In scenarios B and C, participants generally believed the cost of implementing DC power distribution would be similar to implementing AC power distribution. For scenario A, they estimated that outfitting an entire building with DC power distribution would be more expensive than an AC system.

Participants were instructed not to consider costs related to building-level power electronics, appliances, and controls, which the researcher believed would make the responses too variable.

Was the study accurate? Only time will tell. For now, owners have to compare the implementation costs of different DC power distribution system brands on a case-by-case basis. Shortly we’ll review cost considerations of specific DC systems, including PoE.

Obstacles to implementing DC power

Not all building systems are compatible with DC power. In this section we’ll cover factors to consider when researching and choosing a DC power distribution system.

When AC power became the building standard about a century ago, most loads, including incandescent lamps, toasters, and refrigerators, required AC electricity. But, with LED lights, variable speed HVAC motors, EV batteries, and today’s array of digital devices, many loads are shifting to DC electricity. In fact, up to 74% of loads in a building could require DC power, when considering EV chargers and HVAC equipment with DC motors16. This makes the majority of our devices compatible with DC electricity. However, compatibility with DC electricity and compatibility with a DC power distribution system are two different things.

A building’s compatibility with a DC power distribution system depends on the type of system deployed and the compatibility of individual loads with that system. For example, if the lighting system is compatible, then DC power distribution could be implemented just for the lighting system.

Some DC power distribution systems can plug directly into a typical electrical panel, convert AC power at the source, and distribute DC power throughout a building. This reduces the number of conversions down to one. In this scenario, owners must check whether their fixtures have removable drivers, which convert AC to DC electricity. Replacing that driver with an intelligent DC-DC driver will ensure that the correct voltage is provided.

PoE, another option, is safe and easy to install because it uses low-voltage DC power. If power requirements are not high, it can reduce the amount of cabling involved because power and data are transmitted over one cable type. However, it does require a few compatibility checks. PoE can only connect to building systems and devices that are designated as PoE systems.

PoE is currently limited to 90W per cable. Bundles of cable are often necessary to deliver appropriate power to each device, which can increase capital costs. For example, a lighting system in a 25,000-ft2 commercial office might need approximately 4000W, or 45 PoE cables bundled together. PoE cables also have limitations; they can run up to 100m before additional devices are required to extend their data and power reach.

PoE also requires Ethernet (CAT series) cables — which can be more expensive than typical electrical cables — as well as Ethernet switches or injectors17. All these things add complexity and cost to PoE systems.

The compatibility of individual loads with DC is another factor. For example, HVAC systems can benefit from DC power distribution only if they have a DC motor. Many HVAC systems have AC motors, but market demand for HVAC systems with DC motors has increased, largely because they are about 50% more efficient than those systems with AC motors.

Conclusion

Beyond its economic benefits, DC power is safer than AC power and helps futureproof buildings by providing electricity that is directly compatible with digital devices, LED lighting, and HVAC systems with DC motors. Although the number of DC power distribution systems on the market today is limited, they are offered by several brands, including Argentum Electronics, ARDA Power, and Voltserver. When choosing a DC power distribution system, you can also choose a PoE-based solution from vendors such as Cisco, Igor, and Focal Point Lights.

DC power distribution can save building owners and managers energy and operational costs by eliminating inefficient AC-to-DC conversions and by lengthening the operating life of DC powered devices. Depending on the type of DC power distribution system implemented in new or retrofit construction, the ROI can be two to five years.

Reach out to the author by connecting on LinkedIn.

REFERENCES

1. B. Glasgo et al., “Expert assessments on the future of direct current in buildings,” Environ Res Lett, 13, 074004 (2018).

2. E. Kelly, “Why AC power REALLY won the Current Wars,” Argentum Electronics blog (April 14, 2022).

3. B.T. Patterson, “DC: The Power to change buildings,” Construction Canada (Mar. 25, 2014).

4. List of HVDC projects via Wikipedia (updated July 14, 2022).

5. A. Berthou, “The benefits of high-voltage direct current (HVDC) power,” EE Power (Oct. 19, 2020).

6. D. Gunderson, “Stop the waste in your battery-charger conversion,” Electron Des (Mar. 12, 2008).

7. E. Kelly, “5 Reasons DC electricity should replace AC electricity in buildings,” Argentum Electronics blog (Mar. 3, 2022).

8. R. Price and M. Scerbo, “Direct current power systems can save energy, so building developers are getting a new incentive to incorporate them,” Alliance to Save Energy blog (Feb. 26, 2019).

9. E. Kelly, “Was the 100,000 hour LED light bulb false advertising?” Argentum Electronics blog (Sept. 10, 2021).

10. Report ID AA0421078, “Global electric vehicle charging station market,” Astute Analytica (May 6, 2022).

11. Electric Insights YouTube channel video, “What makes level 3/DC charging SO fast?” Argentum Electronics (July 7, 2022).

12. Z. Hoover et al., “How charging in buildings can power up the electric-vehicle industry,” McKinsey & Company (Jan. 5, 2021).

13. A.J. George and G. Ferrand, “Cost study of AC vs. DC data center power topologies based on system efficiency,” Eltek Power, Data Center Solutions white paper.

14. NFPA 70 National Electrical Code, National Fire Protection Association, current edition 2020.

15. E. Kelly, “Electricity You Can Safely Touch!? - Introducing Class 4 (CL4) Power Systems,” Argentum Electronics blog (April 26, 2022).

16. R. Price and M. Scerbo, “New LEED pilot credit encourages energy savings with DC power systems,” U.S. Green Building Council (Feb. 28, 2019).

17. “PoE Switch vs. PoE Injector: Which One to Choose?” Fiber Optical Networking (Nov. 21, 2017).

Get to know our expert

ERIN KELLY is the creative director and digital content researcher at Argentum Electronics. She has a new media degree from the University of Toronto and five years of experience in the communications field. Kelly has created digital content for dozens of clients through her own business, Story Unlocked, and loves technology, especially when it makes the world a better place.

Argentum Electronics provides DC power solutions such as those described in this article.

Extended online version; abridged version published in the October 2022 issue of LEDs Magazine.

For up-to-the-minute LED and SSL updates, follow us on Twitter. You’ll find curated content and commentary, as well as information on industry events, webcasts, and surveys on our LinkedIn page and our Facebook page.

What are the advantages and disadvantages of DC and AC Transmission?

Electric power can be transmitted either by AC transmission system (i.e. the voltage and current are alternating) or DC transmission system (i.e. the voltage and current are direct or unidirectional). Each transmission system has its own advantages and disadvantages. Therefore, we need to discuss the technical advantages and disadvantages of the AC and DC transmission systems so that we can select the right system for the electric power transmission.

AC Transmission System

The AC transmission system is the one in which the alternating current is employed for the transmission of electric power. Nowadays, electric power is almost generated, transmitted and distributed in the form of AC supply.

Advantages of AC Transmission

The AC transmission system has the following primary advantages −

• In an AC system, the electric power can be generated at high voltages (such as 3.3 kV, 6.6 kV, 11 kV).

• The AC voltage can be increased with the help of a step-up transformer or can be decreased using the step-down transformer easily and efficiently. Therefore, the AC transmission permits to transmit the electric power at high voltages and to distribute it at lower voltages.

• The repair and maintenance of AC substation and transmission lines is easy and less expensive.

• The AC switchgears such as circuit breakers are cheaper than DC switchgear.

Disadvantages of AC Transmission

The following are the disadvantages of AC transmission system −

• The construction of AC transmission lines is more complicated than the DC transmission lines.

• AC transmission lines require more conductor material than the DC transmission lines as three wire are required for AC transmission.

• The effective resistance of the AC transmission line is higher than DC transmission line. It is because the skin effect takes place in AC transmission line.

• An AC transmission line has line capacitance. Therefore, there is a continuous power loss in the AC transmission line due to line charging current even when the line is open.

DC Transmission System

The DC transmission is the transmission of electric power when the direct current system is employed for the power transmission.

Advantages of DC Transmission

The high voltage DC transmission system has the following advantages −

• DC transmission requires less conductor material than AC transmission as only two wire are required for the power transmission through DC system.

• DC transmission lines are free from the skin effect. Therefore, the entire cross-section of the line conductor is utilised, hence the effect resistance of the line is small.

• There is no capacitance in the DC transmission. Therefore, there is no power loss due to the charging current.

• There is no inductance, phase displacement, and surge problems in the DC transmission.

• For the same sending end voltage and load conditions, the voltage drop in the DC transmission line is less than the AC transmission line. It is because of the absence of inductance in DC transmission line.

• A DC transmission line has better voltage regulation than an AC transmission line.

• For the same voltage, A DC transmission system requires less insulation material because the potential stress on the insulation is less in case of DC transmission system than that in AC transmission system.

• DC transmission does not suffer from stability and synchronizing problems.

• In high-voltage DC transmission, there is no dielectric losses.

• A DC transmission line has less corona loss and reduced interference with the communication circuits.

Disadvantages of DC Transmission

The main disadvantages of DC transmission are as follows −

• Electric power cannot be generated at high DC voltage because of commutation problems.

• DC switchgears have their own limitations and they are also expensive than the AC one.

• DC voltage cannot be directly step-up or step-down for transmitting the power at high voltages and for distributing it at low voltages.

• It requires extra equipment such rectifier and inverter, etc. which increases the cost of transmission.

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