Page 209 - Applied Photovoltaics

Analysis of an American project that was designed and built to measure the benefits
of grid-support PV (see Section 10.6, below) attributed a value of US$28/kW/year for
offsetting the marginal cost of keeping peak-following generation capacity online
(Wenger et al., 1994). On the peak load day in financial year 1993–94, the nominally
500 kW p, single-axis-tracking PV plant reduced the 4pm peak load by 430 kW and,
additionally, reduced the heat load on the distribution transformer in the period before
the peak, reducing its temperature and enhancing its peak capacity.

Figure 10.8. Distribution transformer load and PV output of a grid-support system
on the peak load day during the monitored year. (©1994 IEEE, Adapted from
Wenger et al.)

Although there is a good match between days of peak load and of peak PV output for
fixed arrays where air conditioning controls the peaks, the time of day is not always
well matched for feeders supplying mainly residential loads, since residential peak
loads tend to lag behind peak insolation. Watt et al. (2003) have proposed the use of
west-facing PV to shift their peak output time to better match the peak summer load.
Of course, this reduces the annual energy output of the array but optimises the value
of its contribution to the grid. Financial arrangements would need to reflect that
increased value in order to make such solutions attractive for householders.

Interestingly, users with PV systems may change their usage habits, perhaps adding
greater value to the PV system via energy management strategies (Haas, 1993).

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