New Age Tech Guru - Solar irradiance and its measurement

 

    Part of a series in renewal energy technologies brought by  M/s Paavi Solar

    

Friends, from the next blog onwards we are going to learn the designing part of Solar PV System. So in this blog, I want to focus on solar irradiance and its measurement as understanding this topic is extremely important for  proper design of the system. In one of the previous blogs, the irradiance curve was explained.  In radiometry, Irradiance is the power per unit area of incident electro-magnetic the radiation falling on a  surface and is measured in watts/m2. In photometry irradiance is known as the amount of light energy falling on a surface per second, weather directly or diffused or reflected, and is measured in watts/sq. mtrs. and denoted by E_e where subscript _e denote energy. Technically speaking it is the light (not heat ) of the Sun which is incident on a solar panel. In laboratory conditions, the irradiance of 1000 watt/sq.mtrs is chosen as test conditions. It is worthwhile to mention that irradiance varies seasonally as well as during the time of the day and hence to know the average irradiance, an irradiance map has been plotted taking into account historical data. Simultaneously placement of Solar panels also affects the amount of Solar radiation falling on the panel.

How much Solar Radiation is available in my area.

Solar irradiance maps based on historical data are available on a monthly average basis for the entire world on a location basis and are freely available on the internet. Also, design software carries an irradiance map as a tool and can generate irradiance data and angle of placement of solar PV panels for maximum radiation at the click of a button. We can easily differentiate between sunshine hours and usable irradiance based on these tools. While designing the system, this data is important for system sizing. Manually also one can measure solar radiation for different times and dates of a month for the location of the System.

 

How to measure Solar Radiation

Solar radiation is measured using an instrument called Pyranometer which has its name derived from the Greek word of “Pyr” meaning fire and “ano” meaning sky. It is a sensor-based instrument that measures solar radiation in Watt/m² and has a field of view of 180⁰. For the measurement of solar radiation, the directional factor is important and so the pyranometer needs to have a directional response to the incoming beam. Pyranometer measures only the light part of sun rays. For measuring the heat part we have pyrheliometers.                                                                               - G P BOSE                                  

 

New Age Tech Guru- Net Metering and Net Meter

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends, we are continuing to learn Rooftop Solar PV System components. As you are aware that there are three types of Rooftop Solar PV System i.e.

1.     Off-Grid Solar Rooftop PV system

2.     On-Grid Solar Rooftop PV System

3.     Hybrid Solar Rooftop PV System

Out of these, systems at S.N.2 and S.N.3 are primarily installed for lowering the electricity bills and we have already learned it in my previous blog.

Now today, we will learn about Net Metering and Net meter. Net metering is a billing mechanism whereby net credit of electricity added(Export) to the Grid by the Solar PV Generator is given. Suppose a Solar PV resident is generating more energy than required in the day time, extra energy is added into the Grid and this energy is metered in Net Meter and reflects as Exported and the Net Metering bill will have an Export Reading column. During the night or sometimes in daytime also, when a customer uses  Grid Electricity, then the incoming Grid electricity is also metered and reflects as import and Net Metering bill will have an Import Reading Column. On the basis of electricity consumed, a net credit is given to the customer if exported electricity units are more than the imported electricity units. Similarly, if the electricity consumed(imported) from the Grid is more than exported electricity, than the customer has to pay for the net electricity consumed. Hence Net Meter is a bi-directional metering device (approved and supplied by DISCOMs as per policies) for calculating the difference of outgoing and incoming electricity units. It may be added here that while providing Net Meter, DISCOM will test your installation for Grid Compatibility and Synchronization (already stated in one of my previous blogs). Meter reading is shown in BSES Delhi Net Metering bill is classified into three categories of Normal, Peak, and off-peak and then the difference is moderated for billing purposes.

-          G P BOSE

New Age Tech Guru - Cables and Connectors

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends we have come afar in knowing the components of the Rooftop Solar PV System. Today s topic is very small but important ie Solar connectors and cables.

Solar panels are connected with each other or to the solar panel combiner boxes through D.C. Cables and MC4 Connectors.

MC4 Connectors- These connectors are used for connecting solar panels or for terminating onto solar combiners boxes. MC in MC4 stands for multi-contact and 4 stands for 4 mm dia. For forming the panel strings by inserting adjacent panel connectors, MC4 connectors come in various models like One way, two-way (two in one out), three-way (three in one out), and four-way (four in one out).MC4 connectors can withstand a voltage of 1500V and are rain and dustproof  (weatherproof). These connectors have plug and socket designs (to minimize wrong connections and covered under a plastic shell. The male connector can be inserted into the female connector up to a notch where it gets attached under a spring pressure to prevent the arc from D.C. These MC4 connectors are an up-gradation over previous MC3 (3 MM dia.) connectors in design and assembly.

D.C. Cables- Solar D.C. cables are used to connect individual solar panels to form strings or used to terminate panels into combiner boxes. These single core pure copper cables are insulated (flame-retardant and halogen-free) and sheathed and can have UV protection/ozone protection as these are used outdoors. These cables can be used for fixed or flexible installations. These cables should have standard electrical/physical/mechanical/chemical/Fire safety specifications. Different D.C. cables are used for outdoors and indoors. For outdoor use D.C. must be treated with UV Stabilizing compound and preferably insulated and sheathed with Cross Linkable LSOH which has UV as well as Ozone protection properties, otherwise, indoor D.C. cables can have XLPE insulation.

A.C. Cables- Connection between inverter to Grid/ switching station and to loads are through A.C. cables and if to be laid underground must be armored and if exposed to Sunlight must be UV protected also

 

-         G P BOSE

 

New Age Tech Guru-- Solar Batteries

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends, our today's talk will be on Solar Batteries. Even though we can use Normal batteries for storage of generated D.C. Charge but due to rampant fluctuations in solar generation due to rain, clouds or shades life of Normal batteries will be severely reduced and hence cost of replacement of batteries at an early life will be an added disadvantage. So in place of Normal batteries, we should use Solar Batteries may be tall tubular batteries or Lithium-ion batteries.

1. Tall Tubular Batteries- These batteries are an up-gradation in Lead Acid Batteries and can charge even at a low current and can store more power. These batteries are more efficient with 1500 life cycles and have more shelf life of 5-8 years. These batteries are having C10 rating whereas Normal Batteries are C20 rating, which means that Solar Batteries can be connected with more load. In order to connect more load to the batteries of the C20 rating, two batteries can be connected in parallel. These batteries need to recouped with water once in 3-6 months. But these batteries are bulky and consume more space and need to installed on heavy structures. Moreover, these batteries are a bit costly.

2.    Lithium-ion Batteries- Lithium-ion phosphate batteries are the best Lithium-ion batteries. These batteries have double the shelf life of 12-15 hrs., Safe and not burnable along with better thermal stability. These batteries have very high life cycles of 5000 or more and have high charge and discharge capabilities.But these batteries are costly.

 

Hence we can make a wise decision based on our requirement of backup.

 

                                                                                                            -G P BOSE

New Age Tech Guru- Solar Inverters

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends I feel sorry that yesterday I could upload any blog due to some personal engagement. We have covered some of the components of the rooftop Solar PV System. Today we are going to learn about Solar Inverter.

A Solar Inverter is a Balance of System component of a Solar PV System and  converts DC current generated by a Solar Panel into Grid compatible(Pure Sinewave output with a specific voltage and frequency) Alternating Current for running the AC load or export to the Grid.  Solar Inverter may have special features like Maximum Power Point Tracking and Anti-Islanding feature for Grid Protection. Here feature of Maximum Power Point Tracking means the ability of the inverter to sense input V_max from the panel and to maximize power extraction. Anti -Islanding feature disables the inverter output, once the Grid supply is disrupted and helps in protection of Grid maintenance personnel, who maybe working on Grid.

 

Types of Solar Inverters

 

1.      Stand Alone Inverters- These inverters are used in Off- Grid Solar PV Systems where batteries have been provided for storage as a backup measure. In this System, Solar PV cells charge batteries through charge controllers and then batteries supply required D.C. Current for conversion into usable A.C. Additionally these inverters may have auxiliary charging circuits for charging the batteries from an auxiliary A.C. Source. It may be worthwhile to mention here that if the user has only D.C. Equipment then there is no need of any inverter and Batteries can be directly connected to load through D.C.D.B. Additionally these inverters may have auxiliary charging circuits for charging the batteries from an auxiliary A.C. Source.

2.      Grid-Tied Solar Inverter-   These inverters are the simplest form of Inverters without any charging function as On Grid Solar PV System does not have any battery backup system. These inverters are having Grid compatible features (Pure Sinewave output with specific voltage and frequency). These inverters as said above have an anti-islanding feature to shut down the inverter output in case of Grid shutdown.

3.      Hybrid Solar Inverter-These are intelligent Grid Tied Inverter with features like auxiliary battery charger circuit and priority setting like distribution of load on battery or Solar or Grid and have MPPT features, Grid compatibility, and anti-islanding features. These Hybrid Solar Inverters, if have additional features like output selector the mechanism, control algorithms are also called Power Conditioning unit.

 

New Development in inverter Technology-  Micro-Inverters

 

Microinverters are very small inverters directly placed behind the Solar PV Panel, encapsulated in an environmental hazard proof casing. These inverters directly convert the DC from the Solar Panels into 240 V AC for running the load. These microinverters have multiple ports for built on current for maximizing power output.

 

How to convert your normal inverter into Solar Inverter. In our houses, normal inverters with battery bank back up are installed where a battery charger circuit for charging the battery from input Grid Supply is provided. During the Grid, failures Charged battery D.C. is converted into A.C. to run the load, otherwise when Grid supply is available the inverter function is disabled and the load is run directly by Grid supply. But for the conversion of a Normal Inverter into Solar Inverter a charge controller device is inserted between the Solar PV Panels and inverter for charging the battery from Solar.

                                                                                                 -G P BOSE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

New Age Tech Guru --- Solar Junction Box and Solar Combiner Box (DCDB)

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends, today we will learn about a very small but one of the most important components of the Roof Top Solar PV System. Friends it may be noted that this blog is about Roof Top Solar PV System only.

These components are

    1.       Solar Panel Junction Box:-  These boxes are pre-installed on the back of a solar panel and collects the charge produced by the panel. These junction boxes have bi-pass diodes installed to protect the reverse current from Charge controllers flowing towards panels. These polycarbonate boxes are weatherproof and prevent the terminals from dust, moisture, etc. Nowadays high power producing panel should have sturdy junction boxes to cope up with the higher power. Some panels use switches instead of diodes as diodes are prone to producing some heat but are too expensive. Nowadays modern technology are evolving which provides features like optimizing, monitoring, and quick shutdown.

    2.      Solar Combiner with protection Box (Also called DC Distribution Box) – When multiple Solar Panels are connected in series for building up the required voltage and current in accordance with designing the systems for a matching inverter and charge controller, this is called an array(string). Multiple arrays(strings) are then combined in parallel to multiply the array(string) output through overcurrent fuses and Surge Protective Device (SPD) for each array and terminated on a combined bus. These Combiner boxes have circuit breakers of required capacity at input and output to segregate the arrays. These polycarbonate boxes are typically non- metallic and are dust and moisture proofing features. These combiner boxes are insulated as per mandate from MNRE and tested up to a voltage of 1000V.

-           G P BOSE

New Age Tech Guru- Charge controllers

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends, we have learned about solar PV Cells and Panels and its specification in detail. The second component of the Solar PV System where storage in the form of batteries has been provided in Off-Grid or Hybrid Solar PV System is Solar Charge Controller. Basic function of any charge controller is to limit the current(charge) supplied to the batteries for charging as the current  supplied by Solar PV Panel is prone to fluctuations due to cloud/rain or shadows and to protect the batteries from overcharging, solar charge controllers are to be provided. Hence charge controllers act as regulator of current at a particular voltage and to safely charge a solar deep cycle battery.

Charge controllers have additional feature like

1.      LVD (Low Voltage Disconnect) for disconnecting a load if it detects a low battery voltage and thus prevent over-discharging of batteries.

2.      Reverse Current Blocking for blocking the drainage of battery charge towards solar panel during night hours and thus discharge of the batteries.

3.      Additionally a charge the controller may have an Electric overload prevention feature and battery status display.

 

Types of Solar Charge Controller

1.     1.  PWM (Pulse Width Modulation) Charge Controller- A PWM Charge the controller is a standard charge controller and works on the principle of two-stage charging, in the first stage maintaining a safe maximum voltage for charging the batteries and when batteries are fully charged, then lowering the charging voltage for trickle charging. This two-stage charging is important for maintaining a battery voltage during the days of low load conditions. PWM charge controllers are best suited for small Solar Power Systems as it is difficult to maintain a matching voltage from Solar Panels and Batteries in a big Solar PV System. These charge controllers are cheaper. For PWM Charge controllers Battery and Panel voltages should match and hence these are least efficient.

 

2.     2.  MPPT (Maximum Power Point Tracking) Charge Controller- Unlike the PWM charge controller, these are complex systems and are costlier. These charge controllers can pair nonmatching voltages of Panels and Batteries and hence panel voltage can be way higher than the battery voltage. These charge controllers can track the maximum power supplied by panels and matches(decreases) the Voltage to the level of Batteries and hence increasing the current, thus maintaining the power output and hence are very efficient. There is a very low loss of electric energy during battery charging.

 

Charge controllers are connected to solar panels and batteries through DCDB.

                                                                                                                                     -G P BOSE

New Age Tech Guru- Understanding irradiance curve of a Solar PV Panel

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends, going further in the specification sheet of Solar Panel, today we are going to learn about the irradiance curve (also known as the I-V curve). Before understanding the irradiance curve, we should know what is irradiance. In radiometry, Irradiance is the power per unit area of incident electro-magnetic the radiation falling on a  surface and is measured in watts/m2. In photometry irradiance is known as the amount of light energy falling on a surface per second, weather directly or diffused on reflected and is measured in watts/sq. mtrs. and denoted by E_e where subscript _e denote energy. Technically speaking it is the light (not heat ) of the Sun which is incident on a solar panel. In laboratory conditions irradiance of 1000 watt/sq.mtrs is chosen as test conditions.

The relevance of irradiance curve --

The irradiance curve depicts the generated power by a solar PV panel under different irradiance conditions and temperatures. In this curve plotting of generated Current and Voltage of a Solar PV Panel is done at different irradiance levels. I_sc (Short circuit current ) and I_mpp are plotted on the X-axis and V_mpp and Voc is plotted on Y-axis where Voc and I_sc are the maximum voltage and current generated by a panel on no-load conditions. Hence P_{max (} Isc x  V_oc) watts is the maximum power generated by a panel at a laboratory condition of 1000 watts/sq. mtrs irradiance. When The solar PV system is connected with load (ie MPPT charge controller or solar inverter ) then the maximum current generated will be I_mpp at a The voltage of V_mpp and the power generated will be I_mpp x V_oc watts. It may be emphasized here that irradiance also depends upon the relative angle of the Sun with respect to the plane of the Solar Panel and power generated is maximum at 25 ^o C and decreases with the increase in temperature of the module of the due to the surrounding temperature. The module generated voltage is directly proportional to the temp. of the module and temp. coefficient of the module is -0.40%/^oC   (  eg. a decrease of 12% if the module temp. increases to 30^o C ie an increase of 5^o C  over ideal temp. of 25^o C). Moreover, every place on earth has different irradiance.

 

So friends by studying this curve we come to know about the power generating capacity of a Power Panel at the different conditions of temperature and irradiance and help in the designing of the PV System.                                                                             - G P BOSE

New Age Tech Guru--- Solar Panel Specifications

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends before going into details of Roof Top Solar PV System designing and installation, we need to understand the specification sheets of Solar Panels and its importance. Moreover, those who are thinking of purchasing Solar Panels need to understand various specifications of Solar Panels to make the right choice. Behind every Solar Panel Serial Number, date of manufacture, and manufacturer details are provided to ascertain the warranty, etc. because most of the manufacturers are giving 25 years warranty. Apart from the above details following the electrical characteristics of the panel is also provided.

Power Max (Pmax) – Maximum power output of the solar panel in Watts at ideal test conditions of 1000 irradiance (Light Intensity of 1000 watts per sq. mtrs.) at cell temp. of 25⁰C(77⁰F).

Open Circuit Voltage( Voc) – This parameter gives us voltage across the solar panel when no load is connected and can be measured when one put a multimeter (voltmeter ) across the +ve and -ve terminal of the solar panel. This is the maximum voltage a the solar panel can produce under ideal test conditions and is a key specification for designing a Solar PV System.

Short Circuit Current (Isc) – This parameter gives us maximum current produced by a Solar Panel under ideal test conditions when the +ve and -ve leads are short-circuited. This current can be measured using an ammeter in series or a clip-on multimeter. This specification is used for the selection of components of a Solar PV system.

Maximum PowerPoint Voltage (Vmpp) – This parameter gives us the actual maximum voltage produced by a Solar The panel under ideal test conditions when the Panel is connected to an MPPT Charge controller or inverter and power output are maximum.

Maximum PowerPoint Current (Impp) – This parameter gives us the actual maximum current produced by a Solar The panel under ideal test conditions when the Panel is connected to MPPT Charge controller or inverter and power output is maximum.

Module Efficiency --   This is the maximum efficiency of the Solar Panel under ideal test conditions and required during the calculation of Solar PV System designing.

Nominal Voltage – Some Solar Manufacturers provide this additional specification and this is not the actual voltage but a category like a nominal 12V solar panel will have a Voc of about 22V and a Vmpp of about 17V.  It is used to charge a 12V battery (which is actually around 14V)

Warranty – Manufacturers warranty, usually 25 years (conditional)

Panel Length/width, thickness etc.

Some manufacturers also provide above specifications under different irradiance levels.

Friends we will study irradiance curve in next blog.                          -G P BOSE

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

 

Friends, yesterday our topic was types of Solar Panels. Today we will learn about new developments in conventional solar panel technology for increasing its efficiency.

Details of new Types of solar panels is as under-

1.      Bi-facial Solar Panel --- Bi-facial solar panels are transparent from their back. These produce some electricity from the rear sides of solar modules out of the reflected solar radiation. Most Bi-facial solar panels are made of monocrystalline modules but can be made of the polycrystalline modules also. These panels have approx. 30% more efficiency. These panels can be frameless also.

2.      Mono Perc Solar Panels ---This new technology for increasing efficiency of solar panels is called PERC (Passivated Emitter Rear Cell) This technology differs from conventional solar cell architecture In conventional technology of manufacturing solar cell rear side of silicon wafer carries a silver film for collecting the generated electrons. But in PERC technology a passivation layer is inserted between the Silicon wafer and back film whereby the heat of the solar cell is dissipated. Actually, Solar radiation when falls on solar panel carries heat also along with light photons and this heat decreases the efficiency of the solar panels with an increase in temperature. To overcome this difficult a passivation layer is provided on the backside of the solar module wafer where heat gets dissipated and certain efficiency gain is achieved through reduced heat absorption and increased generation from reflected radiation.

3.      Half-Cell Solar Panels --- These solar panels have solar cells cut in half to increase the performance and durability of the modules. Traditional Half cut solar panels will have double the number of cells. So when the solar cells are halved, their current is also halved, so resistive losses are lowered and the cells can produce a little more power. Moreover, mechanical stress is also lowered. and higher efficiency is achieved.

 

                            -          G P BOSE

New Age Tech Guru- Different types of Solar Panels (common)

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

Friends, we have learned about the types of rooftop Solar PV Systems based on different types of usage. We have also seen different components of each PV system. Today onwards we will learn about component-level details and we begin by explaining different types of Solar Panels.

As we know now that Solar Panels are made of a number of Solar Cells in series and parallel connections to achieve requisite voltage and current rating. When the solar cells are arranged in series, the current of the entire panel remains constant and equal to as produced by a single cell but the voltage of each cell is added up. In the same fashion if cells are arranged in parallel connection then the voltage of the panel remains constant and equal to across a single cell but the current produced by each cell is added up. All these cells are further encapsulated in a toughened glass casing for transparency and strength.

Types of Solar Panels based on chemical structure(Composition of Silicon)

1.      Monocrystalline Solar Panels:- These panels are made of Solar Cells cut into wafers from ingots containing pure silicon. These cells are darker in color and have a little higher efficiency of 18-22 %. These are somewhat costlier. Solar Panels made of Monocrystalline Solar Cells can be identified easily as the corners of each cell are cut. These solar panels are used in big projects or installations where space is a constraint.

 

2.      Polycrystalline Solar Panels:- These panels are made of Solar Cells cut into wafers from ingots containing silicon fragments of different structures. These cells are in lighter blue color and different fragments of silicon can be easily identified in its grainy appearance. Its efficiency is somewhat lower at 14-16 % and is cheap. These solar panels can be easily identified as the cells are of a completely rectangular shape. These solar panels are generally used.

 

3.      Thin Film Solar Panels:- These portable, lightweight and flexible solar panels are printed over a PVC film and are made of amorphous silicon (a-Si),  cadmium telluride (CdTe), and copper indium gallium selenide (CIS/CIGS). These Solar films have varying degrees of efficiency from 12- 20 % efficiency, cheap in construction but very less life. These are ideal for small applications and where the solar panel(film) needs to be rolled over like over the yachts, cars, or devices.

 

Friends, in the next blog, we will study new developments in Solar PV Panels and also explain the different specifications of Solar PV Modules.             -G P BOSE

 

 

 

New Age Tech Guru- Hybrid Solar PV System

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

Friends, in the previous blog we learned about the On-Grid Solar PV System whereby main motive of the installation was to reduce the Grid electricity bill. Even though this system was cheapest yet it has some inherent drawbacks like

1.      Due to the absence of Battery Bank (storage) off solar hour loads are fully met with The grid in On-Grid Solar PV System.

2.      Suppose Grid supply is not available and technicians are maintaining the Grid then Solar Supply is also cut off to safeguard the lives of technicians.

 To overcome these inherent problems, Hybrid Solar PV System was introduced with an additional battery bank and an intelligent Solar Power Conditioning System. Battery bank stores electricity during the solar day and during grid cut off time, this battery bank supplies the power to the house. Otherwise, Grid becomes the main source of power during off solar hours. The Solar Power Conditioning unit can be adjusted to intelligently switching the power either to Solar or battery bank or to the Grid.

In this the system also, DISCOMs provide Net Meter under the policy of Grid-Connected Solar Roof Top System. Different states have different policies and subsidy guidelines but states follow the directive regulations of MNRE. As this system is connected to the Grid and hence proper installation testing is done by DISCOMs to ensure synchronization and balancing of the systems i.e. feeding the Grid with stable A.C. energy at proper voltage and frequency.

Friends as stated earlier, individual components of the systems will be discussed in detail in coming blogs.                                                                                                                -G P BOSE

 

New Age Tech Guru--- On-Grid Solar PV System

 

Part of a series in renewal energy technologies brought by  M/s Paavi Solar

Friends, let we continue our topic of types of Solar PV Systems. Yesterday, we have learned about Off-Grid Solar PV System. The main objective of the Off-Grid Solar PV was energy security where either Grid connectivity was not available or where one does not want to use Grid Electricity.

Today, we want to talk about a system where Grid Connectivity is available but the objective of the system is to save on energy bills.

First of all, we will see how the On-Grid Solar PV system work and its objectives. As stated earlier the main aim of On-Grid Solar PV Systems is to provide electricity to our units and save on the electricity bills. In this system, some (or total) the load is fed by Solar PV Panels when the solar radiation is available. Otherwise during off solar hours ie during the night or during cloudy/rainy days, the load is run by connected Grid supply. This system does not have any storage (Battery Bank) and hence the system is very cheap as the cost of the battery bank is minimized. One of the main advantages of this system is that one can design the system to partially or wholly supply the loads either from Solar Panels or through Grid or a combination of Solar and Grid together.

 

Main working Principles of On-Grid Solar PV System.

Solar Photovoltaic panels installed on the rooftop (either on G.I. Structures or directly placed on slanting roofs) in arrays of 12V/24V or 48V gather sunlight during the daytime and converts sunlight into D.C. These arrays are connected to  D.C. Distribution Boards. These Distribution boards act as Collector and also contains fuses and Surge Protection Devices (SPDs) along with circuit breakers. The generated D.C. is fed to Solar Inverters containing MMPT or PWM charge controllers and converts incoming D.C. into usable A.C. (single-phase 240V or three Phase 440 V). This A.C. runs loads of the household. After fully meeting the consumption of the household in the day time, if any A.C. is left unused, this idle A.C. energy is fed to the grid through bi-directional Net Meter installed by DISCOMs. Simultaneously if the Power received from Solar Panels in the day time is not sufficient to meet the full load of the household then balance power is received from the Grid. Bi-directional Net Meter installed by DISCOMs calculate the Net Energy consumed or fed(sold) to Grid and accordingly adjusts the future bills. Hence this system is installed for lowering the energy bill.   

There is no battery backup in the system and hence during the night time or off-solar hours due to clouds/rain of shades, the entire load is met with Grid and metered accordingly. This system is cheapest but has certain limitations which are given hereunder.

1.      Due to the absence of Battery Bank (storage) off solar hour loads are fully met with Grid.

2.      Suppose Grid supply is not available and technicians are maintaining the Grid then Solar Supply is also cut off to safeguard the lives of technicians.

 

Main components of this system are given in the flow diagram given here.  These days Hybrid Solar Inverters are also called as Solar Power Conditioning Unit which can be programmed to supply load either on Solar or on Grid or a combination of both.

DISCOMs provide Net Meter under the policy of Grid-Connected Solar Roof Top System. Different states have different policies and subsidy guidelines but states follow the directive regulations of MNRE. As this system is connected to the Grid and hence proper installation testing is done by DISCOMs to ensure synchronization and balancing of the systems ie feeding the Grid with stable A.C. energy at proper voltage and frequency.

Friends as stated earlier, individual components of the systems will be discussed in detail in coming blogs.                                                                                                                                        -G P BOSE