A discussion on life-cycle costs of residential photovoltaic systems Page: 2 of 4
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constant. With these small economic benefits, it is likely that the
decision to purchase a PV system, especially with energy
storage, will be based more on self-reliance and environmental
responsibility than on return of investment.
IS THERE A PRODUCT/SYSTEM INFRASTRUCUTRE
Today, most of the applications are added to existing structures.
Several manufacturers have complete products (kits) that can be
added to existing structures, from about 300 W up to several
kW. This has resulted in reducing the indirect costs of
marketing, distribution, and design. New construction and
integration, especially in manufactured and other standard
housing, represents a potentially large opportunity for PV in the
future. On the other hand, custom design and integration in new
housing could potentially decrease reliability and increase costs.
Customer satisfaction is based upon perceived value, a
combination of benefits including cost and quality of systems.
Quality is dependent upon the design, choice of components,
installation, and maintenance. There is currently a dearth of
training and certification programs that address the quality
issues. The State of Florida has recently begun a certification
program for installers through the Florida Solar Energy Center
which is also developing a hardware and design approval
process through the Florida PV Buildings Program. The
manufacturers of packaged systems are attempting to build
quality into their products by standardized design and by
requiring specific training of its installers.
The weak link currently appears to be in the area of maintaining
systems and components that are being sold with a stated 20 to
30 year lifetime. Only a limited number of electrical
contractors currently have experience with PV systems. The
solar industry and a few states are attempting to improve the
situation through certification programs but this is an area that is
only now developing. Once this situation is corrected, the cost
of the after installation service will still need to be addressed.
WHAT IS REQUIRED TO OWN AND MAINTAIN A
What can be expected from a PV system after installation?
There are simply too few of these systems with a long enough
history to answer this question with certainty. Let's look at
some of the potential sources of problems.
Most of today's systems are placed over an existing roof
structure. The time to replacement of the covering for flat roofs
averages about 8 years in the southwestern part of the country,
and most pitched roofs with standard materials are re-shingled
perhaps every 12-15 years. Because these are the types of roofs
that will potentially accommodate the largest numbers of PV
systems, the labor cost of removal and re-attachment at least
once during the 30-year life of the PV system is a starting point.
The expected lifetime of the inverters even with maintenance is
no greater than its internal components and has been estimated
at 20 years. Thus, there will be the replacement cost of the
inverter. Since the average American moves every 8 years, the
30-year concept has limited value until it is included in and
increases the value of the structure upon resale. However,
depending upon the age of the system and the roof, this could be
a liability. We assume that in time the inverter will be a plug
and play, but probably hard-wired except for ac modules and
that the consumer will be able to perform this action, and that
approach will save time and money. The re-roofing is a
different matter for most.
Lifetime is a function of reliability and value. Once the cost
(real and perceived) to maintain a system exceeds the value (real
and perceived), the system is at end of life. Reliability is
dependent upon the quality of the components, design,
installation, and maintenance. Because the reliability and
maintenance data on the residential application are so limited,
we have no way to assess how the value of these systems will be
impacted over time.
Another issue is general degradation of the system. This takes
two forms, reversible and irreversible. An example of reversible
degradation is soiling of the array which can reduce the output
of an array in a rural or urban setting by as much as 25%. This
is reversible because the array could be cleaned... .at a cost.
Irreversible electrical degradation is seen in almost all modules
and represents about 0.5%/yr. A residential customer could
ignore this small amount of degradation because it will represent
only 50-100 kWh/ten years and the utility is providing back-up.
However, it will diminish the energy value from the system.
A potentially large area of future maintenance will result from
those systems where energy storage is added. While energy
storage represents a very large potential benefit in terms of
system availability, batteries do require routine maintenance, a
special location, and replacement. Clearly there will be
additional costs that must be defined including labor and capital.
In summary, elements that are unique to the purchaser of future
grid-tied residential systems have been discussed to develop a
common understanding of the costs and values of these types of
systems. Investment value is seen as secondary to self-reliance
and environmental concerns. However, these benefits could
easily be overshadowed by hassles caused by poor reliability and
lack of affordable technical support once the system is installed.
*Sandia is a multi-program laboratory operated by Sandia
Corporation, a Lockheed Martin Company, for the U.S.
Department of Energy under Contract DE-AC04-94AL85000.
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THOMAS,MICHAEL G. & CAMERON,CHRISTOPHER P. A discussion on life-cycle costs of residential photovoltaic systems, article, April 11, 2000; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc711740/m1/2/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.