Housing co-op electricity: cut common costs by running loads in cheap hours
A co-op's shared electricity pays for the sauna, the hot-water tank, the garage chargers and often a heat pump. Several of those can wait a few hours for cheaper electricity. Here is which ones, what hardware it takes, and how to get it past the board.
Where a co-op's electricity goes
Common electricity covers everything no single flat pays for: stairwell and outdoor lighting, lifts, ventilation, pumps, the shared sauna, laundry and drying rooms, garage charging and, in many buildings, a heat pump or electric hot-water tank. With a spot-price contract each of those pays a different price every hour. The trick is knowing which ones can wait.
Can wait for cheap hours
The shared sauna's pre-heat, electric hot-water tanks, EV charging in the garage, heat pumps with a hot-water or buffer tank, drying-room heaters, frost heating in storage rooms.
Leave as they are
Lifts, ventilation, stairwell and outdoor lighting, circulation pumps, fire and safety systems. They run when people need them, so there is nothing to move.
Start by measuring
Most boards don't know what their common electricity is spent on — the bill shows one number a month. A Shelly Pro 3EM-3CT63 clamped over the common-area breaker shows consumption and cost in real time, next to the day's spot price, in Elewatt. A month of that data tells you which loads are big enough to bother with.
Then switch the loads worth moving. Single-phase loads up to 16 A go on a metered Pro 1PM, Pro 2PM or Pro 4PM, which gives each device its own savings figure. A 3-phase sauna heater or water heater goes on a Pro 3, or on a contactor driven by one. Elewatt's price filter decides the hours: run in the cheapest ones, pause in the most expensive.
EV charging in the garage
Charging is the load co-ops ask about most, and the easiest one to shift: cars stand in the garage all night. If your chargers run evcc, Elewatt feeds it the day's prices and evcc plans the charging. Simple chargers without their own smart control can be enabled in cheap hours through a contactor.
Residents usually pay for their own charging, and in Finland, for example, every charge point in a co-op must be metered separately. That metering belongs to the charger or a certified meter — Elewatt decides when to charge, it does not replace the billing meter.
Heat pumps and hot water
A heat pump that heats a hot-water or buffer tank is the biggest load a co-op can shift. If it is a Daikin connected to the Onecta cloud, Elewatt raises the temperature in cheap hours and backs it off in expensive ones, and the tank carries the building through. An electric hot-water tank works the same way with a relay — hot water is a battery you already own.
How to get it through the board
A small first step with numbers behind it is easier to approve than a building-automation project.
- 1
Meter the common board
Have an electrician fit a Shelly Pro 3EM-3CT63 (about €131) over the common-area breaker and connect it to Elewatt. Collect a month of real consumption and cost.
- 2
Pick one or two loads
Choose the biggest shiftable loads from the data — usually the sauna, the hot-water tank or the chargers. Run them through the calculator below to see the yearly saving.
- 3
Install the relays
The electrician adds a Pro 4PM, Pro 3 or a contactor for those loads. It's switchboard work measured in hours, not a project measured in months.
- 4
Set the price filter
In Elewatt, add the co-op's electricity contract and grid operator, then create a price filter — for example the 4 cheapest hours of the day for the hot-water tank — and link the relay to it.
- 5
Report back at the AGM
Elewatt's savings page shows what the metered loads cost and how much running them in cheap hours saved. That is the number the next meeting needs to decide on the rest.
Estimate your co-op's savings
The calculator starts with a typical co-op: a common sauna, a hot-water tank and garage charging. Change the power and hours to match your building, or add your own loads.
Savings Calculator
Estimate how much you could save by running your device during the cheapest hours.
List only devices that can wait for cheaper hours. Click a row to see its hours on the chart.
Spot price + grid fees + taxes, Estonia · c/kWh (12-month avg)
Daily usage
101.0 kWh/day
Annual usage
36865 kWh/year
Without Elewatt
27.5 c/kWh avg
10125 €
per year
With Elewatt
12.7 c/kWh avg
4700 €
per year
Your savings
Monthly
452 €
Yearly
5425 €
Shelly hardware (401 €) pays back in
0.9 months
Estonia: spot prices over the last 12 months + grid fees (Elektrilevi) + taxes and VAT. "Without Elewatt" assumes running during the most expensive hours. Actual savings vary by grid package and season.
The Shelly Pro lineup: switchboard hardware without the BMS price
Shelly's Pro devices mount on a DIN rail in the distribution board, connect over Ethernet as well as Wi-Fi, and run the same scripting and schedules as the rest of the Shelly range. An electrician fits them like any other switchboard module, and Elewatt drives them through Shelly Cloud. Shelly sells the Pro line with a 5-year warranty.
| Device | What it does | Use it for | Price |
|---|---|---|---|
| Shelly Pro 3 | 3 relays, 16 A each (48 A total). Switches three separate circuits or one 3-phase load. No power metering. | 3-phase sauna heaters, large water heaters, contactor coils for bigger loads | 90 € |
| Shelly Pro 3EM-3CT63 | 3-phase energy meter, 0–63 A. The CT clamps straight over a breaker. Keeps 60 days of 1-minute data. | Real-time consumption and cost of a sub-board, a 3-phase circuit or a whole flat | 131 € |
| Shelly Pro 4PM | 4 relays, 16 A each (40 A total), with per-channel metering and a small screen. | Radiators by zone, several water heaters, one device per stairwell or room group | 118 € |
| Shelly Pro 2PM | 2 metered relays, 16 A each (25 A total). | Two single-phase loads where you want savings per device | 100 € |
| Shelly Pro 1PM | 1 metered relay, 16 A. | A single water heater or radiator circuit with its own savings figure | 76 € |
| Shelly Pro EM-50 | Single-phase meter with two 50 A clamps, plus a 2 A relay to drive a contactor. | Metering a single-phase flat or cottage; switching a load through a contactor | 102 € |
| Shelly Pro 3EM-400 | 3-phase meter, 0–400 A. | The main incomer of a larger building | 274 € |
- What it does
- 3 relays, 16 A each (48 A total). Switches three separate circuits or one 3-phase load. No power metering.
- Use it for
- 3-phase sauna heaters, large water heaters, contactor coils for bigger loads
- Price
- 90 €
- What it does
- 3-phase energy meter, 0–63 A. The CT clamps straight over a breaker. Keeps 60 days of 1-minute data.
- Use it for
- Real-time consumption and cost of a sub-board, a 3-phase circuit or a whole flat
- Price
- 131 €
- What it does
- 4 relays, 16 A each (40 A total), with per-channel metering and a small screen.
- Use it for
- Radiators by zone, several water heaters, one device per stairwell or room group
- Price
- 118 €
- What it does
- 2 metered relays, 16 A each (25 A total).
- Use it for
- Two single-phase loads where you want savings per device
- Price
- 100 €
- What it does
- 1 metered relay, 16 A.
- Use it for
- A single water heater or radiator circuit with its own savings figure
- Price
- 76 €
- What it does
- Single-phase meter with two 50 A clamps, plus a 2 A relay to drive a contactor.
- Use it for
- Metering a single-phase flat or cottage; switching a load through a contactor
- Price
- 102 €
- What it does
- 3-phase meter, 0–400 A.
- Use it for
- The main incomer of a larger building
- Price
- 274 €
Prices from the shelly.com EU shop including VAT, checked on 29 September 2026. They vary by country and retailer.
Over 16 A? Use a contactor
A Shelly relay is rated 16 A per channel. Heavier loads, and anything with a motor or compressor, should be switched by a contactor that the Shelly controls — standard switchboard work for an electrician, and the way Shelly itself recommends load shedding.
Monitoring, not billing
Shelly meters are accurate to about 1% but they are not MID-certified — Shelly says its devices are not designed for MID. Use them to see and allocate consumption. Where the law requires a certified meter to bill per kWh, keep the certified meter for billing.
Shelly's statement on MID →Shelly's own guides for buildings
Shelly publishes its own material for property managers and installers:
Using a system we don't list?
Tell us what your building runs — a building-automation system, heat-pump brand or charger — and we'll check whether Elewatt can connect to it.
Put your co-op's common electricity on autopilot
Start with one meter and a free account. See the consumption and cost first, automate when the numbers say it's worth it.