Too Much Sun? Curtailment, Negative Prices, and Your Summer Surplus

There is a problem most new solar owners never see coming: not too little sun, but too much. On a clear summer midday your panels are flat out, yet the house is barely using anything, no heating, lights off, maybe nobody home. All that energy has to go somewhere, and sometimes the answer is “nowhere useful.”

Two different ways production gets “lost”

It helps to separate two things that look similar but are not.

The first is inverter clipping. If your panel array is rated higher than your inverter’s AC output, a common and deliberate choice, the inverter simply caps what it pushes out when the array overshoots. On a clear day you see a flat top on your production curve at the inverter’s limit. This is usually by design and nothing to worry about; oversizing the array squeezes more out of cloudy days and shoulder hours.

The second is grid curtailment, and this one is less benign. Sometimes the grid cannot absorb your export. Voltage on your local line creeps up as everyone’s panels push at once, regulatory export caps kick in, or the operator sends a signal to throttle back. Your inverter dutifully reduces output to keep grid voltage within legal limits. The conditions were perfect, but your meter says otherwise.

How to tell which one you are seeing

Clipping shows up as a clean flat line right at your inverter’s rated power on bright days. Curtailment looks different: output held below what the weather justifies, often around midday on sunny, low-demand days, sometimes alongside an unusually high grid voltage reading. Knowing the difference matters, because curtailment can easily be mistaken for your system underperforming, when in fact it is working fine and being held back from outside. This is the kind of thing Volcast’s curtailment detection is built to flag, so you are not chasing a fault that is not there.

Negative prices are no longer a curiosity

There is an economic twist on top of all this. On days that are both sunny and windy, with low demand, wholesale electricity prices can collapse, sometimes below zero. It started as a German headline and is now a regular feature in Poland and across much of Europe. If you are on a dynamic tariff like Pstryk or Tibber, you feel it directly: midday import prices can drop to almost nothing, occasionally to negative, meaning you are effectively paid to consume.

Turn the surplus into something useful

The trick is to stop letting that midday energy leak away as cheap export and start soaking it up yourself. Charge your home battery. Heat your hot water. Pre-cool or pre-heat the house before the expensive evening hours. Charge the EV. Run the pool pump, the dishwasher, the laundry. Anything flexible, push it into the surplus window.

If you are on a dynamic tariff, the logic extends to the grid itself: when midday prices are near zero or negative, it can pay to import, even to charge the battery from the grid, and lean on that stored energy when prices climb in the evening.

Plan it instead of reacting to it

The best part is that none of this has to be guesswork. Tomorrow’s surplus window is predictable, and a multi-day forecast lets you plan the whole week around it: stack your heavy, flexible loads onto the high-surplus days and ease off on the cloudy ones. Too much sun stops being a problem and becomes the cheapest energy you will buy all year.