Photovoltaics are solar cell devices made of semi-conductor materials. The instrument helps in the conversion of sunlight energy into electricity of a direct current. A considerable number of the uses silicon as the semiconductor. Therefore, an example of a solar cell consists of a thin wafer. The wafer has two layers of varying thickness. The thinner layer is an N-type silicon that is doped using phosphorus. On the other hand, the thicker layer is a P-type silicon achieved through doping using boron. As a result, one layer is deficient of electrons while another layer has excess electrons. Consequently, there is a field due to electric current is established close to the top surface at the interface between the two layers. Therefore, when sunlight shines on the surface of the photovoltaic cell electrons are stimulated. Therefore, a voltage difference will exist between the two layers creating an electric field. The influence of the electric field will create momentum as well as, the direction of flow of the photo-stimulated electrons. As a result, a current will flow in case an electrical load is present. The solar systems are grouped into two primary classes: grid-tied and stand-alone systems. Both systems employ the same principle in the production of electrical energy which is the application of photovoltaic panels. However, a significant difference exists in the method in which the produced electricity is stored. A flooded lead-acid battery forms the storage for the stand-alone systems. On the other hand, the grid-tied systems will use the commercial grid. The following paper presents a survey on the components of a grid-tied photovoltaic system, as well as, the some of the policies that influence their residential use.
Grid-tied Photovoltaic systems
A grid-tied solar system of an appropriate size produces an excess electrical energy in comparison to the load the system is designed to operate. Consequently, the extra electricity is transferred into the commercial grid. The photovoltaic panels produce a direct current (DC) while the commercial grid operates an alternating current (AC). Other consumers connected to the grid will use the excess energy uploaded. This is an occurrence when the wattage of the panels exceeds the consumption of the owner. Therefore, the client will sell to the grid. Additionally, it is possible that the consumption by a customer exceeds the wattage of the photovoltaic cells. Consequently, the client will acquire the grid energy to meet the extra demand. In both scenarios, a client will pay the power company the difference between the total electricity consumed less the amount generated. In case the client generates an excess electricity than what is consumed, then the bill is negative.
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Components of a grid-tied photovoltaic system
The essential components of photovoltaic panels connected to the grid include the PV module, a solar charge controller and an inverter. Additionally, the system consists of the balance of system, a data monitor system, power center and the mounting system.
The PV modules are responsible for the conversion of the solar energy into electrical energy. The output energy is in the direct current form. A module constitutes of numerous discrete photovoltaic cells that are in a parallel connection. Such connections helps increase the amount of the total current. However, a simultaneous series connection is also employed to boost the overall voltage of the module. The voltage and amperage requirements of the system determine the number of cells in the module. The recommended industry standard for large scale production of power is thirty-six cells. A transparent material or a tempered glass is used to enclose the module on the anterior surface. However, the posterior surface is covered using a protective material with waterproof attributes. Moreover, the edges of the modules have a weatherproofing wrap. Finally, the module is held in the right position using an aluminum frame. Currently, four types of photovoltaic modules are commercially available.
The mounting unit ensures the solar panels are adequately supported and inclined at the appropriate angle. Consequently, the panels are positioned accordingly to harness the maximum amount of sunlight based on the overhead locus of the sun.
The power center is regularly configured to suit a particular system. It has three main parts: an inverter, an interconnect, and an external connection. The inverter is of low distortion, and it serves to change the DC voltage into an alternating current. This is important since a significant proportion of the electrical appliances operate on an AC voltage. The interconnect forms the bridge between the power from the PV system and the incoming power for the grid managed by the utility company. The external connection links the PV system to a breaker panel.
The data monitor equipment keeps track of the flow of electrical energy. Therefore, it will display the amount of energy that is produced from the sources. Additionally, it indicates the quantity of electrical energy flowing from the PV system into the various loads.
The balance of system is a hardware that consists numerous items such as wiring, terminations, and Ground Fault Interrupter. Moreover, it is made of surge protections, as well as, AC and DC disconnects among others.
The solar charge controller normalizes both current and voltage that flows from the photovoltaic system into the electric appliances. Thereby, it ensures that a uniform electrical energy is constantly supplied to the appliances irrespective of the fluctuations in the amount of energy generated. This is particularly important in areas with considerable variations in the amount of sunlight strength received.
Cost of implementation
For systems that produce a wattage less than 30 kW, the costs for the various components are as follows: PV panels, Balance of System, and Inverter costs $2, $1 and $0.5 per Watt. Moreover, the labor cost for the installation is $3 per Watt. Therefore, the total cost per Watt is $6.5. Consequently, a 5kW system will cost $32.0 while a 6 kW system will require $39.
State and federal policies
The California Solar Initiative (CSI) offers two types of financial incentives. The first one is known as Expected Performance-Based Buy down (EPBB). It consists of a single up-front payment that is founded on the quantity of energy expected to be produced. However, it is applicable for PV systems with a capacity less than 50 kW. The second type is the performance Based Incentive (PBI). The incentive is applicable for any kind of photovoltaic system. However, for systems with a capacity greater than 50 kW, it is imperative. The incentive is determined by the exact amount of energy produced. The payments are carried out monthly for a period of 5 years.
Current utility policy
The consumers will incur charges that they should pay irrespective of the source of the supply. The standing cost is due to amount incurred from supplying the power form the transmission system. The charge for the supply is however determined by the amount energy consumed. This cost is dependent on the choice of the power supplier. The rate for summer months differs from the non-summer rates. The billing is done annually and it takes into consideration the amount of energy used and the corresponding months. Consequently, the average cost per kWh is reflective of the costs.
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