The electric boiler and grid stability: what can it really do?

By AITESA

In a modern power system, not all relevant assets generate power. Some consume it. And in certain contexts, who consumes it can be as important as who produces it.
Electric boilers belong to this second group.
Their function is to produce steam or hot water from electrical energy. However, in an environment with high penetration of variable renewables, their role may go beyond the industrial process.
Their interest lies not only in how they produce heat, but also in how they can be integrated into a plant and the power grid as a large, controllable, fast and predictable load.

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1. What is an electric boiler and what types are there?

An electric boiler transforms electrical energy into thermal energy without on-site combustion. Two technologies predominate in industrial applications.

Resistance boilers generate heat by means of electrical elements immersed in water. They offer precise and stable modulation, suitable for applications where fine load control is a priority.

Electrode boilers generate heat by passing electric current directly through water. They are particularly suitable for high power and allow very fast ramp-up times.

Both share a key characteristic: they are large, fully controllable electrical loads, with a responsiveness that is difficult to match by conventional thermal technologies. This allows them to:

Start from cold to full load in less than 5 minutes.
Go from minimum load to maximum load in approximately 30 seconds.
Modulate power continuously within its operating range.

From the electricity system’s point of view, these characteristics are more similar to those of a regulation asset than to those of a conventional consumer.

2. The structural challenge of the electricity system

The blackout that affected Spain revealed a growing technical difficulty: maintaining stable frequency and voltage in a grid with a greater presence of renewable generation and less synchronous inertia.

When generation is lost abruptly or when there is a rapid imbalance between supply and demand, the system must react within seconds. If deviations exceed operational limits, protections can be activated that trigger cascading disconnections.

In this context, flexibility acquires strategic value.

Traditionally, this flexibility has been provided by generation plants capable of varying their output. However, with the expansion of variable renewable generation, system operators are increasingly incorporating demand-side resources.

That is, consumers able to modify their consumption in real time to help balance the grid.

3. How an electric boiler can participate in grid regulation

The power system must maintain an almost instantaneous balance between generation and consumption at all times. Unlike other industrial systems, electricity cannot be easily stored on a large scale within the grid itself, so any imbalance is immediately reflected in a key parameter: system frequency.

In Europe, the nominal frequency is 50 Hz. It rises when more energy is produced than is demanded and falls when consumption exceeds available generation. These deviations can occur in a matter of seconds, for example following the unexpected disconnection of a generation unit, rapid variations in renewable production or sudden changes in electricity consumption.

To keep the system within its operating limits, operators use various correction mechanisms known as complementary services.

There are three main markets in the Spanish electricity system where flexible resources can participate:

Secondary regulation (aFRR)

Automatically adjusts generation or consumption on time scales of seconds or a few minutes to correct frequency deviations.

Tertiary regulation (mFRR)

It is activated manually by the system operator to restore the balance when the secondary regulation is not sufficient.

Active Demand Response Service (ADRS)

It allows large consumers to reduce their consumption when requested by the operator to relieve the electricity system.

Traditionally, these services have been provided by generation plants. However, European regulation increasingly allows the participation of flexible consumers.

An electric boiler can participate in these mechanisms as long as it has:

Adequate control systems
Telemetry and communications with the operator or aggregator
Sufficient modulation capacity
Compliance with regulatory requirements

In that case, it stops behaving as a purely passive demand and becomes a manageable load from a system perspective. It can increase its consumption when the grid needs to absorb available energy or reduce it when demand relief is needed. For the operator, this is equivalent to having fast regulation capability on the consumption side.

4. Why this matters at the industrial level

An electric boiler need not be analyzed only as a means of producing steam without combustion. It can also be understood as an asset capable of providing flexibility to the electricity system and, in certain markets, of generating a remuneration associated with that availability.

This extends the usual evaluation logic. The boiler is no longer justified solely on the basis of decarbonization or thermal coverage of the process. It can also provide value for its responsiveness.

For an industrial plant, this has relevant implications. The same modulation capability that allows it to adapt its operation to the needs of the process also introduces new possibilities for interaction with the network.

In operational terms, this type of equipment has several particularly interesting features:

Dispatchable demand, capable of increasing or decreasing its power consumption according to external signals
Fast and predictable loading ramps, compatible with the response times required in balancing services
Continuous power modulation within a defined operating range
Natural integration with digital control systems, facilitating coordination with energy management platforms

This means that, in addition to producing steam or hot water for the industrial process, an electric boiler can provide adjustment capacity on the demand side.

A single facility cannot prevent a systemic blackout caused by a large loss of generation. But greater integration of fast, controllable loads expands the system operator’s room for maneuver and strengthens overall resilience.

5. Real profitability and possible profitability when you do not want to operate on a production basis.

This raises a particularly relevant question for many industrial plants: what value can the electric boiler have when it is not interesting to operate it due to the cost of thermal production.

The answer is that, even at such times, it can still be useful as network-ready equipment.

In other words, the boiler need not be analyzed only in terms of the cost of steam produced in continuous operation. It can also be analyzed as a flexible power that the plant makes available to the electrical system in certain periods, especially when it is not convenient to use it as the main thermal production equipment.

This nuance is particularly important given that in many balancing markets not only the energy actually consumed is remunerated, but also the availability of power and responsiveness.

This allows for a different economic logic:

The boiler can remain integrated in the plant, even if it is not the most competitive thermal option in base operation.
Its value can be realized at specific times, when the network needs flexibility
Their potential profitability depends not only on fuel savings or decarbonization, but also on the revenues associated with adjustment services.

Naturally, this profitability depends on several factors:

Price of electricity
Value of availability in regulatory markets
Actual activation hours
Ability to modulate without affecting the process
Thermal alternative available in plant
Technical market access requirements

If the boiler is activated to consume additional electricity, the main operating cost will be the price of that energy. Therefore, the economic logic is not to state that an electric boiler will always be cheap to operate, but to determine under what conditions its flexibility offsets that cost.

In other words, the analysis moves from focusing solely on the cost of producing steam with electricity to incorporating the value that the boiler can generate as a flexible asset within a broader energy architecture.

6. How this logic can enhance the value of cogenerations

In a cogeneration plant, the electric boiler should not be considered as a replacement for the gas turbine, but as a tool to optimize the thermal system according to the energy context.

The logic is simple. In normal operation, the plant can run on natural gas. But when electricity is cheaper than gas in terms of cost to generate the required thermal load, heat production can be shifted to the electric boiler. In those hours, the equipment contributes directly to reducing the overall OPEX.

When that relationship is reversed and it becomes more competitive to operate with gas, cogeneration regains the lead. And yet the electric boiler can still provide value: it can remain available as a flexible load to participate in balancing markets and generate revenue from its responsiveness.

This changes the way the equipment is justified. The electric boiler pays for itself not only in the hours it produces steam, but also in the hours it provides flexibility to the electrical system. Thus, it reduces costs when it is convenient to operate with electricity and generates an additional revenue stream when it is convenient to operate with gas.

Understood in this way, the electric boiler can enhance the value of an existing cogeneration plant, not because it replaces it, but because it widens its margin of maneuver, improves its adaptation to market signals and adds a new monetization channel.

7. The AITESA approach

For this contribution to be real, the boiler cannot be treated as an isolated piece of equipment. It requires electrical and control integration consistent with the plant architecture and network requirements.

This involves:

Proper definition of the electrical connection and protections
Control strategies aligned with DCS or PLCs
Coordination with steam network and process constraints
Assessing operational flexibility without compromising production

The energy transition does not depend solely on incorporating more renewable generation. It also requires assets capable of adapting dynamically to grid conditions.

In such a scenario, properly designed and integrated electric resistance and electrode boilers can bring additional flexibility to the electrical system while ensuring a reliable thermal supply for the industry.

And this is probably the most interesting reading: the electric boiler should not be seen only as a decarbonization device. It must also be seen as an energy asset connected to the system, capable of providing grid stability, opening up new operating options and helping to amortize the investment through its participation in flexibility services.