dsolAsol: TECNOLOGÍA SOLAR

A grid-connected photovoltaic system (GCPS) converts the solar energy into electricity (direct current), which is conducted to the national grid (alternating current) so that any connected user can be supplied.

The rapid expansion of these types of applications has required to develop a specific type of engineering. On one hand, this has allowed to optimize their design and operation. On the other hand, it has allowed to learn more about their impact on the whole electrical system, always taking good care of the systems integration and respecting the architectural and environmental surroundings.

The devices can be mounted either on the Ground or on the Roof of fixed and mobile structures (solar trackers).

Regarding their size, the installations are usually named with the following nomenclature according to the inverter's power:

• Small: up to 20 kW
• Medium: from 20 kW to 200 kW
• Large: over 200 kW
• Photovoltaic Power Plant: installations with an output of over 1 MW

The architectural integration of the GRID CONNECTIONS in buildings, industrials premises or other structures turn the photovoltaic generators into construction elements, such as roofs, façades or devices for solar protection, having a double function:

• To offer a new dimension to the architecture.
• To help meet the power demand by producing energy in a clean, reliable and easy-to-maintain way

ELEMENTS

A grid-connected Photovoltaic Installation consists of the following parts:

1. Modules: They consist of sets of photovoltaic cells (polysilicon: semiconductor and photosensitive material that produces electricity when it radiates), usually welded under a glass layer. It produces electricity without causing emissions, noises and any sort of waste. It can be adapted to different sizes and it has a lifespan of 40 years.
   Within the industry, there are 3 different types of technology that are being fully developed for commercial uses:
   
   
   1. Monocrystalline silicon: The monocrystalline cells are made by cutting wafers of a single pure fused silica. They are the most efficient (between 15% and 20%) but the most expensive too.
   2. Polycrystalline silicon: The polycrystalline cells consist of wafers made up of many silicon glasses. They are less efficient (between 10% and 15%) but cheaper too.
   3. Thin film: It is made up of extremely thin photosensitive materials with a very low cost. These cells are the most efficient in the use of raw material and energy during the production process. Also, they require less workforce and are easier to integrate in the architectural environment.
      
      
   Nevertheless, it is important to prevent degradation problems in the long or medium-term. They are less efficient (between 7% and 10%) thereby, they need to use double the space than the polysilicon to produce the same electricity. Four technologies stand out over the others: aSi, CIGS, CdTe and CIS.
   
   The lack of polysilicon is boosting the development of other new technologies still in a R&D stage such as Multi-junction Devices, Multi-band Cells, Spectrum or Nanotechnology, among others.
   
   
   
2. BOS (Balance Of System): It is the rest of elements making up an installation:
• Inverters
• Cables
• Junction boxes and protections
• The rest of the components that may be required.
3. Support structures: Aluminium or Iron structures, depending on the location, are used in Fixed facilities and, especially, mobile mechanical structures of 1 or 2 axis called "solar trackers" (a wide variety in the market; they increase production between 7% and 12% over fixed facilities).

LIFESPAN

The LIFESPAN of a photovoltaic installation depends on the lifespan of its components:

• Modules: over 40 years.
• Electronic parts (inverters and regulators): between 20 and 30 years.
• Auxiliary elements (wiring, electrical lines, junction boxes, etc.): over 30 years.
• Batteries (off-grid systems): over 10 years for lead-acid batteries and over 20 years for alkaline/nickel/cadmium batteries.

 

LOSS FACTORS:

Production LOSSES in installations have different causes:

• Tolerance: in the values of rated power ranging from +/- 5% to +/- 3%
• Degradation: The Silicon modules that comply with the IEC 61215 regulation, as well as the Thin Film modules complying with the ISO 9001 quality system, should not suffer appreciable degradation, which would be rated between 2% and 5% during their lifespan (40 years) with a minimum loss of power.
• Mismatch: The series connection of a number of modules which do not have identical power resulting that the output of the entire PV series is determined by the solar module with the lowest output.
• Dispersion of characteristics: Variation of the specific lighting conditions, different to those present in the test (standard spectrum AM 1.5). This will cause small angular and spectral losses.
• Dust and dirtiness: The output of the system will decrease if there are dust or dirt in its surface. These losses do not usually go over 3%.
• Temperature: There is a power loss when the module is run with cells in temperatures over those 25º C (77º F) set in the measurement tests in the factory. The loss is estimated to rate 0,5% of power for each degree its temperature increases, in the case of fused silica modules.
• Shading: Losses will be zero since the installation has been designed taking into account this factor.
• MPPT: Losses from the inverter and the Maximum Power Point Tracker (MPPT) range from 4% to 10%.
• Drops in the wiring voltage: They are usually small both in the direct and the alternating current since they have been taken into account when the wiring cross-section was selected and in the determination of the distances.
• Out of order for maintenance: The inappropriate maintenance of an installation may cause very important losses and force to put the system out of order or make it work incorrectly.

Thus, we can say that the optimal loss of a grid-connected photovoltaic installation, under normal conditions, may be 10 percent.