March 2019

34 n EXECUTIVE VIEWPOINT March 2019 www.drivesncontrols.com Saving Energy: the Hybrid Approach “With the options for reducing energy costs by increasing efficiency starting to become limited, the next big step forward is to adopt hybrid power systems with energy storage.” In these turbulent times, the challenges faced by businesses are many and varied. One of the most pressing is the continuing rise of energy costs. This impacts businesses of every kind, as diverse as product manufacturing and the operation of commercial sailing vessels. An effective response is to increase energy efficiency, but a point is eventually reached where further efficiency increases are almost impossible to achieve. Hence, a great alternative is to find a cheaper and more flexible source of energy. It’s time for a more creative solution: hybridisation. At its simplest, this means configuring an installation so that it can be powered from two or more independent sources. For land-based operations, one of the power sources is usually the national grid and the other is often a renewable power system. Having multiple power sources inherently makes supplies more robust, but to make a hybrid system really effective, it’s necessary to add energy storage, usually in the form of batteries. For example, in land-based systems, the batteries can be used to “firm up” the supply when little energy is available directly from the renewable sources. And in marine vessels, the battery can be used to provide propulsion power as an alternative to running the diesel engine. Adding batteries in a hybrid system may seem like an unwelcome complication but in reality it opens up many money-saving options. Before considering these, however, let’s backtrack. Batteries produce DC, but power systems and vessel propulsion motors typically need AC. So how to bridge the gap? The technology needed is already being used in almost every factory in the world in the form of inverters – or, in other words, variable-speed drives. Correctly configured and with the appropriate software installed, these will happily take DC power and convert it to AC. In short, inverters are the key to hybridisation. But why bother? Why add batteries? For shipboard applications, the case is clear – they provide a cost-effective alternative source of power for propulsion and they make possible big savings in the use of conventional fuels – as the ferry operator, Caledonian MacBrayne, has discovered with its hybrid ferries in Scotland. For land-based installations, the need for batteries is less obvious, but think about this. Utilities charge more for power delivered at times of peak demand, so consider charging the batteries during off- peak periods and then using them to supply part of the load at peak times – a technique known as peak shaving. Peak shaving reduces the usage of costly peak-time power and, if the utility imposes a maximum demand tariff, it can also help to reduce peak demand, delivering even more savings. Some hybrid power systems can also generate reactive power on demand, a feature that can be used to improve power factor and thereby save both energy and money. And, of course, if the mains supply fails, the batteries can continue to supply power to critical loads, which means that you may no longer need a separate UPS system. Similarly, on board a ship, if the diesel propulsion fails, the electric drives may get you home or, at least, to a safe haven. With the options for reducing energy costs by increasing efficiency starting to become limited, the next big step forward on land and on water is to adopt hybrid power systems with energy storage. While such systems are at present thin on the ground, so great are their benefits that I strongly believe that they will, in the near future, become the rule rather than the exception. n Country Manager UK & Ireland, Danfoss Drives Alan Baird