5.0 Solar PV (Nour Al Ghussain)5.1 Introduction The portable classroom has the potential to generate much of the electricity it needs as a unit. The electricity can be generated through the use of photovoltaics that are placed on the roof of the classroom. Photovoltaic (PV) cells are made up of at least two Semiconductor layer , one layer contains positive charges while the other layer is negatively charged. The photons from the sun are then absorbed by the negative semiconductor layer ofthe cell, when enough of the photons are absorbed they are then released to the positive layer. The movement of the photons creates a voltage differential, the electrons flow through the circuit creating electricity(SEIA 2015). The photovoltaic system has four major components that create the “Balance of System” BOSthat added to the cells to be installed. The batteries are used to store the excess electricity produced, the energy would be released at night when there is demand. The inverters convert theDC power produced by the PV cell to AC. Controllers are needed inthe system to manage the energy storage to the battery and deliver power to the portable classroom. The structure is the last requirement of the system and they are required to mount or install the PV cells. The portable classroom is connected to the Grid , as such in a design point of view the battery component of the system is not needed. The utility outages are considered rare, and since this is a school the PV system aims to decrease the electricity bill. The classroom has a variety of equipment that can consume electricity, from computers to charges and other heating and cooling systems. The following schematic shows what a typical PV system should look like.

Figure #: The overall system used for the PV cell operation(California EnergyCommission 2015).

5.2 PV design The PV modules will be attached to the roof by a mounting system.This would maximise the area used for solar collection on the south side of the building. The mounting system consists of rails and carrying rows for modules. The PV module is held in place by clamps located in the middle and at the end .

Figure #: The PV roof mounted system (Schletter 2008).The PV module chosen for the system is the SHARP 250 Watt multipurpose module. The model number is ND-250HAC. The followingimage shows the dimensions and characteristics of the PV cell

chosen.

Figure #: The dimensions and characteristics of the SHARP , PV Cell(SHARP 2012). The module was chosen due to the fact that its a competitive PV model in the market and its price is lower than local producers. Further, the classroom needs a system that is moderately priced for irs purposes. The power to be generated in our case depends more on the number of the cells placed rather than the power efficiency of one cell. The tilt angle of the Roof is 20 degrees, this angle is not optimal compared to the 35-40 degrees needed to prevent snow from accumulating. The angle was governed by the acceptable facade design and the ASHREA standard for building parameters.The snow accumulation can be prevented by adding an anti freeze or by cleaning the cells, more will be discussed in the maintenance section. The data used for the PVWatts program isshown in the table below.Table #: The data used to determine the Kw input of the PV systemto be installed.

Roof Area 100.100

solar panel area 1.642

solar panel W 0.994

L 1.652

Tilt angle 20.000

Area of Roof for PV installation 101.140

Number of panels 61.592

Power output per panel (W) 250.000

Over all power (W) 15250.000

Kw 15.250

The data from the PV watts program are shown in table # in Appendix #. A graphical presentation of the data is also shown to quantify the data obtained. The full PV WATTS output is shown in Appendix #.

Figure #: Power production from the PV cells versus month of the year. For a 18,858 Kw per year of produced energy the inverter needed for the assembly needs to be sized. The inverted size is for DC system of 15.25 KW, as such the chosen inverter is Advanced Energy AE 3TL-16 (Civic Solar 2015). The inverter is 16kW and can handle up to a 1000V(Civicsolar 2015) . The inverteR with this size was found from schneider with a peak inverter efficiency of 97.5%, if the resistance of the wires and

connections taken into account the total efficiency goes down to 96%.The total space the inverter takes is 0.5334*0.889*0.2794 = 0.13m3. The image of the inverter is shown in Appendix #.The overall system now consists of the solar PV array the inverter and the wires connected the solar in semi series and parallel configurations. This is done to make the maintenance easier , the cells are connected in series of three to five cellsand those are connected in parallel to the rest. In this case if one of the cells malfunctions the system still functions properly. The assumption that was made in the beginning of the project is that there are no structures shading the array or the building. The cells due to the fact that its roof mounted do not experience any shading. The following section talks about the energy balance. The over all design is shown in figure # in Appendix #.5.3 Energy Balance The overall energy requirements where estimated for the portablein combination with the requirement for lighting and HVAC. The assumption that there was one laptop and one computer and printerworking 8 Hours ,365 days a year was made to estimate overall energy consumption. Table #: The overall energy requirements of the portable classroom.

Energy balance /year

ITEM kWh

computer + monitor 216

laptop 259.2

laser printer 2448

HVAC 5630

lighting 4270

TOTAL (kwh)/year 12823.2

PV Power (kwh)/year 18858

Power Generation (kWh) 6034.8

PV power $/kWh 2112.18

Under the government's feed in tariff (FIT) program the price of the generated electricity per kWh is 0.35 (MOAFR 2015). The rate at On peak is 0.77/kwh (HydroOttawa 2015). On a year basis if it is assumed that all the energy produced by the PV will be distributed evenly to cover all needs, there would be an excess of 6034.8kWh, generating a profit of $2,112. If all the energy produced was sold and fed into the grid the generated profit at 0.354/kWh is $6600. If the cost of buying the electricity from Hydro ottawa is accounted for at an On peak rate, then the profitgenerated per year is $4805.

5.4 Factors Affecting Output The PV cells installed in the building might not produce the output predicted using the PVWatts program. There are several factors that affect the output of the PV cell. Firstly , the solar cells where tested under standard test conditions(STC). TheSTC allow for comfortable comparison between different PV cells and are easily recreated in a factory setting. The conditions are:solar cell temperature of 25C, solar irradiance (intensity) of 1000W/m2 . The results are then modified and used to estimate the output at different locations. Secondly , The cell output will decrease with increased internal temperature. The cells on the roof tend to reach an internal temperature of 50-70 C. for example a 100 watt cell will operate at about 85 watts under fullsunlight conditions. Thirdly, dirt and dust in the summer , snow

in the winter. The dirt , dust and snow, create obstacles blocking some of the sunlight and reducing output. Fourthly , theDC to AC conversion losses. The conversion of the DC cell output to AC using the inverter results in losses of energy , the wires are connected from the rooftop down to the inverter on the group and back up to the grid of the house. The losses accumulate from the wires and the conversion ,decreasing the out out of the PV array.

5.5 Maintenance There are different ways to maintain the PV modules in the harsh weather conditions encountered in ottawa. The following is a listof ways to remove snow from the PV panels:1- There are poles specifically designed to extend and retract asneeded to reach hard places, it also makes the removal easier andmore efficient.2- There are also material that can be sprayed (Anti freeze) on to the panels that can be more convenient. The material prevents the snow accumulation and the snow would wash off rather than turn to ice . 3- The angle of 20 degrees helps with the snow accumulation reduction. As such the steeper the angle the better the removal,although some times you have constraints in terms of the general facade of the house or building designed for. 4- There is a hose it down option , in which the snow can be removed by exposing the snow to hot air using a blower. This makes it easier to remove in general , but also has the ability to raise the solar panel temperature up.

Appendix #:

Table #: The output of PV Watts , AC power production and solar radiation per month.

Month Solar Radiation (kWh/m2/day) AC Energy (kWh)

January 2.21 951

February 3.8 1427

March 4.8 1937

April 5.11 1904

May 5.69 2133

June 6.15 2156

July 6.15 2198

August 5.21 1847

September 4.37 1554

October 3.09 1197

November 1.86 715

December 1.99 839

Figure #: the inverter chosen for the PV system, the capacity is 16Kw(Civicsolar 2015).

Figure #: The solar array installed on the roof of the portable classroom.

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