Page 404 - A Comprehensive Guide to Solar Energy Systems

Chapter 21 • (EROI) and (EPBT) for PVs 413

and body of system (BOS). The output during the lifecycle must be estimated. variables for
output include solar irradiation, conversion efficiency including lifetimes, performance
ratios, and electricity generation efficiency.
21.2.3 Overlapping Energy Input Accounting Methods

In general, there are three different scopes used for collecting energy cost data for an
energy system in the literature [8]. The first is using national energy accounts for direct
energy used. Some countries maintain records of energy used by various industries
including those of their energy industry. This approach takes serious investment in
time, a good library and Internet services, and ideally the assistance of professional
experts in the varying fields being examined. The second is using national accounts
for capital expenditures and other indirect uses. This includes energy used offsite to
produce and maintain the capital equipment used to make pv modules. The indirect
energy costs of some materials and processes are usually known, for example, forming
concrete or aluminum. Other forms of capital must be estimated by converting known
financial values into quantities of energy. The indirect energy cost of dollars spent on
chemicals, steel products, and other relevant capital can be calculated as the dollar cost
times the energy intensity of the formation of that capital. The energy intensity is mea­
sured by the quantity of energy used to produce a dollar worth of output in the indus­
−1
trial sector of the economy (joule ($) ) [19]. Using dollar values is not an ideal method
for capturing energy costs of capital inputs because it carries the errors in generating
financial variables; however, the advantage in using energy intensities to estimate en­
ergy costs is that financial data is more readily available than energy data. These two
procedures have a critical issue of determining a set of boundaries for analyses. Note
that there is no emphasis on differentiating between expressing energy inputs as pri­
mary energy or energy carriers, although a quality correction is required. This correc­
tion is typically applied by multiplying higher quality electricity values by 3 to equate
thermal values [8,19].
The third procedure involves using the values for energy inputs provided in LCAs
and deriving the calculation for measuring cumulative energy demand (CED). The LCA
is a standardized method for analyzing various aspects involved with the development
and lifetime of a product [23]. The methodology of LCA calculates CED, which describes
the total primary energy extracted from the environment to deliver, support and retire a
given system. The CED is informed by data provided in life cycle inventory (LCI) Data­
bases, manufacturer’s technical specifications, and indirect estimates. LCI data includes
direct measurements, expert assessments, company data surveys, and theoretical calcula­
tions. It is common to borrow data from other studies to cover parts of LCA supply chains.
As it is standardized, and therefore, has clear definitions and boundaries of analysis, in
theory the CED method provides the most detailed information on the energy costs of pv
systems available to EpBT and EROI analyses today, although it is not always considered
comprehensive.