Executive Summary



Parallel Electrical Supply System

Final Report

Team Number

May02-12

Clients Name: Ms. Marge Trusty

Faculty Advisors: Dr. John Lamont, Prof. Ralph Patterson, Prof. Glenn Hillsland

Team Members: Luis Lobo, Andrew McArthur, Sean Smith, Joshua Linebaugh

Date Submitted: 4-16-2002

Table of Contents

Executive Summary ………………………………………………. 1

General Background ……………………………………………… 3

Technical Problem ………………………………………………… 3

Operating Environment …………………………………………… 3

Intended Users and Uses ………………………………………….. 4

Assumptions ………………………………………………………. 4

Limitations ………………………………………………………… 4

Design Objectives …………………………………………………. 4

Functional Requirements ………………………………………….. 5

Design Constraints ………………………………………………… 6

Measurable Milestones ……………………………………………. 6

End Product Description …………………………………………... 7

Technical Approaches …………………………………………….. 7

Technical Design ………………………………………………….. 8

Testing Description ………………………………………………... 9

Risk and Risk Management ……………………………………….. 9

Recommendations for Follow-on Work ………………………….. 10

Commercialization ………………………………………………… 11

Personal Effort Budget ……………………………………………. 12

Financial Budget ………………………………………………….. 12

Project Schedule …………………………………………………... 13

Lessons Learned …………………………………………………... 14

Project Team Information ………………………………………… 15

Evaluation of Project Success …………………………………….. 15

Operation of Stand Alone Mode …………………………………... 16

Summary …………………………………………………………... 19

References …………………………………………………………. 19

List of Tables

Table 1: Personal Effort Budget …………………………………. 12

Table 2: Financial Budget...……………………………………….. 12

Table 3: Project Team Information ……………………………….. 15

Table Automatic Operation ……………………………………….. 16

Table Manual Operation …………………………………………... 16

List of Figures

Figure 1.1: Fall 2001 Original Gantt Chart ……………………….. 13

Figure 1.2: Fall 2001 Final Gantt Chart ……….………………….. 13

Figure 1.3: Spring 2002 Original Gantt Chart …………………….. 14

Figure 1.4: Spring 2002 Final Gantt Chart ……….……………….. 14

List of Appendices

Appendix A: Solar Panel Generation vs. Ms. Trusty’s Load

Appendix B: Calculation of Solar Panel Generation

Appendix C: Parts Information

Appendix D: Flow Chart of standalone (LBX) mode

Appendix E: One Line Diagram of Different Conditions

Appendix F: Wiring Schematic of the System

Appendix G: Real Time Current Data taken from Ms. Trusty’s residence, Channel 1 (Leg A)

Appendix H: Real Time Voltage Data taken from Ms. Trusty’s residence, Channel 1 (Leg A)

Appendix I: Trace 5548 Inverter/Charger Information (Trace)

Appendix J: C40 Charge Controller Information (Trace)

List of Acronyms used in this document

A: Amperes

AC: Alternating Current

dB: Decibel

DC: Direct Current

kW: Kilowatt

LBX: Low Battery Transfer

LCD: Liquid Crystal Display

MAE: Mid-American Energy

m²: Square Meters

NEC: National Electric Code

PV: Photovoltaic

V: Volts

Executive Summary

This project involved a study to determine the best way to utilize several electrical supply sources to serve a residential customer, Marge Trusty, who had purchased solar panels storage batteries, converters, inverters, control panels, and a generator. MidAmerican Energy Company (MAE) is serving her load. Conclusions include that the solar panels would be unable to supply enough energy for Marge Trusty’s load over an extended period of time. Recommendations are to first utilize the energy produced from the solar panels either directly or through the battery, and then when necessary, serve her load from the utility.

During daylight hours the solar cells would serve her load and charge the batteries. Over a period of time the energy stored in the battery and that available from the solar panels would not meet her load requirements. At that time the utility source would provide the energy necessary for her load and for battery charging. The switching to accomplish this scenario would be done automatically by the components in the control panels.

The 18kW generator would be used only in an emergency, when there was an interruption to utility service and not sufficient energy available from the combination of the solar panels and the battery. The generator must be started manually and switched into the load only after the load had been isolated from its normal source.

Steps Taken to Complete the Project

The first step taken toward the design of this project was gathering information about all the devices that Mrs. Trusty had already purchased. Furthermore, some investigation was needed to verify the requirements imposed on the design of the project by MidAmerican Energy and the office of the electrical inspector of Iowa City.

The team visited Marge Trusty’s residence on several occasions to gather information such as product documentation, and layout of the components. Also during the visit, the team discussed concerns and desires with MidAmerican Energy and Mrs. Trusty. The team was able to get a feel for what was needed to complete the project with this information that we gathered.

Next, the team determined the most suitable and most cost-effective mode of operation that would meet many of Marge Trusty’s desires. This required several phone calls to representatives of Trace Engineering (the manufacturer of the majority of the devices), along with the manufacturers of Trojan batteries and several distributors of Trace equipment throughout the nation. After determining the best mode of operation, the team developed a suitable wiring diagram (Appendix F) that integrated all the equipment and the devices according to the requirements for the mode of operation chosen.

Recommendations For Future Work

I. Gathering Load and Generation Information

Information can be taken about the system, such as the daily load consumption, peak current, level of charge in the batteries, weather vs. solar output, etc. Load consumption can be taken from Ms. Trusty’s home and solar panel generation data can be taken from the solar panels. This will help to verify the efficiency of the system in place. Regulating the inverters/converters, adjusting the rate at which the batteries can be charged and selling power at the most convenient times would be very useful to insure optimum efficiency.

II. Sound Wall/Sound Diffusion

The 18kW natural gas generator will need some type of sound barrier i.e. vegetation, or a sound wall. The output noise of the generator is 75dB at 7 meters. This could cause several complaints to nearby residences.

Introduction

General Background

The main objective of this project is to design a system that includes a renewable source of energy integrated with a utility supply that would supply the load of Mrs. Marge Trusty. This type of system will allow Mrs. Trusty to reduce her consumption of power supplied by the utility and will also provide an emergency back up in case the utility fails to supply her load. Ms. Trusty purchased this equipment in 1999 in preparation for Y2K. She had concerns about the reliability of the utility grid and wanted a standalone system. Since 1999 the equipment has been partially hooked up by an electrician, but has been idle for the last 3 years. The team’s goal for this project was to produce a wiring diagram that would be approved by MAE and then given to the electrician.

This system includes 24 photovoltaic panels, with a maximum rating of 100Watts per panel, which are located next to the house. It also has an 18 kW generator that will be utilized as a backup when the utility fails and the batteries cannot supply the load. A shed has been built to house all the control equipment for the system since some of these devices are moisture and temperature sensitive. The shed is not adequate for protection from temperature and moisture.

Technical Problem

The system will use a photovoltaic array (solar panels) to generate the electricity necessary to supply Mrs. Trusty’s electrical load. The power generated by these panels is taken directly to an array of 6 Volt batteries wired in series. The panels charge the batteries, weather permitting. Otherwise, the utility will keep the batteries charged.

Two inverter/chargers will be used to change the DC voltage supplied from the solar panels into AC voltage. These inverters/chargers are programmed in a special way for a determined mode of operation, in this case, the low-battery transfer mode. The inverters control the automatic disconnect of the household’s load from the utility when the batteries are supplying the load and isolate the system entirely from the utility.

A single multi-function charging controller (C-40) is used to protect the batteries from overloading (overheating). This controller allows the batteries to reach a proper level of charge without damaging the batteries. An LCD display on the controller shows the levels of charge in the batteries.

An 18kW natural gas generator, along with its controller, is integrated with the system as a backup if there is a utility interruption. However, the generator will not turn on automatically but has to be switched manually after the load has been isolated from its normal source.

Operating Environment

The operating environment will be in the Iowa outdoors, which may be very hostile.

The following are a list of recommendations for altering the operating environment.

1. One set of solar panels are obstructed by a nearby tree. To maximize the capability of collecting sunlight it would be best to trim or remove the obstructing tree.

1. The batteries are located outside the house next to the shed in a plastic container, exposed to the change of temperature but protected from rain and snow. Due to loss of capacitance due to cold temperatures and loss of electrolytic fluid during hot temperatures it is best to store these batteries in a climate-controlled area.

2. The inverter/converter and control system is very sensitive to extreme temperatures, and high moisture. Therefore a shed has been built to house it. It has been recommended that this shed be insulated and heated during extreme weather.

Intended User and Uses

User(s): Mrs. Marge Trusty, homeowner.

Uses: To supply power to Mrs. Trusty’s home, through a renewable source of energy that interacts with the utility as a backup. This will enable Mrs. Trusty to reduce the cost of her utility bill, and at the same time benefit the environment.

Assumptions

• The panels and battery backups may not be able to supply enough power for the entire home at certain times of the year. (See Appendix A)

• Equipment is in good working order even though being without operation for many months.

• Wiring has been done appropriately and compliant with electrical codes.

• The generator is working in good order, even though it has never been used.

Limitations

• Solar panels may not be able to supply the user’s entire load.

• Solar panels will never 100% efficient due to surroundings (like trees, cloudy days, etc.)

• Yard size locating and setting up equipment is very small.

• Generator harmonics will not affect and/or damage electronic equipment in the home.

• The design will comply with NEC, Iowa electrical codes, and utility safety codes.

• Temperature will limit the amount of output from the batteries. The optimal temperature

is around 62° F and the output is effected by every degree away from that point.

Design Objectives

The design objectives have been defined as creating this system in a stand-alone (LBX) mode. This mode has two different subsections, one automatic and the other manual.

1. The automatic subsystems are as follows.

a. Solar Panels/Photovoltaic Cells Subsystem

There are two sets of twelve solar panels, rated at 100Watts each, in series. Each panel is made up of several photovoltaic cells. These cells convert light into a voltage. These panels are connected in series and combined with a photovoltaic source combiner to produce energy that is converted from DC to AC. These panels in parallel with the storage batteries supply power for the load during both daylight and nighttime hours.

b. Storage Battery Subsystem

The storage subsystem will be eight (8)-6 volt batteries rated at 320 Amp/hours that will be set to charge at a predetermined rate by power that is produced by the Solar Panels. These batteries are very similar to a typical lead-acid, deep cycle battery, but they have a much larger capacity. These batteries will supply the load if the solar panels are not producing enough power. Such a case would be the nighttime hours.

c. Utility Backup Subsystem

In case of battery depletion anytime the solar panels are unable to recharge the batteries the utility system will provide energy to the load and also recharge the batteries. When the C40 controller senses the voltage level in the batteries below a specified level, the inverter control will automatically switch over to the utility to supply the load and charge the batteries, until full as indicated by the C40 Charge Controller. Once the batteries are recharged the inverter control will switch the load back to taking power from the batteries once again.

1. The manual emergency generator system.

a. The generator back up system will be used only when the solar panels are not able to produce enough power, the batteries are depleted and MAE is not in service to Marge Trusty’s House. The generator will need to be turned on manually and connected to the load, only after the load has been disconnected from its normal source. This system will work in complete isolation from the normal system and MAE.

Functional Requirements

The functional requirements of the overall project will be to give continuous power to Marge Trusty’s load using a combination of solar panels, batteries, MAE, and a generator. Together these devices will produce a much more environmentally sound way of producing power for the home and reduce the cost of utility bills. The following sections of the functional requirements are defined as follows

1. Provide a primary renewable source of power to the home.

The solar panels and batteries will be used in parallel to supply the power to Marge’s load during the majority of the year. The system will function automatically and will work in unison with MAE. This system is much better on the environment than running a gasoline or any other powered generator to supply energy to the home. This system will use the sun’s energy to supply the load and to charge the batteries. If the solar panels are not producing enough energy then the system uses the power stored in the batteries until the either the solar panels start producing enough energy or until the batteries run down to a specified level set in the C40 battery charge controller. Then the load will be fed from the utility.

2. Provide backup power whenever needed.

In the event the solar panels are not producing enough power and the batteries are depleted then the load automatically switches over to MAE. Once MAE has been switched in it will supply the load and charge the batteries until they are filled to a level specified by the C40 charge controller. Once this level has been achieved the inverter controller will automatically transfer the load back to the batteries and the solar panels.

Another backup need could happen if the solar panels are not supplying enough power, the batteries are depleted and MAE is out of service. Then the natural gas powered emergency generator may be started to supply the load. The generator would have to be started manually. If the generator is used, it must be totally isolated from the utility and inverter/charger. In this case, only the load will be supplied; the backup batteries will not be charged.

3. Reduce the cost of the client’s utility bill

This system has been designed to save as much as possible by using the utility as little as possible.

Design Constraints

The design constraints for this project have been defined as the following

1. There are several standards need to be complied with during the design and implementation process.

The system will have to comply with various codes such as the NEC to isolate the system to ensure that the system will not feed back to the utility during an outage. The NEC has to be followed for wire sizing and breaker sizing. The Iowa City/State of Iowa codes must be followed.

2. Amount of power generated from system

The maximum amount of power generated in the normal mode of the system will be 2.4kW. Overtime the solar panels may be decline in inefficiency due to weather, age, wear and tear, and obstructions from the sun.

3. Temperature changes/environmental changes

Temperature changes and environmental changes may have negative effects on equipment. This may cause problems to the inverters due to their location. The inverters are located out in the shed and are subject to humidity, heat, cold and varying degrees of moisture. Inclement weather could damage the solar panels. Ambient temperature will affect battery capacity.

Measurable Milestones

The measurable milestones have been defined as

1. First meeting with Ms. Trusty, Mid-American Energy engineers.

A meeting was arranged with Ms. Trusty to clarify her goals for the system and to inspect the equipment that has been already purchased.

2. Define possible modes of operation.

Many possible modes of operation were analyzed for possible use.

3. Designing the system based on stand-alone (LBX) mode.

By defining the mode of operation for the system, other aspects of the systems were easily defined. For example the electrical schematics needed to wire the entire system was easily achieved. Furthermore by analyzing the cost of each mode of operation on the basis of how cost effective the system will be for the customer was an important decision.

4. Mid American final approval of the integrated system

Mid American Energy has taken a pivotal roll in this project since they are the power supplier for the customer. For the most part, the approval of Mid American Energy will give a good estimation of how appropriate and successful the project will be.

End-Product Description

The parallel electric supply team has integrated several devices with the purpose of creating a renewable energy source that would supply the electrical loads of a residential household. The system is comprised of 24 Siemens photovoltaic panels, a set of eight, Trojan deep cycle batteries, two Trace converters that are able to convert the DC energy coming from the panels to an AC signal. The converters also provide many other capabilities. Among them is the management of power throughout the whole system, charging the batteries and isolating the system from the utility. Also a generator is integrated into the system so that when the utility and the batteries are not capable to supply the load the generator will be able to be turned on manually to supply the household load. The system mainly will be integrated with a utility supply as a back up in the LBX mode however; the system itself will act as a stand-alone for the most part supplying the load when the batteries are sufficiently charged.

Technical Approaches

The technical approaches that the team considered during the design phase were to design the system as a one that would sell power back to the utility or as a system that would only take power from the utility, different backup power designs, and feasibility of the use of the current generators.

In order to determine which mode of operation the system should be in the team will have to contact the various companies that the equipment was purchased from to gather information on the components and to ask advice from the experts as well ask communicate with Ms. Trusty and MAE in order to determine their concerns/desires. The decision of which mode to use will be determined by which mode will come closest to meeting Ms. Trusty’s goals for the project.

The team will need to develop different designs for possible backup power for the system. Possible sources of backup power are a small generator, an 18kW generator, and the existing utility company.

The team will also need to determine the feasibility of using the 18kW generator. This is a very large generator for residential use. The generator may generate too much noise and may not be cost efficient.

Technical Design

The technical design has been defined as

1. 24-Siemens Photovoltaic Cells rated at 100Watts apiece. These Solar panels are arranged in two sets of twelve and are the main power source for this system. These solar panels are combined in series.

a. The batteries generally will be charged in the daytime and supply Marge’s load in the nighttime.

b. This was modified from the initial concept statement because Marge wanted to sell power to her tenant. The Iowa codes and MAE would not allow her to do this because she was not a licensed supplier of power.

2. Solar array disconnect will disconnect the solar panels from the rest of the system for maintenance/safety reasons.

a. It was determined for this mode of operation, the LBX mode, a disconnect was not needed since the system runs as a standalone system.

b. In the future, a disconnect will need to be added if Marge plans to sell power.

3. Combiner will combine the two sets of solar panels into two legs. The combiner sums the voltage in each photovoltaic panel to create a summed series voltage.

a. This will produce the voltage needed to supply the batteries and SS5548 inverter/charger.

4. 8 Trojan RE-12X Deep Cycle Batteries rated at 320 Amp/hours apiece. These batteries are hooked up in series to provide 48VDC at 320A-hrs. These batteries are made for repeated cycling.

a. The batteries are deep cycle, lead acid batteries made for many cycles of charging and discharging.

b. Batteries are used as the main back up source in the system.

5. Winco 18000W Natural Gas Generator. This generator will be used solely in the case of a utility outage.

a. The generator will need to be turned on manually.

b. A switch will be placed inside of Marge’s house for ease of operation.

c. The generator will run isolated from the utility so no backfeeding occurs.

6. A Trace C40 controller. This controller has several functions. It assures that the batteries are properly charged; It also keeps track of the rate at which the batteries are discharging. Also, it senses the battery temperature and adjusts the voltage level set in the C40 accordingly for possible loss of capacity during cold weather. Finally, it is a protective device to insure that not too much current flows through the system. This is very important so the SW5548 does not get damaged. The C40 charge controller is very important device that senses the voltage level of the batteries, both minimum and maximum

a. The C40 also adjusts for the temperature of the batteries so in extreme temperatures when the voltage drops in the batteries, the C40 will adjust for this level.

7. A Trace SW5548 Inverter/Charge control unit. This device controls the flow of power throughout the entire system and makes sure that the utility feed will be disconnected when the panels and batteries are supplying the power. The SW5548 is the “brains” of the system since it coordinates all the operations needed to assure proper operation of the system.

a. It can control switching of sources; can be programmed to switch sources given different conditions.

b. It can monitor temperature of the batteries, run in parallel with the utility, and can control many features of the system.

8. Utility company (MAE) will provide backup power in case the solar panels are not producing enough power and the batteries do not have enough energy left in them.

The mode of operation selected was the LBX (stand alone) mode. This mode was chosen for a number of reasons. Currently, it is not cost effective to sell power back to the utility. The utility would pay only 1/8 the price that it charges per kWh. It was determined that in the LBX mode, the batteries could be used for storage and to supply Ms. Trusty’s load. In the SELL mode the batteries could only be used for selling power to the utility.

The LBX mode only allows one backup. The backup power source chosen was the utility. The generator was not chosen due to the fact that it is too expensive to operate and too loud to run on a regular basis. The team determined that backup power will be needed on a regular basis during the winter months when power from the photovoltaic cells will be at its lowest.

The 18kW generator is used as an emergency back up source due to Ms. Trusty’s wishes. The generator will be needed when the solar cells, batteries, and the utility cannot supply Ms. Trusty’s load. Ms. Trusty will turn on the generator manually, since in the LBX mode the generator cannot be operated manually.

The team also had to determine the feasibility of running the 18kW generator. This generator is quite large for a residential application. The main concern of running the generator is noise pollution. The generator produces sound that is comparable to that of a busy street. Therefore, the team recommends the installation of a sound barrier that would limit the noise levels of the generator unit.

Testing Description

The testing description have been defined as

1. Mid -American Energy approval of design.

2. Iowa City Electrical Inspector approval of design.

3. Ms. Trusty approval of design.

Currently these tests have not been completed.

Risks and Risk Management

The risks and risk management have been defined as

1. Loss of member of group due to unforeseen circumstances. The management of this unforeseen incident will take place by the other members of the group working much harder to pick up the work of the lost member.

2. Loss of project sponsor(s). In this case the group would need to consult with advisors to see if there are any changes in the expected result after the loss of the sponsor.

Recommendations For Follow-On Work

Recommendations for Ms. Trusty

1. Sound wall/Sound diffusion

The 18kW natural gas generator will need some type of sound barrier i.e. vegetation, or a sound wall. The output noise of the generator is 75dB at 7 meters. This could cause several complaints to nearby occupants.

2. Insulation/heating for the shed

The electronic equipment inside the shed is sensitive to adverse weather conditions. A study could be done assessing the feasibility and cost of heating the shed in the wintertime.

Recommendations for a future senior design group.

1. Legislation may be passed that will allow the customer to buy power for the amount that they sell it.

Any surplus power for the month will be credited toward the next month’s bill. In this case, the “utility interactive, or sell” mode is the most economically sound option. A team could finalize and approve a plan to do this.

2. Gathering load and solar information.

The system can be monitored with several different meters. A meter could be placed to measure Ms. Trusty’s load per day and a meter could be mounted to measure her solar generation capability. Another monitor could be placed to monitor Ms. Trusty’s battery charging and consumption. Using this information, one could easily determine the most effective means of operation. For each user, the recommended settings in the manual are not the most optimal.

Closure Material

Evaluation of project success

The goals attained for this project were as follows:

1. Analyzed each component in the system and understand its function.

a. There was a full understanding about the operation of each piece of equipment in Ms. Trusty’s system. This goal was 100% met.

2. Chose mode of operation that best fits the financial and power consumption needs of Marge Trusty.

a. There were several different modes of operation that were analyzed. The most cost effective mode was chosen, even though inside this mode there were several settings that were not analyzed for optimality. This goal was 80% completed.

3. Created a full wiring schematic for the standalone mode of operation.

a. A wiring schematic has been created that will seem to run under this mode. As of now, it has not been approved by MAE. This goal was 75% completed.

The goals unattained for this project were as follows:

1. Unable to create a system that can sell energy back to a utility in a cost effective manner.

Commercialization

Cost:

Around $20,000

The overall system is not cost effective and the commercialization of this product is not recommended because the profit does not pay back the cost of the components for around 20 years. This would only be recommended for someone who is into conservation and the effects that large power plants have on the environment.

Personnel Effort Budget

Table 1: Personnel Effort Budget

|Team Member |Original Effort |Revised Effort |Revised for March |Actual Effort to |

| |Estimate |Estimate |Estimate |Date |

|Josh Linebaugh |300 |200 |200 |188 |

|Luis Lobo |300 |180 |180 |151 |

|Andrew McArthur |250 |180 |180 |171 |

|Sean Smith |250 |225 |225 |219 |

|Totals |1100 |785 |785 |729 |

It is apparent that the group’s final budgeted hours were very close to revised for March estimate of hours.

Financial Budget

|Table 2: Budget for Parallel Electrical Supply Team | |

|Item |Original Budget |Revised Budget |Revised Budget Estimate|Actual Expenses |

| |Est. |Estimate | |to Date |

|Project Plan Bound |$0.00 |$3.13 |$3.13 |$3.13 |

|Poster |$50.00 |$53.00 |$55.00 |$55.00 |

|  |  |  |  |  |

|  |  |  |  |  |

|Total |$50.00 |$56.13 |$58.13 |$58.13 |

Besides the cost of the poster, there were no additional costs besides binding the reports.

Project Schedule

This is the team’s project schedule for fall semester 2001.

Figure 1.1 – Original

[pic]

Figure 1.2 – Final schedule for fall 2001.

[pic]

Spring 2002 – Figure 1.3

[pic]

Final revision – Figure 1.4

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Lessons Learned

Gathering information and understanding the operation of the system really got the project going. More detail and time early on should have been involved with understanding the workings of each part.

Approving diagrams and making sure the design was up to standard was difficult because of the amount of regulation involved.

Be able to easily adapt to the situation. There were times that the project was going backwards in nature, finding more problems than there were before.

Technical knowledge gained: Understanding the working of renewable energy sources and what it involves with a successful integration of the utility.

Project Team Information

Table 3: Project Team Information

|Name |Mailing Address |Phone Number |E-mail |Major |

|Andrew McArthur |301 S. Fifth St. Apt. 301 |515-663-0802 |amcarthu@iastate.edu |EE |

| |Ames, Iowa 50010 | | | |

|Luis Lobo |743 Garnet |515-233-4810 |llobo@iastate.edu |EE |

| |Ames, Iowa 50011 | | | |

|Joshua Linebaugh |407 S. Fifth St. Apt 129 |515-232-5254 |jlinebau@iastate.edu |EE |

| |Ames, Iowa 50010 | | | |

|Sean Smith |3326 Friley Hall |515-572-5397 |srsmith@iastate.edu |EE |

| |Ames, Iowa 50012 | | | |

|Dr. John Lamont |324 Town Engineering |515-294-3600 |jwlamont@iastate.edu | |

| |Ames, Iowa 50011 | | | |

|Prof. Glenn Hillesland |1111 Coover Hall |515-294-7678 |hilles@ee.iastate.edu | |

| |Ames, Iowa 50011 | | | |

|Prof. Ralph Patterson |326 Town Engineering |515-294-2428 |repiii@iastate.edu | |

| |Ames, Iowa 50011 | | | |

|Ms. Marge Trusty |1012 Cottonwood |319-338-1480 |none | |

| |Iowa City, Iowa 52240 | | | |

|Mr. Terry Harbour |One Riverplace Center |319-333-8327 |tharbour@ | |

| |106 E. 2nd St. | | | |

| |Davenport, Iowa 52801 | | | |

|Mr. Brian Phelps |Mid American Energy |319-341-4402 |bjphelps@ | |

| |1630 Lower Muscatine Rd. | | | |

| |P.O. Box 1760 | | | |

| |Iowa City, Iowa 52244 | | | |

Evaluation of project success

During the development of this project many steps were taken to narrow down the most important issues laid before the team. Systematically, the team made assessments and concrete decisions that would lead to a successful design. One important milestone achieved was the active involvement of the team with MidAmerican Energy engineers and the costumer Marge Trusty. Without their active participation, it would have been very difficult for the team to accomplish as much as it was accomplished. MidAmerican Energy and Marge Trusty’s full cooperation promoted an environment of trust and learning necessary for the project’s success.

The successful selection of the mode of operation for the system developed was critical for the proper functionality of the system. There were many aspect considered during the selection process, among them was the cost effectiveness of the system over a long period of time. According to the team’s estimations the sell mode is not a good cost effective mode since, MidAmerican Energy only would pay Marge Trusty a fraction of the price that she pay’s to buy power from MidAmerican Energy. According to Mid American Energy engineer Chuck Johnson his company only would pay 1.25 cents for every kWh that Marge Trusty could sell back.

Operation of the Stand-Alone (LBX) mode.

Automatic operation

|Case |Mode of Operation |Solar Panels |Batteries |Utility |Generator |

|A |Stand Alone (LBX |Supplying Power greater than load |Fully Charged |Disconnected |Off |

| |mode) | | | | |

|B |Stand Alone (LBX |Supplying Power greater than load |Charging |Disconnected |Off |

| |mode) | | | | |

|C |Stand Alone (LBX |Less than the load requirement |Discharging, making up the |Disconnected |Off |

| |mode) | |difference | | |

|D |Stand Alone (LBX |Less than the load requirement |Batteries reach fully |Utility connects to system; |Off |

| |mode) | |discharged state |go to E | |

|E |Stand Alone (LBX |Solar Panels are directly charging|Charging |Utility supplies load and |Off |

| |mode) |batteries | |charges batteries | |

|F |Stand Alone (LBX |Supplying Power greater than load |Charging/Full |Outage |Off |

| |mode) | | | | |

Manual Operation

|Case |Mode of Operation |Solar Panels |Batteries |Utility |Generator |

|G |Stand Alone (LBX |Less than the load requirement |Fully discharged |Outage |On; Will have to |

| |mode) | | | |switch-over manually |

I. The system operation in general.

The solar panels are feeding the load directly. Any additional power will be used to charge the storage batteries. If the level of the batteries is full, then the C40 controller will not let the batteries overcharge by redirecting the current to the load.

The batteries and solar panels will supply Marge’s load in parallel. In this mode of operation, there is can be only one back up source. The utility is used only as a back up in this mode, and no power is being sold back to the utility. The generator is much more expensive to run as a back up than the utility, so it was decided that the generator should be used solely in case of utility outage and the storage batteries are fully discharged. Then Marge will have to manually flip a breaker that will turn on the generator. This breaker will disconnect the generator from the system so that there will be no chance of back feeding into the utility and will feed only Marge’s load. The batteries will continue to be charged by the solar panel if the panels are generating power. Marge will have to determine when the utility comes back so that they can switch the generator off and switch back over to the utility as the supplier of power. The system will most likely start from Case A.

II. Classification of subsystems in the overall system.

There are three main subsystems that are defined as follows: solar panel subsystem, storage subsystem, and backup utility subsystem.

1. Solar Panel Subsystem

There are two sets of twelve solar panels in series. Each panel is made up of several photovoltaic cells. These cells convert light into a voltage potential. Then, these panels are used in series and combined with a photovoltaic source combiner that yields a usable voltage. This voltage, 48VDC can be converted from 48VDC to 120VAC through a Trace SW5548 Inverter/Charger. These panels are the main source for the load and storage batteries during daylight hours.

2. Storage Subsystem

Any excess power that does not go to the load will go into charging the back up batteries. These batteries are very similar to a typical lead-acid car battery, but they have a much larger capacity. These batteries will supply the load if there is not enough power being supplied from the solar panels. These batteries are the main source for the load at nighttime hours.

3. Backup Utility Subsystem

In case of when the solar panels system and the storage subsystem are not meeting Ms Trusty’s load demands, the C40 controller will sense the battery voltage level in the storage system and then automatically switch over to the backup utility system. When this occurs, the batteries will also act like a load. The backup utility system until the C40 controller senses that the batteries are recharged.

III. Different modes of operation (Cases A-G) Cases A-F are all automatic; Case G is a manual switch-over.

1. Automatic Mode of Operation.

Case A: The solar panels are supplying enough power to Ms. Trusty load and the batteries are full.

In this case, nothing is done. The solar panels will not be used fully to their capacity. The C40 controller in any mode will continuously monitor the battery voltage level.

Case B: The solar panels are supplying power greater than the load and the batteries are not fully charged.

The solar panels will continue to produce power and excess power will be stored in the batteries. If the C40 determines that the voltage in the batteries is maximized and the solar panels are still supplying a surplus amount of power, then the system will go back to Case A. If the batteries are not fully charged and the solar panels are now producing less than the load requirements then the system will go to Case C.

Case C: The solar panels are not supplying enough power to feed the load, and the batteries are not fully discharged.

In this case the solar panels and the batteries will be in parallel supplying Ms. Trusty’s load. This case describes the possible operation of two sub cases, when the batteries are only supplying Ms. Trusty’s load, and when both the solar panels and batteries are working in parallel to supply Ms. Trusty’s load.

Case Ca: The batteries are only supplying Ms. Trusty’s load.

This sub case will occur from dusk, through the nighttime hours, and then to dawn. The batteries will be the only supply of power because the solar panels are producing no power. The batteries will be discharged at a rate needed to supply Ms. Trusty’s load.

Case Cb: Both the solar panels and batteries are working in parallel.

In this case, both the solar panels and batteries are working together to supply Ms. Trusty’s load. The everyday natural cause of this case will most likely occur during the times when sun is rising or when the sun is just about to set. In either case the solar panels are not producing enough power and the batteries will have to make up the difference. During stormy weather this case could also occur when the clouds have really darkened the sky.

The other instance for this case is when Ms. Trusty has a large load attached to the system that requires more power than the solar panels can produce. If this happens, then the batteries will have to make up the difference in power.

The system will continue in Case Ca or Cb until either the sun comes up and the solar panels are producing enough power to supply the load and charge the batteries (Case B) or until the C40 controller senses the batteries reaching the minimum voltage level set by the system (Case D.)

Case D: Batteries are fully discharged.

The solar panels are not producing enough power and the batteries have reached the fully discharged state detected by the C40 controller. The system will automatically go to Case E.

Case E: Utility switch-over.

The C40 has now sensed that the batteries are discharged. The utility will now take over and supply Ms. Trusty’s load and charge the batteries at a rate specified by the user (typically 10-13% of the batteries capacity, so in this case the battery has 100A-hrs then the charging rate would be around 10-13A). In other words, in this mode the batteries also appear as a load to the utility. The solar panels in this mode will only charge the batteries. After the batteries are fully charged by the utility and solar panels, then the system will go to Case A or Case C, whichever one is applicable at the time that this occurs.

Case F: Utility outage and batteries are not fully discharged

If the utility has an outage and the system is currently in Case A, B or C, nothing will happen. If the system is currently in Case E (load dependant on the utility) then the user will have to manually go to Case G.

2. Manual Mode of operation.

Case G: Generator only mode.

There will be a manual switchover to the generator by the user. The generator will be able to be started with a breaker that when one pole is closed, the other pole is open. This allows only the generator system or solar and battery systems to be on. If this breaker is thrown, the utility is cut-off from the system, and the solar panels will only be charging the batteries, if they need charging. The generator will be started and run until the user determines that the utility is back. When the utility comes back, then the system will default back to Case E, or if the batteries are totally charged (unlikely) then the system will go back to Case A or C.

Summary

This project deals with implementing several pre-purchased components and hooking them up to produce a renewable energy source that will be stand-alone in operation. This system will implement a design to minimize the use of a utility as a primary source of energy. With the use of solar panels, this system will help the environment by reducing the consumption of power generated by fossil fuels. The focus of the project was to create a design agreed upon by Marge Trusty, MAE, and Iowa City.

References

Trace Engineering:

Professor Glenn Hillesland – Iowa State University of Science and Technology

Iowa Energy Center: energy.iastate.edu

Mr. Chuck Johnson: Mid-American Energy, Iowa City

Lake Michigan Wind and Sun: 920-743-0456

Appendix A: Solar Panel Generation Vs. Marge’s Load

Table 1: Data of Average monthly solar panel generation in Iowa City and Marge’s load.

|Monthly Average of Solar Panel Production | |Marge's Usage | |Monthly Average of Solar Panel Production | |Marge's Usage | |Monthly Average of Solar Panel Production | |Marge's Usage | |Monthly Average of Solar Panel Production | |Marge's Usage | |Jan-99 |258.6 |kWh | |Jan-00 |258.6 |kWh |463 |Jan-01 |258.6 |kWh |344 |Jan-02 |258.6 |kWh |401 | |Feb-99 |265.7 |kWh | |Feb-00 |265.7 |kWh |447 |Feb-01 |265.7 |kWh |313 |Feb-02 |265.7 |kWh |363 | |Mar-99 |325.6 |kWh |393 |Mar-00 |325.6 |kWh |451 |Mar-01 |325.6 |kWh |298 | | | | | |Apr-99 |299.3 |kWh |485 |Apr-00 |299.3 |kWh |424 |Apr-01 |299.3 |kWh |279 | | | | | |May-99 |306.4 |kWh |424 |May-00 |306.4 |kWh |355 |May-01 |306.4 |kWh |292 | | | | | |Jun-99 |328 |kWh |366 |Jun-00 |328 |kWh |354 |Jun-01 |328 |kWh |238 | | | | | |Jul-99 |306.4 |kWh |425 |Jul-00 |306.4 |kWh |365 |Jul-01 |306.4 |kWh |209 | | | | | |Aug-99 |284.9 |kWh |358 |Aug-00 |284.9 |kWh |403 |Aug-01 |284.9 |kWh |201 | | | | | |Sep-99 |320.8 |kWh |460 |Sep-00 |320.8 |kWh |386 |Sep-01 |320.8 |kWh |201 | | | | | |Oct-99 |318.4 |kWh |441 |Oct-00 |318.4 |kWh |475 |Oct-01 |318.4 |kWh |285 | | | | | |Nov-99 |170 |kWh |471 |Nov-00 |170 |kWh |477 |Nov-01 |170 |kWh |282 | | | | | |Dec-99 |177.2 |kWh |528 |Dec-00 |177.2 |kWh |400 |Dec-01 |177.2 |kWh |408 | | | | | |

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Figure 1: Chart of Solar Panel Generator vs. Marge’s load. (in kilowatts)

Appendix B: Calculation of Solar Panel Generation

Calculation of area of solar panels to conversion from inches to meters.

Solar panels are 23.5” X 59” = 1386.5 sq in. We decided to undersize them to get conservative values. We used 20” X 58” which is 1160 sq in. This equates to 16% less surface area for calculations. 1160 X 24 panels equals 27840 sq in. total. This comes out to roughly 18 m².

(Iowa Energy Center) gives numbers for average power production for Iowa City. This number is given in 1000W/m². These solar panels can only produce 100W per each panel. Each panel is 0.75m² so the number given by the IEC was scaled by a factor of 0.133. The data was used for solar panels mounted at a fixed position at 60 degrees with the horizon. A mounting of 50 degrees makes very little difference in production values.

Appendix C: Parts Information

Parts Information

Solar Panels: S/N: 2054099 - Siemens SR100 Photovoltaic Module

Number in system: 24

Rating: 100W Maximum

Short Circuit current: 6.3A

Rated Current: 5.6A

Voltage = 22.0V

Rated Voltage = 17.7V

Dimensions:

Each individual panel: 23.5”X 59”

Contact Information

800-743-6367

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Winco Standby Generator: S/N 58756099 – Model PSS20000/B

Number in system: 1 unit

Generator: 20000W liquid propane, 18000W natural gas

3600RPM

Voltage: 120/240VAC

dB level: No load 72dB @ 7m, loaded 75dB @ 7m

(this is roughly the same noise as a busy street)

Contact Information

Jim – 507-357-6707 or 800-423-6569

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Winco Automatic Transfer Switch

(For use in conjunction with the Winco Standby Generator)

230/150ATS-3 Transfer Switch.

Number in system: 1

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Trojan Battery Company

Deep Cycle Battery – RE12X (obsolete). “Small battery in large case”

Deep Cycle Lead Acid

Storage: 305Ahrs. (based on 20hr rating)

Voltage: 6V

Configuration: Eight (8) 6V- batteries in series to create 48V.

Cycle usage: At least 600 full cycles (fully charged to empty) More cycles if only partial charging/discharging.

Recharging rate: Can be any rate. Rate set by controller. Recommended to be 10% of capacity of battery or 305*0.1 = 30Amps.

Specific Gravity: Between 12.70 and 12.77

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Trace Engineering SW5548 Inverter/Charger

(See attached manual)

Contact information: 360-435-8826

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Trace Engineering C40 Charge Controller

(See attached manual)

The C40 charge controller is hooked up in “Photovoltaic Charge Control Mode”. This mode is preferred for Solar Panel generation. The C40 allows a 48VDC input at 40Amps. The C40 has a built-in sensor that automatically shuts down if there is too much current flow and will reset after 10 mins if the overcurrent condition is not present. The C40 also automatically disconnects the solar panels from the system when it is determined that the panels are not producing power. This is to ensure that there is no loss in “reverse leakage” of power.

LED status indicator: The C40 uses a green LED to indicate the voltage level in the battery. If the battery is at FLOAT setting then the LED will be a constant green. If the battery is set at BULK setting, the LED will blink rapidly 5 times showing that the battery is fully charged. If the LED is blinking once, this shows the battery is empty.

Finally, if the LED is blinking orange, then the controller has detected an over-current or over-temperature condition. The controller will try to automatically reset. If it does not reset, then switch off all the loads and then manually reset the device.

Contact information: 360-435-8826

Appendix D: Flow Chart of LBX (stand alone) operation

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Appendix E: One Line Diagrams of different conditions

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Appendix F: Wiring schematic of system

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Appendix G: Real time current data taken from Marge’s residence

Channel 1 (Leg A)

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Channel 2 (Leg B)

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Appendix H: Real time voltage data taken from Marge’s residence

Channel 1 (Leg A)

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Channel 2 (Leg B)

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Appendix I: Trace 5548 Inverter/Charger

Disclamer: Material that follows is public domain to all users. This material is for use by the owner, installer, and staff only. This material is reproduced from Trace Engineering.

Appendix J: C40 Charge Controller

Disclaimer: Material that follows is public domain to all users. This material is for use by the owner, installer, and staff only. This material is reproduced from Trace Engineering.

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