How Electric Vehicles can work: PHEV

I looked through all my posts and realized that I didn’t dedicate an entry to a significant piece of research that was published back a few years ago regarding the electric grid and plug-in hybrids, and how we have the necessary resources to move forward with PHEVs. I had touched on it before, but I think its a good time to go over it in depth.

The report (PDF), done by the Pacific Northwest National Laboratory, came to the conclusion that with the grid and transmission network as it was in 2006, we can support anywhere between 43% and 73% of current passenger vehicles (referred to in the report as Light Duty Vehicles, or LDV) depending on how we recharge them – either off-peak only or all day.

The report is very through, and conservative in a number of places: assuming that generation facilities still need time for maintenance by derating the nameplate capacity of coal and natural gas plants by 15%, using power demand for winter and summer days as the limits for the number of vehicles to be recharged (not year-round averages which would be lower), and accounting for the distribution of the size of vehicles (small sedan to large SUV). Also, they accounted for power generation in regions, instead of at a national level, because parts of the grid are lacking in the ability to transmit power generated in one region and send it to another one.

The report recognized the dual-fueling system of PHEVs (gasoline and electricity) in establishing that during summer peak load, some days might not be able to supply PHEVs with the electricity to run the rest of the day or the next day, rather they would need to use a couple of gallons of fuel. 

The 43% LDV fleet replacement for off-peak (6p-6a) times were obtained from looking at all of the available generation capacities minus peaking plants, and the transmission capacity to carry that energy to the cars, and the amount of energy it would take to fill up PHEVs for them to drive 33 miles (the average US commute). They used “valley filling” where PHEVs would be charged in what would be otherwise unused power plants during that time of day.

Amount of oil saved by switching to PHEVs

The 73% LDV fleet replacement for 24/7 charging were determined in a similar way, but allowing vehicles to charge all day. This can complicate things, and to make this practical you would need the grid to exercise some control over the charging rate when demand gets high enough that utilities have to turn on peaking plants. If we were able to achieve this 73% figure, we would reduce oil imports by 6.5M barrels per day, which is about 70% of all gasoline consumption, and 52% of all imported oil. 

During these fringe cases where demand is at its highest, a smart grid would make it possible for the grid operator to tell PHEVs to not request any load on the grid, or possibly put power back onto the grid. The article briefly mentions Vehicle-to-Grid (V2G) technology, but it didn’t investigate it as a mechanism to supplement the grid by having vehicles discharge some of their energy back into the grid to supplement generation capacity. Energy companies have been exercising demand control for years with air conditioner loads during the summer, so its nothing novel or new, but unlike completely turning off your air conditioner for 5 minutes, your PHEV charger could talk to the car and find its fuel and battery level, and request  minimal energy (including none at all) to get it through the day, or possibly just down the street to a fuel station to fill up on gasoline for the day because of the abnormally high demand on the grid and generation facilities.

The numbers, specifically the 43% off-peak number, speak to the capabilities we have as a grid now. However, if you look at some of the regional numbers, you can see what work still needs to be done to allow PHEVs to become more than just a niche player.

Regional Issues

Different areas of the country have different load profiles, generation capacities and transmission (both regional and inter-regional) characteristics. While 73% might be a national figure, this number can vary from region to region. Some areas like ERCOT in Texas could switch all of its vehicles over to PHEVs without any issues. However, other regions are not so lucky. 

We’ll start in the hot, sunny, and green California/Southern Nevada region. They only have the capability to replace 15% of their passenger vehicles with PHEVs currently based on off-peak charging. This is a reflection of the lack of generation capacity available, and the large per-capita car amounts of the region. It might sound like a small amount, but its really 3.9M cars, and it will take a long while before California can boast about almost 4M PHEVs on their roadways – the Volt is only supposed to have 10,000 units built in the first year of production (2011), with it ramping to 60,000/yr vehicles thereafter.

The Pacific Northwest is an area which gets most of its energy from hydroelectric dams, and because of the limited water supplies from snow pack runoff, there is a limit as to how much energy can be extracted from this water on its way to the Pacific Ocean. This means limited ability to generate large amounts of electricity at night, because that energy is needed during the day, and only 10% PHEV penetration based on off-peak charging. However, there is one major upside related to being in the northwest, and that is the tremendous amount of wind power available in areas like Wyoming and Montana. Piping this wind energy in, in combination with smart grid technologies, could provide the northwest with the power it needs to move to PHEVs.