Demand Response
Shifting or reducing electricity use in response to price or grid signals, so heavy loads run when power is cheap or the grid is less strained.
What is demand response?
Demand response is the practice of shifting or reducing electricity use in response to a price or a grid signal. Instead of the grid adapting to whatever a household draws at any moment, heavy loads are scheduled to run when power is cheap, plentiful or least strained. The term comes from energy markets and grid operation, but for a house its meaning is simple: a heat pump, a hot-water tank or a car charger takes a different time slot, and the occupants barely notice.
The idea is not new. What has changed is who sends the signal, how often it changes and how many devices can respond. Demand response covers everything from a utility asking large customers to cut load on a cold evening to home systems following hourly prices. For residential design the second case matters most, because the building itself starts to behave like a flexible asset.
How does demand response work in practice?
Every scheme has three parts: a signal, a flexible load and a rule that decides when the load may move. The signal can be a price, a time window, a ripple-control command from the distribution operator or a request from an aggregator. The controller checks each load against comfort limits and equipment protection before it shifts anything. Comfort comes first. A heat pump paused for an hour should not let the house drop below its setpoint, and a hot-water tank must still hold enough heat for the evening shower.
What makes shifting possible is storage. A well-insulated house keeps its temperature for a while after heating stops, and a water tank holds energy as heated water. A controller can run equipment during cheap or low-demand periods and coast through expensive ones. The hot-water buffer tank is the most common example, because its thermal mass is large, cheap to add and easy to control.
Where did demand response start in Slovakia?
Slovak households have practiced a simple form of demand response for decades. The hromadné diaľkové ovládanie (HDO), a ripple-control system, sends a signal over the distribution network that switches a meter between a standard tariff and a low tariff. Distributors used it mainly for storage heaters, akumulačné kachle, and for electric boilers, which were scheduled to heat during the low-tariff hours, usually at night. The occupant did not decide when the heater ran. The network did, and the household paid the lower rate for those hours.
HDO already combined a remote signal, a flexible load and a tariff reward. What it lacked was granularity and choice: the switch was on or off, and the windows were fixed in advance. Modern schemes keep the principle and add finer signals and better metering.
Which loads are flexible in a Slovak home?
Not every load can move. Lighting, cooking and most appliances need power when they are used. The loads that can shift are those whose service can be delivered at a different time: space heating with thermal storage, domestic hot water and battery charging. In a Slovak house built to current standards, three loads usually matter most.
| Load | Flexibility | How it shifts | Limit |
|---|---|---|---|
| Heat pump for space heating | Medium, depends on building mass | Runs harder before a price peak and rests during it | Indoor temperature must stay in the comfort range |
| Hot-water tank | High | Heats ahead of expected use | Enough hot water must remain for peak use |
| EV charger | High | Pauses or schedules charging | Car must reach the required charge by departure |
| Storage heater (legacy HDO) | Low to medium | Runs in fixed windows set by the distributor | Occupant has little control over timing |
How do dynamic tariffs differ from HDO?
A dynamic tariff changes the price of electricity through the day, often in short intervals, and passes that variation to the customer. HDO switches between two fixed states. A dynamic contract needs a meter that records consumption in short intervals, which is why the smart meter is the enabling device. Without interval data the supplier cannot bill by time of use, and a controller has no basis for scheduling.
European electricity rules have pushed suppliers to offer dynamic price contracts where the market allows, but offers differ by supplier and change over time. In Slovakia, check the current terms with the supplier before assuming one is available.
| Feature | HDO | Dynamic tariff |
|---|---|---|
| Signal | Ripple-control command from the distributor | Published price or market-linked rate |
| Switching | Two fixed states | Continuous, often hourly or shorter |
| Metering | Meter with a ripple-control receiver | Smart meter with interval data |
| Who decides | Distributor, within fixed windows | Household controller, within its rules |
| Typical loads | Storage heaters and boilers | Heat pumps, tanks, chargers and batteries |
How is demand response different from home battery storage?
Both change when a house draws power from the grid, which is why they are often mentioned together. The difference is what stores the energy. Demand response stores it in the building or its equipment: heat in the structure, hot water in the tank, charge in the car. A home battery stores electricity itself. That is more flexible, but it costs more to install and loses some energy on every charge and discharge cycle. Demand response uses storage that is already there, and a battery adds a second option on top.
What are the common misconceptions about demand response?
The first misconception is that demand response takes control away from the household. In a well-designed system the occupants set the comfort limits and the priority of each load, and the controller works inside them. The second is that it matters only for large consumers. For a house the relevant load is usually the heating system, which can be the largest consumer in winter, so its scheduling matters even at small scale.
The third is that a dynamic tariff always lowers the bill. It does so only when the flexible load moves into cheaper hours and the price difference is large enough to matter. A household with a well-insulated house and little flexible load may see little benefit. The fourth is that a smart meter alone creates savings. It supplies the data, but savings require a controller that acts on it.
What limits demand response in a house?
Three limits matter most. The first is comfort. Thermal inertia is real but finite, and an aggressive schedule produces cold rooms or lukewarm showers. The second is equipment. Heat pumps have minimum run times and compressor protections, and frequent switching shortens their service life, so a good controller avoids it. The third is communication. The controller needs a reliable signal, a meter that reports and an interface the heat pump understands. Some heat pumps support the SG Ready interface, which lets an energy manager choose between operating modes. Others need a retrofit gateway, so confirm with the installer before a design assumes flexibility.
Frequently asked questions
- What is demand response in simple terms?
- Demand response means changing when you use electricity, usually in reply to a price or a grid signal. Heavy loads such as heat pumps, hot-water tanks and EV chargers run in the cheaper or less strained hours. The household keeps its comfort limits while the timing moves.
- Does demand response save money?
- It can, when a dynamic tariff makes some hours cheaper and the household's heavy loads can move into them. The saving depends on the tariff terms, how flexible the loads are and how much thermal storage the building has. A flat tariff with little flexible load gives little benefit.
- What is HDO?
- HDO, short for hromadné diaľkové ovládanie, is the Slovak ripple-control system that switches household meters between tariffs. It has run storage heaters and boilers for decades in fixed low-tariff windows, most often at night. Its switching is on or off, with no interval data.
- Do I need a smart meter for demand response?
- For a dynamic tariff, yes, because the supplier needs interval data to bill by time of use. A controller also needs measured consumption to schedule loads sensibly. Older time-switched schemes such as HDO work with the earlier metering arrangement.
- Can a heat pump take part in demand response?
- Many modern heat pumps can, through a built-in schedule, an SG Ready interface or a gateway that an energy manager controls. Whether it is possible in a given house depends on the model and its communication options, so check with the installer.