What began as a strengthening of concern within scientific communities towards the end of the twentieth century has become orthodox wisdom writ large in the popular consciousness: climate change is both real and in need of real redress. The upshot of last year’s special report by the Intergovernmental Panel on Climate Change hit hard in the media: if in the near future global warming exceeds 1.5°C above pre-industrial levels by even half a degree, significant drought and flood events are expected to ensue.
Carbon emissions into the atmosphere, it seems, need to be tamed. And on a number of fronts electrical power seems to offer the way forward. The greening of transport, for example, (ultimately replacing the internal combustion engine with all-electric systems) or of heating systems (moving from fuel burners to electric heat pumps) would get rid of two of the planet’s principal sources of air pollution.
The problem with electrical power, though, is that producing it is still a relatively dirty process. Industrial plants, by burning coal, oil and gas, not only release more carbon into the atmosphere than almost any other sector, but they keep in business a fossil fuel industry that, through mining, drilling and fracking, additionally curtails, fragments and poisons the world’s ecosystems.
Under these circumstances, any significant increase in its production could undermine electricity’s otherwise strong green credentials.
This is where drives come in. By making motor systems more efficient, they bring down the total amount of electricity used. They maximise energy’s usefulness and work against its waste. Drives are, to electrical current, what recycling is to paper, or even what car-sharing is to vehicles: they get more out of less.
Variable speed drives match energy to work: they modify the current coming into the motor so that it does not exceed the requirements of load. Without them, a motor’s speed needs to be scaled down mechanically – with gears or dampers – under pressure of unnecessary power. And with VSDs the current is ramped up softly rather than taken in suddenly, in an inrush. Not only, therefore, is much less electricity wasted in these systems, but the systems’ mechanisms are less stressed and they live longer, more useful lives.
The intelligence of the energy delivery, moreover, is for many VSDs realised dynamically – in response to ongoing process output – by means of closed-loop feedback mechanisms; most commonly PID (proportional-integral-derivative) controllers.
For applications such as fans and pumps, where torque is proportional to the speed squared and power to the speed cubed, energy savings can be significant indeed: a fan running at half speed will draw only one eighth of the power used at full speed.
And rather than being wasted through heat dissipation, any surplus energy returned by a motor as it slows down may be saved too. This is often done by having the energy circulated between drives around a shared DC bus system – one drive that requires energy picking it up from another that is regenerating it. Alternatively (or additionally), bidirectional power flow may be enabled for individual drives by means of integrated regenerative modules.
The overall energy savings achieved by drive-based systems are considerable. And – energy being expensive – they have brought welcome profitability to businesses who commission them when upgrading their operations. It is not unusual in these cases to hear of electricity bills cut by around 75%.
Of course drives of this type are not used everywhere. The range of applications – pumps, fans, compressors, conveyors – is broad but finite. That said, there are some areas, such as the buildings sector (with its various heating and cooling systems) where their relevance is high. And, here alone, enhanced energy efficiency (considered in conjunction with improved insulation practice) is believed to have the potential to see global energy demand decline over the next decades, despite the total area of built-on space continuing to grow.
But there is, of course, a much more radical way in which electricity is being cleaned up. The development of renewable energy sources, notably solar and wind power, into viable suppliers of mainstream current promises to sever the link between electricity and fossil fuels altogether.
It is the other area of progress in which drives are contributing to the greening of energy. Specially configured drive systems have been integral to the design of a number of pioneering renewable power projects, wind and wave turbines among them; as well as to the all-important hooking up of those new production sites to the national grid (even as the grid itself becomes more diverse and distributed).
Saving the planet used to be all about straightforward energy conservation. That picture is changing. There is now – thanks on the one hand to higher efficiency levels in electric powered equipment, and on the other to the increased penetration of renewables into the supply mix – a much altered relationship between kilowatt hours consumed and greenhouse gases emitted.
In fact, with more electrically driven technologies substituting for their fuel-burning counterparts than ever before – in the industrial sector alone one thinks of the induction or infrared heating technologies displacing factory kilns and furnaces – it may now even be possible, in some cases, to equate a rise in electricity consumption with a fall in carbon emissions.
Drives have played no small part in this sea change. And they have done so as part of a larger engineering movement (broadly speaking, automated systems) that prizes long-term efficiency over short-term effectiveness. If drives cannot save the planet by themselves, they are a sign of the kind of smart resource husbandry that can.
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