Modeling and Design of Net ZEBs as Integrated Energy Systems - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 50

distributed electricity generation that can contribute toward grid “peak
demand shaving,” which can help reduce power generation during peak
periods, particularly when space cooling is required. During periods when
excess electricity is produced that cannot be absorbed by the grid, it can be
used to power water heaters, chillers or heat pumps to store heat or cold
(such as chilled water or ice). In commercial building BIPV applications,
on-site electricity generation can meet a portion of the daily electricity
demand, while eliminating grid distribution losses associated with
transporting the same quantity of electricity over long distances from power
plants.
2.2.1.1 Technologies
BIPV Components
PVmodulesusedforcommercial,industrialorresidentialBIPVapplications
consist of three main layers: a highly transparent frontsheet, the PV cell
layer and the backsheet. The PV cell layer is sandwiched between the
frontsheet and the backsheet. Solar radiation incident on the module's
surface is transmitted through the transparent frontsheet, captured and
converted into electricity by the PV cell layer. Typical frontsheets are clear
low-iron (low-Fe) glass with antireflective coating or polymer sheet, such as
ethylene tetrafluoroethylene (ETFE). Polymer frontsheets are significantly
lighter and thinner than glass frontsheets, while still maintaining high
mechanical and impact strength.
The PV cell layer consists of PV cells connected in series and/or parallel and
encapsulated for structural stabilization and protection against weathering
and humidity. Typical encapsulation resins used are ethylene vinyl acetate
(EVA) and polyvinyl butyral (PVB). Currently commercially available PV
modules can convert between 5 and 21% of the incident solar radiation
into electricity. The rest of the absorbed solar energy is converted into
heat and contributes to increase the temperature of the cells. As the cell
temperature increases, the diffusion current on the cells increases, leading
to a reduction of the charges at the edges of the cells. As a result, the
open-circuit voltage significantly decreases, while the short-circuit current
slightly increases, causing an overall reduction of the module power output.
Since PV cell efficiency generally decreases as their temperature increase,
this overheating is usually undesirable. Depending on the technology, the
efficiency of PV modules can be affected at a rate of as much as −0.53%/°C;