When your solar panels lose you money

Solar panels can lose you money in the same hour they produce electricity. On a sunny April afternoon when the spot price goes negative, every kilowatt-hour exported to the grid is paid less than zero. Smart solar — combining self-consumption optimisation, curtailment in negative-price hours, and battery routing — turns this loss into a manageable trade-off.

Sometimes panels work perfectly and the household still loses money in the same hour. April afternoons in Estonia are the canonical case. The spot price goes negative around noon, the grid charges the household for every kWh it pushes back, and the inverter sits there cheerfully exporting at full tilt. The panels did their job. The economics did not.

This is the new reality of residential solar in Estonia. Net-metering and the generous feed-in tariffs that made 2020-era installs a no-brainer are gone. Surplus solar now sells at the Nord Pool spot price for the hour you produced it, and on bright spring days that price collapses, sometimes through zero. A kWh you export at noon might fetch two or three cents. A kWh you consume yourself displaces electricity you would otherwise buy at fifteen to twenty-five cents plus grid fees. The gap is enormous, and it points in one direction: self-consumption is where the value lives now.

Smart solar control is the software layer that closes that gap. The basic move is to route every surplus kWh to the highest-value home load before it ever reaches the meter. Heat pump first if the house wants heat. EV charger next if the car is plugged in. Domestic hot water tank as the cheap thermal battery almost every house already owns. An actual home battery last, because round-trip losses make it the least efficient sink. The order changes hour by hour with weather, occupancy and price.

The second move is curtailment. When the day-ahead price for a given hour is below zero, the rational thing for a solar inverter to do is nothing. Most modern inverters from SolarEdge, Fronius, Huawei, SMA, Sungrow and Solax expose either Modbus TCP or a cloud API that lets a controller throttle output or stop production for a defined window. It feels strange to switch off free electricity, but feeding the grid at negative prices is paying to give your power away. Better to let the panels idle for an hour.

The third move is forecasting. Cloud cover prediction tells you how much you are about to produce. The published day-ahead prices from Nord Pool tell you what each hour is worth. House-load history tells you when the dishwasher and the heat pump are about to draw. Put those three together and you can pre-cool the house at noon, charge the car between eleven and two, heat the boiler before the evening peak, and arrive at 18:00 with a full battery and a warm building just as the spot price triples. The published Estonian day-ahead curves on the regulator and TSO sites (Elering, Nord Pool) make this entirely tractable.

Pairing solar with a battery sharpens all of this. Cheap morning solar that would otherwise export at four cents goes into the battery and comes back out at the 19:00 peak when retail electricity is worth six times more. The Estonian regulator has signalled further tightening of how exported and consumed kWh are accounted for from 2026 onward, which we cover in our note on the upcoming rule changes. In 2025, solar without smart control plus some form of storage is a worse deal every year, and the gap is widening.

The pieces are not exotic. A controller that talks Modbus to your inverter and your heat pump, a price feed, a forecast, and an optimiser deciding what runs when. Volton Home does this in the background: it pulls inverter telemetry, reads the day-ahead curve, routes surplus to whichever load wants it most, and idles the inverter when the grid would charge you for exporting. The panels keep doing their job; the controller just makes sure every kWh they make is worth something.