Introduction:
PV and
genset systems do not have much in common. It is precisely for this reason that
they can be mated to form a hybrid system that goes far in overcoming the
drawbacks to each technology. Table 10.1 lists the respective advantages and
disadvantages. As the sun is a variable energy source, PV system designs are
increased in size (and therefore cost) to allow for a degree of system
autonomy. Autonomy is required to allow for provision of reliable power during
"worst case" situations, which are usually periods of adverse
weather, seasonally low solar insulation values or an unpredicted increased
demand for power. The addition of autonomy to the system is accomplished by
increasing the size of the PV array and its requisite energy storage system
(the battery).
When a genset is added, additional battery
charging and direct AC load supply capabilities are provided. The need to build
in system autonomy is therefore greatly reduced. When energy demands cannot be
met by the PV portion of the system for any reason, the genset is brought on
line to provide the required backup power. Substantial cost savings can be
achieved and overall system reliability is enhanced.
PV/genset hybrid systems have been utilized at
sites with daily energy requirements ranging from as low as 1 kWh per day to as
high as 1 MWh per day, which illustrates their extreme flexibility. They are a
proven and reliable method for efficient and cost effective power supply at remote
sites.
PV/genset
hybrid system description
The PV/genset hybrid utilizes two diverse
energy sources to power a site's loads. The PV array is employed to generate DC
energy that is consumed by any existing DC loads, with the balance (if any)
being used to charge the system's DC energy storage battery.
The PV array is automatically on line and
feeding power into the system whenever solar insulation is available and
continues to produce system power during daylight hours until its rate of
production exceeds what all existing DC loads and the storage battery can
absorb.
Should this occur, the array is inhibited by
the system controller from feeding any further energy into the loads or
battery. A genset is employed to generate AC energy that is consumed by any
existing AC loads, with the balance (if any) being used by the battery charger
to generate DC energy that is used in the identical fashion to that described
for the PV array above.
Figure 3.1 Block diagram of a hybrid PV-Genset
system.
At times
when the genset is not running, all site AC power is derived from the system's
power conditioner or inverter, which automatically converts system DC energy
into AC energy whenever AC loads are being operated. The genset is operated
cyclically in direct response to the need for maintaining a suitable state of charge
level in the system's battery storage bank.
Other
PV/hybrid types
Certain
specific site locations may offer access to other forms of power generation.
Access to flowing water presents the potential for hydro power. Access to
consistent wind at sufficient velocity presents the potential for wind power.
PV/hydro
and PV/wind hybrid systems have been utilized at sites with daily energy
requirement ranges similar to those described for PV/genset hybrids. Their use,
however, is much more site dependent, as their energy source is a factor of
that locations' topography.
PV/Thermoelectric generator hybrid systems have
been used effectively at sites whose daily energy requirement is relatively
low, ranging from 1 to 20 kWh per day. Propane is the fuel source for the
thermoelectric process, and conversion efficiencies of up to 8% can be
achieved. Considerable waste heat is therefore available which may be utilized
for other requirements. In cold climates, this heat is often used to maintain
the battery storage system at desired temperature levels.
Architectural Integration
Motivation
The last two decades have brought significant
changes to the design profession. In the wake of traumatic escalations in
energy prices, shortages, embargoes and war along with heightened concerns over
pollution, environmental degradation and resource depletion, awareness of the
environmental impact of our work as design professionals has dramatically
increased. In the process, the shortcomings of yesterday's buildings have also become
increasingly clear: inefficient electrical and climate conditioning systems
squander great amounts of energy. Combustion of fossil fuels on-site and at
power plants add greenhouse gases, acid rain and other pollutants to the
environment. Inside, many building materials, furnishings and finishes give off
toxic by-products contributing to indoor air pollution. Poorly designed
lighting and ventilation systems can induce headaches and fatigue.
Architects with vision have come to understand
it is no longer the goal of good design to simply create a building that is
aesthetically pleasing - buildings of the future must be environmentally
responsive as well.
For the
developed countries to continue to enjoy the comforts of the late twentieth
century and for the developing world to ever hope to attain them,
sustainability must become the cornerstone of our design philosophy.
Rather than merely using less non-renewable
fuels and creating less pollution, we must come to design sustainable buildings
that rely on renewable resources to produce some or all of their own energy and
create no pollution. One of the most promising renewable energy technologies is
photovoltaic’s. Photovoltaic’s (PV) is a truly elegant means of producing
electricity on site, directly from the sun, without concern for energy supply
or environmental harm.
These solid-state devices simply make
electricity out of sunlight, silently with no maintenance, no pollution and no
depletion of materials. Photovoltaic’s are also exceedingly versatile - the
same technology that can pump water, grind grain and provide communications and
village electrification in the developing world can produce electricity for the
buildings and distribution grids of the industrialized countries.
There is
a growing consensus that distributed photovoltaic systems which provide
electricity at the point of use will be the first to reach widespread
commercialization. Chief among these distributed applications are PV power
systems for individual buildings. Interest in the building integration of
photovoltaic’s, where the PV elements actually become an integral part of the
building, often serving as the exterior weathering skin, is growing world-wide.
PV specialists from some 15 countries are working within the International
Energy Agency's Task 16 on a 5-year effort to optimize these systems and
architects are now beginning to explore innovative ways of incorporating solar
electricity into their building designs.
Planning context of an energy
conscious design project:
The possibilitie of an active and
passive solar energy use in buildings is greatly influenced by the form,
design, construction and manufacturing process of the building envelope. A
promising possibility of active solar energy use is the production of electricity
with photovoltaic’s. This technology can
be adapted to existing buildings as well as to new buildings. It can be
integrated into the roof, into the facade or into different building
components, such as a photovoltaic roof tile. Such an integration makes sense
for various reasons:
·
The solar irradiation is a
distributed energy source; the energy demand is distributed as well.
·
The building envelopes supply
sufficient area for PV generators and therefore
·
Additional land use is
avoided as well as costs for mounting structures and energy transport.
Active and Passive Solar Design Principles
In order
to use PV together with other available techniques of active and passive solar
energy, it must be considered that some techniques fit well together and others
exclude each other. For example: As a kind of a "passive cooling
system", creepers are used for covering the south facade of building. The leaves evaporate water and
provide shade on the facade.
To avoid
such design faults it is necessary to compare and evaluate the different
techniques that are available for creating an energy conscious building. An
overall energy concept for a building should be made at the beginning of the
design process. Therefore, the architect and the other experts involved in the
design and planning process need to work together right from the beginning of
the design and planning process. All together they have to search right from
the beginning for the best design for a building project.
Photo voltaic and
Architecture:
Photovoltaic’s
and Architecture are a challenge for a new generation of buildings.
Installations fulfilling a number of technical approaches do not automatically
represent aesthetical solutions. Collaboration between engineers and architects
is essential to create outstanding overall designs. This again will support the
wide use of PV. These systems will acquire a new image, ceasing to be a toy or
a solar module reserved for a mountain chalet but becoming a modern building
unit, integrated into the design of roofs and facades. The architects, together
with the engineers involved are asked to integrate PV at least on four levels
during the planning and realization of a building:
·
Design of a building (shape,
size, orientation, colour)
·
Mechanical integration (multi
functionality of a PV element)
·
Electrical integration (grid
connection and/or direct use of the power)
·
Maintenance and operation
control of the PV system must be integrated into the usual building maintenance
and control.
Micro grid concept:
To realize the emerging potential of
distributed generation one must take a system approach which views generation
and associated loads as a subsystem or a “microgrid”. During disturbances, the
generation and corresponding loads can separate from the distribution system to
isolate the micro grid’s load from the disturbance (and thereby maintaining
service) without harming the transmission grid’s integrity.
The difficult task is to achieve this
functionality without extensive custom engineering and still have high system
reliability and generation placement flexibility. To achieve this we promote a
peer-to-peer and plug-and-play model for each component of the microgrid. The
peer-to-peer concept insures that there are no components, such as a master
controller or central storage unit that is critical for Fg. This implies that
the microgrid can continue operating with loss of any component or generator.
With one additional source (N+1) we can insure complete functionality with the
loss of any source.
That is it can be attached to the electrical
system at the location where it is needed. The traditional model is to cluster
generation at a single point that makes the electrical application simpler. The
plug-and-play model facilitates placing generators near the heat loads thereby
allowing more effective use of waste heat without complex heat distribution
systems such as steam and chilled water pipes. In fig 3.2
Fig 3.2operation
of the microgrid
Comments
Post a Comment