(14a) Local Renewable Chemical Production for Combined Heat and Power in Remote Locations: Optimal Design and Operation

Generation of electrical power from intermittent sources of renewable energy such as the wind or the sun is a promising approach to improving energy sustainability. Renewable energy storage is necessary to balance this intermittent generation with electrical power demands. Batteries are the most used energy storage technology, but their capital cost and relatively low energy density makes them unsuitable for longer-term, high-capacity energy storage. Production of hydrogen (H₂) via water electrolysis or further processing to ammonia (NH₃) are alternative energy vectors more suitable to seasonal storage. Power generation via H₂-fed fuel cells is well-established whereas NH₃ has received worldwide attention [1-4] for power generation with either fuel cells or traditionally fossil-fueled technologies (e.g. internal combustion gensets) with minor modifications. Previously, we have investigated 1 MW residential electrical power supply systems with chemical energy storage in 15 American cities which represent various climate-demand regions throughout the continental United States [5]. We found that in every location, cost savings can be achieved by using both synergistically. While promising, these systems are not yet economically competitive with centralized fossil fuel-based electricity generation and transmission.

In this work, we optimize and analyze combined heat and power (CHP) systems in remote locations where the conventional supply paradigm is less economically favorable. At present, power and heat supply in these areas is expensive, entailing long distance electrical transmission and the import of fossil fuels for local heating or small-scale local generation. Combining heat and power demands allows for effective utilization of waste heat from power generation and furthermore, renewable-derived H₂ and NH₃ can be used to generate heat using boiler-type technologies [6]. Economically competitive renewable CHP design is complicated and highly unintuitive because these systems inherently operate at unsteady-state and hence their operating schedules should be accounted for at the design stage. To this end, we have developed a mixed integer linear programming combined optimal combined design and scheduling (CODS) model. The model minimizes the annualized system net present cost (NPC) by optimally selecting and sizing the units in the system while simultaneously scheduling the operation of these units (i.e. on/off, production rates, storage inventories) during each distinct period of a scheduling horizon which captures both diurnal and seasonal variation in intermittent renewable generation and power demand. Our CODS modeling framework generates variable length scheduling periods by clustering consecutive hours of full year time series data for wind capacity factor, solar capacity factor and power demand. This temporal aggregation makes the model computationally tractable, allowing for high throughput computational studies.

We specifically use CODS to determine optimal local CHP systems for (i) Mahaka, Hawaii, (ii) Nantucket, Massachusetts and (iii) Northwest Arctic Borough, Alaska. There are approximately 2,500 homes in each location; we consider residential power and heat demands arising from these. To elucidate the true economic potential of renewable H₂ and NH₃ production, we simultaneously allow continued business-as-usual power and fuel purchases while considering installation of PV arrays, wind turbines, batteries, electric boilers, and hot water thermal storage as well as H₂ and NH₃ production and storage to fuel local power generation and/or heat generation. We compare these optimal hybrid systems to business-as-usual only and electrification-only (i.e. batteries, electric boilers, and hot water heat storage) benchmarks. Overall, this analysis provides an understanding of the most economically competitive residential renewable deployments in today’s energy landscape.

References

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[2] Zamfirescu & Dincer. (2008). Using ammonia as a sustainable fuel. J. Power Sources 185(1), 459-465.

[3] Smith, Hill, & Torrente-Murciano. (2020). Current and future role of Haber–Bosch ammonia in a carbon-free energy landscape. Energy Environ. Sci. 13(2), 331-344.

[4] Palys, Wang, Zhang, & Daoutidis. (2021). Renewable ammonia for sustainable energy and agriculture: vision and systems engineering opportunities. Curr. Opin. Chem. Eng. 31, 100667.

[5] Palys & Daoutidis. (2020). Using hydrogen and ammonia for renewable energy storage: A geographically comprehensive techno-economic study. Comput. Chem. Eng. 136, 106785.

[6] Samsatli & Samsatli. (2019). The role of renewable hydrogen and inter-seasonal storage in decarbonising heat – Comprehensive optimisation of future renewable energy value chains. Appl. Energy 233, 854-893.