The Optimum Inclination Angle Engineering Essay

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The purpose of this assignment is to design a basic grid connected photovoltaic system for my own house. The system will be installed on the roof and will consist of a PV array connected through an inverter to AC loads of the house and to the grid. The analysis of the system operation is given in the next section. Furthermore, the report takes into account the site location and determines any aspects that may influence the design of the system. In addition, a suitable PV module and inverter are selected and the calculations regarding the matching of these components are presented, as well as for any other equipment in the system that is required to be rated. Finally, the array mounting method is discussed and the system's contribution to the building's load is estimated.

The data regarding the irradiation levels and the optimum inclination angle for the location of the site are presented in Appendix A.

System Description

The Grid connected system avoids the need and subsequently the costs for electricity storage in batteries by using the grid as a battery system. The produced electricity is sold to the grid. When the system doesn't produce any electricity, power is drawn from the grid. This automated process is performed by a net metering or net billing program. An advanced or second grid meter is added to keep track of how much electricity has been sold to the grid.

The Grid Connected PV system design has the following components:

PV Array or Generator: A number of PV modules connected in series and/or in parallel giving a DC output out of the incident irradiance. The orientation and tilt of these panels are important design parameters, as well as shading from surrounding obstructions.

Inverter: A power converter that inverts the DC power from the panels into AC power. The characteristics of the output signal should match the voltage, frequency and power quality limits in the supply network.

Loads: Stands for the network connected appliances in the building that are fed from the inverter, or, alternatively, from the grid.

Meters: They account the energy being drawn from or fed into the grid.

Grid: A single or three-phase network managed by a Public Electricity Supplier.

A schematic block diagram of a basic grid connected system is shown in Fig. 1.

Figure 1: Schematic diagram of a basic grid connected PV system (source: [6])

The Site

A site visit is required before designing so as to determine the important aspects that may influence the design. These are the solar panel orientation, tilt angle and the solar access to the site. Obstructions that may occur to shading as well as other issues that can increase the installation cost should be also identified. Last but not least, there are installation and legislation standard policies that have to be taken into account.

For the purpose of the project, the house is located in a suburb near Athens, Greece. The property has 110m2 roof south facing with an inclination angle of 30°. The average daily irradiation is 4.944kWh/m2 at the optimum inclination angle 30° (solar data are presented in Appendix A) [1]. The site is characterised by high temperatures in the summer period and clear weather conditions both in summer and winter periods. A picture of the property is shown in Figure 2.

Figure 2: Picture of the property (source: Google Earth)

According to the country's legislation regarding PV systems installed on house roofs; a system should not exceed the capacity of 10kWp.

Another important aspect is that there is enough space under the rooftop that can host the inverter providing protection against heat, rain and minimising the inverter's noise level under operation.

Design and Installation

PV Module Selection

The selected PV module is the Panasonic HIT-H250E01 that generates up to 250Wp output (20.8% cell efficiency and 18% module efficiency). The cell structure comprises a Hetero-junction with Intrinsic Thin-layer (HIT) and is composed of a thin mono-crystalline silicon wafer surrounded by ultra-thin amorphous silicon layers. [2]

The reason for choosing this module is due to its high temperature operation ability, the higher maintenance efficiency compared to other conventional crystalline silicon solar cells.

Panasonic HIT-H250E01 250Wp

Rated Power

250W

Weight

17.5kg

Length

1610mm

Width

861mm

Depth

35mm

Max. Power voltage Vmpp

34.9V

Max. Power current Impp

7.18A

Open circuit voltage Voc

43.1V

Short circuit current Isc

7.74A

Temperature coefficient of Power

-0.3 %/°C

Temperature coefficient of Isc

2.32 mA/°C

Temperature coefficient of Voc

-0.108 V/°C

Module efficiency

18%

Cell efficiency

20.8%

Connector

MC4

Table 1: Panasonic HIT-H250E01 250Wp module specifications [2] Figure 3: Picture of the module

Inverter Selection

The selection of the inverter depends on the energy output of the array, the matching of the allowable inverter string configurations with the size of the array in kW and whether the system will use one central inverter or multiple, smaller, inverters. Typically inverters are rated at 80-90% of the array capacity so that high inverter efficiencies are maintained at lower power levels. This means that very high power levels are sacrificed since they are out of the range of operation of the inverter.

The chosen inverter is the SMA SUNNY TRIPOWER STP 8000TL-10. The output voltage is fixed at 230V and 50Hz. The inverter has a high efficiency of 97.5% and a self-consumption of 1W at night period. [3]

SMA SUNNY TRIPOWER STP 8000TL-10

Minimum Input Voltage

150VDC

MPP voltage range/ rated input

320V - 800V / 600V

Maximum Input Voltage

1000VDC

Maximum Input Current

22A

Rated Power

8200W

Table 2: The SMA Inverter STP 10000TL-10 specifications

Figure 4: The SMA Inverter STP 8000TL-10 [3]

Module and inverter matching

The array voltages are calculated at various conditions, in order to determine the match with the input range of the inverter. Formula (1) is used for correcting voltage values using the temperature coefficient.

(1)

MPP voltage at 60°C:

The MPP voltage at 60°C should be higher than the minimum input voltage of the inverter. Therefore, minimum number of modules in string:

Voc at -10°C:

Voc at -10°C should be lower than the maximum input voltage of the inverter. Therefore, maximum number of modules in string:

17 Modules are chosen to be connected in series.

at STC for single module

at STC (25°C) for 17 panels connected in series:

MPP voltage at STC of the string should be within input voltage range of the inverter

The MPP voltage at STC is very close to the rated input voltage of the inverter 600V, meaning that the system will operate very close to the rated efficiency (97.5%).

System maximum current (Isc at STC) should be lower than the maximum input current of the inverter. Therefore, maximum number of modules in parallel:

The array will consist of modules.

Array capacity: .

The array requires an area of

Inverter/Array ratio:

Other System Equipment

Wiring Specification

Safety allowance on current capacity of wiring set at 25% of the Isc of the array.

Safety allowance on voltage capacity of the wiring set at 15% of the Voc of the string:

MC4 connectors to be used.

Meter

The house meter has to be replaced with a one that tracks the AC electricity drawn from and supplied to the gird.

Mounting method

There is a number of systems which already exist in the market for installing PV systems on to an inclined roof. The property has ceramic roof tiles. The tiles are fitted together overlapping one another and are held mainly by gravity. The most common way to mount PV modules on such a roof is to use a mounting structure. A simple method is to install roof hooks/anchors (Fig.5) on to the sub-structure of the roof and then attach the rails on the hooks (Fig.6). Then the PV modules can be easily attached and fixed on the structure (Fig. 7, 8).Concrete Roof tile hookPantile Roof tile hook

Figure 5: Roof hook [4] Figure 6: Rail attaching the hook [4] Figure 7: Fixing PV module to a rail. [5]pv pro on roof mounting system anti theft

Figure 8: PV modules attaching the mounting system [4]

The 8.5kWp system consists of 34 modules; therefore 34 roof mounting kits are required.

System contribution to the building's load

The 8.5kWp PV system is estimated that can supply an annual power of:

The building's annual energy consumption is estimated (from 12month billing data) to be 10200kWh. The PV system can produce of that demand; meaning that it will produce more than the required electricity, selling the excess energy to the grid.

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