Abstract[edit | edit source]

Purpose - The purpose of this project is to calculate electricity cost, energy yield, and to evaluate financial viability of PV powering Michigan Technological University.

Methodology/Approach - In order to calculate cost, energy yield, and financial viability of PV systems, meteorological information such as irradiation data needs to be gathered and NASA webpage could be considered as a good source for that information. The next step would be gathering available area information for installing solar panels which can be obtained using Google Earth webpage. In addition, the electricity usage and cost for the area needs to be gathered as well. After gathering all the required data, different softwares can be utilized in order to do the evaluations and calculations. In this study RETScreen software is used which can be downloaded from NASA webpage for free.

Load determination, KVA versus KWh -KVA is called as apparent power. This is what the utilities must supply to their customer on the primary side of the facility transformer; whereas, KW is referred to as real power. Power systems would operate at its highest efficiency if all the loads were resistive, but we have motors, capacitors, and transformers which create inductance and capacitance in the power system. These inductive and capacitive devices result in inefficiencies in the network; therefore, some of the energy will be lost to produce magnetic field of the motor, and to create stored energy in the capacitor. For instance, to determine KWh charge: Let's say an organization has 300 bulbs that are 60 watts and are turned on for 12 hours in each day, after 30 days the bill would be: (300*60*12*30/1000) which is equal to 6480 KWh. Electricity data used in this project are given in KWh for each month and the cost associated with this is also provided in dollars.


Determining PV surface area - Different softwares can be used for determining the available rooftop area for PV deployment in a large scale region. The more area (square meter) that is available for installing solar panels, the more power that can be extracted.

  • ArcGIS is a geographical information system for working with maps and geographic information which is used in this project for creating the maps. The software contains a robust set of data manipulation tools along with its mapping capability. The data for the maps provided resides as feature classes in our GIS file database and is transportable.
  • LIght Detection And Ranging (LIDAR) is a remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light. LIDAR uses ultraviolet, visible or near infrared light to image objects. It can target a wide range of materials rocks, non-metallic objects, rain, chemical components and so on. * Another software that can be used is Feature Analyst which is an automatic feature extraction application that utilizes object recognition technology to analyze satellite or aerial images and identify items such as buildings, trees, water features and roads.
  • The data concerning roof areas in most regions does not exist; therefore, the maximum energy potential if PV is installed on every appropriate rooftop in the region remains unknown. In order to overcome this, some algorithms can be produced by using ArcGIS and Feature Analyst. From total roof area, an estimate of rooftop PV potential can be produced by considering some factors such as shading, other uses, orientation of rooftops, PV panel efficiency, and average solar insolation in the region.
  • A five step procedure can be developed for estimating total rooftop PV potential which involves geographical division of the region; sampling using the Feature Analyst extraction software; extrapolation using population relationships; reduction for shading, other uses and orientation; and conversion to power and energy output. First, the renewable energy region is segmented into administrative boundaries so that, land area, population, and population density information can be easily obtained for smaller geographical units within the region. These smaller entities are used as the sampling units for step two, where roof areas are obtained for 10 of the administrative divisions through automated feature extraction techniques. Next, in step three, this sample information is extrapolated to to represent the entire region, yielding an estimate of total roof area. In step four, the total roof area is reduced to represent available roof area for PV deployment. There are many factors which influence the fraction of available roof area, including:
  1. shading, from other parts of the roof or from neighboring buildings and trees;
  2. the use of roof space for other applications, such as ventilation, heating/air conditioning, dormers or chimneys;
  3. the orientation of pitched roofs; and
  4. the installation and racking of the PV panels themselves. From this, an estimate of total power and energy output is obtained.

Main campus map of Michigan Technological University is provided in the following image:

Energy production calculations - RETScreen software is a free energy software package developed by the Government of Canada that includes RETScreen Version 4 and RETScreen Plus.

RETScreen 4 is an Excel-based clean energy project analysis software that helps decision makers determine the technical and financial viability of potential renewable energy, energy efficiency and cogeneration (combined heat & power) projects. Conventional energy projects can also be modeled and compared to cleaner alternatives. Users conduct a five step analysis, including energy analysis, cost analysis, emission analysis, financial analysis, and sensitivity/risk analysis.

RETScreen Plus is a Windows-based energy management software tool that allows project owners to verify the ongoing energy performance of their facilities.

The software integrates a number of databases to assist the user, including a global database of climatic conditions obtained from 6,700 ground-based stations and NASA's satellite data; benchmark database; project database; hydrology database and product database.

In RETScreen 4, different technologies can be evaluated such as photovoltaic, steam turbine, wind turbine, gas turbine, and so on. In this project, photovoltaic is the technology that is being targeted. Grid type can also be chosen as central grid, isolated grid, off-grid, isolated grid and internal load, central grid and internal load. Two methods exist for analysis, and method 2 is the one we need to choose. RETScreen 4 has climate data for all locations around the world which makes it very easy for the user. The climate data that is given on the software includes air temperature, relative humidity, daily solar radiation-horizontal, atmospheric pressure, wind speed, earth temperature, heating degree-days, and cooling degree-days. The irradiation data is required to calculate the output energy that can be obtained throughout the year from the sun. Photovoltaic systems can be integrated into the grid at a central plant or distributed around many locations on the grid. Distributed systems can overcome many disadvantages of centralized integration and it can be mounted on roofs and facades. In distributed integration the PV array will typically locate on a building. PV can be integrated in a central grid or isolated grid, central grid covers a vast geographical area with thousands of generators and consumers, but an isolated grid is a smaller network of generation and distribution facilities not interconnected with central grid that supplies electricity to a limited area such as a single remote community or a community on an island. Off grid system supplies power to a load that is not connected to any grid. Many small loads can be powered by a small PV system and the components of the system would be a PV connected to a battery and a load.

In the energy model section solar tracking mode can be decided to be fixed, one-axis, two-axis, or azimuth. Trackers direct solar panels or modules toward the sun. These devices change their orientation throughout the day to follow the sun’s path to maximize energy capture. In photovoltaic systems, trackers help minimize the angle of incidence (the angle that a ray of light makes with a line perpendicular to the surface) between the incoming light and the panel, which increases the amount of energy the installation produces. Concentrated solar photovoltaics and concentrated solar thermal have optics that directly accept sunlight, so solar trackers must be angled correctly to collect energy. All concentrated solar systems have trackers because the systems do not produce energy unless directed correctly toward the sun.

Single-axis solar trackers rotate on one axis moving back and forth in a single direction. Different types of single-axis trackers include horizontal, vertical, tilted, and polar aligned, which rotate as the names imply. Dual-axis trackers continually face the sun because they can move in two different directions. Types include tip-tilt and azimuth-altitude. Dual-axis tracking is typically used to orient a mirror and redirect sunlight along a fixed axis towards a stationary receiver. Because these trackers follow the sun vertically and horizontally they help obtain maximum solar energy generation. Selecting a solar tracker depends on system size, electric rates, land constraints, government incentives, latitude and weather. Utility-scale and large projects usually use horizontal single-axis solar trackers, while dual-axis trackers are mostly used in smaller residential applications and locations with high government Feed-In-Tariffs. Vertical-axis trackers are suitable for high latitudes because of their fixed or adjustable angles. The use of solar trackers can increase electricity production by around a third, and some claim by as much as 40% in some regions, compared with modules at a fixed angle. In any solar application, the conversion efficiency is improved when the modules are continually adjusted to the optimum angle as the sun traverses the sky. As improved efficiency means improved yield, use of trackers can make quite a difference to the income from a large plant. This is why utility-scale solar installations are increasingly being mounted on tracking systems. There are, however, some disadvantages of solar trackers. Adding a solar tracking system means added more equipment, moving parts and gears, that will require regular maintenance and repair or replacement of broken parts. Also, if the solar tracker system breaks down when the solar panels are at an extreme angle, the loss of production until the system is functional again can be substantial. A solar tracker is also more prone to be damaged in a storm than the actual panels.

In the energy model, slope needs to be provided which is the angle between solar collector or the tracking axes and the horizontal degrees. Depending upon the goal of the system it may be oriented for maximum yearly production, summer use, winter use, reduced capital cost or for integration into the building architecture. For a fixed system we will select the slope that is equal to the absolute value of the latitude at the project site. Several RETScreen project simulations indicate that 30 degrees will result in a higher energy production.

RETScreen has a product database which gives the user the ability to choose manufacturer for photovoltaic products. In addition, model, efficiency, frame area, and capacity per unit of solar panels are also provided; therefore, considering the available area for installing solar panels, the number of panels is determined and the total capacity will be obtained. Module efficiency has a great impact on the output power, and depending on the module type it usually could vary between 5% to 14%. Module efficiency is given under standard test conditions. Solar panel manufacturers test their panels under specific conditions and measure the efficiency of the panel, for instance they put the panels in a flash tester that has been calibrated to deliver the equivalent of 1000 Watts per square meter of sunlight intensity, hold a cell temperature at 25 degrees of centigrade, and assume an airmass of 1.5; therefore, the efficiency of the solar panels will be different after installing at the site. Inverter characteristics need to be provided. For instance, efficiency, capacity, and miscellaneous losses of inverter are items that can be entered to the software for power production considerations.

Basic economic analysis - In some papers, basic calculations have been done for estimating the output power. The following equations explain the procedure:

Pin=I*A

Pout=Pin*efficiency

Where Pin is the input power in KWh, I is the solar irradiation in KWh/m2, A is the area of PV system in square meter, Pout is the output power of the PV system in KWh, efficiency is the efficiency of PV modules.

In another study, annual energy production per watt-peak of a panel has been defined as:

E=S*365/1000 KW-hr per year

Where S KW-hr/day is considered to be the effective solar insolation on a one meter square surface in the geographical location where the solar panel is used.

Energy cost for the solar panel is considered to be:

C=Cs(R+1/15)/E per KW-hr

Where the price is Cs /W-peak and the bank interest rate is R. Watt peak indicates nominal power of a module in watts, it specifies the output power achieved by a Solar module under full solar radiation.

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Authors Negin Heidari
License CC-BY-SA-3.0
Language English (en)
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Created February 19, 2014 by Negin Heidari
Modified February 23, 2024 by StandardWikitext bot
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