Everyone knows that solar panels convert sunshine into a cost-free and 100% renewable source of energy.
But sunlight contains two distinct physical qualities that could be used to generate electricity: light and heat. So, if you’ve ever thought about going solar, there’s a good chance you’ve wondered which of the two you'd be relying on.
The short answer is “light,” but the longer answer is “it depends.”
2 types of panels
That's because there are two different types of solar panels. Photovoltaic (PV) panels, convert the sun's light into energy, and thermal panels, convert its heat.
Any rooftop solar system designed to power a home will use light-converting photovoltaic (PV) panels. Thermal panels, on the other hand, are sometimes used to generate other kinds of energy.
Spotting the difference
The difference between PV and thermal rooftop solar systems is easy to spot.
If you see a few panels with spaces between them or even just a single panel on someone's roof and there's a pipe running across the top, you’re looking at heat-converting thermal solar panels.
Whereas anytime you see a large set of interconnected panels minus any piping, you're looking at light-converting PV solar panels.
Thermal solar installations generally use far fewer panels than PV systems because they do one and only one thing: provide hot water.
In fact, sometimes, instead of a slim pipe, thermal solar panels wear their purpose on their sleeve by sitting below a big hot water tank.
Thermal Solar Pros
If you just want to save a little money on your monthly hot water bill but aren't looking to generate electricity to run your appliances, thermal solar panels can have some advantages.
- Thermal solar panels just use the sun’s heat to raise the temperature of water. So, the technology is much less complex than PV panels.
- Because the purpose is so limited, fewer thermal panels are needed.
- Thermal solar panels are also very energy-efficient, making use of up to 90% of the heat contained in sunlight.
Thermal Solar Cons
As great as all that may sound, thermal solar power has some serious downsides.
- Solar thermal doesn't work all that well in the winter when sunlight contains less heat. In cold-winter states like Pennsylvania, you might be able to get all your hot water from thermal solar panels from April through September. The rest of the year the percentage can drop to as low as 10-20%. The upshot is that, even with solar thermal panels, you’re likely to spend half of every year paying for hot water.
- Thermal panels only produce hot water. They don’t generate energy for any other purpose whatsoever.
- Though the technology is simple, thermal solar power involves pushing water through pipes, which can become damaged and start leaking. A water pump is also necessary, which may not last more than 10 years.
- Because solar thermal panels are more of a niche item, it can be hard to find a reputable installer.
The advantages of PV solar
Instead of using the sun’s heat, PV panels use something called the photovoltaic effect to turn sunlight into electricity.
Though the technology is more complex, the advantages of having a PV system are many.
- PV panels have an incredibly long lifespan. Because there are literally no moving parts involved, a PV solar system will typically provide cost-free energy for 25 to 30 years.
- Thanks to increases in panel efficiency, typical American homeowners and small businesses can now generate all the energy they need with a simple rooftop PV solar system.
- PV solar systems can also be installed without any upfront costs. There are, in fact, two options here. If you want to own your solar system, it's possible to lower your monthly energy bill by financing a PV system without putting any money down.
Power Purchasing Agreements (PPA) provide another way to save money by going solar power without spending a dime. With a PPA, the installer pays for and fully owns the solar system on your roof. So, instead of generating your own solar energy, the installer contracts to sell you electricity at a rate below what you're currently paying. - Finally, unlike thermal solar panels, PV panels actually work more efficiently in cold weather.
Why PV solar dominates the market
In short, the reason that PV solar panels have dominated the market is that they can do everything that thermal panels can plus a whole lot more.
So, at the end of the day, the choice between PV or thermal solar panels just depends on much money you’re looking to save.