The solar panels on the GPI office buildiingThe modern electric grid often seems like a miracle. Thousands of generating sources, from residential solar power systems to huge power plants, kept in almost instantaneous sync with millions of electricity consumers. All with a reliability rate of better than 99 percent.

Utilities and regional grid operators have a complex set of market rules, design standards, and continuous operating procedures to keep the grid in sync—and electricity consumers blissfully ignorant of the miracle going on around them.

But several technological and market changes are underway that are changing how the grid works, posing risks and opportunities. Two such technologies, solar energy and electric vehicles (EVs), have received attention recently with rapidly growing markets and forecasts for declining costs.

While solar and EVs both individually present challenges to our electric grid, strategically combining them on the electric grid provides an opportunity to generate the following benefits:

  • increased reliability
  • reduce customer bills while adding services
  • significant reduction in power and transportation sector carbon emissions

The Solar+EV Project: Increasing Value to the Grid and Electric Customers

The Great Plains Institute is launching a new effort to examine how to combine and manage solar generation along with EV charging to provide maximum value to the grid and to consumers. The work shows so much potential that the US Department of Energy’s National Renewable Energy Laboratory (NREL) selected GPI as one of nine teams to participate in its Solar Energy Innovation Network (SEIN). This collaborative research effort, which will take place in Minnesota, will explore new ways solar energy can improve the affordability, reliability, and resiliency of the nation’s electric grid.

A Tesla at a charging station

Each of the nine Solar Energy Innovation Network teams is exploring a different aspect of how to capture the full value proposition of solar energy through innovative combinations of technologies, strategic location decisions, and new rate designs.  The GPI team is looking at deploying solar with controllable EV charging infrastructure as a single technology with potential value for grid benefits and for the customer who deploys the technology.

The 18-month project has two expected outcomes:

  • To identify use cases where solar+EV (and potentially other clean energy resources or technologies) can provide value for the grid and/or the utility customer, and design pilot projects to test these value propositions.
  • To create a roadmap for market deployment of solar+EV, working with the solar industry, utilities, businesses, and property owners to identify barriers and opportunities to capture the value of solar+EV deployment.

The Solar Challenge

Minnesota’s burgeoning solar energy industry has a different set of characteristics when compared to traditional electric generation. Solar energy generation, for instance, is only “dispatchable” when the sun is shining on the solar collectors (between 15-30 percent of the day depending on system design and location).

But when solar energy is dispatchable, it has effectively zero operating costs; it doesn’t need to be turned on or ramped up, it has no moving parts, and the fuel is free.

Hourly solar resource at groundAs a consequence, solar energy will likely be the lowest marginal cost resource while the sun is shining. This has grid consequences since the cheapest marginal cost resource is also one that is only dispatchable 15-30 percent of the time.

Another important difference is that solar energy can be scaled to be deployed virtually anywhere on the grid; either in the wholesale market (transmission-level or bulk power) or the retail market (at the customers’ premises). Where solar is deployed has consequences, both positive and negative, for the grid.

Minnesota’s solar energy production is still just at two percent of total electricity use. But with a continued decline in costs, solar production is expected to approach and perhaps exceed 10 percent of Minnesota’s electric use by 2030. Increasing amounts of solar generation will eventually raise grid integration issues. Distributed solar, on the customer side of the meter, presents a particular dilemma where energy flows both ways on the grid, and the distinction between producer and consumer is blurred.

The Electric Vehicle Challenge

The rapidly growing electric vehicle (EV) market also challenges our traditional grid management system. EVs present a significant utility revenue growth opportunity in an age when demand for electricity is stable or even declining. However, as the market for EVs accelerates they could also add significant load to the electric grid.

Typical electric vehicle residential charging load compared to other household appliances

Numerous studies have raised the specter of electric grid problems associated with EV charging. While much of the attention is given to fast chargers that can completely charge an EV battery in 20-40 minutes, most charging is likely to happen at home, work, or during errands using slower Level 1 or 2 chargers. Multiple EVs charging simultaneously, even using Level 2 chargers, can create significantly higher demand on the transformers or grid circuits, and exacerbate peak demand on the system.

But unlike other devices, electric use (charging) occurs when the customer doesn’t need to use the vehicle, rather than when the customer is using it.

And since most vehicles are parked for many more hours than they are driven, this opens the door to an opportunity; can the charging of EV batteries be controlled to align with solar energy production?  And can solar production be dispatched to align with EV charging demand?

Maryland statewide load: all vehicles during weekday baselineNREL used its EVI-Pro model to simulate what uncontrolled EV charging would look like in the State of Maryland assuming no change in vehicle use for the existing gasoline fleet of light-duty vehicles. Most charging would occur at home, during the late afternoon, using Level 2 chargers. They found that uncontrolled charging actually results in a dip in charging during the peak of solar production (noon). Such charging patterns would exacerbate peak demand and could contribute to local distribution system problems as well.

Solar+EV Project Status

GPI is currently evaluating a solar+EV pilot project at its headquarters in Minneapolis, MN. A 30-KW solar array is paired with three EV chargers in the parking lot. As illustrated in the graph below, charging is kept to a minimal rate until the solar array is producing power. The charging then will increase as solar production increases, ultimately charging a full Level 2 rate. Preliminary results for this project are currently being evaluated.

Chart showing EV charing following solar energy production

Source: Great Plains Institute

Through the Solar Energy Innovation Network Solar+EV project, the GPI team is working with project partners to develop additional pilot projects that test larger scale deployment, and how different types of charging patterns (e.g., in a residential setting, at park and ride lots, or fleet charging) can be synchronized with solar energy production. The project will also consider the same controlled charging technology for using excess wind energy, and opportunities to link other resources such as battery storage or demand response to EV charging.

Minnesota’s Solar Energy Innovation Network project partners include:

  • Great Plains Institute (project lead)
  • Department of Commerce
  • Department of Administration
  • Metropolitan Council (Metro Transit, Community Development, and Environmental Services)
  • ZEF Energy
  • Minnesota Solar Energy Industries Association
  • Center for Energy and Environment

To assess the various value propositions of solar+EV, GPI will engage a wide variety of market participants and stakeholders including:

  • investor-owned electric utilities
  • municipal and co-operative electric utilities
  • solar energy developers and contractors
  • electric vehicle advocates
  • building managers and developers
  • cities

GPI’s participation in the Solar Energy Innovation Network will include financial, analytical, and facilitation support as the team works to anticipate and address new challenges and opportunities stemming from solar energy and other distributed energy technologies in Minnesota. NREL and Lawrence Berkeley National Laboratory will provide technical support to the project and Rocky Mountain Institute is providing facilitation services.


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