual kWh saved is simply a function of multiplying the difference in watts by the runtimes for the fixtures. For indoor grows, hours of operation are extremely predictable, easy to model, and easy to verify post-facto. Incorporating interactive HVAC benefits–for those utilities who quantify and pay incentives for indirect effects–can also be easily calculated, as described in below.
Utilizing Qualified Products
Seinergy recommends utilizing the DLC’s qualified product criteria, but not requiring fixtures to be DLC listed until the list is more established and incorporates more lighting fixture applications.The DLC’s qualifying criteria for the horticulture spec provides valuable reference points regarding quality assurance, performance and longevity of equipment. Consumers purchasing a DLC listed product should have greater confidence in the product quality, as it has been vetted by a third party entity – and one with keen attention to detail. For utilities, consider offering a 10% bonus to customers using DLC Approved fixtures, as it will save administrative effort for you in assessing whether the fixture should be qualified or not.
Qualifying Product Criteria
Seinergy proposes using the following criteria to approve fixtures not listed by the DLC.
| PPE Data | Published on spec sheet
LM 79 test-derived data Third-party lab test data |
| PPE Threshold | Any PPE threshold allowable
Higher PPE will yield in greater incentive |
| Performance | Require third party LM79 tests |
| Driver Longevity | 50,000-hour minimum |
| Chip Longevity | L90 at >36,000 hours |
| Warranty | 3 years |
Establishing Hours of Operation
Hours of operation for indoor horticulture are very easy to measure and verify. Horticulture lighting for indoor facilities is most commonly configured by room and function, and plants are moved from room to room as they progress from clone to veg to flower. Thus purpose built rooms (e.g.: nursery, veg, flower or mother rooms) can be assumed to have the same photoperiod each day of the year. Although individual growers will articulate their exact lighting plan, the following table can be used for default run times – and we have seen minimal variation from these value.
| Default Hours of Operation | Indoor “Sole Source” | Greenhouse “Mixed Light” |
| Vegetative (Veg, Clone & Mother) | 18 hrs/day | 9 hrs/day |
| Flowering | 12 hrs/day | 6 hrs/day |
| Full Cycle | 13.4 hrs/day | 6.7 hrs/day |
For greenhouses, the 50% photoperiod assumption has proved a useful rule of thumb and has been an easy proxy for much more complicated (and equally uncertain) estimation methods; Seinergy has successfully used the 50% photoperiod value for dozens of greenhouse horticulture incentive applications. A second and somewhat common method to calculate lighting runtime hours for greenhouses would be to estimate how the lighting runtime hours per day would change by month, and then calculate the annual runtime hours. A third, but more complicated and highly variable method is a DLI (“daily lighting integral”) based table, wherein the average solar DLI is provided by month, and compared to the DLI required by the crop, by month. The difference between the two would be DLI required from the grow lights. (From here you would have to reverse engineer the runtime requirements to achieve the required lighting DLI, based on the installed lighting intensity – a conversation for another article).
Three words of caution if using DLI based estimates for runtime hours in greenhouses: 1) solar transmittance from the greenhouse material may vary widely, shading as much as 50% of the natural sunlight, 2) shading of internal structures in a greenhouse (including from the grow-lights themselves) could be anywhere from 10-50%, and 3) for a 12 hour flowering crops you will have to ensure that the full plant’s required DLI is delivered only within its 12 hour flowering period, and not during dawn or dusk, for example.
HVAC Interactive Effects
Efficient lights (e.g.: LEDs) will produce much less heat waste than legacy fixtures like HIDs, and thus the air conditioning has fewer BTUs to cool or remove each hour to maintain optimal operating conditions. To account for these savings you may use the 25% HVAC shortcut, or you may calculate based on SEER value. Alternatively, you could get much more complicated, with diminishing returns for the effort. In other words, for every 100 kWh of lighting savings, you might expect an additional 25kWh of electric savings from the reduced air conditioning burden, basec on typical air conditioning equipment. This value is based on a simple BTU/kW analysis of typical cooling systems, which indicate that between 26-42% additional energy and demand savings for every LED watt reduced,[1] while assuming the room operating temperature is constant and irrespective of outside air temperature.
To calculate the AC savings factor (in %) based on the SEER value of the installed air conditioning equipment the following formula can be employed: AC Interactive Effect = (SEER12)(3,41212000)
Measure Lifetime
LEDs component parts should be expected to last 50,000-100,000 hours. Thus, a fixture used for vegetative growth (that runs for 6,570 hours annually, or 18 hours/day) will have an estimated useful life (EUL) of 8.3-16.6 years. Similarly, the EUL for flowering fixtures (operating 12 hours/day) is 11.4-22.8 years. Most utility programs use an EUL of 10 years; Seinergy recommends 10 years as the EUL for horticulture grow lights.
Market Transformation
Energy incentives, grants and financing are critical at helping transform markets from less efficient to more efficient. Utility incentives are a giant lever that works, and has proven effective in the horticulture lighting industry. Energy incentives reward early adopters and offer a productive, collaborative working relationship between utilities, customers and innovative manufacturers. Incentive and rebates need to be maintained for horticulture lighting–and for any new measure– in new and emerging market sectors.
While it is generally agreed that LEDs are the future, they are not the present. As market saturation for indoor and greenhouse horticulture LEDs hovers around 5-11%, incentives will still be required for some time to effectively encourage early adopters. Incentives are effectively driving this market, encouraging adoption, promoting economies of scale and competition, driving down costs, and promoting increases in market saturation.
We don’t know what we don’t know yet about LEDs and their optimal application for controlled-environment plant growth. Grow-light technology is evolving at a rapid pace. To mandate any particular technology, performance metric or installation criteria today (in 2020) may prematurely restrict innovation and new product development growers and manufacturers. Some states and jurisdictions have prematurely restricted installed watts per square foot for grow lights (for certain crops) without measuring any unintended consequences with regard to yield, revenue, takeback, related increases in crop-canopy, impacts to competitiveness of regulated or substitute products including the impacts on regulated market sales versus illicit market sales. Policies like these are short sighted and provide questionable economic and energy savings outcomes.
Customer Engagement – Talk the Talk!
Utilities have always struggled to connect with their customers around the counter-intuitive–almost too good to be true–value proposition we call energy efficiency. Layer on top of this a cannabis industry that is nascent and perhaps not used asking their utility for energy advice much less cash assistance, and the fact that using electricity to grow plants with such intensity and scale is something new to utilities, a gap in culture and knowledge exists that must be bridged.
Seinergy recommends that every utility publicly and explicitly invite growers into a conversation about energy use and energy conservation opportunities. Don’t bury the opportunity as a footnote to an existing lighting or custom program by mentioning the word “horticulture” or “grow light. This will not suffice. At the very minimum, create a landing page on your website with a glossary of terms you can agree on from an energy standpoint, interactive calculators, specific language about energy rates, power upgrades, health and safety considerations, energy regulations, backup generators and–of course–incentives and rebates! Link to best practices about HVAC, environmental controls, humidity regulation, odor control, waste heat recapture, hot gas re-heat, etc. The body of resources is growing daily; become a clearinghouse for your customers. Help increase the energy literacy of these customers. Let them know that you care about their success and their energy use, and become the trusted energy advisor that you want to be for your customers.
Say cannabis! Familiarize yourself with whatever is legal in your state and market to those growers. Don’t overlook hemp, veggies, ornamentals and flowering plants, as these industries are also migrating increasingly indoors and under artificial lighting.
Seinergy has been having this conversation literally thousands of times since 2014. In addition to a handful of free resources we have turnkey interactive resources available to utilities to help you engage with this growing class or customers and bridge the gap today.
