At the peak of a July afternoon, the house is closed up and the air conditioning is working at full blast. It is the hottest time, and it is also the time when the meter spins the fastest. Outside, the sun beats down directly onto the roof, with all the force it has at this time of year. All that energy passes over the house and continues on its way. Inside, every degree of coolness is paid for to the grid.

There is a mismatch here that few people notice. The energy that the house needs most, and at the highest price, is available in abundance right outside the door, at the exact moment it is needed. It's just that there is no way for it to get in.

Why summer is the most expensive month to cool

A household's energy consumption in summer has an easy-to-predict pattern. It is concentrated during the hottest hours, between midday and mid-afternoon, when the air conditioning has to work harder to compensate for the temperature outside. It is in this window of a few hours that the largest share of the day's electricity is used. The rest of the hours weigh little in comparison.

All this energy comes from the grid. When consumption spikes in the early afternoon, the only available source is electricity that is bought at whatever price it happens to be at that moment. And summer has the particular characteristic of pushing consumption precisely into the hours of greatest solar radiation, which means that you are paying peak expenditure at the time of day when there is the most sun over the house. The cost is not just in the value of the bill. It is in paying dearly for something that, at the very same hour, is in abundance all around the home.

Why is the missing energy passing over the house

It is worth looking at the roof of a house on a summer's afternoon. During those hours, it receives the most intense solar radiation of the year. The amount of energy hitting an exposed roof in the early afternoon of July easily exceeds what the house is consuming at that moment, air conditioning included. The energy is right there, all of it, available and free.

The problem is that a standard roof does nothing with it. The sun heats the tiles and little else. All the radiation that could power the home's consumption turns into dissipating heat, while, metres away, the meter keeps adding up the energy bought from the grid. It is a silent waste, which repeats every summer afternoon without anyone seeing it as such. There is a clear need, energy at midday, and an equally clear abundance, sun at midday, and nothing to connect the two.

When production and consumption happen at the same time

It is precisely this connection that a photovoltaic system establishes. The panels capture solar radiation and convert it into electricity, and they produce more when the sun is strongest. In other words, they produce their maximum at the exact same hours when cooling consumes its maximum. The energy generated on the roof at midday powers the air conditioning that is running at midday. This is called self-consumption, and it is the most direct way to make use of solar production.

There is a doubt that usually stalls those considering panels: electricity is produced during the day, but a large part of consumption is at night, when the sun has already set. It is a legitimate objection for the whole year. In summer, however, it loses force, because the house's highest consumption, cooling, happens precisely during the day, overlapping with production. The limitation feared in other seasons becomes, in summer, the system's greatest virtue. It is the season when production and consumption best coincide.

And it is this coincidence that changes how the investment is viewed. A photovoltaic system goes from being an expense with a distant and abstract return to having a visible effect right in the first summer, during the hours when the bill used to hurt the most. It does not eliminate the connection to the grid, but it reduces dependence on it precisely when it is at its most expensive.

The actual value, however, depends on one thing: how much of the household's consumption actually coincides with the production of the panels. And that cannot be solved with a generic number of panels. It depends on the consumption profile of the home, the orientation and area of the roof, and the cooling equipment installed. An oversized system produces energy that goes to waste; an undersized system leaves consumption uncovered. At Inwatt, the starting point is always the same: assessing the home's consumption and sizing the system to suit that profile. If you are considering using the sun to cool your home with your own energy, request a review and see how much of your summer bill could come from your own roof.