Domestic hot water is typically one of the largest slices of a household's energy consumption — often second only to climate control. Swapping a gas water heater or an electric cylinder for an efficient solution is therefore one of the fastest-paying upgrades available. Two serious candidates remain: solar thermal and a heat pump. This article compares them honestly.
The two solutions, in two sentences
Solar thermal uses roof collectors to heat water directly with solar radiation, storing it in a cylinder. The energy is free, but it only exists when there is sun.
A heat pump water cylinder uses electricity to move heat from the ambient air into the water. Because it does not generate heat by resistance, it typically consumes around a third of the electricity of a conventional cylinder — and it works at any hour, sun or no sun.
Where each one wins
Solar thermal wins where there is good south-facing roof space, where hot water use is high and fairly constant year-round, and where there is room for the cylinder. In the Algarve, with the radiation we have, a properly sized solar thermal system covers a very high proportion of annual hot water needs.
The heat pump wins where roof space is scarce or reserved for photovoltaic panels, where consumption is irregular, and where simplicity is valued — it is a single appliance, with no roof circuit, no thermal fluid and no risk of summer overheating.
The point that changes everything: photovoltaic
A few years ago this comparison was simple. It no longer is, and the reason is that photovoltaic prices have fallen a long way.
If you install photovoltaic panels and use that electricity to run a heat pump, you get hot water at close to zero running cost during the day — and the same installation also powers the air conditioning, the washing machine, the pool pump and everything else. Solar thermal, however efficient, does exactly one thing: hot water.
Put differently: a square metre of roof taken by a thermal collector serves only hot water, while the same square metre of photovoltaic serves the whole house. That is why, for most of the houses we assess in the Algarve today, the combination of photovoltaic plus heat pump makes the most sense.
Space, appearance and maintenance
Solar thermal takes roof space and needs a cylinder, which in thermosiphon systems sits visibly next to the collectors — a sensitive point on villas where appearance matters, and sometimes restricted by municipal rules in historic areas. Forced-circulation systems allow the cylinder to sit indoors, but add a pump and controls.
On maintenance, solar thermal requires periodic checks of the thermal fluid and circuit pressure. A heat pump asks for little beyond filter cleaning and an annual check. Neither is demanding, but the heat pump is clearly the simpler one to live with.
What if I already have a gas water heater?
That is the most common situation in Algarve houses, and also the one where the saving is most obvious. A gas heater only heats when you open the tap, which is convenient, but the cost per litre of hot water is high and there is always the nuisance of bottles or a tank.
Replacing it with a heat pump is usually straightforward: it takes the place of the cylinder or a plant space, connects to the existing electrical supply and needs no roof work. For many families it is the efficiency upgrade with the fastest return of all, precisely because hot water is a daily, constant load right through the year.
A common mistake: sizing by the number of bathrooms
Cylinder sizing should come from the number of people and their habits, not the number of bathrooms. A house with three bathrooms and two people does not need what a house with two bathrooms and five people needs. An oversized cylinder has greater standing losses and costs more; an undersized one leaves somebody without hot water at the end of the day — the complaint we hear most about badly specified installations.
In short
If you have free roof space, high consumption and want the most efficient dedicated hot water solution, solar thermal remains excellent. But for most houses in the Algarve today, the combination of photovoltaic with a heat pump delivers more: it solves the hot water and powers the rest of the house from the same roof investment.
Want to know which pays in your case? We look at your bills, the roof and how the house is used, and tell you which solution actually pays — with no obligation and a reply within 24 hours. Get in touch.
