Outlook 2011: Efficiency is over riding

4 min read

If you could identify one theme which has emerged from the power sector during the past couple of years and which is likely to continue for the foreseeable future, it is likely to be the efficient use of power.

There are a number of reasons for this apparent sea change in an industry's outlook. Firstly – and probably overriding everything else – is the realisation that the Earth's resources are finite. While we wait for the roll out of high efficiency alternative energy sources, our energy needs continue to be met by fossil fuels, with the consequent negative effect on the environment. But there are other reasons; some more prosaic. One is simply the desire for users of consumer electronics technology to use their devices for longer between charges. Given that battery technology has advanced very slowly over many years, it has to be regarded as a limiting factor. So, if you can't get very much more energy per unit volume of battery, the devices which that battery powers must make the power supply last longer. And there is the issue of waste heat. In the past, power supplies – whether board level or system level – have been notoriously inefficient and the energy that is not used was converted to heat. Now, with smaller devices and higher power consumption, heat becomes another challenge. Increase a device's efficiency and the amount of heat generated drops. For the moment, much research and development effort is being expended on ways to convert sunlight into useful energy. It's been a slow burn for some years, but recent work is moving the technology forward, if only slowly. There are a number of research organisations focusing on the area, with Belgian microelectronics specialist imec among the leaders. It has recently announced that its large area silicon solar cells have achieved an efficiency of almost 20%. That may seem low, but it does represent substantial progress on previous attempts. However, reality does not reflect the theoretical efficiency of such cells. imec's large area cells have a surface area of 148cm2, but are just 170µm thick. Achieving efficiencies of almost 20% is said by imec to have proved the viability of large scale manufacture. "The fact that such efficiencies can be obtained by metallisation schemes based on screenprinted silver contacts enables compatibility with present industrial metallisation practice in the solar cell industry," said Dr Joachim John, team manager, industrial solar cells at imec. Scientists at Johannes Gutenberg University (JGU) in Mainz are working on the same problem. They claim computer simulations have highlighted a new way of increasing the efficiency of copper indium gallium selenide (CIGS) thin film solar cells beyond the current 20%. The team has been addressing the 'indium/gallium puzzle', referring to the ratio between the two elements. Calculations originally showed the optimal indium:gallium ratio was 30:70. But the simulations show the maximum efficiency level should be achieved with the exactly inverse ratio of 70:30. "We are currently working on large format solar cells which should outperform conventional cells in terms of efficiency," said Dr Thomas Gruhn. "The prospects look promising." Converting sunlight into energy is only one part of the problem; getting it from the solar cell and into the grid is another. Companies such as STMicroelectronics, National Semiconductor and NXP are developing devices which apply maximum power point tracking (MPPT) to panels. MPPT adjusts for power fluctuations resulting from varying solar intensity, shadowing, temperature change, panel mismatch, or ageing. The companies claim that, without MPPT, the power from a solar panel can fall by up to 20% if even a small percentage of its surface is in shadow. In some cases, this can challenge the viability of the project. NXP's offering, the MPT612, is said to deliver up to 98% efficient power extraction in applications such as solar battery charge controllers, distributed MPTT and micro inverters. Based on a 32bit ARM7TDMI-S processor, the chip features voltage and current measurement, as well as panel parameter configuration. Another promising avenue of research which is looking to do away with the need for batteries all together is energy harvesting and it's another strand of imec's research. Ruud Vullers, principal researcher and micropower program manager, said the target was to generate 100µW/cm2 through the harvesting of vibration, heat, light and rf energy. Admitting energy harvesting is not new, Vullers contended that early devices were big, heavy and expensive. "Size and weight will be important, so we are looking to use MEMS technology to bring the cost down." He envisages building harvesters on 6 or 8in wafers using a cmos compatible process. And packaging will be critical because it will be an integral part of the design. Vullers is exploring electrostatic and piezo based vibration harvesters. Piezo technology currently generates more power and imec has recently generated 100µW using a vibration frequency of 572Hz. "We are now looking to generate 200µW," he added, "and if you can package these devices in a vacuum, it gives a big advantage." Fuel cells remain another potential source of alternative power, but the technology hasn't made the breakthroughs which had been expected. Tom Sperrey is chief executive of UPS Systems. He's forecasting 'significant commercial growth' and believes the UK fuel cell market will change in the near future as costs fall and new products hit the market. "Already, new products are launching into the market and companies continue to show interest in learning more about fuel cells and adopting clean technology." Fuel cells as a whole are receiving the backing of the Technology Strategy Board (TSB), which has recently invested £7million in 15 demonstrator projects. The investment programme in fuel cell and hydrogen demonstrators will fill a gap in the support of these technologies and will assist the efforts of UK companies towards commercialisation of products for the stationary power and transport markets. Iain Gray, the TSB's chief executive, said: "By providing capital funding towards the cost of demonstration, this important programme will enable British companies to collaborate to commercialise fuel cell and hydrogen technologies. Covering both the transport and stationary market applications, the funding will support and take forward already successful research, development and prototyping projects. "We expect the technologies that will be developed and demonstrated to make real progress towards market adoption, providing significant global opportunities for the British companies involved." Yet, despite general enthusiasm for the concept of fuel cells, the market remains technically challenging – particularly for those companies planning to develop products addressing the consumer electronics sector. Much has been said about the potential for fuel cells to replace conventional batteries in such devices as laptop computers and mobile phones, but little has been seen in the way of products. In fact, a number of companies have fallen by the wayside. Despite the enthusiasm, it may well be some time before portable devices feature fuel cells, rather than rechargeable batteries. Meanwhile, power electronics companies continue to develop more efficient components – dc/dc converters, for example – not only looking to squeeze as much from the supplied power as possible, but also doing so within ever smaller volumes. One market driver has yet to be mentioned: cost. Whatever products are being developed, customers want them to be ever cheaper. Graham Pitcher is Group Editor at Findlay Media