PV/GENSET HYBRID

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