Advisor(s)

Bradley M. Lehman

Contributor(s)

Bahram Shafai, Sagar V. Kamarthi

Date of Award

2008

Date Accepted

7-2008

Degree Grantor

Northeastern University

Degree Level

Ph.D.

Degree Name

Doctor of Philosophy

Department or Academic Unit

College of Engineering. Department of Electrical and Computer Engineering.

Keywords

Electrical engineering, Photovoltaic

Subject Categories

Solar cells--Design and construction

Disciplines

Engineering

Abstract

Mass production and use of electricity generated from solar energy has become very common recently because of the environmental threats arising from the production of electricity from fossil fuels and nuclear power. The obvious benefits of solar energy are clean energy production and infinite supply of daylight. The main disadvantage is the high cost. In these photovoltaic systems, semiconductor materials convert the solar light into electrical energy. Current versus voltage characteristics of the solar cells are non-linear, thus leading to technical control challenges. In the first order approximation, output power of a solar array is proportional to the irradiance of sunlight. However, in many applications, such as solar power plants, building integrated photovoltaic or solar tents, the solar photovoltaic arrays might be illuminated non-uniformly. The cause of non-uniform illumination may be the shadow of clouds, the trees, booms, neighbor's houses, or the shadow of one solar array on the other, etc. This further leads to nonlinearities in characteristics.

Because of the nature of the electrical characteristics of solar cells, the maximum power losses are not proportional to the shadow, but magnify nonlinearly. Further, shadows of solar PV array can cause other undesired effects:

• The power actually generated from the solar PV array is much less than designed. At some systems, the annual losses because of the shadow effects can be reached 10%. Thus, the probability for "loss of load" increases.

• The local hot spot in the shaded part of the solar PV array can damage the solar cells. The shaded solar cells may be work on the negative voltage region and become a resistive load and absorb power. Bypass diodes are sometimes connected parallel to solar cells to protect them from damage. However, in most cases, just one diode is connected in parallel to group of solar cells, and this hidden the potential power output of the array.

This proposed research will focus on the development of an adaptable solar array that is able to optimize power output, reconfigure itself when solar cells are damaged and create controllable output voltages and currents.

This study will be a technological advancement over the existing technology of solar PV. Presently solar arrays are fixed arrays that require external device to control their output. In this research, the solar array will be able to self-reconfigure, leading to the following advantages:

• Higher efficiency because no external devices are used.

• Can reach maximum possible output power that is much higher than the maximum power of fixed solar arrays by arranging the solar cells in optimized connections.

• Elimination of the hot spot effects.

The proposed research has the following goals: First, to create a modeling and computing algorithm, which is able to simulate and analyze the effects of non-uniform changing shadows on the output power of solar PV arrays. Our model will be able to determine the power losses in each solar cell and the collective hot spots of an array. Second, to propose new methods, which are able to predict the performance of solar PV arrays under shadow conditions for long term (days, months, years). Finally, to develop adaptive reconfiguration algorithms to reconfigure connections within solar PV arrays in real time, under shadow conditions, in order to optimize output power.

Document Type

Dissertation

Rights Holder

Dung Duc Nguyen

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Engineering Commons

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