Shade from features in the immediate surroundings of your home can greatly affect the level of solar radiation reaching your panels. Trees and buildings, or other landscape features such as hills, can block incoming radiation and cast a shadow, reducing the usable solar radiation. Even a small obstruction, like a leaf, can have a considerable impact on the performance of your system.
Determining whether solar energy makes sense for your particular case depends on a number of factors, such as the level of shade (is it partial or complete?), the time of day when shading occurs (is it for a couple of hours, is it midday, or all day?), and the annual variation of shade (is it seasonal, such as from a tree that will lose its leaves in winter, or is it permanent, such as from a building?). Moreover, the solar panel design will play a role. Solar modules connected in series with a central inverter will be more greatly affected than those connected in parallel with micro-inverters, even if the physical area of shading is small.
Using our tools Sunmetrix Discover and Sunmetrix GO can give you a preliminary idea of what solar energy can do for you. Ultimately though, if shade is a significant factor, a qualified installer should assess the particularities of your situation and determine whether solar energy is right for you.
So what are your options if you are worried about shading on your roof? Here are some practical suggestions.
Use Discover and/or GO
Use Discover and/or GO and run the numbers for your site, changing the shade variable to assess the impact. With the Sunmetrix solar home design tool, you can adjust the roof slope, panel orientation, number of panels and level of shade and see your solar home evolve before your eyes. The expected energy output and your corresponding savings adjust accordingly. This is a great way to better understand what solar energy can do for you and customize it for your situation.
Consider tree maintenance/pruning
We're not suggesting that you cut down all the trees on your property in order to go solar. But sometimes a little tree maintenance, which is a good idea from time to time regardless of whether you are considering solar energy, can make a significant difference. Not only do you want to be considering the impact of shadows cast on your panels but also the impact of falling leaves. A specialist in tree pruning can help you get the most from your panels, while helping ensure that your trees stay healthy and strong for years to come.
Factor in removal of fallen leaves and debris
Spring and autumn cleaning of your panels may help you get the most out of your investment. There are various opinions about the effect of dust and grime build-up on panels and one Californian study suggested that dust removal wasn't worth the cost. Generally, rain takes care of most of the cleaning. However, there are some exceptions. If you live in an area with a lot of birds, your panel output can be compromised by bird droppings that don't easily wash away in the rain. Moreover, in spring and autumn, fallen leaves and seeds can stick to your panels. If you find that they are not blowing away, you may want to consider having them removed by a professional.
Consider micro-inverters (rather than a central inverter)
Micro-inverters are more expensive than central inverters, but they could pay off handsomely if your roof has some shade and/or a complex geometrical shape. Like old-school Christmas lights connected in series, that fail completely when one bulb goes, solar panels attached to a central inverter suffer from the same vulnerability: one shaded panel can stop the entire string from working. This will result in a significant or complete loss of electrical supply, since the central inverter optimizes the output based on the weakest link in the chain. On the other hand, with micro-inverters, if one solar panel is shaded, this will only have a minor impact on your overall system, as they enable each solar panel to perform at its maximum potential depending on weather conditions, shading and other external factors. As a result, one solar panel cannot drag down the entire solar array’s performance. You can read more on central versus micro-inverters here.
Consider community solar
If after considering all of the suggestions above, you determine that solar panels on your roof just don't make sense, because for example there is a big building right next door casting a shadow most of the day, then all is not lost. You may still be able to benefit from solar energy, saving on your utility bill while using clean energy. How? With community solar. A number of companies are springing up that build solar farms on suitable land, or smaller installations on commercial buildings, and then allow people to buy solar credits. This has become a popular option for renters who do not have the option to install solar panels. Perhaps it could also be right for you!
In conclusion, although excessive shading on your roof can be a show-stopper, there are a number of different strategies that can help you manage the impact of shading.