Grid-Connected Nuclear-Renewable Micro Hybrid Energy System

By Hoassam A. Gabbar and Muhammad R. Abdussami

There is a number of initiatives to integrate nuclear and renewable technologies to provide high-performance energy systems with maximum utilization of nuclear power plant resources as well as to achieve balanced energy generation to meet load profiles and demands. However, there is a number of challenges to achieve practical and profitable Nuclear- Renewable Hybrid Energy System (N-R HES), such as scalability, capital cost, project lifetime, construction period, land acquisition, ecological safety, and technological barrier. There are possible ways to overcome some of the challenges of N-R HES by introducing small scale nuclear reactor, called Small Modular Reactor (SMR) or Micro Modular Reactor (MMR). The Nuclear-Renewable Micro Hybrid Energy System (N-R MHES) offers to combine the small scale of Nuclear Power Plant (NPP) with Renewable Energy Sources (RES). The byproduct of the N-R MHES, the thermal energy, is also used in an efficient way to support the thermal load, district heating, hydrogen production plant, heat engine, absorption chiller, etc. The N-R MHES offers the possibility of different coupling options between input and output of the system. The nuclear- renewable integration criteria depend on the availability of the RES and the consumer load demand. The N-R MHES fits best to the remote consumer having an adequate amount of electric and thermal load. The grid-connected N-R MHES provides the opportunity to purchase the electricity in case of emergencies and to sell the surplus energy of the N-R MHES to the grid. In case of unavailability of the grid, an energy storage system can be used to store the surplus energy.

Nuclear-Renewable Micro Hybrid Energy System

The nuclear-renewable integration can be carried out in two ways: large scale and small nuclear-renewable integration. If the RES based power generation systems are installed around the traditional large NPP, it is called large scale nuclear-renewable integration. When the small scale nuclear power, such as SMR or MMR, are moved to the site of RES and integrated with RES based power generation system to support the local electricity demand, it is called small scale nuclear-renewable integration; it is also named as “N-R MHES”. Previously, it was thought that only renewable source is capable of supporting the electricity demand to the remote area. But, due to the irregularity of the RES, it is quite difficult to fulfill the local electricity demand all the time. Moreover, grid-connected N-R MHES makes a worthy solution for large industry, office, and university; it reduces the dependency on grid and lowers the energy cost. Research simulations estimate the criteria and help to choose the appropriate energy system depending on electricity load profile.

Table I. Criteria and Energy System Selection

Types of Electric Load	Types of Energy System
Low electricity demand	Standalone RES-based MEG
Medium electricity demand	Standalone MMR-based MEG
Large electricity demand	N-R MHES

The N-R MHES intends to provide electric and thermal power to the community. The multi-level nuclear-renewable coupling is possible. The N-R MHES includes SMR/MMR, RES, electric energy storage, and thermal energy storage. The N-R MHES also includes electric power grid, but the introduction of the power grid is optional; it depends on the site and situation.

There are mainly four types of coupling method in nuclear-renewable integration:

i) Loosely Coupled

In this process, the RESs are combined with a nuclear reactor and the main consideration is to the electricity generation. The RES and nuclear reactor generate electric power separately and they are linked together at the electricity distribution level. The combined system may supply the surplus electricity to the electric grid. Hence, N-R MHES can be connected with the electric grid as well.

Fig 1. Loosely Coupled N-R MHES

ii) Multiple Tightly Coupled Products

Here, the nuclear reactor is integrated with renewable energy which is also yielded by the nuclear power inside the N-R MHES. In this type of coupling, no external RES are combined with a nuclear reactor. The heat and electric power from the nuclear reactor produce some RES, such as biomass, hydrogen gas, etc., which are integrated with the nuclear reactor to supply electric power. In N-R MHES, the hydrogen and biomass are considered as RES.

Fig 2. Multiple Tightly Coupled Products N-R MHES

iii) Multiple Tightly Coupled Resources

This kind of coupling offers two level energy integration; that is thermal and electric level coupling. There are some RES, such as geothermal power source, concentrated solar power source, etc., which produces a considerable amount of thermal power; this thermal power is added with the nuclear reactor thermal power to generate electricity. Moreover, in the electric level coupling, the electricity generated from a nuclear reactor is linked with the electricity, produced from other RES (wind, solar, hydro, biomass, etc.). An electric grid is also connected to the N-R MHES to take surplus electric energy or to supply electricity to the N-R MHES in an abnormal case. However, the focus of this coupling method is to generate electricity.

Fig 3. Multiple Tightly Coupled Resources

iv) Tightly Coupled

In tightly coupled method, all form of energy mixes with each other for maximum utilization of the available energy in the N-R MHES. All thermal energies are added together and all electric energies are combined together; then all forms of energy are used in the most efficient way. The available thermal and electric energy is used in all possible applications, such as seawater desalination plant, fuel cell, district heating, heat engine, calcination, etc.

Fig 4. Tightly Coupled N-R MHES

A hybrid system may not include all types of RES. The heat generated from N-R MHES is generally used for the industrial purpose; whereas, the generated electricity from the hybrid system is used to support the electric demand. The surplus energy produced from the system can be supplied to the grid and remunerated by “net metering”. If necessary, electric energy can be drawn from the grid and combined with the heat to support the industrial load (e.g. hydrogen demand). Advanced energy storage system plays a very important role in the N-R MHES. A dynamic control strategy is adopted in the N-R MHES to maximize the efficiency of the system.

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