The angle and orientation of your roof is a significant factor when considering installing solar panels. For example a solar panel placed flat onto a west facing wall will produce about half the amount of electricity compared to being placed at a 30 degree angle on a south facing roof. Of course for a domestic installation you would never install a panel flat against a wall but this does illustrate the importance of placement.
Although important your roof angle and the direction your roof faces is not as big of an issue as it used to be. Modern panels are able to perform better at less optimal angles and perform better in the type diffuse light we get in the UK. There is only about a 5 percent loss in power output of solar if the panel are facing south-east or south-west compared to facing directly south.
The following table shows the relative output of solar panels based on their angle and orientation. It shows the further away from being at a 30 or 40 degree roof angle and facing due south the less efficient the panel would be. Interestingly if you placed your panels on a flat roof facing towards the sky they would only perform 10 percent less than optimal.
Depending on whereabouts you are in the world will alter the optimal angle and orientation. These figures are only really suitable for the UK and then there is some variation across the country. In the far north of Scotland your panels would perform better if your roof angle was 40 degrees. For the far south of England the optimal roof angle would be closer to 30 degrees.
Shading is a big problem for solar photovoltaic panels. Even though they can generate electricity on overcast days most systems perform significantly better in direct sunlight. Even a relatively tiny shadow cover just 3 percent of an arrays surface can mean a 25 percent loss of output for the system as a whole.
When we are talking about shadows it is important to point out that for the purposes of solar PV this means a shadow cast over an area of the array for a prolonged period. So if a pigeon lands on your roof aerial casting a small shadow and leaves after a few minutes that is only going to reduce the systems output for that short period of time.
The real problem comes from more permanent structures such as shading from trees, chimneys, dormers and other structures on solar panels. These tend to cast a shadow for a relatively significant amount of time and have an un-proportional effect on solar performance. As the sun moves across the sky from east to west shadows around the building also move. The shadows cast during the winter months will be different from the shadows cast during the summer.
The potential effect of shadowing can be done during the site survey. The surveyor will be able to estimate the shadow angles on the roof from the surrounding objects and calculate how the shadows cast at different time of the year and throughout the day. The estimated impact of shadowing can then be taken into account when deciding if a solar panel installation is going to be financially viable.
The reason that shadowing has such a detrimental impact on electricity generating solar panels is due to the way the panels are connected together. Panels are generally arranged in a string, this essentially means that they are joined together much like connecting several batteries together.
If a shadow is cast on just one of those panels it affects the whole string, which means every panel in that string produces less electricity. This weakest link problem means that careful planning, done through a site survey which is carried out by the installer, is done to reduce the risk of potential shadow problems.
One way to avoid the effect of shadowing if you want to install panels but would get some shadowing is to use micro inverters. A micro inverter is placed on the underside of each panel and replaces the larger single inverter that the panels would have connected to. As each panel now converts the electricity it generates from DC to mains AC electricity the effect of shadowing is greatly reduced. This means that a solar array could potentially increase its output almost negating the effect of shadowing.
The drawback is that a series of micro inverters will be slightly more expensive than a single inverter. You should however recoup those cost through greater panel efficiency. There are also other benefits of using micro inverters such as reduced installation times, individual panel monitoring and more cost effective maintenance.
This is not something to worry about but you should be aware of the different factors involved in purchasing or getting a free solar installation. These factors could be the reason that you have been refused a free solar installation. But armed with this knowledge you could decide to got to another free installer or even consider buying your own solar panel array.
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