When you live in a place with a hot climate, the chances are that your biggest expenditure on energy during the summer will be your air conditioning. So, if you can keep your home cooler and at the same time use the sun’s energy to provide electricity, you’d basically be getting double the benefit. But can solar panels provide that benefit?
Solar panels insulate your roof, though the effect is minor. In summer, solar panels can lower a roof’s temperature by 5°F (3°C), and in winter, they can also slightly prevent a loss of heat through your roof at night. The main temperature benefit from solar panels is in the cooling department.
In this article, we’ll discuss how solar panels act as a roof insulator and how much of an effect they really have.
Do solar panels insulate your roof?
Solar panels do insulate your roof, but how much cooler your house will be in summer and how much heat loss you can expect in winter nights depends on your home circumstances.
Here are a few of the most important factors:
- Is there external insulation on the roof?
- Is the space beneath your roof empty attic or living space?
- Is the space well-ventilated?
- Is the attic insulated?
- What proportion of the roof is covered by the panels?
And although the cooling effect is not significant, it is a free side effect of your solar panels. You may as well make use of it, especially during the summer months.
How do solar panels insulate your roof?
Solar panels essentially act as roof shades. They protect your roof from damage caused by UV radiation and excess heat.
It’s important that there is at least a few inches of space between the panels and the roof. The reason that solar panels can decrease your roof’s temperature is that they capture much of the sun’s energy that would otherwise hit your roof. Most of this energy is converted into heat, which then radiates all around the panel — including toward the roof.
The only reason this radiating heat doesn’t reach the roof and heat it up is that the wind carries it away before it gets the chance to do so. That’s why it’s essential that your panels are installed a few inches above the roof and that wind can flow into the space between.
These panels can reduce the amount of heat that reaches the roof by around 38%, which results in the small temperature decrease I mentioned above. To be specific, they disperse the heat from the sun in four ways:
Energy from the sun is converted into electricity. Most solar panels are around 16-20% efficient – so that between 16-20% of the sun’s energy is prevented from heating up your roof because it is converted to electricity and transported away in cables as DC current. This leaves 80 – 84% of the sun’s energy left.
Reflecting heat means bouncing it away. Solar panels will reflect some sunlight away. They are dark in color, which absorbs heat, but the glass is a shiny, reflective surface, and their metal frames will also reflect energy out and away.
To conceptualize how reflection impacts energy absorption, note the difference in temperature in a car on a hot day. – you could fry an egg on the black hood of a car in very hot weather, yet the windows feel quite cool.
Emissivity is a word that describes how much heat a hot surface is radiating away. Solar panels are dark and do absorb heat, although they do not themselves produce heat (or only in tiny amounts).
But they will emit heat since heat travels from hotter areas to cooler areas, and as the panels themselves heat up, they will become hotter than the surrounding air, and hence emit heat. A proportion of this will be emitted onto the surface of the roof.
Roof panels are placed with a gap of a few inches between the panel and the roof. This allows air to flow through the gap, which can carry off some of the heat by convection. When we talk about the wind carrying away the heat radiated by the solar panel, this is the process we’re referring to.
Solar panels do help to insulate your roof, but the amount of insulation they provide is minimal. Still, the cooling effect is a welcome by-product of the PV panels. Because of their insulating properties, they also help to prevent heat loss during those cold winter nights.
They reduce the heat gained by your roof by reflecting it off, by emitting it and losing it by radiation, by convection using the airspace between them and your roof – and, of course, by converting some of the light energy into electricity – which you could use to run your air-conditioning.
By lowering the temperature of your roof by just a few degrees over time, this can create a saving in energy use and expenditure for you.