What Is Hybrid Energy System

While hybrid energy appears to be an important part of future energy industry, it is important to first define “hybrid energy (power) system.” Hybrid energy system can be defined in a number of different ways. GE (General Electric) defines hybrid power as:

Hybrid power plants usually combine multiple sources of power generation and/or energy storage and a control system to accentuate the positive aspects and overcome the shortcomings of a specific generation type, in order to provide power that is more affordable, reliable, and sustainable. Each application is unique, and the hybrid solution that works best for a specific situation will depend on numerous factors including existing generation assets, transmission and distribution infrastructure, market structure, storage availability, and fuel prices and availability.

This definition of hybrid energy system (or hybrid power) is somewhat restrictive. In this book, we define hybrid energy system in more general terms. First, hybrid energy system has two basic components: power and heating and cooling. GE’s definition is more centered toward stationary power generation. Here we define hybrid energy system as one where single or multiple sources for power or heating and cooling result in single or multiple power or heating and cooling outputs. The system also includes energy storage and transport devices, both of which can also be hybrid like hybrid storage systems or hybrid grid systems which include utility grid as well as micro and/or off-grids. Holistically, a hybrid energy system must consider (a) both power and heat (cold), (b) sources, (c) generation technologies, (d) storage mechanisms, and (e) methods for energy (power) transmission and distribution.

Let’s examine specific examples to further illustrate this definition of hybrid energy system. GE’s definition of hybrid power includes multiple sources power generation (like wind and solar), with energy storage with and without grid. District heating with multiple renewable sources of heat with and without storage is another example of hybrid energy system where power may not be involved. A zero energy building with solar energy to generate power and heat and geothermal energy for heating, ventilation, and air conditioning (HVAC) system, with or without storage, is also another example of hybrid energy system. Here both power and heating and cooling are parts of hybrid energy system. Cogeneration (combined heat and power (CHP)) is another example of hybrid energy system to improve energy efficiency. ExxonMobil and FuelCell Energy’s partnership to generate power by burning coal or natural gas and use fuel cell to generate more power from waste CO, is another form of hybrid energy system where power is generated in two different ways. Using multiple sources (including renewable and nuclear) to generate heat with and without thermal storage for industrial processes ( such as glass making operation) with conversion of waste heat to generate electricity by the process of thermoelectricity is another form of hybrid energy system where industrial heating results in the waste heat to generate power. This is a reverse cogeneration process once again used to improve energy efficiency. Hybrid vehicles can also generate power by IC engine, fuel cell, or battery along with power generated via thermoelectricity of waste exhaust heat. An EV with energy storage (one or more) is also a hybrid operation.

Hybrid energy systems also include hybrid storage systems such as battery capacitors, battery flywheel etc. to match required power and energy density, charge- discharge time, cycle time etc. for the system. Hybrid energy systems also include hybrid grid systems which include hybrid energy and storage sources at three levels of grid: utility level mega grid, hybrid microgrid that can be either connected to mega grid or operated in islanded mode, and off-grid systems that include mini- and nanogrids and stand-alone systems. These systems are generally not connected to mega grid. Interconnection of nanogrids or mini-grids can be linked to microgrids or conventional utility grids. Holistic hybrid energy systems thus have three components: energy generation, storage, and transport.

The book demonstrates that all these elements, source for generation, storage, and grid transport, along with processes to generate additional energy (heat or power) to improve efficiency or to treat waste materials all together define the nature of hybrid energy systems. Such hybrid energy systems are (a) more reliable and flexible, (b) more efficient, (c) more affordable, (d) more environment friendly, and (e) ultimately more durable and sustainable over long term compared to the single component energy sources or systems. Hybrid energy system is essential for the deeper penetration of renewable and non-dispatchable energy (particularly solar and wind which are intermittent by their nature) sources in the overall energy mix in order to reduce carbon emission to the environment. Hybrid energy system is also important for the better use of nuclear heat and suitable power generation by a combination of nuclear and renewable sources. Hybrid storage system is the best way to improve quality of power over a long period. Three levels of hybrid grid transport is the best way to not only increase the level of renewable sources in the overall energy mix but to harness distributed energy resources and serve both urban and rural communities. The choice of hybrid energy system components, their integration and control, and their intelligent management and optimization are also part of assessment and discussion of this book.

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