This work introduces the concept of flexible operation in the design of solar thermal utility systems for low temperature processes. The design objectives are: (a) The supply of the thermal needs of the process (heat duty and minimum required temperature), and (b) the maximization of the operating time during the day. The approach shows how the network structure is defined by adjusting the mass flow rate and the inlet temperature of the working fluid to achieve the smallest collector surface area. This work emphasizes the need to specify the solar network structure, which is comprised of two main elements: The number of lines in parallel and the number of collectors in series in each line. The former of these two design specifications is related to the heat load that the system will supply, while the latter is directly related to the delivery temperature. A stepwise design approach is demonstrated using two case studies where it is shown that the detailed design of the solar collector network structure is fundamental for a successful thermal integration with minimum investment. In this paper, the design methodology is based on flat-plate solar collectors, but it can be extended to any other type of low temperature solar technology.

Heat pump electricity costs grow with a power relationship as the evaporator temperature in the cycle decreases. The thermo-economic study of a solar thermal-assisted heat pump and storage system determines the minimum cost of the coupled system for an evaporator temperature. Through two case studies, one for the dairy industry and the other for 2G bioethanol production, the coupled system was evaluated for different temperatures in the evaporator, from 30 to 90 °C, and the minimum cost of the coupled system was determined. For the dairy industry, the lowest levelized total cost of a heat pump (LCOE) at 50 °C is 0.0799 USD/kWh. The evaluation carried out allowed us to determine the best operating conditions of the heat pump: 50 °C in the evaporator, COP = 4.2, and the work of the compressor of 211.3 kW. In the case of 2G anhydrous bioethanol production, the lowest levelized energy cost is 0.0409 USD/kWh for an evaporator temperature of 30 °C and a payback of 1.8 years. The study carried out makes it possible to guarantee the supply of the heat load at the operating temperature of the process and determines the impact of environmental conditions on the cost of the heat pump assisted with solar thermal energy.

Economic criteria have prevailed in studies on integration of renewable energies. Tons of dangerous emissions are emitted by a biomass fuel, causing negative impacts over atmosphere and health. Current research proposes Pinch Analysis of solar thermal energy and the joint use of biomass (sugarcane bagasse) to produce heat and power in a Caribbean sugar mill; measuring emissions like: carbon oxide $CO,$ carbon dioxide $C{O}_2,$ dinitrogen monoxide $N_{2}O,$ nitrogen oxides $N{O}_x$, sulfur oxides $S{O}_x,$ non-methane volatile organic compounds NMVOC, methane $C{H}_4$, and particulate matters, to have a global and clear view of the impacts of biomass as a renewable fuel. Variables like kWh cost, the installation and device area of renewable energy, and greenhouse gas emissions, are analysed to assess the effect on the integration final design, the target of which is to control the use of biomass. It is possible to produce an economically competitive integration design of solar system $LCO{E}_{th solar}$ = 0.0636 USD/kWh, $LCO{E}_{ele}$ = 0.1392 USD/kWh), zero greenhouse gases emissions $(\Delta T_{minrew}=7 °\mathrm{C}$), and deletion of 378,711.53 t/year of $C{O}_2$ and 9567.56 t/year of solid particles. There are many possibilities that can implemented; in one of them, bagasse burning is reduced by 30% and the solar collector network for required power production is reduced by 68%.

The design of a solar thermal installation is based on the lowest irradiance levels that occur during winter. However, there are consecutive days with irradiance levels well below those used for the design, which are called in this work “critical irradiance levels”. To solve this challenge, a statistical analysis is carried out to find a representative percentile of 22 years of consecutive days with “critical irradiance levels”. A case study of a cotton-dyeing industrial process requires 18.5 m³ of hot water and operates for 2.75 h at temperatures between 40 and 90 °C. Environmental variables for 22 years were analyzed and validated to design a solar thermal installation (solar collector network and storage system) and a coupled heat pump. The fifth percentile, with three consecutive days and low irradiance levels, was the most repetitive. For this case, a storage system of 46.5 m³ guaranteed heat load at target temperature. The simple payback was 14.1 years, and the energy cost was 0.094 USD/kWh, which was competitive against the energy cost from using fossil fuels, 0.064 USD/kWh. The design based on critical environmental conditions guarantees a continuous supply of energy to the industrial process and defines the minimum availability of solar energy to supply a process.

A design methodology to integrate solar heat into industrial process is showed in this chapter, attending restrictions like availability for area of installation, economic, environmental, and operating conditions. The evaluation of each of the restrictions allows responding to real situations that arise in the industrial sector and thereby determining the scenario that best suits the industry. To achieve this objective, the evaluation of two real scenarios was carried out; in the first one there are no installation area limitations, while in the second, only the 50% of required installation area is available. The results obtained when evaluating the scenarios exhibit a direct relationship between the available space, the capital of the investment and the CO2 emissions, but this is not reflected in the same proportion in the operation of the process. In scenario one, the payback of the integrated system is 5.99 years with zero emissions to the atmosphere. For scenario two, the reduction of CO2 emissions is 80.62% with a recovery time of the investment of the integrated system of 2.61 years. In this context, Chemical Vapour Deposition is proposing as a innovative technology to improve the solar devices efficiency.