Header image adapted from Colombi et al. (2026).
How can renewable energy supply industrial heat 24/7?
There are several possible configurations. In this article, we focus on one built around a concentrated solar thermal (CST) field, thermal energy storage (TES) and an additional heat source for periods when the solar resource and stored heat are insufficient.
That additional heat can come from a boiler using a renewable fuel, such as biogas or biomass, or from an electric resistance heater or heat pump supplied with renewable electricity. The electric route considered here uses electricity procured through a renewable PPA or backed by Guarantees of Origin (GOs).
On-site PV or wind generation is another option, but we leave it outside this configuration to keep the analysis focused. In particular, on-site PV does not eliminate the need to address periods without sufficient solar resource: PV and CST are both solar-dependent.
The objective is to combine direct solar heat, stored heat and a renewable backup source so that the system can meet the plant’s heat demand continuously without relying on fossil energy.
What Role Does CST Play in Continuous Industrial Heat Supply?
Concentrated solar thermal (CST) uses mirrors to concentrate direct solar radiation onto a receiver, where it is converted into heat. That heat can be supplied to an industrial process without first being converted into electricity.
Depending on the system, CST can produce hot water, pressurized hot water, steam or heat another heat transfer fluid (HTF) used to deliver energy to the process. CST is particularly useful for industrial processes because it supplies heat directly, without first producing electricity.
In the configuration considered here, the solar field supplies heat when sufficient direct solar irradiation is available. Heat can go directly to the industrial process or to thermal energy storage (TES) for later use.
CST supplies direct renewable heat during solar hours and can also contribute heat for later use through TES.
How Does Thermal Storage Extend the Use of Solar Heat?
Thermal energy storage (TES) allows heat produced at one time to be used later. Part of the heat collected by CST during solar hours can supply the industrial process directly, while the rest can be stored.
For continuous industrial processes, TES extends the use of solar energy beyond the hours when the CST field is producing.
Storage capacity determines how much thermal energy can be shifted between hours. Increasing it does not produce additional renewable energy; it changes when that energy can be used. The required capacity depends on the renewable generation available for charging the TES and the plant’s heat demand over time.
TES separates renewable heat production from consumption, allowing stored energy to supply the process when it is needed.
How Is the Remaining Heat Demand Covered?
During periods of lower irradiation, the CST field may still produce useful heat without bringing the HTF to the required process temperature. An additional heat source can provide the remaining temperature lift.
TES can shift solar heat in time, but it cannot create additional energy. A system designed to supply heat continuously therefore needs to account for periods when the combination of current CST production and stored energy cannot meet the required thermal load.
The additional heat source can serve two functions: raise solar-heated HTF to the required process temperature when CST provides only part of the necessary temperature lift, or supply the required heat directly when solar heat is unavailable or insufficient.
If the objective is 100% renewable industrial heat, the energy used for these functions must also come from renewable sources. Two possible routes are a boiler using renewable fuel and an electric route, with a resistance heater or heat pump using renewable electricity.
Option 1: When Does a Renewable-Fuel Boiler Make Sense?
A boiler can provide the required additional heat using a renewable fuel such as biogas or biomass. It can operate alongside the CST field and TES rather than requiring solar energy to cover every hour of demand.
The amount of fuel required depends on how much of the plant’s heat demand is already covered by direct CST production and stored solar heat. The suitability of the fuel route also depends on fuel availability, cost, existing boiler infrastructure and the characteristics of the industrial process.
Option 2: When Does Renewable Electric Heating Make Sense?
An electric resistance heater or heat pump provides the same additional thermal function through electricity rather than combustion. Both technologies use electricity to supply heat and can raise the temperature of solar-heated HTF to the required process temperature or heat the HTF directly when CST and TES cannot meet the demand.
For this configuration to provide fully renewable heat, the electricity must be supplied as renewable electricity. This can be procured through a renewable PPA or backed by Guarantees of Origin (GOs).
On-site PV or wind could also supply the electric heater or heat pump. We do not consider that configuration further here. On-site PV has a particular limitation for this application because its production is also tied to the solar resource; combining PV with CST does not by itself provide energy during periods without sufficient solar generation. Wind has a different production profile, but its ability to cover the residual demand depends on the site, generation profile and system design.
This power-to-heat route avoids the need to store electricity before using it for thermal demand. The electricity is converted directly into the form of energy the industrial process requires: heat.
How Do CST, TES and Renewable Backup Operate Together?
The operating mix changes throughout the day.
When sufficient solar radiation is available, CST supplies renewable industrial heat directly. Solar heat that is not immediately required can charge the TES.
When CST production falls, stored heat can continue supplying the process. If CST and TES cannot meet the full thermal demand, the renewable backup system supplies the remaining heat. It can also provide the additional temperature lift when CST is producing heat below the required process temperature.
The boiler and electric resistance heater or heat pump are alternative ways of providing this function. Their role in a specific project depends on the selected system architecture rather than on a predetermined operating split.
CST, TES and the additional renewable heat source can therefore be sized and operated as one thermal supply system.
What Determines the Optimal System Configuration?
The capacities of the CST field, TES and additional heat source are defined together.
The plant’s heat demand and required process temperature define how much heat the system needs to supply and when. The solar resource determines the heat available from CST, while the availability and cost of renewable fuel or renewable electricity affect the choice and operation of the additional heat source.
The CST field capacity determines the amount of direct solar heat available and the energy available for storage. TES capacity determines how much heat can be shifted to later hours. The capacity of the boiler or electric heater or heat pump determines how much of the remaining demand it covers and the temperature lift it provides.
The CST field, TES and additional heat source are sized as parts of the same system. Their respective contributions depend on the plant’s heat demand and operating profile, required process temperature, solar resource and the characteristics of the selected backup energy source.
A techno-economic analysis determines the configuration for the plant and compares the renewable-fuel and electric-heating routes where both are technically applicable, taking into account energy costs and available infrastructure.
Process temperature affects CST performance, storage requirements and the capacities needed to reach the required renewable contribution.
The combination is designed so that direct CST heat, stored solar heat and the selected renewable backup source cover the required industrial heat demand.
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