Solar panels, home batteries, EV charging and electricity prices, explained with measured data instead of sales talk. Presented by Joulie, our animated smart meter.
Every video starts from a real question and ends with real numbers. No installer pitch, no jargon you don't need.
Home batteries, heat pumps, EV charging: what they really save over the years.
How your inverter decides where solar power goes, and why.
“Solar is useless in winter.” “Batteries pay back in 5 years.” We test them.
Dynamic tariffs, vehicle-to-home and new battery chemistry, in plain English.
First up: “Are home batteries actually worth it?” using a full season of data from our own 5 kWh battery. Read the numbers and transcript. New: why electricity prices turn negative.
Put in your own prices and battery cost. The defaults are measured data from a real 5 kWh battery in a solar home in Portugal (July–October 2026), with an assumption for winter.
Same battery, same export price and efficiency; only the import price changes. Outlined bar = your price. Dashed line = warranty.
This calculator explains the math; it is not financial or installation advice. It ignores battery degradation, price changes over time, subsidies, dynamic-tariff arbitrage and backup value. Your prices, rules and usage may differ.
The video walks through a whole season of battery data, day by day.
Every kWh the battery delivers in the evening is a kWh you don't buy from the grid. But to store it, you give up exporting it during the day, and some energy is lost in charging and discharging.
A 5 kWh battery in a solar home in Portugal delivered about 4.4 kWh per day from July to October 2026 and was full on 106 of 116 measured days. With an assumed 2.5 kWh per day in winter, that is about 1,370 kWh per year.
That is longer than the 10-year warranty: after 10 years the battery is still about €1,100 short of paying for itself.
| Price you pay | Saving / year | Payback |
|---|---|---|
| €0.17/kWh | €190 | 15.8 yrs |
| €0.20/kWh | €231 | 13.0 yrs |
| €0.25/kWh | €299 | 10.0 yrs |
| €0.30/kWh | €368 | 8.2 yrs |
| €0.35/kWh | €436 | 6.9 yrs |
€3,000 battery, 1,370 kWh/year, €0.03 export price, 95% round-trip efficiency.
It depends mainly on the gap between what you pay for electricity and what you get for exporting it. In our measured case (€0.17 import, €0.03 export) a €3,000 battery saves about €190 a year and takes about 15.8 years to pay back, longer than a typical 10-year warranty. At €0.30/kWh the same battery pays back in about 8.2 years.
Ours delivered about 4.4 kWh per day from July to October 2026 and was full on 106 of 116 measured days. With about 2.5 kWh per day assumed for winter, that is roughly 1,370 kWh per year. Rule of thumb: usable capacity × 0.75 × 365 if the battery fills most days.
Yearly saving = kWh delivered per year × (import price − export price ÷ round-trip efficiency). Payback time = battery cost ÷ yearly saving.
Battery degradation, future price changes, subsidies, dynamic-tariff arbitrage and the value of backup power. These can move the result either way.
Energy Home Lab is an English-language YouTube channel and website that uses measured data from a real solar home in Portugal. Videos are presented by Joulie, an animated smart meter. Watch on YouTube: @energyhomelab.