Energy Intensity

A factory's electricity use rises 5% while production rises 20%, so its energy use per unit may have fallen even though the total bill grew, which is useful information but needs context before calling it an equipment-efficiency gain. The US Department of Energy defines energy intensity as energy needed per unit of output or activity and distinguishes it from efficiency, noting that structural and behavioural factors can change intensity without a technical improvement.

The IEA provides activity-based energy-efficiency indicators across sectors. Choose the activity measure, since tonnes, units, room nights, revenue and floor area answer different questions and the one that best reflects the energy-using process should be selected.

Keep boundaries aligned, so that energy for one factory is divided by that factory's output and not by group-wide revenue, and state the included buildings and processes. Define the energy source, because electricity, gas, diesel and district cooling may need conversion to a common energy unit, and keep the method and conversion factors visible.

Distinguish delivered and source energy, since purchased electricity measured at the site differs from the energy used to generate and deliver it and two methods should not be compared without adjustment. Check meter quality, because missing periods, estimated readings and shared meters can distort the numerator and the data should be reconciled to invoices and site records.

Use the right period, as an annual energy total over annual output is comparable while a winter month over a full-year floor area needs different interpretation, and check zero output, since a shutdown can leave standby energy while production is zero, making per-unit intensity undefined or extreme, so report downtime separately. Adjust for product mix, because a factory making more energy-heavy items can show higher intensity even when each process improves, and analyse product lines where possible.

Account for weather, since heating and cooling loads change with temperature and degree-day or similar analysis can help compare buildings across years, and consider occupancy, because a nearly empty office and a fully occupied office may use similar base energy but different activity and floor area alone can miss that context. Handle revenue denominators with care, as sales value changes with price, currency and inflation, so energy per revenue can fall because prices rose and not because less energy was used.

Look at total energy too, since a lower intensity with rapid production growth can still mean higher absolute consumption and emissions, and do not equate energy and carbon, because electricity emissions depend on generation mix and fuels have different factors. Measure process changes by verifying that compressed-air leaks, maintenance and equipment controls actually affected consumption before attributing a trend, and use a baseline that records the original scope, meters, activity definition and operating conditions, otherwise improvement claims are hard to audit.

Watch outsourcing, since moving energy-intensive work to a supplier lowers the company's direct numerator but not necessarily the overall energy used to make its product. Compare peers carefully, because climate, hours of operation, equipment and products vary and a benchmark without context can mislead, and set targets with evidence, since a reduction goal should reflect feasible operational changes and expected activity and a slogan is not a plan.

Check fixed loads, because lighting, servers and idle machinery use energy even when output falls, so a per-unit metric can worsen during weak demand without equipment failure, and separate efficiency projects by comparing before-and-after use at similar loads, since a fall after a retrofit is not proof that the retrofit caused all of it. Show units prominently, because "150" alone is meaningless while 150 kWh per square metre per year is interpretable, document any gas-to-kWh conversion factor and period because inconsistent conversions can create false trends, and review the data annually, since site openings, meter replacements and product changes may require a revised baseline with any restatement disclosed; for owners, energy intensity connects consumption to useful activity and is strongest alongside total energy, operating context and a clearly defined denominator.