A glossary of definitions and terminologies commonly used in the context of grid-interactive net zero energy buildings has been provided. They may be defined differently in other contexts.
Building Demand Flexibility – Building demand flexibility is the capability provided by on-site DERs to reduce, shed, shift, modulate or generate electricity. Building demand flexibility can be used, typically in response to price changes or direct signals, to provide benefits to buildings’ owners, occupants, and to the grid.
Distributed Energy Resource – Distributed Energy Resources (DER) are small scale power generating stations (3 kW to 50 MW) or energy storage facility/equipment located usually in proximity of the end users. DERs are less expensive alternatives to large power plants offering better power quality, reliability, energy efficiency and energy independence. DER has been in existence in our buildings since many years in the form of back-up generators or Diesel generators. Renewable DERs such as the solar power plant, wind power plant, hydro-power plant are environmentally friendly and help in carbon emissions offset.
Demand Response – The strategy of reducing/ shifting of energy consumption during peak load period with respect to certain financial incentive is the demand response.
Demand-side Management – With the help of flexibility in energy demand, prioritization of critical loads, distributed energy resources (DER) and smart control systems, the load profile of a building can be altered to lower the peak demand, consume energy when the tariff is low and add inductive/capacitive load depending upon the power factor for the stability and lowering cost of operations of the grid and the process of managing loads is called demand side management.
Demand Variability – The variations in the demand of power from the grid within a stipulated period of time is the demand variability. The predictable variation in power demand is different from the uncertainties which occur due to equipment failure or power outages due to natural calamities.
Energy Efficiency – Reduction in the consumption of energy without lowering the requirements and usage is known as energy efficiency. Energy efficiency is achieved by the intervention of technology and best operating practices and the term “energy efficiency” covers a wide ranging topics related to energy efficiency, energy savings, energy consumption, energy sufficiency, and energy transition in all sectors across the globe.
Energy Storage Systems – An equipment with its peripherals which store energy in any form so that it could be utilised whenever needed. Example Batteries storing energy in the form of chemical energy which can be converted into electrical energy. Energy storage systems also help to smoothen the power output, compensating for the spikes and sags of the generation side.
Feed-in Tariff – Feed-in tariffs (FiT) distinguish between on-site electricity generation and electricity consumption from the grid, through differential pricing. This arrangement requires two separate power meters – one to measure the amount of electricity drawn from the grid and the other to measure the outflow of electricity from the site to the grid. FiT is based on time-bound contractual agreement between the consumer and the utility, wherein the utility agrees to purchase renewable power from the consumer at a price that is typically higher than the prevailing retail price. A predefined tariff degression plan reduces the tariff over time.
Feed-in tariff schemes are typically based on a 15-20 year long contract where prices are pre-defined above retail with a tariff degression, which effectively reduces your earnings over time. For every kWh you generate you get paid. Unlike net metering, feed-in tariffs do require prior arrangement and notification. Only six states across the U.S. currently have some form of feed-in tariff scheme as of today: California, Florida, Vermont, Oregon, Maine and Hawaii.
Grid Services – In addition to supplying power, a grid provides a wide range of services optimizing productivity, performance, budget and safety, thereby reducing service disruptions for instance net metering, feed-in tariff mechanism, smart metering and intelligent end devices, distributed energy resources, demand flexibility etc.
Load Forecasting – The prognostication of power demand to meet the short term (few hours), medium term (few weeks upto a year) and long term (more than a year) demands is termed as load forecasting. The load forecast aids to schedule generation reserve required, demand side management and dispatch.
Load Profile – The graph of variation of power consumption with respect to time is the load profile. It represents the pattern of electricity usage of a customer and the information can be used for billing.
Negative Prices – Negative power prices occur when there is a low demand and there is a large power input from an inflexible generating plant to the grid. Inflexible conventional power stations and cheap renewable power are responsible for prices dropping below zero.
Net Metering – Net metering allows consumers to bank excess electricity produced by their solar panels and trade it for electricity drawn from the grid. Net metering requires a bi-directional meter that can measure current flowing in two directions – from the site to the grid and from the grid to the site. Under this arrangement, the consumer sells and purchases power at the prevailing retail value. Net metering is ideal for residential and small commercial buildings.
Peak Demand – Peak Demand refers to the maximum power usage during a certain interval of time and is measured in kiloWatts (kW). In general, daily peak demand on a grid is during the evening when people switch-on the lights and other household appliances.
Ramp Rates – The increase or decrease in output power per minute of a generating unit is called the ramp rate. Ramp rates of flexible power generating plants help to stabilize the grid in case the power input to the grid from other plants alter.
Smart Technologies for Energy Management – Some of the technologies for energy management are building energy management system, home energy management system, Automatic demand response, community energy management system, smart appliances, smart switches, SCADA.