600 words (2 minute read)


In the process of selection, design and installation of an appropriate solar PV system for your home or business, a professional site assessment is a crucial part. Cost and power output of your potential PV System significantly depend on it. The output of a PV module is directly proportional to the amount of sunlight strikes on it.

A proper site assessment significantly contributes to determine and identify a number of factors: the site capacity of generating energy, shading issues, how much revenue will be generated from the power plant, return on investment (ROI), rebates and incentives, structural and electrical concerns. The site assessment also significantly contributes to save money in basic energy efficiency improvements and more lucrative methods to organize a solar project on-site. After reviewing the report, you will be able to make well-versed decisions about your project. The site assessment report will help you to bring your goals, budget and energy needs together with the unique solar opportunities at your location. Every site is different and needs evaluation specific to the site.

Electricity is produced from PV Modules produce when photons on solar cells and knock available electrons loose and into motion. Photons are small packets of energy contained in sunlight. When fewer photons strike on the solar cell, for example due to poor orientation or haze, fewer electrons are put into motion. As a result, little amount of electricity is produced. But if there is shade in the site even with little amount, it can cause shutting down the production completely in some cases.

Modules with built-in bypass diodes contribute to minimize the effects of partial shading. But, even a row of cells with shade can disable the module. Impact of shading requires careful site planning and design considerations for solar PV arrays. Whether it is a neighbor’s multistory home or trees on your property, most sites should be considered at least some shade.  While wide-open, dawn-to-dusk exposure is ideal, PV system designers generally shoot for a shade-free solar window from 9 a.m. to 3 p.m. (“solar time” for all days/months of the year). Majority of solar radiation is available during these hours. However, it may be affected by local climate variations. For example, in some locations, early morning fog can shift the “prime” solar window toward sunnier afternoon hours.

If forecasting shading throughout the year has been done by sight alone from various barriers like tall trees, nearby buildings, roof dormers and even chimney, then it can be challenging which requires many observations over the course of the year. But some tools like the Solar Pathfinder, the Acme Solar Site Evaluation Tool and the SunEye, can assist you to assess shading on your site throughout the year quickly with one site visit. Each tool has different technique and price. But, the job can be done by all these tools.  They can be used at a proposed array location for the evaluation.

Historical solar radiation and weather data for your latitude and longitude and the constantly changing sun elevation angle are considered by these tools. To provide additional data for accurate shade compensation calculations due to tall trees, nearby buildings etc. digital photos are taken at the site. Depending on the solar panel tilt (up and down angle), azimuth (right and left orientation) and whether a tracking system is to be employed, some modifications are done. Wire runs, connections, fuses and breakers, inefficiencies of the inverter and snow shading etc. are also needed to be considered for the final output of power production of potential solar PV system.