Dec 10, 2010 - Then, a potential application to employ it in Texas is presented. ... PV system and development of medium power level utility PV power plants.
CURRENT STATUS AND FUTURE TRENDS IN SOLAR TECHNOLOGY – A COMPARATIVE STUDY OF TEXAS AND CALIFORNIA Prepared by Somasundaram Essakiappan, Souhib Harb, Armando Solar-Schultz Department of Electrical and Computer Engineering
for ECE 689 - 605
Technical Report: TR-2010-ECE689-Fall Group No. 1 December 10, 2010 Texas A&M University College Station, Texas, 77843
EXECUTIVE SUMMARY The United States is one of the leading countries in photovoltaic (PV) installations in the world. California takes the lead as the state with most installed PV capacity, while Texas has only now begun to increase its solar PV capacity. In this report a comparative study of Texas and California in the adoption of photovoltaic (PV) for electricity generation is performed. In doing this comparison, this report will analyze the technology employed, the economics behind California’s relative success and Texas’ barriers to the growth of the PV industry. This study will be divided into three chapters, PV technology, economic feasibility of PV technology, and the barriers to the growth of PV industry in Texas. In the technology part, different PV approaches will be presented. The reliability of the PV system will be discussed, mainly the reliability of new PV approach “AC-Module PV system”. Then, a potential application to employ it in Texas is presented. In the second chapter the economic feasibility of PV in the current scenario is studied. The various incentives provided by the government, the various companies competing in the PV industry and the job creation potential of PV technology are analyzed. The third chapter demonstrates the barriers to growth of PV penetration such as competition from other energy sources and lack of public awareness. A comparative analysis is intended to help us learn from California’s experiences in the growth of the PV technology. This report makes a recommendation to adopt a distributed-but-centralized approach to facilitate the growth of PV industry. This will include of installation of AC-Module PV system and development of medium power level utility PV power plants.
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TABLE OF CONTENTS Executive Summary ........................................................................................................................ 2 1
PHOTOVOLTAIC TECHNOLOGY ..................................................................................... 5 1.1
2
1.1.1
Centralized PV System ............................................................................................. 5
1.1.2
String PV System ...................................................................................................... 6
1.1.3
AC-Module PV System ............................................................................................ 7
1.2
The cost of AC-Module PV system: ................................................................................ 8
1.3
Reliability of the AC-Module PV System........................................................................ 9
1.4
Capacitor Requirements ................................................................................................... 9
1.5
PV Energy Conversion Opportunities ............................................................................ 11
1.5.1
AC-Module PV System .......................................................................................... 11
1.5.2
PSE&G and Petra Solar Corporation ...................................................................... 11
1.5.3
Texas Potential ........................................................................................................ 12
ECONOMIC FEASIBILITY: ............................................................................................... 13 2.1
3
Photovoltaic (PV) System Configurations ....................................................................... 5
Many different incentives have been tried, but the most successful have been: ............ 13
2.1.1
Cash Rebates: .......................................................................................................... 14
2.1.2
Feed-in-Tariffs: ....................................................................................................... 15
2.1.3
Tax Cuts or Tax Breaks: ......................................................................................... 16
2.2
Right of Way Authorizations by the Bureau of Land Management .............................. 17
2.3
Jobs Creation .................................................................................................................. 17
2.4
The results of all these efforts: ....................................................................................... 19
BARRIERS TO THE GROWTH OF PHOTOVOLTAICS IN TEXAS .............................. 20 3.1
Economic Concerns........................................................................................................ 22
3.2
Existence of A Strong Conventional Fuels Industry ...................................................... 24
3
3.3
Competition from other renewable energy sources........................................................ 25
3.4
Public Awareness and Education ................................................................................... 27
3.5
Photovoltaic Power Solution: Location and Distribution of PV In California And Texas 30
4
CONCLUSION: .................................................................................................................... 32
5
REFERENCES ..................................................................................................................... 33
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1
PHOTOVOLTAIC TECHNOLOGY
The photovoltaic (PV) used in harvesting the solar energy and transferring it to electricity is being continuously improved and still it is an active research topic. In this chapter, different PV technologies that have been used will be presented. The PV system consists of two main parts, the PV module and the power electronics stage (Inverter). The main goal of the power electronics technology is to convert electrical power from one stage to another stage as efficient as possible with a high level of intelligence. The PV system could be grid-connected or off grid (stand-alone) PV system. Off-grid PV system mainly is used for mobile remote area applications. This type of PV systems requires energy storage which leads to increase the cost and probably affect the reliability of the system. On the other hand, almost 85% of the PV market is gridconnected where the generated power is pumped to the grid directly. No need for a back up energy storage. For grid-connected applications, there are several standards that must be guaranteed by the power inversion stage in the PV system. The dc-injected currents, total distortion harmonic (TDH), power factor, detection of islanding operation, and other factors all of them are governed by standards like IEEE 1547[1], IEC 61727[2] and NEC 690[3]. These standards aim to guarantee that the inverter injects high quality power to the grid Based on the inverter used, different grid-connected PV configurations can be used. 1.1 1.1.1
Photovoltaic (PV) System Configurations Centralized PV System
PV systems start with the centralized multi-string PV system, Figure 1. This system uses one huge inverter. Each PV string consists of multi-PV panel connected in series where then group of these strings are connected in parallel forming a high power centralized PV system. [4] PV-Module
DC
Grid
AC
Figure 1: Centralized PV-System.
Although no amplification stage is needed but the power losses in the string diodes and the connection cables deteriorate the efficiency of this type. Furthermore, the mismatch between the 5
module’s tracking systems (maximum power point tracking MPPT) reduces the amount of the captured power. Therefore, new PV system approaches were used [4]. 1.1.2
String PV System
Figure 2 shows two PV system approaches, string and multi string respectively. To overcome the losses due to the MPPT mismatch and the string diodes, each PV string is assigned its own inverter. The amplification stage can be avoided if the number of the PV panel is enough to generate the required DC input voltage, ≈ 190V for US system. Each PV-string has an MPPT which leads to improve the overall efficiency by increasing the captured energy. However, the cost of the inverter in this case increased due to the low power level. PV-Module
DC
Grid
AC PV-Module
DC
Grid
AC Strings PV System PV-Module
DC DC Grid
DC AC PV-Module
DC DC Multi-String PV System
Figure 2: String PV and Multi-String PV Systems.
The other approach is the multi-string PV system. In this case, each PV-string is assigned a DC/DC converter and all of them are connected in parallel to one inverter. Also here each string has a MPPT and can be controlled individually. The inverter in this case has a higher power level like in centralized case with higher efficiency. Yet, in both approaches, there is still some MPPT mismatch between the modules of one PV string. Consequently, not all available energy from the sun can be captured by the installed PV system. Hence, the AC-Module PV system becomes the most efficient approach that guarantees 100% harvesting of the available power [4][5][6]. 6
1.1.3
AC-Module PV System
The AC-module PV system is shown in Figure 3; where one DC/AC converter is attached to the PV panel. The definition of the AC-module is given as: “An AC-module is an electrical product and is the combination of a single module and a single power electronic inverter that converts light into electrical alternating (AC) power when it is connected in parallel to the network. The inverter is mounted on the rear side of the module or is mounted on the support structure and connected to the module with a single point to point DC cable. Protection functions for the AC side (e.g. voltage and frequency) are integrated in the electronic control of the inverter.” [5].
PV-Module
Grid
DC AC Figure 3: AC-Module PV System.
Figure 4 shows real implementation for the AC-Module PV system [7]. It is believed that this approach will be the trend for the future PV industry. In this type of PV system, the MPPT problem is completely solved since each PV module is connected to one inverter that has an MPPT. The AC-Module PV system offers Plug-N-Play concept. This option gives a high order of flexibility. This flexibility in the system makes it more common and easy to be used for end user application. Moreover, the modularity provided by the AC-Module PV system makes the future expansion of the whole system easier.
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Figure 4: AC-Module PV System.
1.2
The cost of AC-Module PV system:
Figure 5 shows the cost of each component in the PV system. It is clear that assembling the whole PV system costs two to three times of the module cost. This consists of the inverter, cables, connectors, etc. Figure 6 shows that the inverter cost just 15% and 45% is due installation and balance of system (BOS) [7].
Figure 5: The cost of PV system.
Using the AC-Module PV system will significantly reduce the cost. Primarily, it is meant to be connected directly to the load (utility-grid). Hence, no cables and connectors are needed between
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modules. Here, it worth to mention that in order to exploit (benefit) all advantage AC-Module offers we have to use in the right applications. This will be discussed later in this chapter.
45%
40%
PV modules
15%
Grid-tie inverter Installation and BOS
Figure 6: PV system cost break-down.
1.3
Reliability of the AC-Module PV System
The micro inverters are mounted behind the panel, figure 4. Hence, the life-span of the inverter should be comparable to that of the PV panel; which is more than 20 years. The micro inverter is fully exposed to the weather conditions (e.g. high temperature), this will deteriorate its life-span. The available (commercial) inverters have a life-span less than the PV panel; about 6-10 years. Although, many researches have been done to solve this issue and find a new inverter with high life-span, yet this problem is one of the biggest challenges that researchers trying to solve. The reliability of the inverter is measured by two indices, mean time to first failure (MTFF) and mean time between failures (MTBF). Inverters nowadays have 5 years for MTFF and 10 years for MTBF. The most vulnerable parts in the inverter are the power switches and the power decoupling capacitor; which have a strong negative impact on its life-span [4][8][9][10]. 1.4
Capacitor Requirements
The output instantaneous power of a single-phase inverter is given by (1). This equation shows that the power consists of two terms, the first term represents the average power and the second one is a time varying AC power. 𝑃𝑃0 (𝑡𝑡) = 𝑉𝑉0 𝐼𝐼0 𝑠𝑠𝑠𝑠𝑠𝑠2 (𝜔𝜔0 𝑡𝑡) = 𝑃𝑃0_𝑎𝑎𝑎𝑎 + 𝑃𝑃0𝑎𝑎𝑎𝑎 (𝑡𝑡)
(1)
Assuming lossless inversion process, the output power from the PV panel will be equal to the average AC output power. The remaining time-varying term
Po ac (t)
will deteriorate the MPPT
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performance; and as such, this pulsating power must be handled by an energy storage device (power decoupling capacitor), whose size is determined by: 𝐶𝐶𝐷𝐷 =
𝑃𝑃𝑖𝑖𝑖𝑖 𝑤𝑤0 𝑉𝑉𝐷𝐷𝐷𝐷 ∆𝑣𝑣�
(2)
where Pin is the rated power of PV panel, VDC is the DC level voltage across the decoupling � is the maximum allowable peak-to-peak ripple, and ω0 is the line frequency. capacitor, ∆v
Usually, a capacitor is connected in parallel with the PV panel, which results in a very large capacitance since the allowable voltage ripple must be held to very low values (
