CHP With Fuel Cells in the Buildings Domain

Fuel cells are suitable for micro-cogeneration and CHP because the technology inherently produces electricity and heat from a single source of fuel such as hydrogen, and systems can also run on traditional fuels, such as natural gas. Currently, the CHP fuel cell units are installed in buildings, being functional in individual regimes, but such systems with low power capacities are under development, the projects having the objectives oriented towards the energetic support of the collective houses with several apartments. In this type of application, the fuel cell with proton exchanger membrane is commonly used, which works and ensures the energy demand both during the day when peaks are recorded and at night. Solid oxide fuel cells can also be used in residential micro-cogeneration systems, having a relatively efficiency equal to that of PEMFCs. Because SOFCs use higher operating temperatures than PEMFCs, they are more tolerant to carbon monoxide in the fuel, and this allows for some simplification in terms of system configuration.

All CHP technologies offer increased combined efficiency compared to traditional solutions for separate generation of electricity and thermal energy. Cogeneration with fuel cells can exceed the value of the "traditional frontier" in terms of energy efficiency due to the special performances that this type of technology achieves (Table 4) [69,70]. PEMFC and SOFC are usually used for energy supply systems for small residential applications, and SOFC, PAFC and MCFC for systems that energetically support large commercial and industrial applications.


**Table 4.** A brief summary of the CHP performance of fuel cells adapted from [69,70].

The starting point for this sector is the project initiated in the 1990s by the Japanese government which supported the research activity in order to develop a city-gas-derived hydrogen system that would generate both electric and thermal energy for individual residential buildings, following which was developed the system of residential micro-cogeneration recognized worldwide under the name of Ene-Farm [71]. At the end of 2018, 200,000 PEMFC units were reported as being implemented as part of the Ene-Farm project [23]. In the future, a system similar to the one developed by the Ene-Farm project is planned by Japan to be installed in collective apartment buildings. The success of Ene-Farm has inspired various demonstration projects in other parts of the world, including Korea, Denmark, Germany, the USA and the UK [23,71].

Backup Power Systems wich Using Renewable Energy Sources or Converting Waste into Energy

This type of function involves storing and increasing the degree of use by avoiding the losses associated with the excess energy produced in the power plants that operate by exploiting the renewable energy sources. Various concerns in this sector have laid the foundations for the research and development projects of these systems, being currently in progress or in validation of the obtained results. As an example: Solar to Hydrogen—MYRTE combines solar energy with electrolyzers, hydrogen storage and fuel cell usage, and the project was a partnership between French Nuclear and Alternative Energy Commission, the energy company AREVA and the University of Corsica [72].

It is worth mentioning the recent initiative undertaken by the European Commission that funded through the public-private partnership Fuel Cells and Hydrogen Joint Undertaking (FCH JU) within the Assessment of the Potential, the Actors and Relevant Business Cases for Large Scale and Seasonal Storage of Renewable Electricity by Hydrogen Underground Storage in Europe project (HyUnder) [73]. The idea behind the project was to establish a European initiative for the implementation of energy technologies based on hydrogen generated by increasing the percentage of the use of renewable resources. This project aimed at researching large-scale hydrogen storage in underground caverns, an aspect related to the energy market and existing storage technologies, and aims to identify and analyze the areas of applicability, potential stakeholders, safety rules, the regulatory framework and the societal impact on public acceptance. Within this project, case studies were provided in several areas of Europe. Each case study analyzed the competitiveness of hydrogen storage compared to other types of energy storage, the geological potential of hydrogen storage and the way in which this hypothesis hydrogen storage can be implemented on the energy market. National Research and Development Institute for Cryogenic and Isotopic Technologies—ICSI Rm. Valcea, Romania, participated in the mentioned project through the National Center for Hydrogen and Fuel Cells.

Hydrogen production by water electrolysis leads to the consumption of water resources. In some areas, this is not a problem, but elsewhere it is a huge barrier to the implementation of hydrogen fuel cell technology. For these reasons, a series of studies have been directed towards methods of obtaining hydrogen from various wastes of which can be exemplified: preparation and catalytic steam reforming of crude bio-ethanol obtained from fir wood [74], pyrolysis-catalytic steam reforming of agricultural biomass wastes and biomass components for production of hydrogen/syngas [75], methodology for treating biomass, coal, msw/any kind of wastes and sludges from sewage treatment plants to produce clean/upgraded materials for the production of hydrogen, energy and liquid fuels-chemicals [76], biohydrogen production from solid wastes [77], not least, carbohydrate-to-hydrogen production technologies [78]. Table 5 presents the main hydrogen production methods in terms of efficiency and energy consumption.


**Table 5.** Hydrogen production methods-efficiency and energy consumption adapted from [70,79,80].

The production of hydrogen from fossil fuels and biomass, including the catalytic reforming of natural gas, appear to be environmentally unresponsible methods [81], especially due to carbon emissions that qualify the processes as a negative emission technology. In this regard, concentrated research efforts are being made to develop cleaner hydrogen production systems. Thus, a series of high purity hydrogen production installations, which work with carbon capture and storage (CCS) or post-combustion carbon capture (PCC), are demonstrated. Noteworthy in this direction is the research activity supported by Graz University of Technology, Institute of Chemical Engineering and Environmental Technology, Austria by Bock, Zacharias and Hacker. They studied and demonstrated the production of high purity hydrogen (99.997%) with the co-production of pure nitrogen (98.5%) and carbon dioxide (99%) with a raw material use of up to 60% in the largest loops with fixed beds worldwide [82].

Prime Power Generation Large Capacity Electric Power Stations

Several types of fuel cells find applicability in power generation for large stationary applications. AFC, PAFC, PEMFC, SOFC and MCFC systems are used worldwide for the generation of distributed

electricity for local use [83]. Figure 12 illustrates the relative weight of the various high-capacity fuel cell technologies installed by the end of 2018 [22–24]. It is noted that the sector is dominated by three types of technologies, MCFC having the highest weight, followed by SOFC and PAFC. To date, only a small number of high-capacity installations based on PEMFC and AFC technologies have been implemented.

**Figure 12.** Large scale stationary fuel cells.
