Electrical Engineering Issue III Mechanical Engineering Volume XXIII

V2G: How Electric Vehicles Can Save Solar

About the Author: Keshav Sriram

Keshav Sriram is a junior studying electrical engineering at USC. He enjoys board games and jazz music, and he drives a dependable Volkswagen e-Golf.

Abstract: The electric grid has recently been under duress. While lots of electricity is generated in the afternoon, demand is higher in the evening as people turn on their high-energy appliances. This problem has been worsened by extreme weather and the rise of solar energy. As millions of electric cars hit the roads, researchers have proposed using batteries to address this issue. In the afternoon, the excess energy can be stored in batteries, and in the evening, this energy can be released to offset the high demand. This solution is called Vehicle to Grid (V2G), and significant research has been done to confirm its viability. However, policy makers have found that V2G is unpopular with consumers since it restricts their freedom to make spontaneous trips. Without the proper incentive for private car drivers, V2G will more likely be used with school buses and trucks instead, which have a more predictable schedule.   A Hot Topic In the fall of 2022, brutal heat waves hit California, hitting temperatures upwards of 116 degrees [2]. The oppressive heat made a walk in the park feel more like an extended stay at the sauna. The worst part of it, though, was the constant stream of text messages from the electric company asking everyone to consume less power. How could our government expect us to set our thermostats to just 78 degrees during the hottest summer ever? We were not the only ones suffering—the electric grid had its fair share of trials as well. With its fleet of power plants and miles of cables, the electric grid is able to supply power all over Western US, but it, too, has its limits [2]. As people statewide switched on their ACs to full blast, the power system simply could not keep up. The energy company was forced to send those text messages to avoid having to turn the power off altogether. This all-around disaster may be in our past, as electric cars will soon have the ability to give power back to the grid during times of need. As more electric vehicles hit the road, we could be in the midst of an energy storage revolution that could address renewable energy’s biggest drawback.   An Energy Storage Crisis The heat wave issue is just one example of a much larger problem in this area of engineering, which involves balancing out the demand for electricity over the course of a day. You have probably noticed that on your electric bill, you are charged more for electricity in the evening. This is because people return from work at that time, turning on their ACs, washing machines, and other high-energy appliances that demand more electricity [3]. On the other hand, in the afternoon, when people go to work, they do not use much electricity, so more energy is generated than used. This is reflected in Figure 1, which shows the demand on the electric grid over the course of the day [4]. In the afternoon, the demand goes very low before sharply peaking in the evening. The chart’s distinctive shape has led researchers to call it the “Duck Curve”.

Figure 1: Net Load in the California grid over a day (Duck Curve) [4]

The high demand during the evening places a huge burden on the electric grid. One way to prevent this is to store the extra energy generated in the afternoon. Then, in the evening, all the stored energy can be released to help the grid through the peak hours. This problem is also known as “smoothing the Duck Curve” [3], since it would increase the load in the afternoon while decreasing it in the evening, flattening the Duck Curve. However, a recent energy trend has made this issue much more urgent. You may notice that in Figure 1, the “belly” of the Duck Curve has been getting deeper every year. This is a result of the large increase in solar energy, especially in states like California. As shown in Figure 2, solar energy generation peaks in the afternoon, when the sun shines the brightest, but it drops off sharply in the evening [5]. This has resulted in a seemingly strange issue: we are generating too much electricity.

Figure 2: Solar energy generated over a day [5]

Overgeneration occurs when the supply of electricity is much more than the demand, which can damage the electricity grid and it can cause damage to the grid [6]. To prevent this, grid operators have manually decreased the output from renewable energy plants in the afternoon. Unfortunately, this decreases the efficiency of renewable sources, making them less competitive economically. Because of this, finding a solution to the energy storage crisis is important for the future of renewable energy.   Supersizing the Battery Generally, a solution to the energy storage crisis is some kind of battery: something that charges in the afternoon and discharges in the evening. Of course, when faced with a system as massive as the state electric grid, you’ll need a really big battery. Researchers have looked into the idea of creating giant batteries to smooth out the Duck Curve, but they have also considered other unconventional “batteries”. These include pumping water into a dam with the excess electricity [7] or storing the energy long-term in alternative fuels like hydrogen or methanol [8]. However, these solutions are not viable in the short term since they all require new infrastructure. The government has no plans to create dams or methanol plants at the scale needed to smooth out the Duck Curve, and any new proposals would take decades to go through. What if we used a lot of small batteries instead of a few large ones? There is a plan currently in motion that would create an army of small, rechargeable batteries within the decade. If these were integrated into the electrical grid, it could be the most realistic solution to the energy storage crisis.   Surfing the Electric Wave Have you noticed how a lot of car companies have suddenly come out with their own electric car models? This is no coincidence: electric vehicle (EV) sales have doubled over the past year [9], and car companies have tripled their EV ad spending, hoping to capitalize on the revolution [10]. The optimism surrounding electric vehicles has convinced state governments to set aggressive goals to remove gas vehicles from the market entirely; California plans to make the switch as soon as 2035 [11]. As people nationwide adopt this technology, there will soon be millions of electric vehicles on the road. As a consequence of the electric vehicle boom, millions of batteries will be produced in the next few years. This has inspired a new strategy known as Vehicle to Grid, or V2G for short [12]. When electric cars are not being driven, their batteries can be used to smooth out the Duck Curve. Comparing figures 2 and 3, you can see that the time where a car is parked at work overlaps almost exactly with the availability of solar energy [13]! This makes electric vehicles ideal for absorbing all the extra solar power, preventing the problem of overgeneration. When cars return home after work, the energy stored up in the afternoon can be returned to the grid during the time of highest demand. V2G appears to check all the boxes for an energy storage solution.

Figure 3: Parking patterns over a day [13]

  One Way, Two Way Although V2G works well in theory, there are a number of technical issues to consider before implementing it. For example, V2G chargers are very specialized, so it would be difficult to create a lot of them in a short time [12]. Therefore we cannot rely on V2G alone, at least not in the short term. Researchers have proposed supplementing V2G with smart charging, also referred to as V1G [12]. This involves shifting the charging patterns of the electric car so that it charges a lot during the afternoon and charges very little during the evening. The difference between the two systems is shown in Figure 4 [14]. V1G is less flexible than V2G, but it is much easier to quickly implement V1G on a large scale. Therefore policy makers must take advantage of both V1G and V2G when creating charging infrastructure.

Figure 4: V1G vs. V2G [14]

What would the results look like with each of these charging methods? Scientists at the Lawrence Berkeley National Laboratory have tried to answer that question with their simulator V2G-Sim [15]. By simulating 3 million vehicles of different models, they have created charts such as the one shown in Figure 5, which represent the potential impacts of smart charging as accurately as possible.
  • No smart charging (Red): This will actually increase the demand in the evening, which creates an even greater burden on the grid. Clearly, some kind of smart charging is necessary to prevent this.
  • V1G (Dark Blue): In the afternoon, it does a much better job of preventing overgeneration and does not create extra demand in the evening. However, it still does not smooth the duck curve in the evening.
  • V2G (Green): In this case, the demand in the evening is significantly flatter than before. The duck curve is smoothed in both the afternoon and the evening, showing that V2G has the potential to almost entirely solve the energy storage problem.

Figure 5: Simulation of V2G and V1G [15]

Based on the results of this simulation, V1G should be installed at work for use in the afternoon, while V2G should be installed at home for use in the evening. V1G can absorb the extra solar energy, and V2G would flatten the Duck Curve by releasing that energy. This would provide all the benefits of V2G but without having to build V2G stations at workplaces, making it more practical to implement.   2G, or Not 2G? Although smart charging seems like a surefire engineering solution, there has been some controversy about the human impacts. What if you needed your car due to an emergency, but it did not have enough charge because it had been discharging? Would it be stressful to constantly have to check your car’s power level? To answer some of these questions, researchers have conducted trial runs to gauge user feedback. They found that a lot of the backlash to V2G comes from citizens’ distrust in their government and utility companies as well as concerns about freedom. One participant in a United Kingdom study stated that they “wouldn’t trust [the electric company] to make sure my car is charged in the morning” [16]. Participants in a German study also reported anxiety about constantly having to plan ahead and manage their power, which reduced their ability to go on spontaneous trips [17]. Clearly, whoever uses V2G has to give up a lot of freedom and control to the power company; not everyone is going to agree to this. Therefore, V2G will have to be implemented on a voluntary basis. This could be difficult, especially in a country like the United States where individual rights are particularly important. On the other hand, money talks, so a financial incentive could encourage users to adopt V2G. The simplest way to do this would be to pay users extra for the electricity they give back. However, cost-benefit analysis has shown that these payment plans only amount to a few hundred dollars per year, which is hardly enough to convince anyone to make the switch [18]. The analysis suggests that V2G will only be viable if “benefits exist on the scale required to entice the average electric vehicle owner.” Because of this, creating a big enough market for V2G to be useful is perhaps the biggest challenge that the technology faces to become a reality.   Building a Battery-Powered Future Of course, even without a stable commercial market, V2G can still see some use for government and industrial vehicles. One popular test case for V2G is with school buses, with ongoing trials in some Nevada school districts [19]. These vehicles are popular because, unlike personal vehicles, they run on a consistent schedule. As a result, they do not have to make unexpected trips in the afternoon and evening, allowing them to give and receive electricity as necessary. In addition, V2G buses have much greater economic incentives: a single bus is estimated to save a district $13,000 each year, which can amount to tens of millions for a full fleet [20]. The results from school bus trials agree with this forecast, with efficient technology and promising financial results [21].  As a result, V2G will still have a significant niche in a future filled with electric vehicles and renewable energy. While it may not be a catch-all solution, V2G remains the easiest way to immediately handle the energy storage crisis. As the technology and its associated economic benefits continue to develop, it will likely expand from school buses to trucks, and it may eventually be the norm for charging all electric vehicles. Therefore, you shouldn’t be surprised if the next text message from your electric company asks you to opt in to V2G.   References
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