Process steam required in industrial processes is conventionally produced by combustion of fossil fuels. Decarbonisation of this sector requires a switch into renewable energy sources, some of which are intermittent and weather-dependent. Integration with energy storage solutions is necessary to fully exploit the potential of renewable energy. Supply of process steam requires a certain temperature level in the storage tank. It can be achieved by utilising latent heat of a phase change material (PCM) whose melting temperature matches the required temperature of the steam. The presented case study investigates a chemical factory in which steam is provided by combusting hard coal in grate boilers. A photovoltaic (PV) farm is installed in the factory. Electric energy from this farm is mainly used to cover own electric needs of the factory, but there are some periods when there is excess energy available. A thermal energy storage system (TES) has been designed to utilise the excess energy for production of process steam. A zinc-aluminium alloy with melting temperature of 381°C has been selected as the PCM. An analysis of the energy balance (electricity demand and production, steam demand) of the factory in a hourly resolution is presented. Surplus solar energy is used to heat up and melt the PCM; the stored heat is later used for steam production, reducing the fuel consumption in the boilers. A simulation model of the combined energy system is used (in hourly resolution) to calculate the yearly consumption of electric energy and coal in the variants with and without the use of the TES. Various sizing of the TES system is analysed, as well as the effects of installing more PV power. The results show that the investigated photovoltaic plant is too small and does not provide enough excess electric energy to noticeably reduce the dependence of the factory on coal. As many as 30 TES tanks with a total heat capacity of 8 MWh are needed to utilise the 250 MWh of excess electric energy throughout one year (reducing the coal consumption by less than 1%), but the tanks would be idle most of the time. High capital expenditures of the TES system combined with low fuel savings and relatively low coal prices result in lack of profitability of the investment. In order for the analysed use case of the TES to be economically attractive, much more excess solar energy is needed.