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Battery/fuel-cell EV design packages     CHAPTER 6.1

           of five connected in series to give maximum output of  current commercial process taking 3 hours. An EC study
           1.3 watts (0.6 A at 2.2 V). Some ten modules might be  has also shown that mass production of solar cells could
           used in a solar panel giving 13 watts output in summer  bring substantial benefits and that a £350 million plant
           conditions. Power vs voltage and current vs voltage are  investment could produce enough panels to produce
           shown at (a) for so-called ‘standard’ and ‘typical’ oper-  500 MW annually and cut the generating cost from
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           ating conditions. 100 mW/cm solar intensity, 0 C cell  64 p/kWh to 13p.
           temperature at sea level defines the standard conditions
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           against 80 mW/cm and 25 C which represent ‘typical’
           conditions at which power output per cell drops to 1 W.  6.1.2.6 Lithium-ion
           Temperature coefficients for modules are 0.45% change

           in power output per 1 C rise in temperature, relative to  A high energy battery receiving considerable attention is


           0 C; cell temperatures will be 20 C above ambient at  the lithium-ion cell unit, the development of which has
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           100 mW/cm incident light intensity. Variation of solar  been described by Nissan and Sony engineers who point

           energy at 52 north latitude, assuming a clear atmo-  out that because of the high cell voltage, relatively few
           sphere, is shown at (b). On this basis the smallest one  cells are required and better battery management is thus
           person car with a speed of 15 mph and a weight of 300 lb  obtained. Accurate detection of battery state-of-charge is
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           with driver would require 250 W or 50 ft (4.65 m )  possible based on voltage measurement. In the battery
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           of 5% efficient solar panel – falling to 12.5 ft (1.18 m )  system developed, Fig. 6.1-6, cell controllers and a battery
           with the latest technology cells. A 100 Wh sealed nickel–  controller work together to calculate battery power, and
           cadmium battery would be fitted to the vehicle for  remaining capacity, and convey the results to the vehicle
           charging by the solar panel while parked.          control unit. Charging current bypass circuits are also
             The future, of course, lies with the further de-  controlled on a cell-to-cell basis. Maximizing lifetime
           velopment of advanced cell systems such as those by  performance of an EV battery is seen by the authors to
           United Solar Systems in the USA. Their approach is  be as important as energy density level. Each module of
           to deposit six layers of amorphous silicon (two iden-  the battery system has a thermistor to detect temperature
           tical n-i-p cells) onto rolls of stainless steel sheet. The  and signal the controllers to activate cooling fans as
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           4ft (0.37 m ) panels are currently 6.2% efficient and  necessary.
           made up of layers over an aluminium/zinc oxide back  Nissan are reported to be launching the Ultra EV in
           reflector. The push to yet higher efficiencies comes  1999 with lithium–ion batteries; the car is said to return
           from the layer cake construction of different band-gap  a 120 mile range per charge. Even further into the future
           energy cells, each cell absorbing a different part of the  lithium–polymer batteries are reported to be capable of
           solar spectrum. Researchers recently obtained 10%  giving 300 mile ranges.
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           efficiency in a 12 in (0.09 m ) module.
             Rapid thermal processing (RTP) techniques are said to  6.1.2.7 Supercapacitors
           be halving the time normally taken to produce silicon
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           solar cells, while retaining an 18% energy conversion ef-  According to researchers at NEC Corp. , the super-
           ficiency from sunlight. Researchers at Georgia Institute  capacitor, Fig. 6.1-7, will be an important contributor to
           of Technology have demonstrated RTP processing in-  the energy efficient hybrid vehicle, the absence of chem-
           volving a 3 minute thermal diffusion, as against the  ical reaction allowing a durable means of obtaining high




















           Fig. 6.1-6 Overall system configuration.


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