The basic operation of a grid connected system for small or large power plants is similar. In this system, the Solar Photo Voltaic system in connected with the help of inverter to the local utility grid. This system is beneficial when the power generated in day time is utilized by the owner and any surplus is supplied to the utility local grid without any noise or distortion. During the evening, when solar electricity is not generated, electricity is drawn from the local grid avoiding the need of costly battery banks. You pay only for the electricity consumed from utility grid provider. Whereas some utility grid providers pay for the surplus power feed into the local grid at higher rates.

The basic operation of a grid connected system for small or large power plants is similar. In this system, the Solar Photo Voltaic system in connected with the help of inverter to the local utility grid. This system is beneficial when the power generated in day time is utilized by the owner and any surplus is supplied to the utility local grid without any noise or distortion. During the evening, when solar electricity is not generated, electricity is drawn from the local grid avoiding the need of costly battery banks. You pay only for the electricity consumed from utility grid provider. Whereas some utility grid providers pay for the surplus power feed into the local grid at higher rates.

System components:

The solar PV Power Plant comprises of the following major components and services. The components, assemblies, sub-assemblies are selected with stringent criterion like long life, highest reliability, minimum maintenance etc. All the systems and sub systems are supported by comprehensive application notes & documentation.

1. Solar PV modules
2. Module mounting structure
3. Inverters with string monitors etc.
4. DC/AC cable junction & combiner boxes & cable trenches
5. Control panels
6. Plant monitoring systems

Solar PV modules:

We use two major types Solar PV module i.e 1. Crystalline Silicon (c-Si) and 2. Thin film modules.

Crystalline Silicon Solar PV module: Crystalline Silicon (c- Si) is a term used for the crystalline forms of silicon encompassing multi- crystalline silicon (multi-Si/ Poly-Si) and mono- crystalline silicon (mono-Si), the two dominant semiconducting materials used in photovoltaic technology for the production of solar cells, that are assembled into a solar panel and part of a photovoltaic system to generate solar power from sunlight.

Thin Film Module: A Thin Film solar cell (TFSC), also called a Thin Film photovoltaic cell (TFPC), is a second-generation solar cell that is made by depositing one or more thin layers, or thin film of photovoltaic material on a substrate, such as glass, plastic or metal. Thin film solar cells are commercially used in several technologies, including cadmium telluride (CdTe), Copper Indium Gallium- di-selenide (CIGS), and amorphous and other thin film silicon (a-Si, TF-Si) etc.

Film thickness varies from a few nano-meters (nm) to tens of micro-meters much thinner than thin film’s rival technology, the conventional, first generation crystalline silicon solar cell (c-Si), that uses silicon wafers of up to 200 micro meters. This allows thin film cells to be flexible, lower in weight, and have less drag. It is used in building integrated photovoltaic, and as semi- transparent photovoltaic glazing material that can be laminated onto windows. Other commercial applications use rigid thin film solar panels (sandwiched between two panes of glass) in some of the worlds largest photovoltaic power stations.

Inverter:

A Solar Inverter converts the variable direct current (DC) output of a Solar photovoltaic (PV) panel into a utility frequency alternating current (AC) that can delivered to the load or to be fed into a commercial electrical grid. It is a critical BOS component in a photovoltaic system, allowing the use of ordinary AC powered equipment. Solar inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti- islanding protection.

Grid-connected Inverter delivers the solar power to the AC power grid. The PV array is configured so that it operates within a specific range of DC voltages to suit grid connected inverter’s specifications. The inverter will convert the solar DC power to an AC sinewave that matches the AC supply in voltage and frequency to which it is connected. These inverters cannot independently produce a grid equivalent AC sine wave, the inverter must reference the grid to be able to operate. The grid’s voltage and frequency must fall within the predetermined range required to be able to output any power to the grid. They are designed to shut down automatically upon loss of utility supply. They do not provide backup power during utility outages.

Grid connected Inverter- String & Central: String inverters are the most commonly used in small grid connected PV systems. String inverters for small grid application will have one Maximum Power Point Tracker (MPPT) and the DC input voltages could vary from ELV right up to 1000 VDC. The MPPT uses electronics so that solar array operates to produce the maximum amount of power possible. It can vary the electrical operating point of the modules to ensure optimum performance, which means maximum output.

A multi string inverter is only one inverter with number of MPPT inputs. Therefore, solar array can be divided into multiple strings. Hence even for Sub- megawatt scale Solar system choice of string inverter provides very good flexibility both technically and commercially. It not only allows ease of installation but also user-friendly operation.

Central Inverters are used for large grid connected solar systems. They provide high total performance based on high efficiency, low auxiliary power consumption, together with verified reliability using proven concepts for maximum uptime. These inverters are available from 100 kW up to 1000 kW and are optimized for multi-megawatt PV power plants.

Solar Micro- Inverter: Solar Micro or Modular inverter is designed to operate with a single PV module. The micro inverter converts direct current output from each panel in to alternating current. Its design allows parallel connection of multiple, independent units in a modular way. The advantages of micro inverter reside mostly on single panel power optimization, independent operation of each panel, plug and play installation, improved installation and fire safety, minimized cost with system design and stock minimization.

Module mounting structure:

Module mounting structures are used to mount the PV modules in particular orientation to collect maximum sunlight. The two main types of PV mounting systems in use are roof mounted and ground mounted. The design of module mounting structure should consider local site conditions such wind speed, rain fall & temperature etc. it is important that structure galvanization should be sufficient to protect it from corrosion.

DC & AC Cables:

DC cables conduct solar electricity from PV array the string junction box and from string junction box to the inverter. They are to carry the required current along with necessary safety margins and also limit the voltage drop (resistance losses). As a general practice, the DC wiring should not cause more than 2% power loss in the system. The DC cables used in solar strings use specialized connectors. These connectors are characterized by their electrical properties, mechanical properties and weather resistance. As these connectors are usually installed outdoors, they should be IP67 rated UV and fire resistant with typical operating temperature.

AC cables carry the AC power of the PV system from the Inverter to the metering point. It is to be selected critically to ensure safety as well as minimize power loss. As a general practice, AC wiring loss of PV system should not exceed 2%.

String combiner box:

The string combiner box also called as Array Junction box (AJB) or PV Generator junction box, combines multiple DC strings in parallel. SJBs should be weather resistant as they are typically installed outdoors. SJBs commonly houses the input overcurrent protection fuse assemblies for several strings, as well as the combined bus of these inputs into a single main output. Combiner box may also house several other components for the site, such as DC disconnect, surge protective devices and in some cases, string monitoring hardware.

 AC Distribution Box (ACDB):

ACDB should be placed close to the inverter immediately after the inverter. The primary function of the ACDB is to isolate the PV system (including PV modules and inverter) from the grid. ACDB should also contain Miniature Circuit Breakers to disconnect incoming and outgoing AC connections, Residual Current Circuit Breakers (RCCB) and SPD.

 Grounding/ Earth pit & Lightening arrestor:

The main reason for doing earthing in electrical network is for the safety. When all metallic parts in electrical equipments are grounded then if the insulation inside the equipment fails there are no dangerous voltages present in the equipment case. If the live wire touches the grounded case then the circuit is effectively shorted and fuse will immediately blow. When the fuse is blown the dangerous voltages are away.

A lightening arrestor is a device used on electrical power systems and telecommunication systems to protect the insulation and conductors of the system from damaging effects of lightening. The typical lightening arrestor has a high voltage terminal and a ground terminal.

 Energy monitoring system:

The solar PV plant monitoring system monitors energy generated per day, week, month & year. Each inverter will be connected via communication cable and string monitors which in turn is finally connected with the Web Box and the data of each inverter shall be monitored via RS485 LAN/ web interface. The major components offered by us in data monitoring system is, 

• Web box- for communication
• irradiance sensor- for monitoring solar yield
• Ambient temperature sensor- for monitoring the ambient temperature
• Module temperature sensor- for monitoring the module temperature

 Power monitoring:

A complete data logging system shall be furnished with the solar plant. The system will monitor the plant on line and display the following-

• KWp and KWH produced
• The cell temperature of module
• daily energy produced in KWH. In addition to above the total energy produced by the plant daily, cumulative total of the energy produced monthly and yearly shall be displayed.

 The system shall display all the above parameters in a PC provided in the control room at the plant site, and shall have provision to transmit the data via internet to a remote monitoring system. The system shall be capable of providing performance data, for each inverter.

 Solar Photo Voltaic Grid connected system can be used for following applications.

•  Solar Rooftop
•  Ground mounted Power Plants for Corporate offices, Industrial use, Institutional, Residential, domestic etc. use.