Solar+Storage/Method and Modeling Assumptions
Methods and Modeling Assumptions
- 1 Methods and Modeling Assumptions
More than 24,000 scenarios were modeled to identify cost-optimal solar and/or battery storage system configurations for 73 commercial electricity rates for the utilities with the largest number of customers in each climate zone.
Commercial buildings were modeled for 16 locations, representing every climate zone across the U.S.
Utility Rates Modeled
Commercial utility rates were selected for the utility with the largest commercial customer base within each climate zone. Rates and building types were matched, based on the load profile of the building and the eligibility requirements stated in the utility’s rate tariff sheet.
The modeling included a variety of tariffs. Some have demand charge elements, some have time-of-use elements, some have both time-of-use and demand elements, and a few were flat rates. All of the tariffs were taken from NREL’s Utility Rate Database and were up to date as of January 2017.
Buildings and Load Profiles
Hourly load profiles from the DOE Commercial reference buildings were used to model 16 building types.
Hourly load profiles for the reference buildings were adjusted for each of the ASHRAE climate zones.
Technology Cost Assumptions
Optimization modeling was conducted for seven solar photovoltaic and battery storage price points, representing anticipated cost trajectories.
Cost Point A represents conservative technology costs in the current market. Some stakeholders are reporting current costs closer to Cost Points B and C.
Cost Point G represents estimated technology costs by 2037.
The solar technology cost trajectory is based on NREL’s Annual Technology Baseline. Battery storage costs are based on NREL discussions with a variety of battery suppliers and developers.
Components included in the Cost Assumptions
|Battery & Hardware Costs|
|Inverter - power conversion|
|Container or housing|
|Container extras (insulation/walls)|
|Electrical conduit (inside of container)|
|Meter (revenue grade)|
|AC main panel|
|AUX power - lighting etc.|
|Engineering, Planning & Construction Costs|
|Loading & drive from OEM site|
|Lifting & hoisting by crane on site|
|PE stamped calcs & drawings|
|OEM testing and commissioning|
|Electrical BOS outside of container (conduit, wiring, DC cable)|
|Structural BOS (fencing)|
|EPC overhead & profit|
|Developer cost (customer acquisition)|
Policy & Financing Assumptions
|Unless otherwise noted:|
|System life||20 years.|
|Net metering is not included. When included, system size is capped at 100% load.|
|30% Investment Tax Credit is included.|
|"Modified Accelerated Capital Depreciation (MACRS):||5 year + bonus depreciation for solar and battery system components (if battery charged >25% from grid, 7 year depreciation).|
|No other state or federal incentives are included.|
|Inverter & Storage Replacement||In Year 10|
|Total Round Trip Efficiency||82.9%|
|Initial State of Charge||50%|
The REopt Model
The Renewable Energy Optimization Model (REopt) provides cost-optimal technology solutions at a single site, or across a portfolio of sites.
REopt is a mixed integer linear program that outputs optimal technology sizing and hourly dispatch strategies, along with financial data.
REopt can identify optimal system sizes, given other parameters, or can output financial data for set system sizes. Multiple on-site technologies, including existing diesel generators, can be considered in the optimization.
The REopt model is currently run by NREL analysts, in-house. A web-based version of the tool is currently in development, and expected to be released as a beta-version in September 2017.
For more information about REopt, visit: https://reopt.nrel.gov/