Heat pump, water heater or battery: which suits flexibility best?

All three devices can deliver flexibility to the grid — but each in its own way. The home battery reacts fastest and never affects comfort. The electric water heater or heating element is the simplest and cheapest way in, because the water acts as a natural energy store. The heat pump commands the largest energy store of all — the warmth of the house itself — but must be controlled gently. So the short answer is: the best device for flexibility is usually the one you already have at home. You do not need to buy anything new to get started.

What do we mean by flexibility?

Flexibility means that a device’s electricity consumption (or delivery) can be moved in time without compromising what the device is there for: hot water, a warm house, power in the socket. That flexibility has two uses:

• Shifting consumption after the spot price. Electricity prices are set hour by hour on Nord Pool and swing over the day — typically cheap at night, expensive at the evening peak. Read more in our article on electricity prices hour by hour.
• Selling reserves to Energinet. The grid must hold the frequency at 50 Hz, so Energinet buys reserves such as FCR-D in daily auctions. Household devices can deliver them when pooled into a virtual power plant — that is the core of ancillary services.

The first use is a saving; the second is an income. Most devices can contribute to both.

The three devices compared

The comparison is qualitative — what your specific device can contribute depends on its size and your consumption pattern. See how earnings are calculated on the earnings page.

Water heater and heating element: the easy start

Water is an excellent energy store. A tank full of hot water does not care whether it was heated at 3 a.m. or 5 p.m. — the water is just as hot when you step into the shower. That is why an electric water heater or heating element can be switched off and on for short periods without anyone in the household noticing.

That makes it the simplest entry point to flexibility: if you have a Metro Therm hot water tank made after 2010, a licensed electrician fits HeatSync in about 20 minutes, and if you already have a Shelly on the water heater, it can be signed up for free. From then on, the tank is part of NM1’s virtual power plant and offers capacity to Energinet’s FCR-D market. Activations are short — seconds to minutes — and designed to affect neither comfort nor equipment.

The heat pump: large potential, gentle control

A heat pump heats the whole house, and the house itself is a large thermal store: walls, floors and furniture hold their heat long after the heat pump has taken a short pause. That is why a heat pump’s electricity consumption can be shifted without the temperature changing noticeably.

The control does need to be intelligent, though. The compressor must be treated properly, and comfort must never become a bargaining chip. NM1’s control is built for exactly that: short, gentle activations within the heat pump’s normal operating pattern. Larger installations from 10 kW connect through Balance. Heating devices are NM1’s speciality — NM1 is one of the only aggregators running heating devices at scale, where most others work exclusively with batteries.

The home battery: the fastest reserve

The battery is flexibility in its purest form. It has no comfort duty to protect — its only job is to move energy in time. It can react within seconds and both relieve the grid (stop charging) and support it (deliver power). That is why batteries are the fastest reserve on the grid and an obvious fit for FCR-D.

NM1 integrates the battery through the inverter manufacturers, including Solplanet, so no extra equipment needs to be installed. The battery also has more income legs than the other two devices — solar self-consumption, spot arbitrage and ancillary services — which is covered in detail in our article on home battery price and earnings. Through NM1, the battery earns from ancillary services today. Control by electricity price, so the battery also charges in the cheap hours, is something we are working on — it is coming soon.

What if you have more than one device?

Then you are particularly well placed. The devices do not exclude each other — on the contrary, they complement each other because their strengths differ: the battery takes the fast, short tasks, while the water heater and heat pump move larger amounts of consumption across the day. A home with both a heat pump and a battery can offer more combined capacity and contribute more to the balance of the grid. The FCR-D income is shared between you and NM1 and paid out quarterly as an ordinary bank transfer — regardless of which device type delivers it. See what your devices can earn under calculate your earnings. Keep in mind: FCR-D prices are set in daily auctions and vary, and historical earnings are no guarantee of future earnings.

How to get started

1. Identify your device. Do you have an electric water heater, a heating element, a heat pump or a home battery? Start with what you have — do not buy new equipment for the sake of flexibility alone.
2. Check your wifi. All devices need a stable connection, typically 2.4 GHz, to be controlled.
3. Choose the product. HeatSync for Metro Therm hot water tanks is coming soon — an electrician fits it. If you have a Shelly or a home battery, we connect it through the integrations, and larger installations from 10 kW through Balance.
4. See the earnings. On the earnings page you can see how your device type contributes and how the settlement works.

Whichever device you start with, the principle is the same: your flexibility helps Energinet keep the grid in balance — and you receive a share of the payment for it. The background is covered in our articles on grid balancing and ancillary services.