# Performance Analysis of a Zero-Energy Building Using Photovoltaics and Hydrogen Storage
## 1 Introduction  
The storage of volatile electricity is a critical issue for achieving sustainability, by extending the exploitation of renewable energies. A lot of research is conducted in this direction because the existence of a significant capacity can increase the stability of the grid [1]. Besides the concept of batteries and hydropower storage, hydrogen is a critical weapon for facing the challenge of energy storage and the hydrogen economy is the challenge of the next years [2]. Moreover, the \"Power-to-X\" concept, which is usually based on the \"Carnot Battery\" [3], is an alternative choice to the existing storage technologies with significant economic [4] and environmental benefits [5]. In the case that the \"X\" in the previous equation is the \"hydrogen\", then the \"Power-to-Hydrogen\" concept can be developed, aiming for sustainability with the possibility of long-term storage [6]. The thermal storage in thermal pumping storage units [7], practically Carnot batteries configurations, presents drawbacks such as thermal losses, restricted storage time, and exergy losses during the storage, a problem that does not exist with hydrogen, which can be stored for long-term periods with a high storage volume. Moreover, it is useful to state that the \"Power-to-X\" concept will reach the capacity of 500 MW in countries such as France and Germany by 2025, so it is characterized as a technology of the future [8]. The hydrogen can be produced by water electrolysis and this is a usual strategy in the Power-to-X configurations [9]. It has been found that the efficiency of the electrolysisconversion and the electrolysis capital cost plays a significant role in the sustainability of these systems [10]. Practically, the production of hydrogen from renewables makes it a green fuel that can be reused in fuel cells for recovering electricity [11]. In addition, there is the possibility to produce any other useful output such as feedstock or fuel in various industries (e.g., steel, food, and chemicals) [12]. So, it is clearly highlighted that hydrogen production gives great flexibility in its further utilization; something that makes it a promising future solution for achieving sustainability. In addition, hydrogen is an important weapon for facing challenges in the domain of transportation [13]. The literature includes different studies which are based on hydrogen production from renewable and alternative energy sources for storage and possible re-utilization. A critical domain in which hydrogen can be an important solution is the building sector, especially nearly zero or zero-energy buildings, as well as buildings that are not connected to the grid. Hydrogen can be also used as a storage solution with high storage density, and it can be produced from the grid or renewable electricity through electrolysis, as a usual choice. So, this domain regards the recent literature trends that are examined by various researchers. [PERSON] et al. [14] examined an off-grid building in the climate conditions of Iran and they emphasized hydrogen storage with a battery. Their work indicated that around 75 m\({}^{2}\) of photovoltaics (PV) can provide the needed electricity for a building of 150 m\({}^{2}\) area. Moreover, they examined the thermal comfort conditions inside the building. [PERSON] and [PERSON] [15] investigated the use of PV, building-integrated PV and geothermal energy for a 20-floor building in Canada which also includes hydrogen storage. The studied configuration can cover all the energy needs of the building with an overall energy efficiency of 19% and an overall exergetic efficiency of 11%. [PERSON] et al. [16] studied the use of PV, solar thermal collectors, and geothermal energy in a building for covering all its needs. The studied location was Kuwait and the goal was to achieve a zero-energy building. They found a 33% reduction in CO\({}_{2}\) emissions compared to the design with fossil fuels. The idea of power to hydrogen storage in buildings has also been studied by [PERSON] et al. [17].