Concentration and Storage of Solar Energy in Mining Facilities

Our project is to develop a testing bed that will help determine the feasibility of storing solar energy within a mining facility. Mining operations leave behind a plethora of usable materials such as mine waste rock, overburden, and/or tailings, Carbon Dioxide and a large amounts of usable land. We wish to take these leftover materials and put them to use storing solar energy.

=Problem Definition= Active and legacy mine sites in the United States present many large-scale environmental challenges. Active mining requires permits that require mine development and closure plans that adhere to strict environmental regulations regarding water, land, and habitat resources. Many legacy mines were closed prior to enactment of modern environmental regulations, and they have since become large-scale sources of land and water contaminants. At some legacy mines, contamination of nearby land and/or water resources will continue into perpetuity without large-scale site reclamation.

All mines ultimately close once the ore is exhausted either due to total removal by mining or loss of value. With mine closure comes loss of mining jobs.

A profitable nexus may exist between the mining industry and the renewable energy storage industry. In this project we ask the question: Can the heat from concentrated sunlight be efficiently stored in mine waste rock, overburden, and/or tailings? Active and legacy mine sites contain billions of tonnes of mine waste rock, overburden, and/or tailings in the USA alone and many more billions of tonnes worldwide. The next few decades are expected to experience a huge increase in demand for grid-scale storage of intermittent renewable energy sources such as solar and wind, and we think this could be a solution.

Background
Ray Donelick approached the University of Idaho seeking assistance in designing a small scale solution. Ray envisioned a system to focus solar energy and store the heat generated inside of a back-filled mining pit. Solar collectors will focus the energy on a receiver carrying Water. The water will then pass through a heat exchanger depositing the energy into Carbon Dioxide, one of the major pollutants from fossil fuel energy generation. the hot carbon dioxide will then run underground to the thermal storage container. This container consists of a insulating outer barrier with mining waste rock on the inside. The carbon dioxide will run into the thermal storage container and deposit the heat into the mining waste rock where it can be stored for long periods of time. Once the energy is stored, the consumer can tap into the available energy when solar energy cannot be readily collected.

Deliverables
The deliverables for this project is a complete testing bed to provide a proof of concept. The parts that will make up this testing bed are as follows:
 * One in-line air heater: This will heat take the place of a solar collector for testing purposes.
 * One pump: To move air through the thermal storage system.
 * Piping system: This will allow us to direct air into the testing or control chamber.
 * The thermal collection testing chamber: to perform various experiments and collect temperature data on heated rocks.
 * Temperature collection system: this will consist of a thermocouple array to collect temperature data along the chamber length.

=Specification= As this is a testing bed, we want to be able to apply a wide range of values for fluid temperature and flow rates. We also wish to construct the system as close to real-life conditions as possible and collect accurate temperature data for various experiment run times. Below are some general requirements of the system.

Thermal Chamber
The thermal chamber must be able to perform under the following conditions:
 * Contain 2 meters cubed worth of gravel.
 * Be assembled from basic construction materials.
 * Be able to have a test chamber that can be modified for various experiments.
 * Withstand temperatures of up to 600 Fahrenheit.
 * Not allow the working fluid to leak from the system.

In-Line Heater
The in-line heater must be able to perform under the following conditions:
 * Heat the working fluid within a range of 200-600 Fahrenheit.
 * Operate at a variety of fluid flow rates.

Air Blower
The air blower must be able to perform under the following conditions:
 * Operate at fluid temperatures between 200 and 400 Fahrenheit.
 * Supply the required static pressure to allow fluid flow through the chamber.
 * Supply a variety of fluid flow rates.

Data Collection System
The data collection system must be able to meet the following requirements.
 * Collect temperature data with a total accuracy of one degree Celsius.
 * Collect data at multiple locations within the test chamber simultaneously.
 * Store large amounts of data in a usable format.
 * Collect data for large experiment run times.

=Design Considerations= There are several large considerations we have had to deal with. The biggest considerations are as follows:
 * All our equipment must be able to run on standard household 240V/120V power.
 * All materials used to construct the testing chamber must be commercially available at most department stores.
 * Piping materials and sealants must be able to withstand the temperatures of the working fluids within them.
 * Temperature and pressure wires and connections must be able to be buried within the chamber.
 * The data collection system will have to store data for long periods of time, preferably within a CSV or TXT file.

=Project Learning= Our main purpose for this project was to concentrate solar energy and store it in a test system. However due to cost issues we were not able to acquire a solar collector. The scope of our project then changed to the design of the testing bed and building a scale model. I have attached the latest system diagram below. The testing bed requires a thermal chamber, an in-line heater, an air blower, an air compressor, and several globe valves. The following sections will describe the learning associated with each part of the project.

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 * Thermal system.PNG

Solar Collection System
The largest component of our project was a solar concentrating device. This would focus sunlight into a single line where it could heat the working fluid. These devices are readily available and come in several different configurations. Solar troughs use a parabolic trough to focus the sunlight to the central point. These tend to be the most efficient but are the most expensive and most susceptible to weather. Linear Fresnel Mirrors act like a parabolic trough, but use an array of flat mirrors to imitate the parabolic curve. This creates less weather susceptibility at the price of efficiency. Both of these ideas were considered and two major problems arose. One, the size of these devices varies, but is no smaller than 70 squared feet. This is larger than we had room to house. Another issue was the cost. A single system at 70 square feet came with a price of $10,000 which was well outside of our budget. For more information on these systems, click the links under the pictures below. For more information on concentrated solar power in general click here.

Thermal Chamber
Since a solar collection system has its own inherent difficulties, we decided to focus more on the thermal chamber aspect of the project. Our current restrictions are mainly size orientated. We have been allotted a space of about 15X15X10.5 feet to house the chamber and all components. We chose to go with a long, double pipe chamber. This will allow us to have a control and experiment path. The chamber will be accessible from the top via a removable lid. We also decided to construct this chamber from lumber and cement board. This will allow for simple construction and immediate access to materials. The 3D-model of our testing chamber is shown on the left, a photo of the completed chamber is on the right and the full construction plans are available [here].

In-line heater
A in-line heater will take the place of the solar collection system for our testing. We need a heater that can heat air to 600 Fahrenheit and handle multiple flow rates. We purchased a heater from the supplier OMEGA. The heater can heat air up to 600 Fahrenheit and runs off of either 240 or 120 volt power supply. The heater is rated for up to 200 CFM volumetric flow and can supply 500 to 2400 WATTS of energy to the air. For more detail about this specific heater, click here.

Air Blower
We have determined that for our testing system, a blower with a one HP motor will meet our requirements. a one HP motor will be able to apply 7.0 in-SP, moving the air through the chamber at a rate of ~ 3 CFM volumetric flow. We have narrowed down the selection to several different blowers. The blowers require a power range of 120V to 430V. We still need to determine if our power supply is 3-phase or 1-phase power. For a full comparison of the motors we are deciding between, see the blower section of the system design document.

Data Collection System
The data collection system had to inexpensive, accurate and simple to implement. We chose K-Tyle thermocouples as our sensors within the chamber. Thermocouples, while less accurate than RTD's, came in longer lengths, were less expensive and met our accuracy requirements. The thermocouple signal will be passed into operational amplifiers, these will boost the signal to be read by our central data collector. The operational amplifiers we chose come on a PCB with all connections easily identified and a calibration equation supplied. The thermocouple, operational amplifier, and signal headers will all be soldered together for strong connections. For a central data collector, we decided to use an ARDUINO MEGA. This microprocessor can handle 16 analog inputs, allowing for 16 simultaneous temperature readings. The temperature readings will be sent from the ARDUINO into a desktop computer to a TXT file. The TXT file will contain all the temperature readings for later data analysis. We can set the microprocessor to take readings at discrete time steps, and since we are connected to a desktop computer we do not have to worry about space.

=Final Design=

=Validation=

=Team Members=

=Additional Documentation=

Project Schedule

[[Media:project schedule.pdf|Project Schedule]]

Meeting Minutes

[[Media:Meeting Minutes 9-10.pdf|Meeting Minutes September 10th]] [[Media:Meeting Minutes 9-17.pdf|Meeting Minutes September 17th]] [[Media:Meeting Minutes 9-24.pdf|Meeting Minutes September 24th]] [[Media:Meeting minutes 10-9.pdf|Meeting Minutes October 9th]] [[Media:Meeting Minutes 10-16.pdf|Meeting Minutes October 16th]] [[Media:Meeting Minutes 10-23.pdf|Meeting Minutes October 23th]] [[Media:Meeting Minutes 10-30.pdf|Meeting Minutes October 30th]]

Presentations

[[Media:Meeting 10-02.pdf | Solar Collection Methods]] [[Media:Thermal Analysis .pdf | Early System Analysis]] [[Media:design review meeting.pdf | Design Review Presentation]]

Snapshot Posters

[[Media:snapshot 1 poster.pdf | First Snapshot Posterboard]] [[Media:snapshot 2 poster.pdf | Second Snapshot Posterboard]]

Reference Materials

[[Media:Re technologies cost analysis-csp.pdf|Cost analysis of Renewable Energy Technologies]] [[Media:Solar trough mathmatical report.pdf|Heat Transfer Analysis and Modeling of a Parabolic Trough Solar Receiver Implemented in Engineering Equation Solver]] [[Media:Thermal analysys of the performance of linear fresnel collectors.pdf|Thermal Analysis of the Performance of Linear Fresnel Solar Concentrator]] [[Media:Thermal efficiencies of linear fresnel collectors with other working fluids.pdf|Methodology for the Thermal Characterization of Linear Fresnel Collectors: Comparative of Different Configurations and Working Fluids]] [[Media:1-s2.0-S1365160902000229-main.pdf|A modeling approach for analysis of coupled multiphase fluid flow, heat transfer, and deformation in fractured porous rock]]