Integrating Distributed Energy Resources into the Distribution System Handout|Resources Definition of DERs DERs are supply resources that generate electricity, store electricity, or control electricity usage at the distribution level. Note that resources connected to the bulk electric system are not DERs. DERs may be connected: 1) Behind the customer meter, or 2) directly to the distribution grid Copyright Enerdynamics 2019 Types of DERs There are three key categories of DERs. Within each category, there are numerous technologies. Demand side management Distributed generation (DG) Distributed storage (DS) (DSM) Production of electricity that is Absorption of electricity, coupled Electric loads whose usage can be either consumed internally or that with supplying energy back at a altered, either permanently or is injected into the distribution later time, either for internal temporarily. system. consumption or for injection into the distribution grid. Examples include: Examples include: ▪ Combined heat and power (CHP) ▪ Energy efficiency Examples include: ▪ Demand response by controllable ▪ Rooftop solar PV ▪ Reciprocating engine gensets ▪ Thermal energy storage loads ▪ Gas microturbines ▪ Battery storage ▪ Controllable electric vehicle ▪ Fuel cells ▪ Flywheels charging Copyright Enerdynamics 2019 Value for the grid DERs provide these benefits to distribution utilities and DER owners. We will discuss them throughout this course. Voltage support DERs installed with smart inverters have the potential to provide reactive power to the grid, providing a resource that can be used to manage voltage on distribution circuits. Congestion management DERs under control of the distribution operator may be used to reduce loading on circuits that are approaching their design capabilities. Loss reduction Since DERs are located at or near loads, they may reduce the amount of current that a distribution circuit must carry thus reducing circuit losses Lower costs DERs used in a non-wires alternatives program may provide resources that eliminate or defer the need to upgrade distribution facilities Policy goals DERs may be used to achieve renewable energy or storage mandates and/or other regulative or legislative policy goals Resilience / reliability DERs provide a new source of supply that may be available to restore the distribution grid after an outage or when included in a microgrid to maintain service during an outage. Copyright Enerdynamics 2019 Distribution basics To understand the potential impact of DERs, we must understand how the distribution system is planned and operated to provide reliable service at a reasonable price. Reliability includes delivering electricity to consumers 1) within accepted voltage and frequency standards and 2) with minimal outages. Distribution systems include: • Substations • Primary feeders • Secondary feeders Typical connections voltages: • Utility-scale DERs such as large wind turbines and solar farms typically connect to the distribution system on primary feeders. • Behind-the-meter DERs often connect to secondary feeders. Copyright Enerdynamics 2019 Components Substation components Substation transformers traditionally are designed for one-way transformation from higher transmission voltage to lower distribution voltage. Transformers Transformers not rated for two-way flow may need replaced and sizing adjusted as DERs impact load profiles. Breakers protect system components by isolating substation equipment during excess current flow. Protection schemes that dictate breaker Circuit breakers operation may need reconfigured to accommodate two-way flow. Breakers may need resizing to match new fault current ratings. Switches control flow from the substation into the distribution feeders. As DERs grow, switches may need resized or reconfigured to match Switches flow conditions. Voltage regulators traditionally are designed for typical transmission system voltages and voltage parameters of connected feeders. Voltage Voltage regulator regulation schemes may need redesigned to account for DER impacts. Line components Feeder circuit Protect substation from excess fault currents by opening when required. DERs may increase fault currents thus requiring more robust breakers. breakers Line switches direct power flow by connecting or isolating feeders or mains. Automatic switches can be part of a protection scheme. As DERs Line switches grow, switch control systems may need redesigned to account for backflow. Fuses, reclosers, and automatic switches are used to isolate faults. As DERs grow, protection schemes require redesign to account for possible Protective equipment higher fault currents and backflow Voltage regulators including fixed transformers, locally controlled tap changers, fixed capacitors, and switched capacitors, are used to control Voltage regulator voltage levels on the lines. Line voltage may become volatile as DERs grow and DER output is varied. Such volatility may be addressed by adding more voltage regulation devices or through careful DER control. Line transformers reduce voltage as an intermediate step between higher and lower voltage lines or at the customer service. With more DERs, Line transformers transformers may need resizing to account for different amounts of normal and fault current. Conductors are wires that transmit the electricity. They are sized based on maximum current flow. As DERs grow, conductor sizing may change Conductors based on forecast amounts of normal current. In some cases, this can result in savings as DERs reduce the need for flow from the substation. Service components Depending on the type of DER, a new meter is often required. DR programs often require an interval meter that can verify performance over short time Two-way meter periods. DG and DS installations require a meter that can determine both energy consumed and energy provided to the grid. Wind, solar PV, high-speed gas turbines, fuel cells, and batteries all require an inverter that converts DC power to AC power used by consumer appliances and Inverter the grid. In the case of batteries, an AC to DC converter is also required when the battery is charging. An automatic disconnect switch is required to isolate DG and DS from the grid in the event of unexpected outages and during planned outages for Disconnect switch maintenance. The disconnect is necessary for safety since otherwise, the DER could flow energy onto the grid when utility workers expect that the grid is de- energized. Copyright Enerdynamics 2019 Interconnection Inverters Remote control and monitoring For DC power systems such as wind, solar, and batteries, In many cases, a third-party service provider or a system and for fast-spinning gas turbines, an inverter is required operator must monitor and/or control DERs. In some to convert to AC power. The inverter type is critical to how cases, monitoring and control coupled with backend IT DERs interact with the grid. Smart inverters provide the systems allow multiple DERs to be aggregated into useful technical capability for DERs to become grid resources. blocks of capacity. When multiple assets are owned by Convert DC power to AC power one customer, they can be optimized on a portfolio basis. Smart inverters include: • Power conditioning • Control of real and reactive power output • Remote control capabilities • Bi-directional communications capabilities Copyright Enerdynamics 2019 Simple and complex interconnections Simple interconnection Bi-directional The meter must be able to record flows into the facility and the Distribution grid meter distribution grid. Sometimes a simple energy meter is enough, but other times a smart meter is necessary to record time-of-day interval data, real power (kW), energy (kWh), and reactive power (kVA). A communications Bi-directional line that allows remote meter reading also may be required meter Breaker box The breaker box contains the primary disconnect for the loads as well as disconnects for each circuit. This part of the customer wiring is separate from the DER interconnection. Customer loads Disconnect DG and DS require a disconnect switch to prevent supply from feeding Disconnect Breaker box switch switch into the grid during outages or maintenance. Often a visible air-gap switch provides a verifiable break between the DER and the grid. Either the disconnect switch or the inverter must automatically disconnect the DER from the grid during an outage Inverter Inverter The inverter converts the DC power from the PV panels to AC power. Certain inverters are certified to automatically disconnect during outages. Smart inverters provide equipment status monitoring and remote control including control of real and reactive power output. Smart inverters may PV panel also provide ride-through for short frequency or voltage disruptions Bi-directional A bi-directional inverter is required since power flows into and out of the inverter batteries. When power is discharged it converts DC power to AC power, More complex interconnection and when the batteries are charged it converts AC to DC. Bi-directional The meter must record flows into the facility and the distribution grid. Bi-directional Bi-directional meter Since the facility will provide grid storage services, a revenue-grade meter inverter Breaker meter Distribution grid is required to measure time-of-day interval data, real power (kW), energy (kWh), and reactive power (kVA). Air-gap switch Inverter System operators rely on inverter controllers to remotely manage battery controller functions. Air-gap switch A