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Electric Vehicles (EVs) are coming, but they have several technological hurdles before they become common on the road. Today’s EVs aren’t practical for the average consumer, and several components need more development. Here is a list of major technological barriers, based upon what you can buy today.
1. Electricity Storage or Generation
Onboard power is the biggest limitation – batteries for most EV designs. There are several different battery chemistries, but some suffer from short range while others are not easily available.
Lead Acid batteries are easy to buy, but not all of them are suitable for EVs. They must be matched and then carefully conditioned to yield best service. They are heavy and don’t provide a lot of range. Many car and light truck chassis must be reinforced before they can carry enough batteries to obtain usable range, and the weight vs. range trade-off peaks out around 40 miles per charge.
Nickel-Metal Hydride batteries are lighter and yield better range, but are tightly rationed. They tend to self-discharge and deteriorate during storage. They must be conditioned to produce best service, and cannot tolerate over-charging. More development will probably wait until the current patent expires in another year or so.
Lithium-Ion batteries are available in several chemistries, are even lighter and provide greater ranges. However, they are expensive and require careful monitoring and charging. They can be ruined by small amounts of overcharging or overdrawing, and by temperature. Lithium-Ion batteries need better quality control. They are not easily available in large packs that produce voltages high enough for EVs.
All current battery technologies share several problems. Using household current, it takes 6 hours or longer to recharge them every time they’re used. Range decreases by as much as half during cold weather. Battery packs are made of many cells where one cell or connection failure can disable the vehicle. Battery packs also have difficulty supplying auxiliary loads such as headlights, heating, air conditioning, power brakes, power steering and entertainment systems. Most packs require replacement after only a few years at high cost.
It may be possible to generate electricity by another method. Many people tout photovoltaic cells, but those produce much less power than motors consume – the amount of cells that can fit on a vehicle will take several days to recharge a battery pack. Others, such as fuel cells, require their own extensive development. Super capacitors can provide quick energy bursts for going up hills or passing other cars, but they are not yet substitutes for batteries because their discharge is measured in seconds – not tens of minutes as needed for EV trips.
Most motors powerful enough for an EV are designed for industrial applications, running at constant speeds and loads for days. EVs need motors that run at variable speeds and loads, for hours. Industrial motors can be used in EVs, but not at their best efficiency. They are generally heavier than necessary and not sealed against the environment. Other motors, such as forklift, can be used, but they are not designed for the higher speeds and sustained loads of EVs. Industrial motors are designed for high power grid voltages with unwavering duty cycles, not the falling power of discharging battery packs.
There are several interesting new motor designs in laboratories. Among them are axial flux permanent magnet motors and multiphase DC motors. The challenge is to get them into fleet testing and then production.
Essentially, motor controllers are variable power supplies. Most of today’s mobile controllers are low frequency analog designs that generate a lot of heat and are not hardened for the automotive environment. Power devices used to pass battery current need lower internal resistance, higher current capacity and easier control. Motor controllers are starting to include microprocessors, but they are just scratching the surface of decision power and of communications busses. Many controllers need to be trained to best utilize the motors and battery packs connected to them.
Battery chargers and battery management systems need to be better matched to battery chemistries. Most battery chemistries cannot tolerate unattended trickle charging like we use on automobile starting batteries. Battery cells within packs are very sensitive to small differences in their own internal chemistries as well as heating effects from surrounding cells, requiring sophisticated monitoring and dynamic charge loading. Since batteries are rapidly evolving, chargers and monitors will have to keep up.
Regenerative braking / battery recharging systems need to develop more power while minimizing physical drag. Braking effects are effective today if controlled correctly, but regenerative power is too small to add significant range. Drivers must be retrained to utilize regenerative braking / recharging effectively.
Charging stations must be everywhere, particularly while battery packs require frequent recharging. Stations must handle high charging currents. Many homes require wiring changes to accommodate charging. Stations need to provide a significant amount of recharging in about the same time that it takes to refuel a gasoline vehicle. Travelers need assurance that during long trips they can find recharging power and that the trip will not be unduly extended while awaiting recharging. The power grid may need upgrades, even if most people restrict recharging to late night hours.
Swappable battery packs will be feasible if they become more compact, accessible and lighter. Battery chemistry and management must become bulletproof so consumers are assured that replacement packs are as good as the packs they replace. The industry needs to standardize connectors for battery pack connections and charging.
EVs are mostly touted as short commuters. That makes 4-cylinder compact cars their main competition, and those cars list for under $20,000. Price estimates for EVs are at least double that. Consumers may be willing to pay a premium for an EV, due to the difference in fuel costs, but will they pay double? The first challenge is to get production costs down so EVs can compete directly on price. The second challenge is to get comparable range between EVs and 4-cylinder cars. It can be argued that 40 miles is enough range for daily commuting, but when consumers compare EVs to gasoline cars they realize that 40 miles is a short leash.
Battery packs must also come down in price since they are only expected to last a few years, and because they are the most expensive component in an EV. Prices for competing electricity storage or generation products are as high – if not higher – than batteries.
Can these technological barriers be overcome? Certainly, given enough time and resources. The biggest hurdle will be public acceptance of our current technological limitations, as well as learning how to use and care for their EVs.