Joshua D. Rhodes

Data management for a large-scale smart grid demonstration project in Austin, Texas

This paper presents a data management scheme for the Pecan Street smart grid demonstration project in Austin, Texas. In this project, highly granular data with 15-second resolution on resource generation and consumption, including total consumption of electricity, water, and natural gas and solar generation, are collected for more than 100 homes. Furthermore, this testbed, see Figure 1, of homes represents the nation’s highest density of rooftop solar PV and electric vehicles, and includes a substantial subset of homes that are highly instrumented with meters on up to 6 sub-circuits in addition to the whole-home meter. Consequently, this demonstration project generates a one-of-a-kind dataset with excellent temporal and geographic fidelity.One consequence of this extensive dataset is that there are hundreds of parallel data streams that need to be remotely (wirelessly) collected, filtered, processed, managed, stored and analyzed to be useful for researchers. Cumulatively, they represent 100s of gigabytes of data after just a few months of collection, which represents a formidable barrier to conducting research.In partnership with the Texas Advanced Computing Center (TACC), which is an NSF-sponsored cluster of supercomputers at UT-Austin, a data collection and management scheme has been developed. For storing the data, we have built a single column oriented database that so far has shown tremendous performance benefits. This paper shows the data schema, an example of MySQL query, and a developed program for rapid and automated data extraction, analysis and display. We expect that the findings of this work will be beneficial to researchers interested in grid-scale data management.© 2012 ASME

Modeling a Combined Energy-Water Storage System for Residential Homes and Analyzing Water Storage Tank Size

Air conditioning systems (AC systems) are the primary driver of summer electricity use and peak power demand in residential homes in Texas, mostly due to the refrigerant compressor in the condenser unit. The power demand for a residential AC compressor is on the order of kilowatts. Peak power demand from residential AC systems could be reduced by means of pre-cooling a thermal storage reservoir, which can be used as a heat sink instead of the air-cooled outdoor condenser that is subject to ambient conditions. The concept of thermal storage is not new, and is in widespread use in large-scale HVAC systems for the commercial and industrial sectors. However, residential thermal storage systems, while available, are not widespread due to high costs relative to the costs of the AC system.This paper discusses the development of a simplified thermodynamic model of a water-based sensible thermal storage reservoir for reducing peak AC compressor loads, and determines optimal tank sizing based on a few key design parameters. The motivation behind this project is the idea of utilizing a large water reservoir that could be on-site for other purposes already, specifically large rainwater collection systems. Such a combined energy/water storage configuration might increase the cost effectiveness of both a thermal storage system and a rainwater collection system by means of shared costs and avoided energy and water expenses.The system configuration consists of a typical direct expansion residential air conditioning system with a typical air-cooled condenser unit, but with an additional thermal storage condenser/evaporator heat exchanger connected into the refrigerant lines with reconfigurable flow paths and solenoid valves to control the discharging and recharging of the thermal reservoir. The large volume of stored water acts as a lower temperature thermal reservoir for the secondary condenser. The lower temperature and better heat transfer capabilities of water improve operating efficiency and reduce power consumption when used instead of the air-cooled condenser during the hottest hours of the day.The system model was evaluated using cooling load outputs for a simulated 1800 square foot home in Austin, Texas based on weather data from summer 2011, which was a record hot summer that stressed the Texas electricity grid to its limits. Preliminary analysis based on a simplified model of the system, along with the specified model parameters, suggests that thermal storage systems would be on the order of several thousand gallons, which corresponds to that of a large rainwater collection system. Additionally, the analysis suggests that power demand reduction during peak is likely the primary benefit of the system, with an average reduction on the order of 30–70% less than the system without storage, depending on operating parameters. However, total energy consumption could be either slightly higher or lower than the baseline, depending on a variety of factors such as diurnal temperature swing, discharge/recharge control, compressor efficiency, and tank size.Copyright

The Role of Small Distributed Natural Gas Fuel Cell Technologies in the Smart Energy Grid

As the utility grid evolves to transmit information along with energy and water to the end-user, the traditional grid model is changing. The Pecan Street Smart Grid Demonstration Project in Austin, TX is at the leading edge of the evolution of the smart grid. Currently, over 100 homes, soon to be 1,000, have electricity demand information being measured on a 15 second interval. Using the highly granular energy use and solar generation data from Pecan Street, we attempt to estimate the potential for small natural gas fuel cells as distributed firming power for intermittent renewables in the built environment. Micro-grids have traditionally relied on the macro-grid for stabilization in the event of local interruptions in generation. In this paper we analyze the utility, economic, and system efficiency impacts of small distributed natural gas fuel cells as an alternative to the macro-grid for stabilization. Using our unique dataset, we have determined that the average home could utilize a 5.5 kW fuel cell either for total generation or backup, and the average home could operate as its own micro-grid while not sacrificing core functionality. We also explore the utility of matching the thermal output of a possibly smaller fuel cell, used in combined heat and power mode (CHP), to an absorption refrigeration system in place of traditional space cooling. With these types of energy assets, homes could possibly participate with local electricity markets, or the grid at large, in a highly dynamic way. A home energy network could, given homeowner set-points, adjust home uses of energy and sell high priced electricity back to the grid, possibly from both solar PV and fuel cell production, possibly eliminating energy bills. Lastly, we estimate that the system efficiency could possibly double by transporting natural gas to the end user to be converted into electricity and hot water as compared with traditional methods of using natural gas for power generation followed by electricity delivery.Copyright

Community-scale air conditioning control for high penetration of rooftop photovoltaics

This paper investigates the potential of coordinated air conditioning control for a simulated community of 900 homes with a high penetration of rooftop solar photovoltaic (PV) panels. The simulated community of homes is created from an extensive data set including home energy audits, homeowner surveys, and electricity meter measurements from actual homes in Austin, Texas, USA. Coordinated air conditioning control in the homes is simulated using a rolling horizon model predictive controller to minimize the peak demand of the community using both centralized and decentralized control methods. By manipulating thermostat set points, the controller takes advantage of the thermal mass of the buildings to store thermal energy. In all cases considered, the centralized controller outperforms the decentralized controller, but both lead to significant reductions in peak electricity demand. We find that decentralized control achieves nearly the same peak reduction as the centralized control method when all homes have rooftop PV. We also find that coordinated air conditioning control achieves a marginally smaller benefit as the penetration of rooftop PV increases.