Analysis of power losses and increasing the efficiency of solar power generation systems connected to the home grid

Dissertation for Master's degree

In the field of power oriented electrical engineering

Abstract

Limited fossil fuel resources and the possibility of running out of fossil energy reserves, global warming, environmental pollution, price instability, as well as the increasing need of industrial and urban centers for energy, have made the international community think of suitable alternatives. Nuclear energy, solar energy, geothermal energy, wind energy and ocean waves are such. The relatively high price of converting renewable energies is an inhibiting factor for the development of grid-connected systems and limited the use of these energies to situations where the use of the national electricity grid was not possible, such as remote areas. During the past years, a lot of research and investigations have been done on the connection of renewable energy conversion systems to the grid, and a lot of progress has been made in this field. Solar energy, along with other types of renewable and clean energy, has been widely studied as the main source of renewable energy.

So, at first, the structure of the photovoltaic cell was discussed briefly, and then we reached a simplified exponential model by examining various models for simulating the solar cell. Then the effect of various factors on the characteristics of the solar cell and the waveform results obtained in the characteristic curves were given. In the continuation of the work, due to the fact that in order to produce higher voltages and currents, we must connect series and parallel combinations of these cells, so the formulas and relationships used for the combinations of these cells were given. Finally, according to the aim of the thesis, we studied the methods of increasing the efficiency of the solar system by increasing the efficiency of the system elements. Also, in the last chapter, ANFIS, FLC methods are compared and the response speed of these two methods will be presented in the final chapter.

Key words: solar cell, maximum power detector, control

1-1- Introduction

Limited fossil fuel resources and the possibility of fossil energy reserves depletion, global warming, environmental pollution, price instability and also the increasing need of industrial and urban centers to Energy has made the international community think about suitable alternatives. Nuclear, solar, geothermal, wind and ocean wave energy are such. The relatively high price of converting renewable energies is an inhibiting factor for the development of grid-connected systems and limited the use of these energies to situations where the use of the national electricity grid was not possible, such as remote areas. During the past years, a lot of research and investigations have been done on the connection of renewable energy conversion systems to the grid, and a lot of progress has been made in this field. Solar energy, along with other types of renewable and clean energy, has been widely studied as the main source of renewable energy. Partially and generally, solar energy supplies a significant part of the electrical energy required by electrical networks. Figure (1-1) shows the types of energy sources used to produce electrical energy and how they are connected to the grid.

The relatively high price of converting solar energy into electrical energy has been the biggest concern of researchers in the way of using this type of energy and is considered the biggest negative feature. In contrast, the availability and high reliability of photovoltaic systems is considered a positive feature. Figure (1-1) Types of energy sources used to produce electrical energy and how to connect them to the grid In the past, the price of the solar cell was the main factor determining the price of the entire photovoltaic system. High construction cost, non-advanced construction technology and low efficiency of manufactured products have been the factors preventing the use of this energy. With the passage of time and the development of construction technology, we have seen a decrease in prices and an increase in efficiency in solar systems. The amount and growth rate of using solar energy is lower than other types of renewable energy. The investments made in the field of solar technology and the mass production of photovoltaic cells have led to a reduction in the cost of producing one kilowatt of energy from solar arrays. This price reduction is an important factor in increasing the popularity of using solar energy.Photovoltaic inverters connected to the grid are being developed day by day in industrial and laboratory fields, and as you can see in figure (1-2), according to the prediction of the European International Institute, this energy will have the largest share in the energy market by 2050.

Figure (1-2) Forecast of the percentage of use of different energies until 2050

1-2- The importance of optimal and accurate growth of photovoltaic systems in Grid

In Europe, since 2009, photovoltaic systems have been selected among the top three technologies used (Figure 1-3). In 2011, photovoltaic systems were more used and connected to the grid than gas and wind technologies with 21.9 GW of energy. The total installed capacity of photovoltaic systems in Europe at the end of 2011 is equal to 51.7 GW and provides enough energy for 15 million homes in Europe. Photovoltaic systems produce a significant share of the total energy in Europe, so that 2% of the total energy consumption and 4% of the European peak load are caused by these systems.

At the end of the year In 2011, Italy generated 5% of its total customer demand and 10% of its country's peak load through photovoltaic systems. In general, in Europe, it can be said that about 15 countries supply 10% of their energy needs from solar cells, and in a part of Spain [1], this number reaches 18%.

This rapid growth of solar cells has attracted a large and astonishing number of investors and retailers. But in fact, in recent years, the amount of solar power required by Europe and the amount of development and growth of the photovoltaic system have been negligent. Figure (1-3) Net added capacity in Europe in the years (GW) 2000 to 2011. To date, six members of the union have determined their 2020 plan, and the rest of the members must do this by 2015. Based on EPIA's calculations, the power required and used until 2020 is more than twice the amount predicted by NREAPs, and in fact, at least 200 GW of solar power is needed until 2020, which must be provided.

These disturbances in the forecasts cause deviation from the optimal process and finding the effective amount of solar system power forecast in the future. For example, in Germany in 2005, in order to facilitate operation in the distribution system when critical conditions arise and disconnect network connectors and increase the frequency, it was decided to reduce this limit of frequency from 50.5 to 2.50 Hz. Based on this decision, the installed photovoltaic systems remained at their limit value and were even allowed to leave the grid under the assumption that they have no impact on the system, while the rapid growth of photovoltaic systems in Germany showed that this decision was not applicable and would have freed and moved away from several hundred thousand systems that are now installed.

As a result, future policies should be such that both Decarbonization strategies are satisfied and the network and its reliability constraints are not harmed. Therefore, the power system planner and system policy maker must determine the exact amount of the required and optimal photovoltaic system for medium and long-term conditions. This information and accurate predictions help investors to make the best decision in transient and short-term conditions. [1]

1-3- General classification of photovoltaic systems

Photovoltaic systems are used in two ways, connected to the grid and independent from the grid. Of course, sometimes the combination of these two is also used. In the past, independent photovoltaic systems have been mostly used to provide electricity to remote areas. Nowadays, most of the photovoltaic systems are connected to the grid because they do not need large support batteries, they have a simple control system and their maintenance costs are lower.[2]

The production of cheap and high-reliability photovoltaic inverters has been introduced as a very important challenge for many researchers, which has caused an increase in the variety and number of these inverters. In general, photovoltaic inverters must perform two important tasks correctly: [3]

1.

Solar arrays have non-linear behavior and transmit the maximum possible power at a specific voltage and current, which is known as the maximum power point [3].