Like most households and businesses, we wanted to find a way to cut energy costs — so we turned our problem-solving attention to our own bills. What started as a casual conversation about an unusual electricity tariff ended up becoming a genuine product that saves people money within weeks while putting wasted green energy to good use.
A friend introduced us to a tariff that offers electricity prices based on the fluctuating wholesale rate, published in 30-minute slots for the day ahead. Prices move with demand and with the energy mix being generated at any given time — green energy is typically much cheaper than gas. Occasionally there's so much renewable energy on the grid that prices drop below zero, meaning consumers can effectively be paid to use electricity, because it's cheaper for the grid than curtailing wind farms or firing up gas plants to balance the spikes.
We wanted a way to shift our electricity usage to these cheaper — sometimes negative-cost — periods, and ideally to store that cheap energy for later use. Home battery systems were far too expensive to test the idea properly.
We realised a hot water tank could act as a simple energy store, much like a battery, except it stores hot water rather than electricity. Better still, most homes already have one installed and ready to go. All we needed was a way to control the immersion heater so it converted cheap electricity into hot water at the right times.
So we built our own smart switch, paired with a simple web app that decides when to turn the immersion heater on and off, and gives clear insights into the best times to run other appliances day and night.
The results surprised us. In month one, we expected only modest savings while we fine-tuned the system — instead, we saved over £100 compared with the same period in the previous two years. The savings continued, so we built more units and tested them with friends to rule out a fluke. They weren't a fluke, so we turned the idea into a proper product.
That product, Ecomise, is now a polished, compact, DIY-installable unit requiring just four connections — a world away from the original prototype, and now part of Agentrify's product range. We're proud that it not only saves people money within weeks, but also helps tackle the wider problem of green energy going to waste simply because it can't be used when it's generated.
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