How to map a factory's energy use and find the savings

Why start with a map

In 2023 the Department for Energy Security and Net Zero (DESNZ) published a study of energy efficiency in manufacturing, based on a 2021 survey of 1,114 manufacturers. Of those firms, 98% used electricity and 41% used natural gas, but only 11% monitored both their energy use and their energy efficiency.

What most sites lack is a breakdown of which system uses what. A few sub-meters or clamp-on loggers are a low-cost way to start one.

The same map gives you your emissions. Once each energy source is recorded, converting it to tonnes of carbon dioxide equivalent (tCO₂e) with a named conversion factor takes little extra work. It also shows which savings matter most for your carbon figures as well as your bills.

Build the map in five parts

India's Bureau of Energy Efficiency describes energy mapping as understanding how much energy a facility uses, how it flows through the plant, how it divides between uses and how it relates to production. Any site, in the UK or India, can map itself the same way.

1. 1SourcesList every form of energy you buy: grid electricity, gas, oil, LPG, diesel for plant and generators, and any other fuel. Collect twelve months of bills and purchase records for each.
2. 2FlowSketch where each source goes: which buildings, sections and machines. A single-line drawing of the electrical supply and the fuel lines is enough to start.
3. 3Division by useEstimate the share taken by each main system: furnaces and boilers, motors and pumps, compressed air, lighting, heating and cooling. Use sub-meters where you have them, and equipment ratings and running hours where you do not.
4. 4Link to productionDivide energy by output each month to get your specific energy consumption, such as kWh per tonne. It is the most useful single number on the map.
5. 5Technology gapsFor the largest users, note the age, rating and condition of the equipment, and whether a more efficient model exists. An energy auditor can complete this part.

Match the conversion factor to the country: the DESNZ set for the year you are reporting on UK sites, and the Central Electricity Authority's CO₂ baseline database for grid electricity in India. Record which factor you used next to each figure.

Track a few numbers every month

A map is a snapshot. Monitoring shows whether things improve. Pick a short list of measures for your main systems and record them on a fixed routine.

Three habits keep the log useful. Record production alongside energy, or the months cannot be compared. Note anything unusual, such as a breakdown, a new product or a holiday. And keep the same method each month, so a change in the figure reflects the plant rather than the arithmetic.

Where the savings usually sit

The Carbon Trust's guide to energy saving in manufacturing (CTV059, 2018) gives a sense of scale for the common systems. Use its figures as a guide to where to look. Your own measurements decide what applies to your site.

Compressed air

Industrial sites often lose up to 30% of their compressed air through leaks, and an idling compressor can still draw up to 40% of its full-load power. Survey and tag leaks regularly, switch compressors off when production stops, and generate at the lowest pressure your most demanding tool needs. Up to 90% of a compressor's heat can be recovered to warm water or space.

Boilers, ovens and furnaces

This is where most on-site fuel is burned, and where most Scope 1 emissions come from. A poorly maintained boiler can use 10% more energy than a well-maintained one. Service the burners, insulate pipework, valves and tanks, survey steam traps and recover heat from flue gas and exhaust.

Lighting and the building

LED lighting can save up to 80% compared with older lighting types, and movement and daylight controls can cut lighting energy by a further 30 to 50% in typical office areas. Space heating uses around 11% of the energy consumed by manufacturing industry, so heat offices and production areas separately, match heating times to shifts and insulate the roof first.

Base load

Plot monthly energy against production. If the line is still high when output is close to zero, plant is being left running with nobody using it. Walk the site at night and at a weekend, note everything running, and track weekend energy use as a standing measure.

Motors and drives

Motors run the pumps, fans, conveyors, compressors and machine tools on a site. The Carbon Trust estimates they use around a quarter of the electricity on manufacturing sites (CTV059, 2018), and most sites have more of them than they think.

Many run at full speed all the time, with a valve, damper or bypass holding back the output. For fans and centrifugal pumps, power falls roughly with the cube of speed, so a small cut in speed brings a large cut in power. The Carbon Trust puts it at about half the power for a 20% cut in speed (0.8 × 0.8 × 0.8 is about 0.51). A variable speed drive lets a motor run only as fast as the process needs.

1. 1Make a motor listList every motor above a few kilowatts with what it drives, its rating, running hours and age. Nameplates and maintenance records are the start. The list shows which motors matter and which are now oversized for their job.
2. 2Log the largestLog the power draw of the biggest, longest-running motors over a typical week, alongside production. Many savings turn out to be motors running when nothing needs them.
3. 3Replace rather than rewindWhen a motor fails, compare a high-efficiency replacement with a rewind over the rest of its life, not on purchase price. Over a motor's life, the electricity it uses usually costs far more than the motor.
4. 4Fix the systemBelts, gearboxes, throttling valves and dampers waste energy downstream. Look at what the motor drives as well as the motor itself.

Motor efficiency is graded in classes from IE1 to IE5 under the standard IEC 60034-30-1. Since July 2021, Ecodesign rules in the EU and Great Britain have required most new motors from 0.75 kW to 1,000 kW to meet IE3. Since July 2023, many motors from 75 kW to 200 kW must meet IE4. Older motors already installed may sit well below those classes.

Drives add small losses of their own and can affect power quality, so an engineer should size and specify them for your site.

Prove the saving

A saving that is not measured is easy to doubt. For a customer, a lender or an energy service company paid from savings, it has to be measured against an agreed baseline and adjusted for anything else that changed. The International Performance Measurement and Verification Protocol (IPMVP) is a widely used framework for doing this.

1. 1Set the baselineEnergy use before the change, over a representative period, with the production it supported.
2. 2Note the adjustmentsChanges in output, shifts or weather that would have moved energy use anyway.
3. 3Measure the reporting periodEnergy use after the change, on the same meters and on the same basis.

When you show the emissions saving, use the same conversion factor before and after, so a change in the grid is not counted as your work. Then keep watching. Settings get changed, bypasses get opened and new equipment is added, so check the per-tonne figure each month for the systems you changed.

How ESGen helps

ESGen is not an energy auditor, installer or engineer, and we do not certify savings. Our part is the data. The platform records electricity, gas, diesel and petrol for UK sites, by site and meter, from your bills, and converts them with DESNZ factors. It keeps the bill and the calculation behind every figure, so the effect of a change shows in your footprint with its evidence. See carbon assessment.

Our manufacturing page sets out what the platform and our team cover for factories. To see your own sites and meters set up from a year of bills, book a demo.