Off-grid hybrid renewable energy systems represent the most modern and flexible solutions that can cover a wide range of energy efficiency needs for household consumers. In the current context, these systems must be taken into account by most household consumers, given the fact that the price of energy has increased. This paper proposes an experimental analysis of the behavior of such a system, in real operating conditions, considering two renewable energy sources, wind and photovoltaic sources, using an experimental stand. It can be considered a testing platform for hybrid energy production systems, in that the power installed in the two sources can be scaled up. The platform has the advantage of allowing the implementation of different load and wind curves through a programmable logic controller; in this way, it is possible to evaluate the degree of coverage of the energy consumption produced from renewable sources, in the north-east of Romania, in the Suceava County region. The experimental study also involves an analysis of the storage capacity in relation to the consumption and the electricity produced by the two renewable sources. In this regard, three scenarios differentiated by the state of charge (30%, 50% and 70%) have been established. The results indicate that, for each of the imposed scenarios, the energy required to cover consumption is produced by renewable energy sources (42%, 47% and 53%), to which the energy stored in batteries (39%, 28% and 18%) is added.

Increasing the energy efficiency of a drug factory is the main purpose of this paper. Different configurations of cogeneration systems are analyzed to meet most of the heat demand and to flatten the heat load duration curve. Due to the variable nature of heat demand, there is a need for heat storage, but there is also a need for the fragmentation of power into two units of cogeneration to increase the operational flexibility in these plants. When the heat produced by the combined heat and power (CHP) unit is insufficient to meet the heat load, the heat stored can then be used to meet that demand. Heat storage plays a significant role in managing the heat supply and demand profiles in the CHP system, and in reducing its capacity and size. Trigeneration and heat storage are used as options to increase the operating time of cogeneration units and, implicitly, the amounts of heat and electricity generated in cogeneration. The results of this study demonstrate the economic and technical viability of the cogeneration and trigeneration solutions proposed. For the values of electricity and natural gas prices at the time of the analysis (2021), Scenario 4 is characterized as the optimal economical and technical option for the current rate of consumption, as it ensures the highest values of heat and electricity production and the shortest investment payback period (5.06 years). Compared with separate heat and power generation, we highlight a primary energy saving of 25.35% and a reduction in CO₂ emissions of 241,138 kg CO₂/year.

Solar air heater systems are equipment that uses energy captured directly from the sun to heat an existing airflow through the module. The technology to operate these systems is based on clean, renewable and free energy. Solar air heaters absorb thermal energy from the sun using an ab-sorption surface and achieve a transfer of heat from the absorption surface to the air flow supplied by one or two fans. This type of equipment can be used for space heating, drying, or ventilation processes. In addition, the equipment is capable of operating in cogeneration with other systems, e.g., preheating the air used for drying wood, preheating the air used to heat industrial premises, or preheating the water used in different heating systems. This scientific work is meant to reveal the current research context and the future opportunities in the case of cogeneration applications of solar air heaters, which are analyzed in light of their actual evolving dynamics. On this basis, we highlight expectations regarding the main problems that the regenerable energy is currently facing in this specific research and development environment as well as focusing our direction on the eventual solutions that are considered in the present and on their shortcomings in the future with evolved necessities.

This paper presents a method for choosing the energy sources that are needed for the following building utilities following building: lighting, domestic hot water, heating, ventilation, and air conditioning. The novelty of this paper consists of applying the concept of the energy hub and considering the cost of carbon dioxide emissions when selecting the available energy sources in the building’s location. The criterion for selecting the energy sources is the minimum overall cost of all forms of energy that are consumed in the building over its estimated lifetime. In order to estimate the overall costs, it is necessary to know the power that is installed and provided by the energy production technologies that are inside the building, as well as the capacity of energy that is required from outside energy sources. An office building that was proposed for refurbishment has been investigated as a case study. In the paper, we have analysed four scenarios. The results indicate that more favourable alternative solutions can be obtained compared to the traditional scenario (Scenario 4—heat and electricity by public utility networks). The overall costs are 46.17% (212,671 EUR) lower in Scenario 1, 25.35% (116,770 EUR) lower in Scenario 2, and 10.89% (50,150 EUR) lower in Scenario 3. Additionally, the carbon dioxide emissions are 22.98% (49 tonnes CO₂/year) lower in Scenario 1 and 8.91% (19 tonnes CO₂/year) lower in Scenario 2. Thus, renewable energy sources can occupy a growing share of the total energy consumption of the building. The proposed algorithm can be used for both the refurbishment of existing buildings and the design of new buildings.