EMS
The energy management system for every energy flow in my house: it buys electricity when it is cheap, uses it when it is expensive, and keeps the sun’s energy in the house.
What it is
With a dynamic energy contract the price of electricity changes every quarter hour, with the market. EMS makes the most of that. It reads the smart meter about every ten seconds and steers the home battery, the solar panels, the car charger and the heat pump around the price, the weather and what the house is likely to use.
I built it for my own home, where it runs in a container on a small server and talks to most devices over the local network.
At home
EMS manages the energy in my own house. What its battery and solar panels came to, through 3 November 2026:
- Battery saved
- €351.82
- Solar value
- €1,873.43
- Net energy cost
- −€157.72
- Battery cycles
- 203
- Round trip
- 68% last 30 days
| October 2026 | November 2026 | All time | |
|---|---|---|---|
| Battery saved | €20.31 | €0.00 | €351.82 |
| Solar value | €184.70 | €17.03 | €1,873.43 |
| Net energy cost | €142.63 | €24.22 | −€157.72 |
| Battery cycles | 10.2 | — | 203.4 |
| Charged at | 20.7 ct | 43.7 ct | 17.0 ct |
| Discharged at | 44.7 ct | — | 32.6 ct |
| Spread | 24.1 ct | — | 15.6 ct |
| Round trip | 70% | — | — |
Battery saved is what its discharge was worth less what charging it cost; solar value is the power generated, valued at what it displaced or earned; net energy cost is grid import less export revenue, so below zero is money earned. Prices are per kWh. Round trip is the energy the battery gives back per kWh put in. Whole days only, updated daily. All time is since 24 February 2026.
Plans ahead
Every few seconds EMS plans the next 36 hours, quarter hour by quarter hour: charge the battery in the cheapest windows and discharge it in the most expensive, but only when the difference is worth the energy a round trip loses.
Solar first
Surplus sunshine goes into the battery rather than the grid. When the grid charges for exported power, EMS turns the panels down; when it pays you to use power, it charges from the grid instead.
Forecasts
It forecasts the panels’ output from the weather, calibrated against what they actually produced, and the house’s use from its own history. Beyond the published prices it estimates the next days from the wind and sun forecast.
Car charging
The car charges at the cheapest hours, is ready by a set time, or simply charges at full power. EMS reads its state of charge from the manufacturer, and can top it up from the battery when that beats the grid.
Heat pump
Through the worst price peaks it puts the heat pump on standby, and switches it back afterwards.
Dashboard
An installable web app shows the house live, with price and history charts, energy and cost reports, the weather, and push notifications when tomorrow’s prices are out. In English and Dutch, light or dark.
Devices
Only a smart meter reader is required; a battery, solar inverter, car charger, car and heat pump are all optional, and EMS does what it can with what is there. It works with equipment from about 50 brands.