• Smart Energy Resources

    Increased demands on the nation's electrical power systems and incidences of electricity shortages, power quality problems, rolling blackouts, and electricity price spikes have caused many utility customers to seek other sources of high-quality, reliable electricity. Smart Energy resources provide an alternative to or an enhancement of the traditional electric power grid. Smart energy resources include solar power, wind power, fuel cells, bio-fuel systems, battery storage systems, electric vehicles, etc.

    Solar PV : Solar panels consist of solar cells that contain PV material, which exhibits PV effect. Solar cell that is exposed to light transfers electrons between different bands inside the material. This in turn results in potential difference between two electrodes, which caused direct current (DC) to flow. There are several main PV applications, such as solar farms, building, auxiliary power supply in transportation devices, stand-alone devices, and satellites. In order to incorporate solar farm into utility power system, alternating current (AC)/DC converter is needed as well as the corresponding relay protection. The main issue with PVs is intermittency. Since PV is unreliable power source that cannot always be counted on, several efforts have been undertaken to increase the reliability of PVs. One of the most successful ones was adding the battery storage. where electric energy is stored during the off-peak hours or curtailment period, and then reused when PVs are not available.

    Solar Thermal: Solar thermal energy (STE) is a technology that converts solar energy into thermal energy (heat). There are three types of collector levels that are based on the temperature levels: low, medium, and high. In practice, low-temperature collectors are placed flat to heat swimming pools or space heating, medium-temperature collectors are flat plates used for heating of water or air, and high temperature collectors are used for electric power production. In essence, heat gain is accumulated from the sun rays hitting the surface of the object. Then, heat is transferred by either conduction or convection. Insulated thermal storage enables STE to produce electricity during the days that have no sunlight. The main downside to STE plants is the efficiency, which is a little over 30% at best for solar dish/stirling engine technology, while other technologies are far behind.

    Wind power: Wind power is obtained by converting the energy of the wind by wind turbines into electricity. It is highly desirable renewable energy source because it is clean technology that produces no greenhouse gas emissions. The main downside of wind power is it intermittency and visual impact that it creates on the environment. During the normal  operation, all of the power of the wind. farm must be utilized when it is available. If it is not used, the wind farm is either curtailed or power generated can be used to charge the battery energy storage(BES) if one is associated with wind farm. Wind power is higher at higher speed of wind, but since the speed of the wind constantly changes, power comes and goes in short intervals. Inconsistency in power output is the main reason why wind  farms cannot be used in utility’s base load generation portfolio. Capacity factor of a wind power turbine ranges anywhere from 20% to 40%.

    Hydro power: Hydroelectricity is the most widely used form of renewable energy and its potential has already been explored to a large extend or is compromised due to issues such as environmental impacts on fisheries, and increased demand for recreational access. Modular and scalable Next generation kinetic energy turbines can be deployed in arrays to serve the needs on a residential, commercial, industrial, municipal or even regional scale. Microhydro kinetic generators neither require dams nor impoundments, as they utilize the kinetic energy of water motion, either waves or flow. No construction is needed on the shoreline or sea bed, which minimizes environmental impacts to habitats and simplifies the permitting process. Such power generation also has minimal environmental impact and non-traditional microhydro applications can be tethered to existing construction such as docks, piers, bridge abutments, or similar structures.

    Waste-to-energy: Municipal solid waste (MSW) and natural waste, such as sewage sludge, food waste and animal manure will decompose and discharge methane-containing gas that can be collected and used as fuel in gas turbines or micro turbines to produce electricity as a distributed energy resource. Additionally, these waste materials, such as sewage sludge, can be transform  into bio-fuel that can be combusted to power a steam turbine that produces power. This power can be used in lieu of grid-power at the waste source (such as a treatment plant, farm or dairy).

    Geothermal: Geothermal power is extracted from the earth through natural processes. There are several technologies in use today, such as binary cycle power plants, flash steam power plants, and dry steam power plants. The main issue with geothermal power is low thermal efficiency of geothermal plants, even though capacity factor can be quite high (up to 96%). Geothermal plants can be different in size. Geothermal power is reliable and cost effective (no. fuel), but initial capital costs associated with deep drilling as well as earth exploration are main deterring factors from higher penetration of geothermal resources.

    Vehicle-to-grid: Future generations of electric vehicles may have the ability to deliver power from the battery in a vehicle-to-grid into the grid when needed. An electric vehicle network has the potential to serve as a distributed energy storage system (DESS).

    Combined heat and power: Combined heat and power (CHP) systems, also known as cogeneration, generate electricity and useful thermal energy in a single, integrated system. CHP is not a technology, but an approach to applying technologies. Heat that is normally wasted in conventional power generation is recovered as useful energy, which avoids the losses that would otherwise be incurred from separate generation of heat and power. While the conventional method of producing usable heat and power separately has a typical combined efficiency of 45 percent, CHP systems can operate at levels as high as 80 percent.

    Energy storage elements:

    1. Flywheel Energy Storage – FES:

    A flywheel device stores electric energy as kinetic (or inertial) energy of the rotor mass spinning at very high speeds. Fig. shows the structure of a conventional flywheel unit. The charging/discharging of the device is carried out through an integrated electrical machine operating either as a motor to accelerate the rotor up to the required high speeds by absorbing power from the electric grid (charge mode) or as a generator to produce electrical power on demand using the energy stored in the flywheel mass by decelerating the rotor (discharge mode). The system has very low rotational losses due to the use of magnetic bearings which prevent the contact between the stationary and rotating parts, thus decreasing the friction. In addition, because the system operates in vacuum, the aerodynamic resistance of the rotor is outstandingly reduced. These features permit the system to reach efficiencies higher than 80%. They take up relatively little space, have lower maintenance requirements than batteries, and have a long life span. Flywheel devices are relatively tolerant of abuse, i.e. the lifetime of a flywheel system will not be shortened by a deep discharge unlike a battery. The stored energy is directly proportional to the flywheel rotor momentum and the square of the angular momentum, a reason why increments in the rotation speed yield large benefits on the storage energy density. Keeping this in mind, the classification in two types of flywheels arises: high speed flywheels (HS: approximately 40000rpm) and low speed flywheels (LS: approximately 7000rpm). High-speed flywheels allow obtaining very compact units with high energy densities.

    2. Pumped hydro storage (PHS):

    Pumped-storage hydroelectricity (PSH), or Pumped Hydroelectric Energy Storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing. The method stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power. Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest.

    3. Superconducting magnetic energy storage (SMES): SMES systems work according to an electrodynamics principle. The energy is stored in the magnetic field created by the flow of direct current in a superconducting coil, which is kept below its superconducting critical temperature (4-100 K). The main component of this storage system is a coil made of superconducting material. Additional components include power conditioning equipment and a cryogenically cooled refrigeration system. The main advantage of SMES is the very quick response time: the requested power is available almost instantaneously. Moreover the system is characterized by its high overall round-trip efficiency (85 % - 90 %) and the very high power output which can be provided for a short period of time. There are no moving parts in the main portion of SMES, but the overall reliability depends crucially on the refrigeration system. In principle the energy can be stored indefinitely as long as the cooling system is operational, but longer storage times are limited by the energy demand of the refrigeration system.

    4. Ultracapacitors: It deliver quick bursts of energy during peak power demands, then quickly store energy and capture excess power that is otherwise lost. They efficiently complement a primary energy source in today's applications because they discharge and recharge quickly. Due to their many benefits, ultracapacitors are currently being utilized in thousands of different applications (Harvest power from regenerative braking systems and release power to assist train or hybrid buses acceleration, open aircraft doors in the event of power failures, provide energy storage for firming the output of renewable installations and increasing grid stability), and considered in an equally diverse range of future applications.

    Utilities are being required to interconnect these resources with the grid  to improve the efficiency and reliability of power system operations. They offer consumers the potential for lower cost, higher service reliability, high power quality, increased energy efficiency, and energy independence. The use of renewable distributed energy generation technologies and "green power" can provide a significant environmental benefit. Smart energy resources are electric generation units located within the electric distribution system at or near the end user.