Page 163 - Applied Photovoltaics

more efficient than conventional AC units, therefore requiring much smaller
photovoltaic systems. Aspects that contribute to their efficiency include:
x shape
x increased insulation
x tight door seals
x compartmentalisation, with independent thermostat control of each
x efficient compressors/motors with efficient heat removal (without fans)
x manual defrosting
x top loading.
Consumer education on the best use of a refrigerator is important if the advantages
outlined above are to be realised, and the power supply is to be minimised. This
should include (Ball & Risser, 1988) knowledge of the thermal effects of:
x refrigerator location, including the need for ventilation for heat dissipating
coils
x door opening habits
x seasonal variations in use (in general, this is well matched to photovoltaic
output)
x time and temperature of loading.

8.11 PHOTOVOLTAIC POWERED TRANSPORT
Transport of people and goods is an energy challenge that is difficult to meet directly
with solar cells owing to the relatively small collecting areas on vehicles and the large
power and energy demands. Solar power may be used to help power conventional
systems, using an existing grid as effective storage, such as the tramway in Karlsruhe,
Germany. Photovoltaic modules (100 kW p ) on the roof of the Centre for Art and
Media (ZKM) supply power for the Karlsruhe urban tram system. The energy is fed
directly to the DC system to power the trams with additional requirements supplied
by the usual grid-based system. The large DC loads make storage and inverters
unnecessary. A similar, 250 kW p system operates in Hanover. A fixed, ground-
mounted 24 kW p photovoltaic array supplies sufficient energy to the grid to offset the
energy demands of the funicular railway near the Parliament Building, Bern,
Switzerland. The system was installed in 1992 and produced 105% and 95% of the
railway’s energy requirements in 1993 and 1994, respectively. A 36 kW p installation
meets the entire energy needs of a funicular near Livorno, Italy (EC, 2002).

On-board solar assistance for transport is also quite practical. Several small road cars
with photovoltaic roofs have come to market, but to date have experienced small sales
volumes. A solar-assisted bus, using 15 photovoltaic laminates integrated into the
roof, carries disabled visitors around Kew Gardens in the UK, and a supermarket
chain in the UK uses top-mounted photovoltaics to power refrigeration in truck
trailers. Similarly, PV arrays on trucks are being trialled in the US as a means of
keeping batteries topped up while drivers stop at truck stops, without the need for
idling the motor.
Highway noise barriers represent a huge investment in expensive structures that have
been found a second use as mounts for large numbers of grid-connected photovoltaic
modules in Europe. Apart from being convenient support structures, they provide an

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