- Choosing where and how to use hybrids for maximum gains by
- Environment | 4 p.m. | Thu 18 Oct 2007
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What is the ideal application for a hybrid engine, and where should development effort be concentrated to maximise environmental improvements?
So far, car manufacturers have concentrated on developing hybrid versions of medium-size, five-seat cars. This makes sense because the family car market is so huge. Even if only a small percentage of customers switch to hybrids, the technology can be proven in service. There’s also plenty of room for hybrid technology in a family car as opposed to, say, a small hatchback, which might otherwise seem the more logical vehicle for "green" marketing.
However, it may be more beneficial to the environment to treat other vehicles as a priority for hybridisation.
Hybrids offer the greatest benefits when they are used in vehicles with a low average power demand and frequent bursts of high power. An HGV used mainly for overnight trips on motorways would be a poor choice as the engine is running at near its optimum performance for hours on end. Indeed, there is a good environmental case for discouraging long-distance road freight and transferring as much as possible to electrified rail, which produces far less emissions than the most efficient lorry, whether hybrid or not.
However, road sweepers, recycling lorries, maintenance and delivery vehicles are ideal applications. A dust cart is a particularly good candidate for conversion to a series hybrid (i.e. one in which the vehicle is propelled by electric drives with the battery being topped up by a small engine running continuously) as it operates on a stop-start duty cycle and has high and "peaky" auxiliary loads of crushers, conveyors and lifting jacks, which could be operated by electric motors fed from the main battery.
Assuming that the demand for hybrid cars grows faster than the availability of advanced materials to make the batteries , there will be a choice of where they should be sold for the greatest benefit.
Mountainous areas like Norway or Switzerland may be the best places, as hybrids can use their electric power to drive up mountains and reclaim it, through regenerative braking, on the way down. Conurbations with slow-moving traffic and many junctions must take a close second place. At the other end of the scale, flat sparsely-populated areas, like Wyoming or central Australia, are fundamentally bad places to introduce hybrids.
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I largely agree, but I would explain it differently, and have a few additions.
Hybrids have zero fuel costs when they recover energy from braking, way low fuel costs if recharged from the grid when demand is lowest during the day, still low cost if recharged when demand is relatively low, but more than with a gasoline engine if recharged during peak periods during the day. (The consumer faces these differences with recharging if electric pricing reflects time of day; the utility otherwise. Either way, society feels them.) Once the charge is exhausted, hybrids have no advantage in fuel use. At the same time, hybrid engines are more expensive to manufacture.
An advantage for society is that hybrids recharged during the lowest demand time of day add no incremental carbon to the atmosphere. Thermal base load power plants are not turned off at night, since they take days to warm up, so this power is produced whether or not hybrids use it. This power just goes to a more valuable use with hybrids present. Recharging at another time of day leaves a carbon footprint at the power plant, but a dramatically lower one at the car. The total carbon footprint is still usually lower than with a gasoline engine.
An electric motor also provides its power with greater torque than does a gasoline engine.
Thus, hybrids are best employed if:
1. They can be plugged into the grid to be recharged.
2. They are used on vehicles that get frequent use.
3. They are used for drivers that take trips below 40 miles or so before recharging. Commuting vehicles, urban delivery vehicles, and postal delivery vehicles could be good candidates.
4. They are used for drivers that brake frequently, either urban drivers or drivers in mountainous areas.
5. They are employed for uses where high torque is needed, such as with some trucks.
If any of the first three conditions is not satisfied, hybrids are likely to be a bad choice. They make little sense for vehicles that would usually go long distances between recharging, that could not plug into the grid, or that would be used so little that the higher initial cost would be prohibitive.
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