Solar site surveys: Onsite vs. Remote

The site survey is one of the most crucial parts of any solar installation project. After your installer makes an initial assessment of your property, they'll conduct a site survey to obtain detailed information on the condition of your roof and take measurements to assist the engineers in design. But how exactly do installers get this information?

In the past, the only option was to climb up on the roof and take measurements by hand. While this is still the most common method, some new remote technologies are beginning to offer compelling advantages that change how site surveys are conducted. In this article, we'll dive deeper into the pros and cons of each method.

Before we examine the different types of site surveys, you'll need to know what information installers are looking to collect in the first place! This can be broken down into three main categories: physical measurements, roof shading, and roof condition.

Physical measurements

Physical measurements include several important data points, such as available surface area, the angle or tilt of the roof relative to the sun (azimuth), and the presence of any potential obstacles, including chimneys, AC units, or water tanks. These pieces of information are crucial to any solar project, as engineers will need them to design the system, and financiers will need them to calculate system costs.

Roof shading

Data on shading is also critical, as it can present a significant issue in energy production. Depending on the type of solar system and the location of the shading, some studies have indicated that even the shading of one out of 36 cells in a small solar module can reduce power output by over 75 percent. Thus, it's vitally important that your installer has accurate information on your roof's shading so they can accommodate these potential issues.

Roof condition

The final component of a site survey is an assessment of your roof. Your installer will need to determine the type of roof you have, the weight it can bear, and its condition to determine if roof work will be necessary to install your solar system safely and effectively.

Installers have several ways to collect the necessary information from a site survey. We'll look at some of the most common methods, from the completely onsite "on the roof" method to the completely remote LIDAR technology.

Traditional "on the roof" method

With this method, a site surveyor will come in person and climb up on the roof of your house. They'll measure dimensions, inspect roof quality, and usually record this data by hand on paper. Additionally, they'll likely use SunEye, which allows them to assess the available sunlight by day, month, and year by measuring shading patterns.

The pros of this method are thoroughness and familiarity for the installer. Most installers have been doing this site survey for quite some time and are used to the process. It also allows surveyors to see the highest level of detail on the roof and physically feel any potential anomalies.

The cons here are safety, time, and potentially accuracy. Because the surveyors are up on the roof, they are at an increased risk of physical harm, which may be unappealing to them and you. This process also takes the longest of the three methods mentioned here, with the surveyor needing to spend up to 90 percent more time than the other two methods. Furthermore, accuracy can potentially suffer: although the surveyor has an up-close and in-person view of the roof, inaccurate measurements, poor communication with the engineer, and human error can all cause problems for the project down the line.

LIDAR method

LIDAR stands for Light Detection and Ranging and is a remote sensing technology that uses light to measure distances of objects from the Earth's surface. LIDAR has several exciting applications, including self-driving cars, the Mars rover, and now solar site surveys. It works like this: a LIDAR scanner is attached to a plane and emits pulses of light (in the form of a laser) at the ground. It then measures the time it takes for that light to return to calculate distance. A shorter time means a taller object, and a longer time indicates a shorter one.

This data is then used to construct a "point cloud map," a 3D model of a town, city, or neighborhood. Because plane flights are expensive, this process is usually performed in a whole city or town rather than for individual houses. This data is then provided to the public for solar installers to use in residential projects. Check out Google Project Sunroof to see LIDAR technology in action for yourself!

The pros of LIDAR are accuracy, time, and cost. A study by the National Renewable Energy Laboratory (NREL) concluded that LIDAR site surveys were within 3.5 percent accuracy of measurements taken by hand. Shading reports are also extremely quick to generate–often taking less than 15 minutes to complete–and can be done remotely. These time savings also represent substantial cost savings potential: NREL estimates that integrating LIDAR could reduce industry soft costs by $0.17 per watt. That's equivalent to half the cost of the average string inverter! Overall, LIDAR allows for faster and cheaper site surveys without meaningful loss of accuracy.

The downside of LIDAR is availability. As mentioned before, due to the cost of flying, LIDAR scans are usually performed on a city or neighborhood scale. LIDAR data might be unavailable to your installer if your area is not mapped. However, the good news is that with the demonstrated success of this technology, more areas are being mapped all the time. Check out this map to see if your area has been covered.

Drone method

Drones have become increasingly popular in recent years, moving from recreational use to commercial applications. Regarding solar site surveys, drones offer a compelling mix of remote and onsite options, combining perhaps the best of both worlds. During a drone site survey, a surveyor will come to your house and, with your permission, fly a drone around your property. The drone will take pictures to create a 3D model with nearly perfect measurements–more accurate than hand measurements or LIDAR–of key data such as roof angle, shading, and surface area. Check out our article on drones in solar for a complete picture of this fascinating technology.

There are many upsides here: drone surveys are quick, taking only around 8 minutes for an installer to complete. They're also safe, with the surveyor piloting the drone safely from the ground. And, crucially, they're accurate, eliminating human error in by-hand measurements and providing higher quality images than LIDAR (because of the camera's proximity to the house). These three factors ultimately save you time and money, making life easier for you and your installer.

The downside is that this technology is still relatively new. Most installers still prefer to take measurements by hand–because this is what they're used to–but with drone software companies offering training programs to help installers take advantage of this new technology, this is beginning to change.

Although manual, in-person site surveys are still the most common, remote options like LIDAR and drones are gaining the attention of more and more installers. As these installers begin to recognize the benefits of the new technologies, they will likely become a more significant part of the site survey process, helping more people go solar with confidence.

If you're interested in installing a solar system on your property, check out the EnergySage Marketplace to compare quotes from the top installers in your area. If you're interested in installers using one or more of these site survey methods, be sure to make a note in your EnergySage profile–even if your installer doesn't yet offer these methods, you could be the impetus for them adopting a new technology!