Tracy K. Price is founder & CEO of Qmerit, a leader in implementation solutions for EV charging and other electrification technologies.
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Around 1880, the U.S. entered a fork in the road on how to broaden the use of electricity. Newspapers dubbed it "The War of the Currents," for it pitted the alternative current (AC) approach of George Westinghouse and Nikola Tesla against the direct current (DC) camp of Thomas Edison.
It’s a fascinating story, the net of which—spoiler alert—AC won as the best way to provide electricity at scale. An impressive display by Westinghouse/Tesla at the 1893 Chicago World’s Fair led to an installation with the Niagara Falls Power Project, which sealed the deal for AC as the way to make electricity common.
But this rivalry—or the distinction it created between the two forms of electricity—wasn’t done. Yes, AC dominates today because its alternating magnitude allows utilities to efficiently push power to homes and businesses. But plucky DC carved out a niche serving batteries, computers and other gadgets that need a direct and calmer current.
In the near term, we could see this 130-year divide come together to create another key moment in America’s energy journey; AC and DC may soon join forces to give the grid a new level of strength and flexibility to meet rising energy demands while reducing pollution and carbon.
As this happens, I believe the hero of this new tale will be the market’s embrace of electric vehicles (EVs) that feature an emerging innovation known as bidirectional technology.
Bidirectional technology enables an EV’s battery to both receive energy and send its excess to other locations throughout the home or building—or even to the grid. It overcomes the hard fact that EVs run on DC power while homes, buildings and utilities need AC. Without bidirectional EVs, it’s harder to convert a car’s DC energy into the AC used by other sources.
Ford helped introduce bidirectional technology about two years ago when it released its F-150 Lightning truck, touting how it provides backup power to the home during emergencies and that it can combine with solar panels to provide even more energy independence.
Today, other automakers are rolling out EVs with bidirectional capabilities, including Kia, Hyundai, Nissan and Volkswagen. In August, General Motors announced this will be a standard across its Ultium-based EVs by model year 2026. Earlier Tesla said all of its EV models will be power sharing by 2025.
From a grid standpoint, the more cars with bidirectional technology, the more we have a new source of power that utilities can tap to meet rising demands. It becomes feasible for our AC-based utilities to enjoy all of the DC out there in the form of cars, trucks and buses. Combine that with a utility’s traditional energy sources and I foresee a transformed grid, one that smartly flexes on sources both old and new based on changing conditions.
To that point, I think EVs could spur the country to do more with virtual power plants (VPPs), which are software systems that assimilate thousands of distributed energy resources (DERs)—things like EVs, solar panels and wind turbines and batteries—into the grid. The energy institute RMI believes that 60 gigawatts of VPP power could be deployed in the U.S. by 2030, with The Brattle Group adding that this amount "could meet future resource adequacy needs at a net cost that is $15 billion to $35 billion lower than the cost of alternative options over the ensuing decade."
The benefits of this transition are significant, and while solar panels and wind turbines will certainly play a role, I see EVs and batteries being the main contributors given their ubiquity. With the Edison Electric Institute projecting 26 million EVs in the U.S. by 2030, you can see the potential for bidirectional technology’s impact on a new energy grid.
Bidirectional EVs and their relationship to the grid is an emerging concept; the implications are yet to be precisely defined. However, one move that most companies can make to get ahead of this revolution is converting their fleets to bidirectional vehicles. Doing so can help lay a foundation that enables you to play into this new world in a variety of ways.
For one, more electric vehicles with this capability helps scale up the number of distributed energy resources your local utility can draw upon—it gives the utility more of the regional assets it needs to align with a virtual power plant.
From a company perspective, fleet conversions also create a win for carbon reduction programs as they bring quantifiable results that can be reported to stakeholders. They also put your organization in a position to explore utility programs where you are paid for excess energy or get billed less for charging when rates are lower.
Arguably the most strategic question businesses face in exploring a fleet conversion is whether the charging is done at employees’ homes or on company property. For large companies with concentrated hubs, and given that today more than 86% of all EV charging can be done at home, the real questions become: What are you going to do with all of those fully charged batteries descending on your campus or building? Are you going to incentivize your employees to help offset your demand charges by plugging into the company microgrid? If so how much? Bidirectional creates all kinds of interesting shared economic models.
With all this in mind, let’s note that 1893 was not only the year Westinghouse and Tesla made their splash at the Chicago World’s Fair; it was also when Henry Ford invented a one-cylinder internal combustion engine that led to his first vehicle. Perhaps it took a while, but that development could become the envoy that gives the Current War a lasting peace.
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AC/DC is not just the name of a popular band. AC (alternating current) and DC (direct current) power are actually the two different types of electricity. The vast majority of power grids distribute AC electricity, but it's been over 100 years since AC became the standard. Since then, much has changed. For example, a growing fraction of the electricity consumed in modern buildings is either "consumed as DC or passes through a transient DC state on its way to being consumed" (according to Physics World). Because of this, and other inherent benefits of DC power, many experts agree that adopting direct current into commercial and residential power systems could result in safer, more comfortable, and more energy efficient buildings.
DC electricity was developed by Thomas Edison. Edison invented an incandescent light bulb that could last for 14.5 hours in 1879 and used DC electricity to power it. AC electricity came on the scene a little later when Nikola Tesla (working for Edison at the time) popularized it with his many inventions. Tesla first demonstrated his AC (alternating current) electricity at the World Columbian Exposition in Chicago in 1893. Tesla ultimately won the so-called "War of the Currents", and AC electricity has been used as the standard ever since. But technology, devices, and infrastructure have changed dramatically since the 19th century, and this begs the question, should AC electricity still be the standard?
In this article we'll explain briefly what the differences are between AC and DC electricity, and what these differences mean for building managers and designers who are considering powering their building systems (like lighting and HVAC) with DC power.
Essentially DC electricity travels in a straight line (directly) on a graph of voltage vs. time, meaning that it does not have a frequency, and its voltage remains constant. On the other hand, AC electricity alternates polarity 50 - 60 times per second (depending where you are in the world). This gives it a frequency, and also means that its voltage is not constant over time (it increases and decreases).
Frequency: The number of complete alternations per second of an alternating current.
These graphs visualize how the two types of current would appear if they were being viewed on an oscilloscope (a device for viewing voltage changes over time):
AC (Alternating Current)DC (Direct Current)
An increasing number of modern devices use DC electricity, including LED lights, HVAC systems, laptops, microwave ovens and more. In fact, DC consumption currently makes up about 32% of total energy loads, and could climb as high as 74% in buildings that have electric vehicles and HVAC equipment with DC motors. Currently, power grids distribute AC electricity to homes and buildings, meaning these devices must convert the AC power they get into the DC power they need.
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In order to do this, these devices are equipped with drivers and converters, which can be efficient (up to 96%) when cost is no concern, but efficiency is the first thing to be sacrificed when manufacturers cut back on production cost. This means that manufacturers will often buy cheaper drivers to produce a cheaper product. At Cence, we conducted some primary research (lab testing) to determine just how inefficient some LED drivers are, and how common it is for drivers in LED lights to be inefficient.
An inefficient driver essentially burns energy in the form of heat during the conversion process of AC to DC power. In our own in-lab testing at Cence, we’ve done comparison tests between different LED light bulbs and found that most drivers for LED lights are inefficient (80% on average), especially in residential lighting. In fact, on average about 20% of energy is lost during conversion. Ultimately, by providing these systems and devices directly with DC power, the need for these inefficient drivers is eliminated.
LED Bulb Diagram
Knowing that we mostly use DC power today, It may seem intuitive to simply distribute DC power directly to buildings and DC powered devices, and there are a few different methods of doing so that exist. Most systems that distribute isolated DC power do so via the use of a transformer. Transformers have two main purposes:
The problem is that transformers only work for AC electricity, which is one of the benefits of AC, and essentially why AC is standardly used in high voltage transmission systems.
So how can DC distribution and transmission systems use transformers when DC power isn't compatible with transformers? Great question.
If DC electricity was compatible with transformers, DC electricity would be the cheaper and more efficient option in distribution and transmission systems. This is because, in contrast to AC power, DC power is entirely made up of active power, meaning that there are almost no losses due to the capacitance of wires when DC power travels long distances. In fact, high voltage AC transmission systems have losses of 7% to 15% with aboveground transmission.
Unfortunately, however, the reality is that DC power is not compatible with transformers, but voltages still need to be stepped up and down when DC power is distributed. Even with this limitation, there are still dozens of HVDC transmission systems in the world today, and that's possible because engineers developed a work-around that is used most of the time in DC power distribution. If AC electricity was being transmitted into a building, for example, a transformer would be used to step-down the voltage to the desired level, then power would be converted from AC to DC, and DC electricity would be distributed throughout the building. However, if the voltage needed to be stepped down further, an inverter would be used to convert the electricity back to AC, then it would be stepped down with a transformer, and converted back to DC. This process is a little cumbersome, and expensive when it's being done at a large scale for transmission systems. So when is it worth it to distribute DC power throughout a building or via a transmission system when this inefficient work-around needs to be used? The answer to this question depends.
Energy saved by distributing DC power directly to devices > Energy wasted by inefficient drivers in the conversion process of AC to DC power
Power is to be transmitted underwater, underground, over 600km on land, or across country borders. In these cases, enough energy would be lost in the process of transmitting AC power, that the cost of rectifier stations can be justified.
The answer to this question has a lot to do with how electricity works, which is out of the scope of this article. If you'd like to learn more about it, we recommend this video by The Engineering Mindset:
DC electricity will become the standard in power systems throughout the world when a better solution is devised to step up, step down, and isolate high voltage DC power, and make the transmission of it safe. Once this advancement in technology is made, the benefits of DC power transmission will far outweigh the benefits of AC power transmission. In turn, once high voltage DC transmission systems are standardized, buildings will receive DC power, and the need for inefficient conversions from AC to DC power will be eliminated. In fact, a study featured on ScienceDirect highlights how distributing DC electricity has been proven as an effective way to reduce electrical consumption in commercial buildings through the reduction of power conversions and facilitation of a transition to efficient DC appliances. In the study, they also show that residential buildings experienced savings of up to 25% when solar PV was distributed to all home appliances, and when battery storage for excess solar energy was considered (solar power provides DC power, and batteries store DC power). These results are promising, but the best way for buildings to receive DC power is for power grids to supply it. This will happen when a technological solution is devised that will replace the need for, or decrease the cost of expensive rectifier stations in HVDC transmission systems.
As mentioned above, most modern devices and systems require DC electricity, and this is no different for smart buildings or homes. Sensors, cameras, LED lights, and other devices necessary for smart buildings, are all powered with DC electricity.
Smart buildings are designed to be more energy efficient. For example, they can usually collect data on environmental quality and occupancy of a space in order to enable the optimization of energy use. But if high consumption devices, like LED lighting and HVAC, still have to convert AC to DC electricity, energy is still being wasted. To sum up this point, Brad Koerner said it best at the Smart Building Conference (2020): “we need a revolution in just basic electricity before a lot of our smart building technologies will actually be implemented”.
Regardless of whether you’re working with AC or DC electricity, it’s never perfectly safe. So always take precautions. Alternatively, if you’re not sure of what you’re doing, it’s safer to get in touch with a professional. That being said, while both are dangerous, AC electricity is more dangerous to work with due to these reasons:
LED lights are a great example of an efficient DC powered device; they use 75% less energy than AC-powered incandescent lighting. If a building is powered by DC electricity, the building manager would have more of an incentive to incorporate energy efficient DC powered devices into their building systems. For example, if a building had an HVAC system with an AC motor, they might decide to upgrade their HVAC system to one with a more efficient DC motor. DC HVAC motors operate at least 50% more efficiently than AC motors, so this switch alone saves a significant amount of energy. Integrating more DC power distribution systems into our way of life creates an incentive for more DC-powered technologies capable of increasing efficiency within buildings.
According to the US Green Building Council’s (USGBC) website, LEED (Leadership in Energy and Environmental Design) is the most widely used green building rating system in the world. For a building to be LEED certified, means that it’s been globally recognized as a symbol of sustainability, achievement and leadership. There are four possible levels of certification: certified, silver, gold and platinum. The more points a building has towards a LEED certification, the higher the level they can be eligible for. The LEED program does, in fact, provide points for DC powered buildings, legitimizing the case for the proliferation of DC powered buildings in the market.
But why care about being LEED certified? The benefits of being LEED certified include:
The USGBC website also mentions that additional benefits to designing a green building with the LEED framework include: health benefits for occupants and employees, reduced pollution, reduced energy use and carbon emissions, water conservation, and a reduction in waste.
The LEED program provides 18 points for DC powered buildings as a way of influencing the market to improve energy efficiency, resilience and reliability of electrical systems in buildings. The LEED program’s DC power credit also complements LEED’s Renewable Energy and Grid Harmonization credits because solar photovoltaic (PV) power systems (like solar panels) provide DC power. This means that the DC power credit additionally encourages people to invest in renewable energy sources.
At Cence, we can help your building gain points towards a LEED certification by answering questions such as: “how do I power major systems, such as lighting and HVAC, with DC electricity?”.
As it becomes more beneficial than ever for buildings to reduce their energy consumption, it's time to reconsider whether AC electricity should remain the standard type of electricity transmitted throughout the world (or at least in buildings). AC electricity was chosen as the standard in the late 19th century when Nikola Tesla won the War of the Currents. But that was over a century ago. At the time, Tesla's advancements in AC power distribution were chosen as the standard way to transmit electricity over long distances because the infrastructure for it was cheaper. AC electricity was cheaper to transmit over long distances because it is compatible with transformers. As technology advanced, the first high voltage DC transmission system was implemented in the 1950s via the development of rectifier stations or mercury arc values. Rectifier stations convert DC power to AC in order to step up or step down voltages, and then they convert AC electricity back to DC electricity for transmission or distribution. As we discussed in this article, these stations can be relatively inefficient, and are significantly expensive. In the future, when this technology is developed further, and infrastructure costs for DC transmission systems lower, DC electricity can be distributed directly to buildings. This would save our many DC powered devices a significant amount of energy by eliminating the need for inefficient power conversions at the load level.
Although there are some DC transmission systems in the world, chances are, your commercial building is not connected to one. Therefore, the only way to reap the benefits of distributing DC power to your building systems is by implementing a DC power distribution system at the local level. At Cence, that's exactly what we provide. If you're looking for an easy to install DC power distribution system, we invite you to review how our system works. Our system does not use a transformer, and our patented technology safely and efficiently distributes power to all DC powered devices.
If you're interested in learning more about the Cence DC power distribution system, talk to a DC power specialist, or request access to view our whitepapers, spec sheets and more reach out to us through our contact form.
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