As someone interested in green roofs, you might also be interested in other ways to make your home more sustainable, like solar panels. Although I had seen both green roofs and solar panels on various roofs before, I could not recall having seen both being used simultaneously. This left me wondering: could green roofs and solar panels be used together? Here is what I found
Green roofs can be combined with solar panels. By choosing suitable mounts for the solar panels and using an extensive green roof, combining the two should be no problem. They can actually be beneficial for both the solar panels’ efficiency and the biodiversity of the green roof’s vegetation.
However, it is important to keep in mind that you are combining the green roof and the solar panels. Although there are some great benefits to this, as I will get into, one compromise that will have to be made is that you cannot fill the entire roof with densely packed solar panels and expect the green roof to survive and flourish the way you would like it to. Some steps need to be taken to ensure that the panels and the vegetation both work on the same roof.
Extensive green roofs work best with solar panels
Green roofs can be divided into three main categories: extensive, semi-intensive, and intensive green roofs. For a bio solar roof, the preferred type of green roof is an extensive green roof. This type of green roof can be seen as the simplest type. The growing medium is the thinnest out of the three types, at about 6 to 20 cm. The vegetation consists of mainly grasses and mosses, which are resilient to harsh circumstances like drought and heat and require zero to minimum irrigation.
One of the reasons that the extensive green roof type is particularly suited for concurrent use with solar panels is that the vegetation present on these roofs does not grow very high. If the plants were to grow higher than the solar panels, they might throw partial shade onto the panels, which could reduce the solar panels’ efficiency to a large extent.
Another reason to go with an extensive green roof is that the sediment layer of an extensive green roof is the right thickness to use as ballast with some of the existing specially designed mounts for the solar panels. By using the sediment as ballast, the mounts can be installed without having to penetrate any waterproof layers in the roof structure itself, which comes with the benefit of making the installation less complicated.
Choose the right mounts to elevate the solar panels off the roof
To make the most out of the combination of solar panels and a green roof, the right mounts are a must-have to ensure that the green roof will survive and even experience benefits from the solar panels above.
One of the mounts’ prerequisites is their mounting height; the solar panels need to be elevated off the roof further than they would typically be if there were no green roof elements present. This is because the extra height will allow sunlight and rainwater to reach the vegetation beneath the panels, two things the plants can’t live without.
Also, the panels should not be packed too densely together. If the panels are packed so closely together that hardly any water or light can penetrate to the roof, the plants will not be able to thrive up to their full potential. Again, be sure that you are actually combining both the green roof and the solar panels, not just slapping them both on the roof and hoping that it all works out.
How the green roof increases solar panel efficiency
Although it is true that on a scorching summer day, solar panels produce the most electricity, it is certainly not because of the extreme heat. In fact, the heat is actually detrimental to the amount of electricity that the solar panels can provide. This is because solar panels work optimally at a temperature of around 77°F (25°C), and their efficiency starts to take a significant hit as the temperature climbs over that.
And the temperature will climb over that. In the summer, roofs can get pretty hot! Depending on the weather and the climate where you live, roof temperatures of 150°F (65°C) are not uncommon. If solar panels get up to that temperature, some can lose up to 20% of their output, which is a pretty drastic loss. It would be great if that loss could be cut down, where green roofs come in.
Green roofs have a cooling effect which is mainly caused by evapotranspiration. Evapotranspiration is the combined process of water evaporating from the roof and water transpiring from tiny holes in the plants’ leaves, called pores. The process of turning water from its liquid state to water vapor takes a lot of energy in the form of heat. This heat energy is drawn from the green roof, cooling off the roof in much the same way that sweating cools you off when you start to overheat and need to lose some of that heat.
This heat-reducing effect is one reason that combining green roofs and solar panels can provide extra benefits. Because the roof does not get up to the same temperatures that a regular roof would, the solar panels take less of a hit in their performance, leading to some sweet extra energy being generated in the long run.
How the solar panels increase green roof biodiversity
Not only can the green roof have a positive effect on the solar panels, but the solar panels can also have a positive effect on the green roof. This is because the solar panels can change the living conditions of the plants underneath in several ways, which causes a wider array of vegetation to live on your roof.
One way that the solar panels can help the biodiversity on the bio solar roof is because they cause differences in the intensity of sunlight that reaches different spots on the roof. For example, some plants may not tolerate super intense direct sunlight every day. The solar panels will provide areas of partial or even full shade and indirect sunlight, allowing some of these plants to live on the green roof when they would normally not be able to.
The solar panels also provide a variation in the amount of water present at different places on the roof. Some places might experience less water because they are right underneath one or more solar panels. In contrast, other places will be damper than average because they are under the solar panel’s run-off area, so the rainwater that falls on the solar panels drains off and collects there. This variation will allow for more biodiversity in much the same way as the variation in sunlight will.
Green roofs can save you energy in other ways
Although solar panels are great for reducing your electricity bill, there are also other ways in which green roofs can help you save some money. In this case, it is not by producing energy but by saving energy.
Green roofs can save energy by reducing the amount of energy spent on climate-controlling your house, both by reducing cooling energy during the hotter times of the years and potentially also by reducing heating energy during the heating season.
The cooling effect that green roofs can offer is caused by a combination of the vegetation’s shading effect, along with the effect of evapotranspiration from the green roof system. The sediment layer largely causes the potential insulating effect.
To learn more about this, I have written an article dedicated to the energy-saving capabilities of green roofs. You can check that article out with this link.