PowerDay: a power cut tracker for places where the grid goes off

The problem

Simple questions, answered with a notebook every evening

In Lagos, as in Karachi, Accra or Beirut, the grid goes off and on several times a day. Homes run inverters, batteries and generators, and almost nobody knows how many hours of grid power they really get in a week, or what a unit costs once the generator’s fuel is counted.

Those are the numbers that decide whether a bigger battery or a solar upgrade is worth the money. We built the app that keeps them for you.

What we built

Five pages and a plan, each with one job

• HomeIs the power on or off, and for how long. One big button to log the change, the last 24 hours as a picture, and a tile for each page.
• GridOne tap when the power goes and one when it is back, a seven day chart, and the prepaid units bought. In Nigeria it sends people straight to their DisCo or bank app; PowerDay never takes payment.
• SolarBattery tonight. Add what is switched on, from 5 W bulbs to a 2.5 hp air conditioner, and it says how many hours are left, when the battery runs out and what to switch off to reach 7 in the morning.
• GeneratorOne button when it starts and when it stops. Oil change and service reminders by running hours, fuel bought, and fuel used per hour.
• ReportsThe month: hours of power, the longest cut, money spent on fuel and units, and what one unit really costs from the grid and from the generator. Shared as a picture on WhatsApp.
• Plan solarAn inverter, battery and panel size worked out from the household’s own cuts and appliances, ready to take to an installer.

What made it hard

The parts that took the time

1. Time that crosses midnight. A cut that starts at 11 pm and ends at 2 am belongs to two days, and clocks change in some countries. The totals have to agree with the picture every time, so 30 automated tests run before every release.
2. Battery hours from real appliances. Bulbs, fans, televisions by screen size, fridges, pumps and air conditioners by horsepower, or watts typed in. The answer is a time on the clock, which is the number people actually want.
3. Offline first. Every page is saved on the phone, so the app still opens when the power and the mobile data are both down.
4. Private by design. No account, no ads and no tracking. Everything logged stays on the phone, with a backup file and a single button that deletes it all.
5. The method stays on our server. Solar sizing runs on our own server, so the working is never shipped inside the app.
6. Store rules before launch. Google Play’s target API level, the data safety and financial features forms, and a 14 day closed test with at least 12 testers before an app can go public.

Where it stands

Version 0.2, in closed testing on Google Play

Google approved the first release for testing on 15 October 2026, and the redesigned version 0.2 followed a day later. When the closed test finishes, PowerDay moves to the public Play Store. We will publish user numbers when there are real ones to publish, and not before.

The same habits go into every client build: the sums checked by tests, private data kept private, the method kept on our server, and pages that still work on a bad connection.