Solar may be the future of energy production, but for the time being, it causes a lot of problems. Energy producers, grid managers, and energy markets have struggled to adapt to the growing amount of solar panels being installed, especially in areas like California.

In short, the problems stem from two simple facts: first, that solar doesn’t produce at night, and second, that we do not yet have large, grid-level batteries capable of storing excess solar power and releasing it after sundown.

Part of the solution is to use the many smaller batteries already attached to the grid, namely those powering electric cars, an idea generally referred to as vehicle-to-grid, or V2G. While this idea has been around for several years, progress has gone at a snail’s pace, but researchers have recently hit some important milestones toward achieving commercial use of V2G.

The Problems with Solar and the Duck Curve

Energy companies need to tweak production to meet consumer demand, which is easy with non-renewable sources such as the burning of hydrocarbons. But with solar energy, production is limited to the hours the sun is up. When the sun goes down and people draw more from the grid to turn on lights, for example, energy companies need to quickly increase production from coal, natural gas, and other sources. This is both expensive and taxing on infrastructure, because power plants and staff are not designed or trained for this.

This rapid increase is best illustrated by the duck curve. The amount of non-renewable energy consumed during the day and the sharp uptick later in the afternoon resembles the shape of a duck.

If areas like California, where this graph comes from, continue to add photovoltaics at the projected rate, by 2020 they are at risk of overproducing. In fact, Hawaii’s rapid adoption of solar creates such a sharp uptick when the sun goes down that their graph has been dubbed the Nessie curve, after the Loch Ness Monster’s long neck. Some developing countries have an even more pronounced late-day rise, creating what some have called the shark curve.

Another problem is that solar plants are too good at producing electricity during the day. They produce so much that some need to be taken offline to avoid oversupplying the grid, a process known as curtailment. This weakens grid reliability, makes building new plants financially unattractive, and throws a wrench into energy markets, as energy prices are largely determined by supply and demand.

The long-term solution to these problems is batteries large enough to store excess solar power. Although there are many of these being developed, hurdles still exist for wide-scale implementation.

Vehicle-to-Grid

Until bigger and better batteries are employed to store excess solar energy, energy companies, car manufacturers, regulators, and researchers are turning to the batteries already in electric cars. Because many of these cars are idle roughly 80 percent of the time, their batteries can be used to feed energy back into the grid during peak demand hours and to store excess solar energy during peak production hours.

While this sounds relatively simple, a quick foray into the field reveals a host of complications. For example, electric car batteries are lithium-ion, and these only have a lifespan of under 500 cycles of charging/discharging. Being forced to go through more cycles reduces their longevity, although the research results vary quite a bit by how much. However, efforts are underway to replace lithium-ion with lithium-sulfur, magnesium-ion, or sodium-ion batteries, which offer longer life spans.

Another problem is that most batteries and hookups for electric cars are not bidirectional—that is, energy can only flow one way, and reversing the flow would require inverters to convert a battery’s DC current into the grid’s AC current. This can cause a significant loss in energy.

It also needs to be figured out who pays for the loss in battery life and the inverters. Do consumers need to shoulder the extra cost, or is it the responsibility of energy companies? What incentive is there for car manufacturers to produce bidirectional batteries and hookups?

These are probably the biggest questions, but others exist. For example, is it voluntary for customers to allow their batteries to be used this way or should it be mandatory? How would grid managers schedule and control the release of stored energy to avoid overloading the grid? What kind of regulations need to be passed for this to work?

Current Research

To help answer some of these questions, researchers like those at Pecan Street, an Austin-based nonprofit, have been performing extensive tests. In particular, with funding from Austin Energy and the Department of Energy, they have focused on the new Nissan LEAF, which is among the first commercially available cars to offer vehicle-to-grid.

Just recently, they successfully transferred energy back into the grid and collected a myriad of data points to scrutinize. With this data, the company is analyzing how the local grid is affected, the efficiency of the charging stations, the effect the process has on the battery, energy loss over a given distance, and many other data points, all of which are necessary to help Austin and surrounding areas increase the amount of solar energy they produce, an integral part of Austin SHINES.

Pecan Street also has hundreds of volunteer homes across the country that allow for data collection on energy usage, as well as the amount they produce from their own solar panels, which is being used by researchers around the world to help integrate renewables into their local grids.

Scott Hinson, the chief technology officer at Pecan Street, believes vehicle-to-grid tech will not solve the solar energy problem on its own, but in conjunction with other methods it can help mitigate the problems with solar. In an interview with Singularity Hub, he pointed to the fact that V2G could be used during emergencies, as the average electric car battery can power a household for several hours during a blackout.

He also believes that a part of pushing people to adopt this technology will be financial incentives. For example, if people charge their batteries during the day when electricity is cheap and sell if back in the evening when electricity is more expensive, they could actually make a profit.

Overall, Scott is optimistic about V2G. “Electric vehicles by themselves have great potential for cleaner transit, but using them as energy storage can unlock the ability to have more renewable generation from wind and solar and a cleaner energy system,” he said.

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