In Search of the Energy-Efficient Family Car

Written by: Karen Lightman, Executive Director, MEMS Industry Group
(as published in Design News on 09/06/2013)

Buying a car just isn’t as easy as it used to be, especially when you know just enough about alternative-fuel-source vehicles to make that decision very difficult. As my husband and I debate the merits and faults of energy-efficient cars (as the end date of his leased Prius looms in the background), I feel as though we must make a smart choice that is right for us and right for the planet. Perhaps you relate to such a quest for the perfect car that balances safety, comfort, fuel efficiency, and style.

When I entered this decision tree of what fuel-efficient car to buy, I initially thought that an electric vehicle (EV) would be the simple solution. EVs, which run on chargeable batteries, seem to make sense for our family. We live in an urban area and rarely take long trips requiring a long charge. We’ll just plug the car in at night and stop using petroleum that pollutes the air. Right?

Not quite. As I started discussing the decision with my MEMS colleagues (all with their EEs and MEs), I quickly learned that it’s not that simple. First, the biggest limitation is the battery itself. The energy-to-weight ratio for EVs is quite abysmal compared with gasoline. Up to one-third of an EV’s total weight can be attributed to the battery pack alone, and most of the batteries hold a charge for a few hundred miles at best. That’s a deal breaker for many.

Tesla appears to be the only EV company that is seriously attacking the battery issue. Its CTO has said battery energy density is improving about 7 percent a year. This clearly shows that his company understands one of the biggest roadblocks to EV adoption. Tesla has designed a beauty of a lightweight car that is chock full of MEMS/sensors and showcases an iPad-like dash between the passenger and driver. Plus it has two trunks; that is just so cool. (It’s the reason my 12-year-old daughter insists we buy a Tesla.)

Until we have cars that run on solar panels, energy is never free. Even if you decide to buy a Tesla, you have to think about where the energy is generated to recharge the battery every night. For me in Pittsburgh (and for most of the Northeast), the source is typically coal. Uh, oh. That means I would deplete more fossil fuels and release more greenhouse gases if I bought an EV. Another important issue is the disposal of heavy-lead lithium batteries. Some EVs need to replace their batteries after three years. So if you are the average American who holds on to a car for five years, you’ll need to dispose of (and pay for) two batteries and consider the environmental impact of that decision.

Let’s face it — the batteries for EVs (and for most consumer electronics) are still inefficient. Here’s where my MEMS brain starts to activate and I start thinking about energy harvesting. Can’t we find ways through MEMS to harvest the car’s vibrations at least to power its electronics?

I bet the folks at MicroGen Systems are already looking into this. I actually know of a few more companies (big and small) that are looking into ways to make vehicles smarter and energy efficient from the get go through a combination of MEMS and sensors. Examples include energy harvesters in the tire that capture the vibrations and power the tire-pressure monitoring system, as well as sensors embedded into an engine to maximize fuel efficiency. Take it one step further, and HVAC monitoring systems managed by an in-car sensor network could keep passengers comfortable as the vehicle passes through varying daylight and temperature conditions. MEMS will make this happen.

I guess I will have to wait until there’s smarter battery technology that recharges an EV by green energy. In the meantime, I’ll be asking my local car dealer how many MEMS and sensors are inside the vehicle. The car with the most MEMS wins.

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