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When buying a high-efficiency motor we mostly think of the saving on the electricity bill; but the motor's environmental impact is not limited to the use phase. A motor's life-cycle carbon footprint (CO2) is the sum of the grey (embodied) energy from raw-material extraction, material production, manufacturing and transport, plus the carbon of the electricity it consumes over its years of operation. Life Cycle Assessment (LCA) shows us a striking fact: in a typical industrial motor, the use-phase carbon is far greater than the manufacturing carbon. In this article we cover in detail the grey energy and use-phase carbon, the logic of LCA, why the use phase dominates, the carbon return of the IE3-to-IE4-to-IE5 transition, and the payback of the investment; the aim is to put the purchasing decision on a sound footing both economically and environmentally.
What Are Grey (Embodied) Energy and Use-Phase Carbon?
We can split a motor's carbon footprint into two main components. The first is grey energy (embodied energy): all the energy spent to bring the motor into existence and the associated emissions. This includes the production of the electrical steel laminations, the copper winding, the aluminium die-casting and body material, plus machining, assembly and transport. The second is use-phase carbon: the emissions from generating the electricity the motor draws while running. This second one is directly tied to the motor's efficiency and running hours.
What matters is the ratio of these two components. In most industrial motors the grey energy makes up a small part of the total life-cycle carbon; the lion's share belongs to the use phase. This is because a motor often consumes the energy spent on its manufacture within the first few weeks or months of operation. So the most effective environmental lever is to make the motor more efficient and lower the use-phase carbon.
- Grey (embodied) energy: Raw materials, material production, manufacturing, transport.
- Use-phase carbon: Emissions of the electricity consumed while running.
- End of life: Recycling and scrap value (usually a small negative/positive effect).
- Dominant component: The use phase, the large majority of the total in most motors.
The Logic of Life Cycle Assessment (LCA)
Life Cycle Assessment (LCA) is the method that evaluates a product's environmental impact across all its stages, "from cradle to grave". For motors these stages are summarised as raw-material extraction, material production, manufacturing, distribution/transport, the use phase and end of life (recycling). LCA computes the energy and emission contribution of each stage separately and produces a total carbon footprint.
The common finding of motor LCAs is clear: in a continuously running industrial motor the use phase makes up, mostly, more than 90% of the total carbon; manufacturing and raw materials together have a small share. This also answers the question, "Which is greener, a cheap motor using less material, or a motor with a bit more copper but higher efficiency?": the efficient motor more than offsets the small extra material in manufacturing with the large saving in the use phase. We covered where efficiency losses fall (iron, copper, friction) in our efficiency losses: iron, copper and friction article, and the efficiency/life difference of copper versus aluminium winding in our copper versus aluminium winding difference article.
| Life-cycle stage | Typical share of total life-cycle carbon |
|---|---|
| Raw material + material production (grey energy) | 2% - 5% |
| Manufacturing + assembly | 1% - 2% |
| Transport / distribution | < 1% |
| Use phase (electricity consumption) | 90% - 96% |
| End of life (recycling) | Small (partial recovery) |
The shares in the table are for a typical industrial motor running continuously for a long time; in a motor that runs very little (a few hundred hours a year) the share of grey energy rises relatively. But the great majority of industrial applications are in the continuous-running category.
Why Does the Use Phase Dominate So Much?
The monetary and carbon value of the energy a motor consumes over its life is many times the purchase price and the manufacturing energy. We can understand this with a few simple observations:
- Long life: Industrial motors usually run 15-20 years and longer.
- High running hours: In continuous processes the motor turns thousands of hours a year.
- Continuous energy flow: The kW drawn each hour accumulates over the years.
- Small efficiency difference, big total: Even a 1-2% efficiency difference turns into large energy and carbon over the life.
So in motor selection, "total cost of ownership" (TCO) and life-cycle carbon should be considered instead of the "first price". You can find the TCO comparison in detail in our IE5, IE4 and IE3 total cost of ownership (TCO) comparison article; this comparison shows that the environmental and economic decision point in the same direction.
The Carbon Return of the IE3 -> IE4 -> IE5 Transition
As the efficiency class rises, the electricity the motor draws to do the same work falls; this directly lowers use-phase carbon. Each transition from IE3 to IE4, and IE4 to IE5, cuts the losses one step further. Although the absolute efficiency differences look like small percentages (for example a few points), in a motor with high running hours this difference corresponds to tonnes of CO2 saved over the life.
The carbon return of the transition depends on the motor's power, annual running hours, load profile and the carbon intensity of the electricity. In a heavily used, high-power motor the move to IE5 offers a quick payback both economically and environmentally; in a lightly used small motor the return stays more limited. So the transition decision should be assessed per motor by running hours and power. We covered whether the efficiency gap between IE5 and IE4 justifies the investment in our IE5 or IE4, efficiency gap and payback article, and the IE4 transition decision by power and running hours in our stay with IE3 or move to IE4 article.
| Transition | Typical direction of loss reduction | Carbon effect |
|---|---|---|
| IE2 -> IE3 | Losses fall markedly | Use-phase CO2 drops |
| IE3 -> IE4 | Losses fall one step further | Additional CO2 saving |
| IE4 -> IE5 | Remaining losses fall even more | Meaningful extra saving under continuous load |
Payback: Economic and Carbon
The extra cost of a high-efficiency motor is repaid both in money and in carbon. The economic payback is the extra investment amortising itself through the energy saving; in a continuously running motor this period is often limited to a few years. The carbon payback is the extra grey energy in the motor's manufacture being offset by the saving in the use phase; LCA studies show that this period is usually very short (on the order of weeks/months), because the use phase dominates.
These two paybacks point in the same direction: in a heavily used motor, high efficiency protects both the wallet and the environment. We covered the consumption and payback calculation of replacing an old motor with an efficient one in our replacing an old motor with IE4, consumption and payback article, and the rewind-or-buy-new question in our rewind a motor or buy a new one article. Because the efficiency of a rewound motor usually drops, in terms of life-cycle carbon a new efficient motor is often the more advantageous choice.
Non-Efficiency Ways to Lower Use-Phase Carbon
Raising the efficiency class is the most direct way to lower use-phase carbon; but it is not the only way. There are complementary methods that reduce the same dominant item:
- Correct sizing: An oversized motor runs inefficiently at low load and needlessly raises use-phase carbon. Correct sizing saves.
- Variable speed with a drive: On pumps and fans, lowering the speed via the affinity law greatly reduces energy and so carbon.
- System efficiency: Improving not only the motor but the pump, pipe and transmission losses together lowers total carbon.
- Maintenance: Correct lubrication, alignment and clean cooling surfaces preserve efficiency.
You can study how oversizing eats the saving at low load in our part and low-load efficiency, correct sizing article, and the holistic efficiency of a pump system in our real efficiency in a pump system article. Combined with a high-efficiency motor, these methods minimise the life-cycle carbon.
End of Life, Recycling and the Magnet-Free Rotor
The last stage of LCA is end of life. Most of an electric motor (electrical steel, copper, aluminium, cast body) is made of recyclable materials; this allows part of the grey energy to be recovered. Magnet-free IE5 motors such as synchronous reluctance, because they contain no rare-earth magnets, are easier to recycle at end of life and carry less environmental load. Considering the environmental cost of mining and processing magnets, a magnet-free rotor offers an extra advantage for sustainability.
That said, because the end-of-life effect is a small part of the total carbon, the main determinant of the decision is again the use-phase efficiency. You can find the recycling and sustainability advantage of the magnet-free rotor in detail in our IE5 motor recycling and sustainability article.
Frequently Asked Questions
Is an efficient motor with more material more harmful to the environment?
No. An efficient motor usually contains a little more copper and better steel; this raises its grey energy slightly. But because the use phase makes up the large majority of the total carbon, the saving the efficiency improvement provides in the use phase offsets the small extra load in manufacturing quickly and many times over. The net effect favours the environment.
Does it make sense to move to high efficiency on a lightly used motor?
The return depends on the running hours. In a motor running only a few hundred hours a year the use phase is relatively small, so both the economic and the carbon payback lengthen. In heavily used motors, moving to high efficiency pays back quickly. So priority should be given to the most heavily used and highest-power motors.
How can I estimate the life-cycle carbon?
Roughly, you compute the motor's annual energy consumption (power x running hours x load factor / efficiency), multiply it by the carbon intensity of the electricity and spread it over the life years; a small manufacturing (grey energy) share is added. A high-efficiency motor reduces the total carbon by lowering the use phase, the dominant item of this calculation. To verify the nameplate efficiency by field measurement, our reading nameplate efficiency and IE code article is useful.
Practical Tips for the Right Choice
- Make the decision by life-cycle carbon and TCO, not by first price alone.
- Give efficiency priority to the most heavily used and high-power motors.
- Because the use phase dominates, efficiency is always the main lever.
- Compute the carbon and money payback of an IE4/IE5 transition together under continuous load.
- For end of life, consider a recyclable and, if needed, magnet-free-rotor motor.
- Verify the nameplate efficiency by field measurement.
At HEM Motor we offer motors in the IE3, IE4 and IE5 efficiency classes that lower life-cycle carbon and energy cost, with fast delivery from stock. To determine the efficiency class that will provide the highest carbon and cost return for your motor fleet's running hours and power, to reduce your life-cycle CO2, and to request a quote, get in touch with our engineering team. Let us choose the right efficiency class together, for both the environment and the budget.
