Annual energy is a measure of the total quantity of electricity generated by the system over a single year. SAM reports an annual energy in Year 1 value in the Metrics table on the Summary tab of the Results page, and annual energy values in the Energy section of the cash flow on the Cash Flow tab.
Notes.
SAM calculates annual energy values adding up time series (hourly or subhourly) power values over one year.
For electric power generation systems, SAM calculates the monetary value of electricity delivered to the grid on a time step basis to account for time-dependent factors such as time-of-use rates for behind-the-meter projects, and time-of-delivery price multipliers or market prices for front-of-meter projects. The total annual electricity to/from grid results tell you about quantities of electricity, but not necessarily the monetary value of that electricity.
Annual Energy in the Metrics Table
The annual energy value in the Metrics table depends on the performance model:
•For electric power generation systems, Annual AC energy in Year 1 is electricity delivered by the system in Year 1 of its operation.
•For industrial process heat (IPH) systems, Annual energy in Year 1 it is the total heat delivered to the heat sink over the year.
•For the solar water heating systems, Annual AC energy saved in Year 1 is the electricity saved by the water heating system, assuming that the system replaces an electric water heating system.
For electric power generation systems, annual AC energy depends on the type of project you are modeling:
•For front-of-meter projects (PPA, Merchant Plant, Community Solar financial models), Annual AC Energy in Year 1 is the total net electricity delivered to the grid. This is the electricity sold by the project to earn revenue. It is the electricity generated by the system less any electricity purchased from the grid to charge batteries or for system loads such as photovoltaic inverter standby loads at night, or freeze protection loads in a concentrating solar power system (CSP).
•For behind-the-meter projects (Residential, Commercial, Third Party Ownership), Annual AC Energy in Year 1 is the total net electricity delivered to the grid and load. This is the electricity used to reduce the project owner's annual electricity bill. Electricity generated by the system may be delivered to a building or facility's electric loads, or it may be delivered to the grid in exchange for energy credits or dollar payments. It may also charge batteries or meet system loads such as for inverter nighttime consumption. Behind-the-meter projects may also purchase electricity from the grid to charge batteries or meet these loads.
Cash Flow Energy Values for Electric Power Generation Systems
The Energy line items in the cash flow indicate the total electricity delivered to and received from the grid for each year. These values are useful for estimating relative energy values, and for analyzing annual changes in energy over the analysis period. Annual changes in energy values may be caused by system degradation, battery degradation, battery replacements, or geothermal reservoir replacement.
Electricity to grid, kWh
The sum of AC electric power delivered to the grid in each time step over the year. Depending on the system design, this electricity may be generated by the system, discharged by the battery, or both. SAM calculates the value by adding up the positive values of the time series System power generated variable.
For front-of-meter projects, the PPA revenue, production-based incentives, and variable plant operation and maintenance costs are calculated from the time series "to grid" values. Because time-of-delivery price multipliers, market power prices, and escalation rates may apply, the annual revenue from electricity sales is not necessarily the product of a single power price and electricity to grid.
For behind-the-meter projects, the time series "to grid" values determine the value excess generation as defined on the Electricity Rates page, and of production-based incentives and variable plant operation and maintenance costs.
Electricity from grid, kWh
The sum of AC electric power delivered by the grid in each time step over the year. Depending on the system design, this electricity may be delivered to the load, used to charge the battery, and/or used to meet system loads. SAM calculates the value by adding up the negative values of the time series System power generated output variable.
For front-of-meter projects, the cost of electricity purchases are calculated from the time series "from grid" values.
For behind-the-meter projects, the time series "from grid" valued determine the energy charge and demand charge portions of the monthly electricity bill.
Electricity to grid net, kWh
The difference between Electricity to grid and Electricity from grid. SAM calculates the value by adding up all of the values of the time series system power generated variable.
This value may be useful for reference as a quick way to compare different systems, but SAM does not use it for any cost or revenue calculations.
Electricity generated without storage, kWh
For systems with battery storage, the total AC electricity generated by the power system over the year.
Battery annual energy discharged, kWh
For systems with battery storage, the total AC electricity discharged by the battery over the year.
Cash Flow Energy Values for Industrial Process Heat (IPH) Systems
The energy line items in the cash flow indicate the total amount of delivered to the thermal process in each year.
Thermal energy, kWht and MMBtu
The total energy delivered to the heat sink in kilowatt-hours and million Btus.
Revenues, costs and incentives defined in $/MMBtu are calculated from the thermal energy in MMBtu.
Cash Flow Energy Values for Solar Water Heating Systems
The energy line item in the cash flow indicates the amount of electricity saved by the solar water heating system over the year.
Electricity net generation, kWh
The total electricity savings in each year.
