In considering options for solar systems, there are four basic components that you need to understand: the solar panels, the inverter, the mounting system and the racking system.
Types of Solar Panels
There are a handful of different panels on the market today, and over 95% of these are based on Crystalline Silicon Technology. There are two basic types of Silicon Panels.
Monocrystalline Silicon Solar cells, also called single crystalline or Mono-Si, have a distinct, even coloring and uniform look due to their high-purity silicon content. This pure form of silicon makes them highly efficient, with an efficiency rating of up to 20% for converting sunlight into electricity. This efficiency allows them to be more compact—you can get the same power output from fewer solar cells. Another advantage of these panels is that they last longer and come with warranties of up to 25 years.The downside is that they are significantly more expensive than alternatives. When considering the total project cost they may not be the best solution. Additionally, due to the nature of how they are designed and manufactured, they produce far more silicon waste then alternatives.
The other option is to use Polycrystalline Silicon cells, also known as polysilicon, Poly-Si, or multisilicon. They use a much less pure version of silicon and are manufactured in a far simpler fashion.The result is a material that is much less expensive to manufacture and produces much less waste. The downside is that they have a lower efficiency rating, of between 13-16%.This lower efficiency makes them less space-efficient. One other drawback is that they have a lower heat tolerance and do not perform as well in very hot environments. Finally, they also do not have the aesthetically pleasing color and consistency of mono-Si panels. But dollar for dollar, you can get more power using Poly-Si panels.
Beyond Mono- and Poly-Si panels there are a range of newer technologies that have come onto the market, ranging from Thin Film to Amorphous Silicon.In general, unless you have a unique site or a specific request from a customer, you will probably be choosing between the two silicon-based panels.
The inverter converts the direct-current (DC) output collected by the solar panels into alternating current (AC) to power homes or businesses. There are many different manufacturers and suppliers of inverters. In the past, it was common for an inverter to only be 80-85% efficient, but more recently, inverters have gotten much more efficient and reliable. Today's inverters are generally rated to be 92-96% efficient.
There are two main types available today: central inverters and micro-inverters, both of which have some pros and cons depending on the particular project and site design. Central or string inverters are currently the most cost-effective inverter option available in the U.S. and have been used for decades. This type of inverter "strings" panels together to create a single solar system. This approach is sometimes called "stacking," or running the inverter in series. It is a tried-and-true technology that is reliable and easy to install. If a roof is fully exposed to sunlight throughout the day and faces in a single direction, a central inverter is a good option. However, if one or more of the solar panels are likely to be shaded during any part of the day, the power output from all the panels that are strung together would be reduced to the lowest panel production level. This is a common issue when solar panels are installed on a roof with multiple planes and/or facing different directions, such as a gabled roof. In these cases, the solar output from each panel can vary greatly and the system will only "see" the output up to the level of the lowest panel power. This can result in far less power being generated. One other issue with central inverters is that all the power is aggregated so that any monitoring system only sees the system output in total and cannot identify problems with any specific panel.
Microinverters are a newer technology and are rapidly gaining popularity, especially for residential solar systems. They are more expensive than central inverters, but as they become more commonplace, cost is anticipated to come down. Unlike a central inverter, where all panels are strung together into a single system, one microinverter is installed on each panel. This is sometimes called running the system in parallel. With the electric conversion taking place at each panel, one of the major advantages of microinverters is that they mitigate the negative impacts of partial or complete shading, making them a good choice for roofs with shading or direction issues. Microinverters also monitor the performance of individual solar panels, making it easier to identify failure points.
Roof or Ground Mounting
Defining the right mounting solution system for a solar system will have the biggest impact on the scope and challenges of the installation. The vast majority of solar systems utilize the roof of the structure as the mounting location.That being said, rooftop mounting still requires more time and equipment than the alternatives. Installing a roof-mount system requires the installer to be more than a solar expert: you are now in the home construction business. Roofs have their own set of concerns--everything from durability to drainage--that need to be considered when installing a solar system on a roof.
The challenge with roofs is that no two are exactly alike. Each rooftop is unique and will have its own set of variables—such as pitch, shingles, vents, drains and chimneys—that can complicate the design and installation process. This is compounded by the fact that you really do not know what you will find until you are up on the roof and peal back the shingles. These unknowns can add up quickly and the amount of time spent designing and installing a rooftop solar system can become a large part of the total project cost. Roof installations also require a great deal of staging. Depending on site constraints you will need to have the materials, time and staff to set up staging to allow for easy access to the roof.
A great alternative to roof-mount solar is a ground-mount PV system. By eliminating the obstacles that accompany roof installations, ground-mount systems offer much faster installation times. Unlike a roof-mount system, much of the ground-mount system site work can be done in advance. In addition, a ground system has much easier access and will not entail the staging and logistical challenges of a roof-system. In general, a roof-mount system has lower site costs (the roof is already there) but has far higher labor and logistical costs as you try to work the solar system into an existing structure. In contrast a ground mount system requires more upfront investment to prepare the site, but is less complicated for the actual installation process
Active-Tracker Racking Systems
Dual-Axis tracker systems are a more advanced version of a ground-mount system. With a tracker system, the panels are mounted to a rack system that has a small motor drive that allows the panels to move and follow the sun during the day. Typically, the panel array is mounted on top of a mast supported by an easily assembled racking system, which allows for panel rotation. By following the sun, the tracker is more efficient than a standard fixed system, and can generate up to 45% more power.
In general, a tracker system is not much more complicated to install than a standard ground-mount. The trackers come with an integrated motor drive and gear system that moves the panels a total of 6" every 8 minutes. This allows the panels to be optimized to capture solar power during the entire daylight period. This efficiency allows the customer the flexibility to generate more power with the same number of panels, or they can choose to reduce the number of panels to reach their targeted power production.