Page 22 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

Renewable Energy Systems: Technology Overview and Perspectives 9

generator, and an AC/DC rectifier. The reminder of the electric power system, including a DC/AC
inverter, together with power supply cabinets, transformer, and switchgear, is fitted in a multilevel
14 m tall structure within the base of the turbine tower [12].
Most of the new installations of multi-MW turbines are part of large wind farms, which aggregate
the individual contributions into a power station. Traditionally, most wind farms have been onshore,
but present plans and ongoing developments exist for very large offshore deployments that would
benefit of better wind conditions and will be remotely located from the countryside. Examples
include the Anholt 400 MW wind farm commissioned in 2013, which is the Denmark’s largest off-
shore park and one of the largest in the world. This installation, which is illustrated in Figure 1.12,
is operated by the Danish utility company Dong Energy and comprises 111 Siemens wind turbines,
each rated at 3.6 MW.
For solar energy, there were also many recent record-breaking developments. These include,
for example, the recent completion in early 2015 of the 550 MW Desert Sunlight solar PV power
plant built by First Solar near Joshua Tree National Park in California, which generates enough
electricity to power 160,000 homes [13]. The long-standing record of leading innovations in solar
PV technologies of companies such as SunPower now includes smart grid solutions for residential
and commercial installations and integrated micro-inverters [14].
Another example is from the Atacama Desert in Chile, South America, where Abengoa developed
a 110 MW solar thermal plant using tower technology. Remarkable is that this includes 17.5 hours of
thermal energy storage using molten salts, which aims to ensure dispatchable electricity throughout
24-hour cycles, responding to all periods of demand [15].
While wind and solar may already be cost-competitive, depending of course on regional and
particular conditions, other renewable energy technologies still require substantial developments. Fuel
cell systems may be included in this category, as they have been expected for many years to increase
their presence in applications over a wide range of power ratings. The typically low-temperature pro-
ton exchange membrane (PEM) technology and the higher-temperature solid oxide fuel cells (SOFC)
type can be applied for large power supplies, with some demonstrators being completed for uninter-
ruptible power supply (UPS) systems. The fuel, represented by hydrogen in combination with air/
oxygen, is converted into electricity and some heat using a system topology of the type schematically
presented in Figure 1.13. An example of hardware implementation is further shown in Figure 1.14.
The power electronics system for fuel cell applications incorporates a DC/DC converter, which
ensures power extraction maximization, and a DC/AC inverter for grid connection. Challenges
being addressed by ongoing research programs include improvements in efficiency and specific

FIGURE 1.12 Denmark’s largest offshore wind farm of 400 MW installed at Anholt. (Courtesy of Dong
Energy Wind Power.)