Scalable Solar Water Heating: Engineering System Models

This report presents a set of solar water heating (SWH) simulation models. The SWH models are created with a goal to depict the impacts of potential population-level water heating (WH) technology upgrades at various SWH project scales, from an individual household to a group of households. To successfully achieve this goal, the models introduce two key novelties: (1) computational effectiveness in executing California-wide SWH project simulations at several different scales using conventional computers, and (2) system component auto-sizing capability. The models were successfully applied in a CEC-funded California-wide multiscale SWH cost and benefit study. This report provides the data sources used, outlines the methodology applied, and details the mathematical models implemented and validated, before presenting several example model application cases.

The system models distinguish between two fundamentally different SWH configurations, each featuring a hot water thermal storage tank: (1) solar thermal, utilizing solar thermal collectors, and (2) solar electric, relying on photovoltaic (PV) panels and heat pumps (HP). The component models are  organized into energy converters, energy storage, and water distribution. The auto-sizing rules, developed using physical and empirical relations, rely on the number of project households and their occupancies. The mathematical models, both found in the literature and new, were implemented in the Python programming language as a software package called Multiscale Solar Water Heating (MSWH).

The example cases illustrate hourly and annual SWH system model performance. Solar thermal system examples show performance comparisons between existing WHs and SWHs at two scales: individual and a group of four households. Solar electric system examples depict impacts of two different PV sizes. We used the MSWH model simulation to generate annual averages and hourly performance profiles. The results illustrated the time-varying effects of solar thermal storage and intermittent solar radiation when exposed to realistic hourly hot water end-use load profiles, in relation to specific SWH component sizing. 

The models can further be applied in research topics such as advanced component sizing, load flexibility, and dynamic energy pricing. The models may inform energy and policy research, aid in the development of rebate programs, and serve as an educational tool.