A number of low voltage direct current (LVDC) trials are preparing the ground for a wider use of the technology, both in developed and developing countries.
LVDC is seen increasingly as a green and efficient method of delivering energy, as well as a way of reaching the millions of people without any access to electricity. It’s fully in line with the UN’s Sustainable Development Goal 7, of providing universal access to affordable, reliable and modern energy services by 2030.
In direct contrast to the traditional centralized model of electricity distribution via alternating current (AC), LVDC is a distributed way of transmitting and delivering power. Today electricity is generated mostly in large utility plants and then transported through a network of high voltage overhead lines to substations. It is then converted into lower voltages before being distributed to individual households. With LVDC, power is produced very close to where it is consumed.
Using DC systems makes a lot of sense because most of the electrical loads in today’s homes and buildings – for instance computers, mobile phones and LED lighting – already consume DC power. In addition, renewable energy sources, such as wind and solar, yield DC current. No need to convert from DC to AC and convert back to DC, sometimes several times, as a top-down AC transmission and distribution set-up requires. This makes DC more energy-efficient and less costly to use.
IEC expertise comes in handy
The environmental gains from using a more energy-efficient system supplied from renewable sources make LVDC a viable alternative for use in developed countries as well as in remote and rural locations where there is little or no access to electricity. “The potential benefits of LVDC already have been demonstrated by a number of pilot projects and niche studies in developed nations. For example, a pilot data centre run by ABB in Switzerland running on low direct current power has shown a 15% improvement in energy efficiency and 10% savings in capital costs compared to a typical AC set-up. This is interesting because data centres consume so much power,” comments Dr Abdullah Emhemed from the Institute of Energy and Environment at Strathclyde University in the UK. Dr Emhemed leads the University’s international activities on LVDC systems. He is a full member of the IEC’s new Systems Committee (SyC) on LVDC and LVDC access. He is also a member of the IEC UK National Committee (NC).
According to Emhemed, further standardization work is required on “voltage levels, as well as safety and protection issues” amongst other things. The IEC is leading efforts to promote the benefits of LVDC and to assist in the specification and ratification of these new Standards. SyC LVDC has begun standardization work through a systems-based approach, identifying gaps where International Standards are needed.
Many of these gaps can be filled by adding provisions about DC into existing Standards. The IEC has also published a number of Standards and Technical Specifications (TS) already relevant to LVDC. They include IEC 62031 on the safety specifications for LED modules for general lighting, published under the remit of IEC Technical Committee (TC) 34: Lamps and related equipment, for instance.
IEC TC 82: Solar photovoltaic systems, provides another example. It has published a number of TSs on rural electrification, the IEC TS 62257 series, which make a huge raft of recommendations for renewable energy and hybrid systems.
Trial and error
Japan is one of the countries in which DC trials have mushroomed. More than ten different projects scattered across the country rely on DC power. They include the hybrid AC/DC Fukuoka Smart House inaugurated in 2012, which utilizes energy supplied from a number of different DC sources.
In Europe, one of the most advanced projects is in Finland. LVDC RULES began in October 2015. It is led by the Lappeenranta University of Technology (LUT) and financed by the Finnish Funding Agency for Technology and Innovation (TEKES).The project aims to take the final steps towards the industrial scale application of LVDC in public distribution networks by building on the data gathered from laboratories and research sites and transferring the technology into everyday use in Nordic distribution companies. The data is drawn from trials which started in Finland as early as 2008.
“The LVDC RULES project consortium has put together complete specifications for LVDC equipment optimized for public power distribution, especially in a Nordic environment,” explains Tero Kaipia, one of the researchers from LUT involved in the project. “The development of the equipment is in good progress and the critical tests have been completed. The construction of the pilot installation into the distribution network will start in 2018. Design methods and practical guidelines have been developed to enable the economic utilization of LVDC networks as part of a larger distribution infrastructure,” he adds.
While this project demonstrates a workable LVDC system, a number of key outstanding challenges have been identified by the researchers involved. Chief among them is the lack of appropriate Standards. “Standardization at system and equipment level is an essential prerequisite for the wide-scale rollout of LVDC in Finland,” says Tero Kaipia. “Without standardization there will be incompatible components and it will be difficult to construct systems using components from different manufacturers. And most of all, the network companies will not buy LVDC systems, if the certified components and standard design guidelines are not available.”
In India LVDC is seen as one of the solutions for bringing electricity to the millions of homes which still have no or only intermittent access to power, as is the case in many other developing nations.The Indian government’s Ministry of Power and the Rural Electrification Corporation (REC), a public infrastructure finance company in India’s power sector, are piloting a number of projects.
One of these is the Solar-DC initiative led by the Indian Institute of Technology Madras (ITT-M). As a result, an ecosystem for DC appliances and DC microgrid projects is emerging. As part of this global effort, ITT-M has been working in collaboration with Telangana State Southern Power Distribution Company Ltd and REC to bring uninterrupted power to four hamlets in rural Telangana, which had been living without electricity for six to eight hours a day. The technology in this particular case comprises a 125 W solar panel, a 1 kWh battery, an inverterless controller unit and DC loads operating on a 48V DC internal distribution line, installed in each small hamlet.
Other similar trials have also been taking place in the Indian states of Bihar, Assam, Rajastan, Karnataka, Odisha and the city of Chennai. The Bureau of Indian Standards (BIS), which is the IEC’s Indian NC, has been drafting documents based on these trials aiming to standardize 48V for microgrids.
“India is in the process of finalizing a 48V standard for electricity access suited to local needs. It is my hope that this new standard will be presented soon to the IEC community, as an input for further discussions to formulate a universally accepted IEC Standard for electricity access,” says Vimal Mahendru, member of the IEC Standardization Management Board (SMB) and Chair of the IEC SyC LVDC.
By Adrian Pennington