Prof. Sukumar Mishra Indian Institute of Technology Delhi ROOF TOP PV Prof. Sukumar Mishra Indian Institute of Technology Delhi

Non-conventional Energy Sources Need Environmental Concerns – Reduces CO2 emissions Reduces dependence on fossil fules Solution for meeting fast growing power requirements Types Solar Energy Wind Energy Geothermal Energy Biomass 11/17/2018 12:23:16 PM

Non-Conventional Energy Scenario in India 11/17/2018 12:23:16 PM

Photovoltaic Power Generation Electricity is generated from the solar energy using photovoltaic (PV) cells. PV cell is a silicon PN junction device 11/17/2018 12:23:16 PM

Operation of PV cell Typically, a PV cell generates a voltage around 0.5 to 0.8 volts depending on the semiconductor and the built-up technology. This voltage is low enough for any use. Therefore tens of PV cells (involving 36 to 72 cells) are connected in series to form a PV module. These modules can be interconnected in series and/or parallel to form a PV panel. 11/17/2018 12:23:16 PM

PV cell characteristics 11/17/2018 12:23:16 PM

PV Array Formation 11/17/2018 12:23:16 PM

PV characteristics These characteristics depend heavily on insolation and temperature. Series and parallel resistance also varies the characteristics. 11/17/2018 12:23:16 PM

Partial Shading scenario Shading may occur due to clouds, environmental obstructions such as trees and buildings, self-shading between panels in parallel rows, dirt and dust, bird droppings etc. These shading effects may be static, i.e. slow due to sun-light angle during the day or may be very dynamic (e.g. moving clouds). 11/17/2018 12:23:16 PM

Series-Parallel Connection of PV Cells 11/17/2018 12:23:16 PM

Effect of partial shading Leads to change in characteristics 11/17/2018 12:23:16 PM

Effect of partial shading (Cont.) Leads to heating in the cell due to losses in the current flowing through the shunt resistance. This leads to hotspot at the nth cell and fire hazard in the PV park 11/17/2018 12:23:16 PM

Use of bypass diode A diode is put in parallel to the cell to bypass the sheded cell and avoid hotspot. 11/17/2018 12:23:16 PM

Use of blocking diode Blocking diode blocks any circulating current flow to the shaded cell in parallel connected PV strings. 11/17/2018 12:23:16 PM

Mismatch in PV characteristics due to manufacturing The electrical characteristics of PV panels have some manufacturing variance (e.g. 5%) at manufacturing and it gets worse with temperature changes and over time (and PV systems are usually installed for many years). Since the string has the same current for all panels, traditional inverters try to find the optimal current that will fit most of the panels. However, there will be some energy penalty that may reach 3-5% overall and even more over time. 11/17/2018 12:23:16 PM

Uniform Shading If all sub-strings have the same illumination/shading, then the total current/power will be degraded according to the shading ratio. But if the substrings have different shading, then like partial shading in a serial string, the total power performance will be degraded by more than the shading ratio 11/17/2018 12:23:16 PM

Concern for whom On large solar plants, this is not really a problem as the panels are cleaned regularly and they have been constructed and designed to avoid any shading. Solar fields are also usually away from tall building and other obstructions. But on a residential or commercial roof top, you can have a lot of ways there can be shade 11/17/2018 12:23:16 PM

Benefit of Micro-inverter compared to string inverter Solution Micro inverters instead of string inverters Benefit of Micro-inverter compared to string inverter The string voltage is typically about 700-1600 V, which means it is enough to seriously electrocute someone. If you have a fire in your building, you could shut off the AC, but these things [solar panels] are sitting in the sun – if it’s daylight – and they are at open circuit voltage. If you get a fireman spraying water on that roof and he is on a fire truck or a ladder, he would get electrocuted.” If each panel has an inverter, however, this would not happen as the voltage would be too low to cause any harm. 11/17/2018 12:23:16 PM

MPPT tracking Techniques have been developed to extract maximum power from the PV system. Perturb and Observe Incremental Conductance Fractional open circuit voltage Fractional short circuit current Fuzzy logic control Neural Network 11/17/2018 12:23:16 PM

Pros and Cons of Solar Electricity 11/17/2018 12:23:16 PM

Growth of PV systems in India Jawaharlal Nehru National Solar Mission Target of deploying 20000 MW grid connected solar power by 2022. Grid connected solar power in India (till 31/03/2014) – 2647 MW Off grid solar power (till 31/03/2014) – 174.4 MW 11/17/2018 12:23:16 PM

Grid Connected PV System 11/17/2018 12:23:16 PM

THANK YOU 11/17/2018 12:23:16 PM