DC power and renewable resources

The use of DC for technology that could consume renewable energy (RE) or for an RE-related interconnection into the electric utility is of particular interest.

12/18/2012


The consulting specifying engineer, by definition, is interested in the here and now and has limited bandwidth for monitoring emerging technologies. One trend the CSE should not miss, however, is the advent of greater use of DC power for many applications. DC’s significant advantages over AC in key instances make this trend “when,” not “if.”

By the way, if you haven’t seen it, I recommend getting your hands on the November/December issue of Power & Energy magazine put by the IEEE Power & Energy Society, which is devoted to "Plugging into DC."

The use of DC for technology that could consume renewable energy (RE) or for an RE-related interconnection into the electric utility is of particular interest. Solar photovoltaics (PV) produce DC energy. Wind power is more efficient and less capital intensive if it is done in DC versus AC. In most environments today, however, we take the DC output of a renewable source, invert it into AC, then connect it to facilities and or to the grid. In many cases, ironically, once that DC power has been inverted to AC, a myriad of devices require that it gets rectified back into DC, whether it's computers, electric drives, lighting. Those DC-AC-DC conversions waste as much as 15 percent of the original renewable energy.

Eliminating 15 percent inefficiency would push renewable energy much closer to cost parity with fossil fuel sources. And, for example, one of the most costly and high-maintenance elements of a wind turbine is the complex transmission that is required to allow the unit to generate AC power. If a turbine only needed to output DC power, the mechanism would be simpler, less expensive and lower maintenance.

For these and other reasons, the use of DC is being explored for facility distribution purposes and even interconnection into the electric utility. So-called solid state transformers are currently under development right now and they were described in a recent CSE webcast in early November available here. (Registering for the webcast enables replay on demand.) A DC transformer can transform power to different voltages of DC or perform a DC-to-AC conversion. The fact that this is done via power electronics, versus traditional copper and steel magnetism, opens all kinds of possibilities.

For example, by controlling the characteristics of the power electronics it's possible for solid state transformers to be used for voltage and VAR support, power factor correction – the sorts of things that utilities frequently need when connecting renewables into the grid at both transmission and distribution levels.

To be sure, these sorts of commercial applications remain a couple of years off. Today we do not have building codes that address how DC should be wired, protected, etc., in either a home or industrial environment. Further, while the DC solid state transformers themselves are currently under commercial development, a number of standards addressing safety and reliability need to be developed for their deployment.

Despite the current immaturity of this technology, when a CSE is planning a major industrial project with an industrial substation, he or she would be well to discuss these emerging technologies with their client, particularly when a solar PV installation is involved. This is the lowest hanging fruit, because eliminating the need for an AC inverter greatly reduces the cost of the PV array. DC can be used directly to recharge battery banks for energy storage. It can be used directly for office lighting, for heating, for electronics products. In the near future we’ll see many consumer electronics, from flat-screen TVs to PCs, sporting both AC and DC inputs. So the first applications may well be rooftop solar PV feeding DC current into an office building.

The knowledge of this new technology coming along suggests that, at the very least, provisions be made or consideration be given not only to the photovoltaic panel design itself but also to how the system is wired and connected. The design should accommodate the eventuality of DC generation feeding DC consumption. It would be an absolute disaster at this point to put up a PV array that had an integral DC to AC conversion in the panel itself, obviously, because then the conversion waste is built into the system.

The use of DC may take a number of directions. Some visionaries in the industry believe that DC codes would require no changes to existing wiring practices, because the voltage level on DC might be different. Others think we’ll need separate wiring, separate facilities. There are two efforts afoot at IEEE to resolve these issues.


Sam Sciacca is an active senior member in the IEEE and the International Electrotechnical Commission (IEC) in the area of utility automation. He has more than 25 years of experience in the domestic and international electrical utility industries. Sciacca serves as the chair of two IEEE working groups that focus on cyber security for electric utilities: the Substations Working Group C1 (P1686) and the Power System Relay Committee Working Group H13 (PC37.240). Sciacca also is president of SCS Consulting.



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
Strategic outsourcing delivers efficiency; Sleeve bearing clearance; Causes of water hammer; Improve air quality; Maintenance safety; GAMS preview
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Your leaks start here: Take a disciplined approach with your hydraulic system; U.S. presence at Hannover Messe a rousing success
Flexible offshore fire protection; Big Data's impact on operations; Bridging the skills gap; Identifying security risks
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Applying network redundancy; Overcoming loop tuning challenges; PID control and networks
Putting COPS into context; Designing medium-voltage electrical systems; Planning and designing resilient, efficient data centers; The nine steps of designing generator fuel systems
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me