Solar air conditioning: how it works and who it really pays off for

The problem this equipment solves

Air conditioning is the appliance that pairs best with solar energy, and hardly anyone takes advantage of it. The reason is a simple coincidence: the hours when the house most needs cooling are exactly the hours when the panels produce the most. Between eleven and five, in a Portuguese summer, the sun is beating down on the roof and heating the house at the same time.

The usual way of bringing the two together is expensive. You install a complete photovoltaic system — panels, inverter, protection devices, possibly a battery — and then plug the air conditioner into a socket like any other appliance. It works, but it means building all the infrastructure before you see your first euro of savings.

Hybrid solar air conditioning cuts that path in half. The panels connect directly to the unit in direct current, with no inverter in between, because the inverter and the MPPT controller are already built into the outdoor unit.

How it works, without the jargon

The outdoor unit accepts two inputs at the same time: the household mains, at 230 V, and the solar panels, at between 80 and 380 V direct current. The electronics inside decide where to draw the energy from, moment by moment.

With enough sun, it runs on solar. If a cloud passes and output drops, it tops up from the grid without anyone noticing — no cut-out, no restart, no drop in temperature. At night it runs 100% on the grid, like a normal air conditioner.

It does not need a battery. That is what surprises most people who have already looked into the subject: since consumption happens at the same time as production, there is no energy to store. A battery would only be needed to run the unit on solar at night, and at that point the cost no longer pays off.

The model we install has a capacity of 3.5 kW — 12,000 BTU, enough for a large living room or two bedrooms — with R32 refrigerant and an EER of 4.07 W/W. It also heats in winter, which changes the numbers considerably: a unit used six months a year pays for itself twice as fast as one used only in summer.

Who it pays off for, and who it doesn't

It pays off for people who spend the day at home. Remote workers, retired people, families with babies, small offices, shops. That is where consumption coincides with production, and where the saving is real and immediate.

It pays off for people who don't have photovoltaics yet and don't want to make the whole investment at once. A solar air conditioner with its own dedicated panels costs a fraction of a complete system, and it is a first step that closes no doors — anyone who later wants the full system can still install it.

It pays off for people with a small or shared roof, where a complete system won't fit but two or three panels will.

It does not pay off for people who are only at home at night. At night the unit runs on the grid, and in that case you are paying for solar electronics you don't use. Nor does it pay off for people who already have a well-sized photovoltaic system with surplus going unused: in that case the better deal is to connect a normal, cheaper air conditioner to the system that is already there.

What it costs and what it saves

The unit costs €2,366 in our catalogue. Installation comes on top of that, quoted separately because it depends on the distance between the units, the type of wall and where the panels go.

On savings, we deliberately don't give a round number. It depends on the hours of use, the orientation of the roof and the tariff you are on — and any number given to you without knowing that would be made up. What we do is work it out with your own data during the site visit, which is free.

What can be said with confidence is where the saving lies: in summer, at peak hours, which are the most expensive on the tariff and the ones with the highest solar output. It is the most favourable combination there is.

Installation is not optional, and there is a reason

Deye expressly excludes from the warranty any faults resulting from installation by anyone who is not a certified HVAC technician. It is not small print designed to make anyone's life difficult: a badly installed unit that combines a refrigeration circuit with direct current at 380 V is a safety problem, not just a performance one.

In practice, this means that buying the cheapest unit you can find online and asking an acquaintance to fit it costs you the manufacturer's five-year warranty. We are certified and we install, which is why we sell it with installation and not without.

A note on the manufacturer

Deye is a Chinese manufacturer founded in 2000 in Ningbo, with more than two million solar inverters installed in more than 140 countries. In Portugal it is best known for its hybrid inverters, which we have been installing for years — the same company that makes the SUN-12K found in half the three-phase installations in the country.

The unit is shipped from the European warehouse in Germany, with CE and TÜV SÜD certification. The warranty is five years.