Alternating Current (AC): The type of electricity that powers home appliances and electronics. Solar energy produces Direct Current (DC), which converts to AC power at the inverter.
Ampere-hour (Ah): the measured flow of a current (in amperes) over one hour. An Ampere-hour can be used to measure battery capacity.
AC rating: The AC rating is a measurement of how much useable electricity can potentially be generated by a system in real-world conditions. The AC rating of a solar system is calculated by multiplying the number of solar panels in the array, times the solar panel’s listed PTC rating, times the inverter efficiency.
Ancillary Services: These are services that assist grid operators in maintaining system balance and regulation. Ancillary services are frequently mentioned as a potential value stream from energy storage systems.
Application Program Interface (API): In computer programming, an API is a set of protocols for building software applications, allowing direct communication with other software applications. For example, ETB has an API integration with the NREL, PV Watts solar production calculator.
Array: A solar array is an interconnected system of PV modules that function as a single electricity-producing unit.
Azimuth: The direction that a solar panel or array of solar panels is facing, measured in degrees away from North (North = 0°, East = 90°, South = 180°, West = 270°). Azimuth can also be called orientation.
Balance of System (BOS): The collection of the smaller parts of a complete solar system, including rail, mounts, clamps, and bolts, among other items. BOS generally includes all material other than the solar panels and inverter for a Solar PV system.
Baseload: the average amount of electric power that a utility must supply in a period. Baseload generating plants are typically coal or nuclear-generating units committed and dispatched at constant or near-constant levels with minimum cycling.
Battery capacity: the maximum total electrical charge (expressed in ampere-hours)a battery can deliver to a load under a specific set of conditions.
Battery cycle life: the number of cycles to a specified depth of discharge a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.
Battery energy capacity: This is the total energy available (expressed in kilowatt-hours) to be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cut-off voltage.
Battery Management System (BMS): The BMS is the (software) system that manages the battery bank (hardware). We use the term BMS to define the strategy or algorithm that tells the battery how to operate. The default BMS control strategy in ETB is a ‘peak-demand shaving’ algorithm. Generally speaking, Advanced Energy Storage battery manufacturers will provide a BMS in conjunction with their battery bank.
Billed Demand: Billed demand is the amount of demand, measured in kilowatts (kW), that the utility bills a customer for in each billing period. The ‘billed demand’ can differ from ‘measured demand,’ which is the highest kW interval recorded during a billing period if the utility rate schedule has a ratchet.
Building-Integrated Photovoltaics (BIPV): Building-Integrated Photovoltaics. A type of solar panel that seamlessly integrates the building envelope, most commonly as solar roof shingles or laminates.
Capacity factor: This is the ratio of the average load on (or power output of) an electricity generating unit or system to the unit’s capacity rating over a specified period.
Capacity reservation level: In regards to Critical Peak Pricing (CPP) rates, the capacity reservation level is the specified portion of customer load to be shielded from CPP rates.
CARE Discount: California Alternative Rates for Energy (CARE) is a residential low-income customer billing program available in certain California utility territories. Under this program, customers receive a 30-35 percent discount on their electric and natural gas bills.
CEC Rating: The California Energy Commission (CEC) has created the CEC system rating for determining rebate levels. This CEC-AC rating for a solar array is the PTC rating of solar array times the inverter’s CEC efficiency.
Charge controller: A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.
Charge efficiency: The efficiency, expressed as a percentage when energy is charged into a battery bank. This includes all losses from both the inverter and battery bank during charging.
Charge rate: The current applied to a cell or battery to restore its available capacity. A charge control device commonly normalizes this rate with respect to the rated capacity of the cell or battery.
Coincident demand: the simultaneous demands of a group of appliances or customers taken as a whole. Diversified demands may be determined by direct measurement or by the addition of the load curves of the individual appliances or customers in the group, also referred to as coincident demand or group demand.
Critical Peak Pricing (CPP): A specific type of rate tariff, whereby a customer pays a markedly higher rate for electric usage during a few peak-load or emergency periods—CPP events—designated by the utility. In exchange, the customer receives a discount on demand and/or energy charges during the rest of the year.
CSV (comma-separated values) file format: The comma-separated values (CSV) format is a widely used text file format that contains multiple records (one per line), and a comma delimits each field. The file format is commonly used in Microsoft Excel and has become a standard to exchange data between different applications. Many Green Button Data files come in “CSV” form.
DC Rating: The DC rating of a solar array is commonly referred to as the ‘nameplate rating’ and is calculated by multiplying the DC wattage of each panel times the number of panels. The DC rating of a panel is synonymous with the STC, an acronym for “Factory Standard Test Conditions,” which is 1,000 watts per square meter solar irradiance, 1.5 Air Mass, and 77 degrees Fahrenheit cell temperature.
Deep discharge: Discharging a battery to 20% or less of its full charge capacity.
Demand: The rate at which electric energy is used at a given instant or averaged over a designated time interval such as 15, 30, or 60 minutes. It can be expressed in kW, kilovolt-amperes, or other units for a system, group of customers, or per customer basis.
Demand Charge: a charge related to maximum power measured in kilowatts (kW). It is the highest average kW over a continuous 15 minute period during the billing period.
Demand Response: The process of using voluntary load reductions during peak hours.
Depth of discharge (DOD): The percentage of battery discharge in relation to the total battery capacity. For example, if you discharge 6 kWh from a solar battery with a capacity of 8 kWh, the battery's depth of discharge would be 75% (6 kWh / 8 kWh).
Direct Current (DC): Low voltage electric current produced by solar panels. Must be converted into AC current by an inverter before being used by home appliances.
Discharge: Generally meant to mean the withdrawal of electrical energy from a battery.
Discharge efficiency: The efficiency, expressed as a percentage, with which energy is discharged from a battery bank. This includes all losses from both the inverter and battery bank during discharge.
Discount Rate: The discount rate is the rate of return used in a discounted cash flow analysis to determine future cash flows’ present value. Companies have different ways of identifying the discount rate. A common method is using the expected return of other investment choices with a similar level of risk.
Distributed Energy Resources (DER): A variety of small, modular power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity delivery system, whether or not those technologies are connected to an electricity grid.
Distributed generation: A popular term for localized or on-site power generation. Normally distributed generation is synonymous with being located on the customer-side-of-the-meter.
Effective date: Regarding a utility rate tariff or rate schedule, it is the date that a particular schedule or tariff went into effect.
Energy: For the electric industry, energy is the quantity of kilowatt-hours supplied or used (consumed). It is the product of power in watts and the time during which the power was used or.
Fixed tilt array: A photovoltaic array set in at a fixed angle with respect to horizontal.
Frequency: The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).
Frequency regulation: This indicates the variability in the output frequency. Some loads will switch off or not operate correctly if frequency variations exceed 1%.
Gigawatt: A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.
Granularity: Meant to describe the level of detail in a set of data. When referring to interval usage data or solar PV production data, the most common granularity types are 5-minute, 15-minute, 30-minute, and 60-minute.
Grid-tied/Grid-connected: A solar system connected to the Utility grid and uses it as an alternate source of power.
Ground mount: A type of solar installation built on the ground instead of a “roof-mount” installation.
Hybrid system: A solar electric or photovoltaic system that includes other technology types or sources of electric generation, such as an Advanced Energy Storage system.
Interconnection: The process of hooking up a solar electrical system to the power grid.
Internal Rate of Return (IRR): The discount rate used that makes the net present value of all cash flows from a particular project equal to zero. Generally speaking, the higher a project’s internal rate of return, the more desirable it is to undertake the project. The IRR will be different for different terms of the project (10-year, 20-year, 30-year).
Interval: The period in which the flow of energy is averaged in determining demand, such as 15, 30, or 60 minutes.
Inverter: The electrical device that converts direct current (DC) electricity into alternating current (AC) electricity.
Irradiance: The direct, diffuse, and reflected solar radiation that strikes a surface—usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation.
Irradiation: The amount of solar energy in an area over time (kWh/m^2/day).
Kilowatt (kW): A standard unit of electrical power equal to either: 1000 watts or energy consumption at a rate of 1000 joules per second.
Kilowatt-hour (kWh): 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy—1 kWh=3600 kJ.
Kvar: a unit of reactive electric energy. Though “imaginary,” the reactive power has great physical significance and is essential to the operation of the electrical system as a whole. While the real power P is used to supply the energy required to perform actual work (such as running a motor), the reactive power regulates the voltage in the system.
kWh – (kilowatt-hours): the units in which electric meters measure usage. 1 kWh equals 1000 watts of electricity supplied for one hour.
Lead-acid battery: A general category that includes batteries with plates made of pure lead, lead-antimony, or lead-calcium immersed in an acid electrolyte.
Lifetime cost of energy (LCOE): The cost of energy of a solar system based on the system’s installed price, its total lifetime cost, and its lifetime electricity production.
Load: The demand on an energy-producing system; the energy consumption or requirement of a piece or group of equipment. Usually expressed in terms of amperes or watts in reference to electricity.
Load factor: Load factor measures the volatility or “spikey-ness” of a customer’s usage. It is calculated by dividing average demand by the maximum demand occurring in a specific period. Load factor is expressed as a percentage.
Max Demand: the highest kW demand for the billing period.
Max Depth of Discharge: How much power, specified in percentage terms that can be instantaneously discharged from a battery. For example, a 100 kW rated battery, with an 80% max depth of discharge, can discharge a maximum of 80 kW.
Max Discharge Power (kW): how much power, measured in kW, that a battery can discharge instantaneously.
Maximum power point tracker (MPPT): Means of a power conditioning unit that automatically operates the photovoltaic generator at its maximum power point under all conditions.
Measured Demand: The amount of demand or highest kW interval that a customer recorded during a specified billing period. ‘Measured demand’ can sometimes differ from ‘billed demand,’ which is the amount of demand the utility billed them for during that billing period if the utility rate schedule has a demand ratchet.
Megawatt: 1,000 kilowatts, or 1 million watts; a standard measure of electric power plant generating capacity.
Megawatt-hour: 1,000 kilowatt-hours or 1 million watt-hours.
Minimum Charge: The minimum amount that a customer must pay under the contract and applicable rate schedule.
Monocrystalline panel: A solar panel made from a large, single silicon crystal and has a patchwork pattern. Monocrystalline panels are typically more expensive and more efficient than multi- or poly-crystalline panels.
Multicrystalline panel: A solar panel made from small silicon crystals oriented in lots of different directions. Multicrystalline panels are less expensive and less efficient than monocrystalline panels. (Also see “poly-crystalline panel”).
Multiplier: Used to calculate actual usage for meters that register only a portion of kilowatts or kilowatt-hours used. The meter multiplier is usually shown on the face of the meter and is shown on the bill.
Net meter: An electricity meter that can track both how much electricity your solar system puts into the power grid and how much electricity your home pulls out of the grid.
Net Present Value (NPV): The difference between the present value of cash inflows and the present value of cash outflows. NPV is used in capital budgeting to analyze the profitability of an investment or project.
Nominal voltage: A reference voltage used to describe batteries, modules, or systems (i.e., a 12-volt or 24-volt battery, module, or system).
Non-Coincident (NC) Demand: Non-Coincident Demand. The sum of the individual peak demands of the components of the customer/group/class or system within a specific period regardless of the time of occurrence For electric TOU accounts, the greater of the highest kW demand for the billing period or 50% of the highest kW demand from the previous 12 months.
Off-peak: A designated period of time (hours) that the system load is considered low as specified by the utility or energy supplier. Typically, costs are measurably lower than the average costs of generation.
On-Peak Demand: For electric TOU accounts, highest on-peak kW demand for the billing period.
On-peak: The designated period of time (hours) that the system load is considered high as specified by the utility or energy supplier. Normally, costs are measurably higher than average costs of generation.
Open-circuit voltage (Voc): The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.
Orientation: Generally meant to refer to the direction that a solar panel or array of solar panels is facing, measured in degrees away from North (North = 0°, East = 90°, South = 180°, West = 270°). This is also referred to as azimuth.
Payback period: The period of time it. This is also referred to as the capital recovery period.
Peak demand: The maximum energy demand or load in a specified time period.
Peak sun hours: The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1,000 w/m2.
Photovoltaic (PV): The process of converting light into direct current electricity.
Photovoltaic conversion efficiency: The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.
Photovoltaic (PV) system: A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.
Power factor: The ratio of actual power being used in a circuit, expressed in watts or kilowatts, to the power that is being drawn from a power source, expressed in volt-amperes or kilovolt-amperes.
Power Purchase Agreement (PPA): A contract between a power producer and a power consumer that states the consumer will purchase a certain amount of power from the producer.
PTC: “PVUSA Test Conditions.” Began in 1986 as an alternative to STC to reflect real outdoor field-tested conditions. These are the variable conditions at which the solar modules are tested: 20 deg Cel ambient temp, wind 1 m/sec, 1000 W/m^2 irradiance.
Ratchet (demand): A demand ratchet is a feature incorporated into some utility rate designs, which is a means of applying a minimum bill, which gets calculated based on a given percentage of their peak use over a specified period of time, for example, a customer may have an 80% ratchet on their trailing twelve-month peak demand.
Renewable Energy Credit (REC): Renewable Energy Credits (RECs), also known as Green tags, or Renewable Energy Certificates, are tradable, non-tangible energy commodities that represent proof that one megawatt-hour (MWh) of electricity was generated from an eligible renewable energy resource (renewable electricity). Solar renewable energy certificates (SRECs) are RECs that are specifically generated by solar energy. In the ‘Incentives’ tab of our ‘Company Settings,’ a user can specify the default REC price to be used in each state.
Return on Investment (ROI): Return on investment (ROI) is the benefit to an investor resulting from an investment. ROI is used to evaluate the efficiency of an investment by expressing profits in relation to capital invested. To calculate ROI, the benefit (return) of an investment is divided by the cost of the investment; the result is expressed as a percentage or a ratio.
Semi-peak: The designated period of time (hours) that the system load is considered to be medium as specified by the utility or energy supplier.
Service voltage: Several electric tariff schedules provide a lower charge or a discount based upon the customer’s desired voltage level. SDG&E’s service levels are secondary -less than 2,000 volts; primary - 2,000 to 25,000 volts; transmission - more than 25,000 volts; and system peak - the entire system’s max demand.
Single-axis tracking: A system capable of rotating about one axis.
Smart grid: An intelligent electric power system that regulates the two-way flow of electricity and information between power plants and consumers to control grid activity.
Solar noon: The time of the day, at a specific location, when the sun reaches its highest point in the sky.
Solar resource: The amount of solar insolation a site receives, usually measured in kWh/m2/day, which is equivalent to the number of peak sun hours.
Stand-alone system: An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most stand-alone systems require batteries or other storage forms.
State-of-charge (SOC): The available capacity remaining in the battery, expressed as a percentage of the rated capacity.
STC (Standard Test Conditions): “Standard Test Conditions.” The standard variables at which most solar modules are tested for performance: Cell temperate 25 deg. Celsius, light irradiance held to 1000 W/m^2
String: A number of photovoltaic modules or panels interconnected electrically in series to produce the operating voltage required by the load.
System operating voltage: The photovoltaic array output voltage under load. The system operating voltage is dependent on the load or batteries connected to the output terminals.
Tariff: The official terms and conditions statement that utilities publish, which contains information on how a customer is billed.
Thin-film panel: A solar panel that is thin and flexible. The term refers to both amorphous photovoltaic solar panels, which use silicon as their semiconductor and panels that use other semiconductors like cadmium telluride and copper indium gallium diselenide.
Tilt angle: The angle a solar panel makes with the horizon. The ideal tilt for a location will mean that the panels absorb as much sunlight as possible. The ideal fixed tilt of a solar panel, as a rule of thumb, is typically equal to its latitude.
Time-of-use (TOU) rates: A billing system employed by utilities that measures and charges for kilowatt-hours consumed and/or peak demands by a specified time period. Time of use rates provide different price signals that can vary seasonally, by day and by hour. Seasonal price differentials and time of day price differentials encourage customers to move their load to off-peak periods or add incremental load during off-peak periods.
Tracking panels: Solar panels that can change the direction they face to follow the sun’s movements. The tracking device can be on a single-axis, which follows the sun’s movement throughout the day, or a dual-axis, which follows the sun’s movement throughout the day and year.
Typical meteorological year (TMY): TMY weather data is specially selected data representing typical or average weather for a location, which is generated from a data bank of roughly thirty years. The data that gets selected presents the range of weather conditions for the location in question, while still giving monthly and annual averages that are consistent with the long-term averages for the given location. Basically, the hourly data that the TMY model accounts for variance reflects the fact that there will be good solar days, bad solar days, and everything in between.
Volt (V): A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.
Watt: A unit of power equal to amps times volts. A solar panel’s wattage is found by calculating short-circuit amps (Isc) times open-circuit voltage (Voc).
Watt-hour: The unit of electric energy expended in one hour when the power is one watt.
Wholesale Energy Rate: The rate (expressed in $/kWh) at which excess over-production over the course of a 1-year Net Metering cycle is valued. The wholesale energy rate only applies when the customer is a net-exporter on an annual basis. In California, the Wholesale Energy Rate (aka Net Surplus Compensation rate) fluctuates month-to-month and is currently roughly ~$0.05/kWh.
XML - file format: XML is a common, machine-readable file format used to share data. Many utilities make Green Button Data available in an “xml” file format.