Page 145 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

132 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
®

reduction, the PV industry is transitioning from being driven by subsidies into a viable option for
investment for both large power plants and residential installations on a pure cost competition basis [2].
Residential PV systems are a key element in the success story of PV rooftop installations, and
large utility-scale plants share about 50% of new installations today.
This chapter discusses the design of residential PV installations, with focus on rooftop grid-
connected systems, which represent the vast majority of small-scale PV systems.
Residential rooftop systems may be considered a special case when it comes to the sizing and
design of the system. While in the case of ground-mounted systems (typical for utility-scale plants),
the type of components, placement, and layout can all be optimized for the design criteria, typically
to minimize the levelized cost of energy, in the case of residential rooftop systems, several factors
may influence the design, such as the roof area, angle and shape, and easthetic requirements.
In the following sections, the general guidelines for the designing and sizing of residential PV
systems are given. The example is for Denmark; nevertheless, the same methodology can of course
be applied to other countries as well.

6.2 DESIGN PROCEDURE FOR RESIDENTIAL PV SYSTEMS

The task of designing PV systems is a very tricky process due to the fact that PV panels are still rela-
tively expensive and energy production is very sensitive to atmospheric conditions and the physical
location. In the case of ground-mounted PV systems, one can choose the optimum tilt angle and ori-
entation, and often the physical size is the only limiting factor. In the case of residential PV systems,
PV panels are usually mounted on the roof, which might not have the optimum angle or orientation.
Besides these limitations, the size of the roof is fixed; therefore, several parameters are already fixed
at the beginning of the design. Such design parameters or constraints will affect the following:
• The required annual energy production (AEP)
• The available budget for the installation
• Location-specific limitations: roof size, tilt, and orientation

The first task is to decide whether the PV system will be connected to the electrical grid. Afterward,
the load pattern should be evaluated in order to estimate power and energy requirements. When these
requirements have been defined, the PV cell technology can be chosen; the PV array can be sized for
the required amount of power. Furthermore, the PV array needs to be configured to fit the specifica-
tions of the PV inverter. Finally, at the end of this chapter, the whole design procedure is evaluated
through a case study, by using freely available design tools. The results are presented and discussed.

6.2.1 Grid-Connected or Stand-Alone Systems
Residential PV systems can be divided into two major groups: grid connected or stand-alone. A PV
system can be connected to the electrical grid when the house is connected to the low-voltage (LV)
utility network; thus, the power network can be used to dump the surplus energy production. The
PV system can be connected to the energy meter of the house, thereby increasing self-consumption.
Another solution is to add an individual energy meter that measures the energy that the PV system
produces, which is then accounted for separately. Both energy metering solutions are presented in
Figure 6.1.
In both cases, the grid is used like a large battery, storing the surplus energy produced by the PV
system. Thus, in such a case, during periods with high irradiation and low load conditions, the grid
will be stressed, leading to voltage rise, due to the mainly resistive nature of the LV network. To
mitigate the problem of voltage rise, PV inverters are nowadays required to support the grid with
reactive power, thereby keeping the grid voltage within the limits imposed by the grid codes.
On the other hand, in houses in remote areas that are far away from any electrical network, a
stand-alone PV system has to be installed. The complexity of the design will increase, since one