DiOrio, Nicholas A | Search NASA

DOE OSTI2020

Field-Aging Test Bed for Behind-the-Meter PV + Energy Storage

Small DC-coupled battery test systems are deployed at the National Renewable Energy Laboratory to evaluate capacity fade models and report on performance parameters such as round-trip efficiency under indoor and outdoor deployment scenarios. Initial commercial battery products include LG Chem RESU lithium-ion (Li-ion) and Avalon vanadium redox flow batteries. Adapting indoor lab-scale test methods to outdoor systems has challenges, including maintaining constant temperature and fully controlling batteries through standard discharge curves. Initial measurements show the Li-ion battery systems performing within expectations, near 85% round-trip efficiency. Initial lifetime modeling and measurements indicate that battery capacity could degrade by 20%-35% over 10 years at current rates.

14 SOLAR ENERGY↗

DOE OSTI2019

Research Opportunities in the Physical Design Optimization of Hybrid Power Plants: Preprint

With renewable energy growing to 10%-20% or more of overall electricity generation, design objectives for renewable power plants are shifting from producing energy at the lowest levelized cost to maximizing profitability. Several research and commercial efforts have investigated how to size respective generation and storage assets together for hybrid power plant systems - including wind, solar, battery storage and other technologies. However, the physical design of hybrid power plants has yet to be considered in detail. Even the design of individual solar and wind power plants is complex with large numbers of design variables, constraints and complex physical interactions across subsystems. Developing an integrated approach for the design of hybrid power plants including multiple generation technologies compounds this complexity and requires domain knowledge across the technologies as well as new approaches for addressing the statistical representation of resource availability and revenue opportunities. To inform the research needs on physical design of these hybrid power plants, a workshop was held in December 2018 at the National Renewable Energy Laboratory. This paper provides a summary of findings from the workshop on research needs for hybrid power plant design.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2019

DC-Connected Solar Plus Storage Modeling for Behind-the-Meter Systems in SAM

A detailed model for PV plus DC-connected batteries was developed. This model was compared to an existing AC connected battery model in the System Advisor Model (SAM) tool using a hypothetical Honolulu residence with a PV plus storage system. The stand-alone PV system was shown to provide the most value; however due to the increased difficulty of PV systems being approved for grid interconnection in Hawaii, it is valuable to install an AC or DC connected battery to enable full PV self-consumption under a less restrictive interconnection option. In that case both battery systems enabled full PV self consumption at the residence, requiring no power to be exported to the grid. The DC-connected battery system captured energy from the PV array which would have also been clipped due to inverter limitations. For a PV system with DC/AC ratio of 1.23, the battery configurations produced net-present values within 1% of each other, but when the DC/AC ratio increased to 1.85, the DC-connected system increased the net-present value by 13%.

14 SOLAR ENERGY↗

DOE OSTI2019

Field Aging Testbed for Behind-the-Meter PV + Energy Storage

Small DC-coupled battery test systems are deployed at NREL to evaluate capacity fade models and report on performance parameters such as round-trip efficiency under indoor and outdoor deployment scenarios. Initial commercial battery products include LG Chem RESU Lithium-ion and Avalon vanadium-redox flow batteries. Adapting indoor lab-scale test methods to outdoor systems has challenges, including maintaining constant temperature and fully controlling batteries through standard discharge curves. Initial measurements show the Lithium Ion battery systems performing within expectation, near 85% round-trip efficiency. Initial lifetime modeling and measurements indicate battery capacity may degrade by 20%-35% over 10 years.

25 ENERGY STORAGE↗

DOE OSTI2019

Hybrid Systems to Enable High Penetration PV: Preprint

A model for PV plus energy storage and fuel cells was developed in the System Advisor Model (SAM). This model was used to evaluate the ramp rate and interconnection capacity factor for a hypothetical utility-scale plant for several configuration options. For PV only, the plant experienced 3345 violations of a 10%/minute ramp up limitation and a interconnection capacity factor of 17.6%. Adding a battery reduced the violations to 154 per year and the magnitude of the average violation to 2%. Adding a fuel cell to the PV system increased the capacity factor to 78% without improving ramp violations. Using a combined PV plus storage plus fuel cell arrangement maintained the improved capacity factor while reducing ramp up violations to 23, illustrating the potential to operate a hybrid system both to enable grid integration requirements and increase utilization of the interconnection.

14 SOLAR ENERGY↗

DOE OSTI2019

Hybrid Systems to Enable High Penetration PV

A model for PV plus energy storage and fuel cells was developed in the System Advisor Model (SAM). This model was used to evaluate the ramp rate and interconnection capacity factor for a hypothetical utility-scale plant for several configuration options. For PV only, the plant experienced 3345 violations of a 10%/minute ramp up limitation and a interconnection capacity factor of 17.6%. Adding a battery reduced the violations to 154 per year and the magnitude of the average violation to 2%. Adding a fuel cell to the PV system increased the capacity factor to 78% without improving ramp violations. Using a combined PV plus storage plus fuel cell arrangement maintained the improved capacity factor while reducing ramp up violations to 23, illustrating the potential to operate a hybrid system both to enable grid integration requirements and increase utilization of the interconnection.

14 SOLAR ENERGY↗

DOE OSTI2018

DC-Connected Solar Plus Storage Modeling and Analysis for Behind-the-Meter Systems in the System Advisor Model

A detailed model for PV plus DC-connected batteries was developed. This model was compared to an existing ACconnected battery model in the System Advisor Model (SAM) tool using a hypothetical Honolulu residence with a PV plus storage system. The stand-alone PV system was shown to provide the most value; however due to the increased difficulty of PV systems being approved for grid interconnection in Hawaii, it is valuable to install an AC or DC connected battery to enable full PV self-consumption under a less restrictive interconnection option. In that case both battery systems enabled full PV selfconsumption at the residence, requiring no power to be exported to the grid. The DC-connected battery system captured energy from the PV array which would have also been clipped due to inverter limitations. For a PV system with DC/AC ratio of 1.23, the battery configurations produced net-present values within 1% of each other, but when the DC/AC ratio increased to 1.85, the DC-connected system increased the net-present value by 13%.

14 SOLAR ENERGY↗

DOE OSTI2018

Solar System Modeling at NREL

This workshop walked through a description and demonstration of solar modeling data and tools available from the US National Renewable Energy Laboratory (NREL). The topics included: The National Solar Radiation Database (NSRDB) - updates and ways to access this sub-hourly gridded resource data; PVWatts - recent updates to include the NSRDB - opening up much of North and South America for analysis; System Advisor Model (SAM) - SAM is now open source, includes PV + batteries, bifacial panels, and much more; REOpt Lite - an online tool for quick PV and battery sizing for commercial buildings; PV Component LCOE Calculator - Allows for module costing based on components; A detailed demonstration of the SAM model for modeling a PV system with a battery and some of the questions that can be answered.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2018

Economic Dispatch for DC-Connected Battery Systems on Large PV Plants

Falling costs of energy storage combined with an increasing need to mitigate variable generation integration issues is leading to more PV projects that include batteries. Large PV plants that include batteries face challenges optimizing the value of the power they produce, especially when the batteries are DC-coupled and otherwise clipped power (due to high DC/AC ratio) is available. Multiple charging times and sources must be considered, including: grid charging, charging from PV that would otherwise be exported to the grid, and charging from clipped PV power. Then discharge schedules must be optimized against time-of-day pricing. The National Renewable Energy Laboratory in partnership with Southern Company has developed a heuristic algorithm in the System Advisor Model (SAM) which strategically charges the battery from PV and discharges the battery depending on the time-of-day prices of the PPA, the forecast PV production, and the estimated wear cost of the battery. The algorithm and case study results from a generic plant will be presented with recommendations for future work.

25 ENERGY STORAGE↗

DOE OSTI2018

Bifacial Simulation in SAM

A bifacial irradiance model is introduced within the System Advisor Model (SAM). The modeling steps and implementation in SAM are presented. The results of a bifacial simulation are compared against several other modeling programs and shown to match within 1 - 2 percent for fixed-axis and horizontal single axis tracked systems. An example case study is presented to demonstrate how the model can be used to evaluate bifacial systems, with a variety of results presented to illustrate different sensitivities.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2018

DC-connected Solar Plus Storage Modeling and Analysis for Behind-The-Meter Systems in the System Advisor Model: Preprint

A detailed model for PV plus DC-connected batteries was developed. This model was compared to an existing AC connected battery model in the System Advisor Model (SAM) tool using a hypothetical Honolulu residence with a PV plus storage system. The stand-alone PV system was shown to provide the most value; however due to the increased difficulty of PV systems being approved for grid interconnection in Hawaii, it is valuable to install an AC or DC connected battery to enable full PV self-consumption under a less restrictive interconnection option. In that case both battery systems enabled full PV self consumption at the residence, requiring no power to be exported to the grid. The DC-connected battery system captured energy from the PV array which would have also been clipped due to inverter limitations. For a PV system with DC/AC ratio of 1.23, the battery configurations produced net-present values within 1% of each other, but when the DC/AC ratio increased to 1.85, the DC-connected system increased the net-present value by 13%.

14 SOLAR ENERGY↗