The plug-in hybrid is a hybrid electric-gasoline powered automobile that has a significantly large battery capacity. Unlike the normal hybrid it can be plugged into the utility grid, allowing its batteries to be charged up with electricity rather than the gasoline engine. Some people like to call the plug-in hybrid the GO-HEV (Gasoline Optional-Hybrid Electric Vehicle). Personally, I have a pathological hatred of acronyms.
Since most people only commute a short distance every day, the plug-in has the potential to shift the majority of the transportation load off oil and onto electricity. At the same time, the plug-in hybrid retains the range and acceleration of its simpler basic hybrid cousin.
According to the Office of Energy Efficiency (of Canada) the total annual energy consumption of the passenger transportation sector was 1,322.4 PJ in 2003. That number corresponds closely the with the gasoline consumption of the nation. The freight transport sector consumed 945.8 PJ (mostly diesel). The total overall energy consumption was 8,457.3 PJ, so passenger transport consumes about 15.6 % of the total energy production of the country. About half of the cars on the road are driven less than 30 km a day. Current plug-in hybrid technology is easily capable of meeting this demand. Thus, in a country of about 33 million people, the plug-in hybrid is realistically capable of shifting 500 PJ of load from oil to electricity. This works out to about 11.5 kWh per person, per day! That's a lot of electricity demand. I personally only consume about 7 kWh per day, and I live alone, have electric baseboard heat, and an electric range.
The major drawback of the plug-in hybrid is its higher capital cost from the extra battery capacity. The other issue of the plug-in is that it is hardly a better solution if the electricity comes from coal or some other polluting resource.
The solution is two-fold. The first solution is to give the utility companies charging control over the plug-ins. This necessitates not only a 220 V wall plug, but an internet connection for a plug-in hybrid. The other side of the plug-in hybrid coin is a feebate program to reduce the associated capital costs. I will have to talk about that in another post.
The advantage here is that it creates a large, flexible demand for the utilities to fill (obviously the utility will have to guarantee a given level of charge in the morning). Why does this matter? Let's take a look at Texas' daily ramping power demand:
We can see that the demand varies from about 30,000 MW in the early morning to a peak of 50,000 MW at mid-day. Texas' grid is almost completely independent of the rest of the USA. There's probably less than 1000 MW of transmission connectivity between Texas and the outside world. That's a big shift, as it means during the course of a day almost 70 % more capacity has to be warmed up and brought on-line. Generally speaking, this doesn't happen. Power produced in the morning is often simply wasted (known as power shedding). Giving the utilities control over charging hybrids will give them the ability to fill in that valley, operating more efficiently by smoothing the demand variance, or having the demand follow supply rather than the other way around. Of further benefit, it will allow much more reliable forecasting, so power will not be wasted by overestimating demand.
Just how much flexible demand can the plug-in hybrid create? Consider that I claimed plug-in hybrids could supplant 500 PJ per year for Canada, and Canada consumed about 1900 PJ of electricity in 2003. Then slightly over 20 % of total electricity demand could become 'flexible' through the wide-spread introduction of the plug-in.
Of course, plug-in owners need to be compensated for providing this service to the utilities. Collectively, transmission services such as load-following, voltage-regulation, spinning reserve, etc. are known as ancillary services in the grid world. With controllable demand, the plug-in can take over many of these functions when acting as a demand sink. How valuable are ancillary services? Typically they will run from $0.01 - 0.03 / kWh, a significant chunk of the cost of electricity. If plug-in owners are paid for the ancillary services they are de facto selling, and their rates are reduced appropriately, they could see a very significant reduction in the cost of running their vehicle.
This flexible demand is valuable now, with our current energy grid. If we introduce more and more intermittent sources (i.e. wind, solar, tidal, wave), that flexibility will become even more valuable. Hence renewables and the plug-in hybrid are complementary technologies.
This idea of course, will go nowhere without government intervention. As hybrid vehicles become more common, and the introduction of the plug-in appears on the horizon, it would be prudent for governments to establish rules reguarding their use and interaction with the grid. Otherwise we risk extra-strain on the grid, as demand skyrockets whenever rush hour ends and millions of plug-ins start eating electrons.