Discover how the battery surpasses other power sources on readiness and efficiency but lacks on longevity and cost.
One hears about wonderful improvements in battery technologies, each offering distinct advantages, but none provides a fully satisfactory solution to today’s power needs. While the battery serves many markets well, it has definite limitations and cannot serve all energy needs effectively. This article begins with the positive traits of the battery and identifies limitations where other power sources are better suited.
Batteries store energy well and for a considerable length of time. Primary batteries (non-rechargeable) hold more energy than secondary (rechargeable), and the self-discharge is lower. Alkaline cells are good for 10 years with minimal losses. Lead-, nickel- and lithium-based batteries need periodic recharges to compensate for lost power.
A battery may hold adequate energy for portable use, but this does not transfer equally well for large mobile and stationary systems. For example, a 100kg (220lb) battery produces about 10kWh of energy — an IC engine of the same weight generates 100kW.
Batteries have a huge advantage over other power sources in being ready to deliver on short notice — think of the quick action of the camera flash! There is no warm-up, as is the case with the internal combustion (IC) engine; the power from the battery flows within a fraction of a second. In comparison, a jet engine takes several seconds to gain power, a fuel cell requires a few minutes, and the cold steam engine of a locomotive needs hours to build up steam.
Rechargeable batteries have a wide power bandwidth, a quality that is shared with the diesel engine. In comparison, the bandwidth of the fuel cell is narrow and works best within a specific load. Jet engines also have a limited power bandwidth. They have poor low-end torque and operate most efficiently at a defined revolution-per-minute (RPM).
The battery runs clean and stays reasonably cool. Sealed cells have no exhaust, are quiet and do not vibrate. This is in sharp contrast with the IC engine and larger fuel cells that require noisy compressors and cooling fans. The IC engine also needs air and exhausts toxic gases.
The battery is highly efficient. Below 70 percent charge, the charge efficiency is close to 100 percent and the discharge losses are only a few percent. In comparison, the energy efficiency of the fuel cell is 20 to 60 percent, and the thermal engines is 25 to 30 percent. (At optimal air intake speed and temperature, the GE90-115 on the Boeing 777 jetliner is 37 percent efficient.)
The sealed battery operates in any position and offers good shock and vibration tolerance. This benefit does not transfer to the flooded batteries that must be installed in the upright position. Most IC engines must also be positioned in the upright position and mounted on shock- absorbing dampers to reduce vibration. Thermal engines also need air and an exhaust.
Lithium- and nickel-based batteries are best suited for portable devices; lead acid batteries are economical for wheeled mobility and stationary applications. Cost and weight make batteries impractical for electric powertrains in larger vehicles. The price of a 1,000-watt battery (1kW) is roughly $1,000 and it has a life span of about 2,500 hours. Adding the replacement cost of $0.40/h and an average of $0.10/kWh for charging, the cost per kWh comes to about $0.50. The IC engine costs less to build per watt and lasts for about 4,000 hours. This brings the cost per 1kWh to about $0.34. [BU-1101, Battery Against Fossil Fuel]
With the exception of watering of flooded lead batteries and discharging NiCds to prevent “memory,” rechargeable batteries require low maintenance. Service includes cleaning of corrosion buildup on the outside terminals and applying periodic performance checks.
The rechargeable battery has a relatively short service life and ages even if not in use. In consumer products, the 3- to 5-year lifespan is satisfactory. This is not acceptable for larger batteries in industry, and makers of the hybrid and electric vehicles guarantee their batteries for 8 to 10 years. The fuel cell delivers 2,000 to 5,000 hours of service and, depending on temperature, large stationary batteries are good for 5 to 20 years.
Like molasses, cold temperatures slow the electrochemical reaction and batteries do not perform well below freezing. The fuel cell shares the same problem, but the internal combustion engine does well once warmed up. Charging must always be done above freezing. Operating at a high temperature provides a performance boost but this causes rapid aging due to added stress. [BU0502, Discharging at High and Low Temperatures]
Here, the battery has an undisputed disadvantage. Lithium- and nickel-based systems take 1 to 3 hours to charge; lead acid typically takes 14 hours. In comparison, filling up a vehicle only takes a few minutes. Although some electric vehicles can be charged to 80 percent in less than one hour on a high-power outlet, users of electric vehicles will need to make adjustments.
Nickel-cadmium and lead acid batteries contain hazardous material and cannot be disposed of in landfills. Nickel-metal-hydrate and lithium systems are environmentally friendly and can be disposed of with regular household items in small quantities. Authorities recommend that all batteries be recycled.
Last Updated 2015-01-19
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