Colin SheppardOver half of Humboldt County’s energy-related greenhouse gas emissions come from transportation. Nationwide, the transportation sector contributes 28% of all greenhouse gas emissions. Plug-in electric vehicle (PEVs) present a compelling opportunity for communities to dramatically reduce these emissions along with air pollutants responsible for a wide range of adverse health impacts.
To support the successful introduction of PEVs to the North Coast, SERC is serving as the technical lead on the North Coast Plug-in Electric Vehicle Readiness Study. Funded by the California Energy Commission, this work is being done in partnership with the Redwood Coast Energy Authority and local engineering firm GHD.
One of the key questions we have addressed is how to deploy PEV chargers throughout the region in a cost-effective manner. This is a complex question. Where will PEV drivers live? Where will they drive? How long will they spend at their destinations? How will drivers adapt when they need a charge but no station is available?
Our approach to answering these questions was to develop an “agent-based” simulation model of PEV drivers in Humboldt County. Individual PEV drivers (or agents) are simulated as they conduct their daily travel throughout the county and interact with a hypothetical charging network. Drivers begin a day with a vehicle, an itinerary of trips, and a set of rules for how to behave. An example of a rule would be that drivers seek out a charger if their battery doesn’t have sufficient energy to make their next trip. Another example would be that some drivers elect to charge their vehicle even if it’s not necessary.
The simulation evolves over the course of the day as drivers follow their rule sets, interact with the charger network, and respond to changing circumstances. At the end of a simulation run, we can summarize the day’s events in a multitude of ways. Where, when, and how often did drivers charge? How many drivers experienced inconvenience of some kind (e.g., experienced a delay while waiting for a charger)? By repeatedly running the simulation with different charger locations, we can use the model to evaluate the impact of any hypothetical infrastructure scenario on driver inconvenience.
For a given penetration of PEVs into Humboldt County, we used optimization to find the infrastructure scenario that provided the greatest benefit to drivers for the least cost. The map of Eureka below provides an example of the recommended infrastructure for 2% penetration of PEVs, or roughly 3000 vehicles. Maps of the whole county can be downloaded at www.schatzlab.org/projects/policyanalysis/pev.html.
We also developed some general conclusions about the optimal siting of PEV chargers in Humboldt, which are likely transferable to other rural communities:
- Overall, relatively few chargers are needed to support a large number of PEV drivers. Approximately 45 public chargers were sufficient to support about 3000 drivers in the 2% penetration scenario. Drivers will be able to accomplish most of their travel needs (~90%) just by charging at home.
- Chargers tend to be sited in and around population centers and major regional corridors.
- Level 2 chargers (which can charge a Nissan Leaf in ~5-6 hours) provide a more cost-effective means of supporting PEV drivers than DC fast chargers (which can charge a Leaf in less than 1 hour). This is primarily because DC fast chargers are about 10 times more expensive to install and only charge batteries to 80% of full capacity.
- Exact siting of chargers is flexible. Chargers can be sited in one zone or a neighboring one and the overall impact on PEV drivers will be about the same as long as the total need for chargers in that region is satisfied.
Our deployment guidelines wouldn’t be complete without an estimate for when the infrastructure should be in place. To answer this question, we looked at the historic adoption of the Toyota Prius and other hybrids in Humboldt. If we assume that drivers will adopt PEVs at the same rate as hybrids, then we would expect that 1% of the light duty vehicles in Humboldt will be PEVs by approximately 2018 and 2% by 2025. In other words, there’s little time to spare in rolling out PEV chargers.
Fortunately, the North Coast PEV Readiness team is already working on a near-term implementation plan. Critical to this plan is identifying specific sites where the first wave of PEV chargers might be installed. This process involves soliciting input and feedback from a variety of municipalities and local stakeholders to ensure that the final sites reflect the needs and priorities of the whole community. If you’d like more information, or want to participate in this process, contact the Redwood Coast Energy Authority.
