Page 201 - Applied Photovoltaics

On-site storage can also be used as a demand-side management tool, to reduce peak
load power requirements, and hence costs, for the building as well as providing high
value peak load power to the grid. An emerging market is the provision of PV-
powered uninterruptible power supplies (UPSs) for buildings or equipment,
particularly where grid supply is unreliable, but also as an option to diesel systems
currently used, particularly in commercial buildings. For these applications, some
form of on-site storage is included, but otherwise storage is currently not a typical
option for grid systems.

10.2.4 Size and economics
To make much impact on typical household electricity use, a photovoltaic system of
2
about 2 kW p , or 20 m , would be needed (SERI, 1984). A system rated at 3–4 kW p
would supply most household needs. Depending on the house design, a limit of about
2
7 kW p , or 70 m , is often imposed by the available roof area.
The cost of photovoltaic modules suitable for household use in the USA in 2004 was
about US$3.20–5.00/W p (Solarbuzz, 2004b). Total grid-connected PV system costs
can be up to double this. For economic viability at current electricity prices, system
costs need to be further improved. The cost-effective price for an end user is still
higher than for central power supply. In 2004, delivered PV power cost around
US$0.30/kWh, which was 2–5 times average residential electricity tariffs (Solarbuzz,
2004c). Note that prices vary from country to country. Average Australian module
prices in 2004 were about A$7/W p and typical turnkey grid-connected system prices
ranged from A$12/W p for small systems down to A$6/W p for large systems (Watt,
2004).
Technology experience curves are used to monitors falling prices as industry
experience and cumulative production grows (Poponi, 2003). These curves may be
used to predict ‘break even’ years, although the results are sensitive to the
assumptions adopted.
Based on PV learning curves over the past three decades, and expected growth, PV-
based electricity prices are expected to be close to grid electricity prices in Australia
from about 2015 (Australian Business Council for Sustainable Energy, 2004a). In
countries like Japan, where electricity prices are higher, breakeven prices may be
reached sooner, although lower annual output compared with Australia will impact on
the timing.

To keep costs down, more emphasis needs to be placed on simplification of design,
provision for maintenance, standardisation, and in-built protection and control
systems. ‘Net’ metering, with a single, bidirectional meter, also minimises system and
billing costs (Poponi, 2003). Net metering is mandated in many US States and is
common in Europe. It is available from many Australian electricity retailers, but the
use of separate meters is likely to remain common until electronic metering becomes
more widely available. Net metering is not suitable for feed-in tariff or other
differential tariff regimes.

10.2.5 Other issues
Other issues that need to be addressed for household photovoltaic systems include
(SERI, 1984):

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