Friday, January 24, 2014

Performing a Solar Site Analysis

The site analysis is a critical junction in the process of selling and installing a solar system.  Proper information gathering leaves your installation team with everything they need to know to prepare for the install.  Leave out the wrong piece of info and there could be last minute design changes, emergency trips for more equipment, and an overall lack of professionalism in the eyes of your customer.  A good site analysis will give you all of your design information in an efficient and structured manner and leave a lasting impression on your customer.


The roof analysis begins by noting the roof type and condition.  If it’s a flat roof, make sure you get the roofing material correct.  This is important for ballasted systems (common on flat roofs) where roof pads may be needed to protect the roof from sharp metal edges in the solar racking.  If it’s pitched, the same question on roofing material needs to be answered.  Shingle roofs are most common, but if it’s a metal roof you need to note whether it’s corrugated, pro-panel, or a standing seam roof.  Tile roofs can be flat tiles or curved Spanish tiles, each require their own specialized attachment.  Getting the roof right will ensure you get the proper roofing protection, whether that is flashings, roof pads, or tile hooks. 

Obstructions can come from a variety of sources.  Parapet height needs to be measured for southern roof edges.  Vents, pipes, skylights, and other roof obstructions need to have their location noted if they will affect the solar window in your planned mounting area.  Rule of thumb is 2.5 times the height of the obstruction is the length of the shadow it will case on the winter solstice, read my blog post on calculating shade spacing for a more in-depth analysis.  One way to make measuring obstruction locations easier is to use two measuring tapes or one tape and a long string.  Lay the string/tape out in a perpendicular or parallel line from your obstruction then use your measuring tape to take measurements off of this straight line.  This way, complicated areas and weird geometry can be accounted for.

One thing you can do to save time on the roof is do “roof triage” where you focus your measurements and analysis to the areas of the roof you know will fit solar, and ignore/do a cursory examination of the rest of the roof.  This can be especially relevant if there are a large obstructions off-property shading the roof like trees or buildings, or if there are so many roof obstructions an array just won’t fit there.

Sometimes for roof mounted jobs the AHJ/permitting office will require framing diagrams of the underlying roof structure, even for flat roofs.  To ensure you have this information, take pictures of the attic or refer to the building plans to find the framing direction and spacing on the roof.  This also helps you plan out your roof penetrations and framing layout for your solar system.

Something many installers forget when they’re looking at a roof is how they plan to run wire and conduit within the solar array and back to the point of connection.  Sometimes you are forced to break the array up over multiple roof sections, and running strings or branch circuits across the roof can get expensive.  It’s very important to consider the conduit run and location, it can be a very visible and expensive element on the roof unless properly designed. 


An analysis of a site for a ground mount is pretty straightforward.  Begin by looking for sufficient roof for the solar array.  The big thing to look out for is a septic system or leech field which is usually placed in an open area directly adjacent to the house (sound familiar?).   Underground lines and pipes all need to be accounted for in the array location as well, and avoided at all costs.  Make sure the point of connection on the building is known, because the trenched wire run back to that location needs to avoid these as well.  Something that may not be on your radar when doing a ground mount is the water table and drainage.  If there’s a drainage path or high water table, a solar array cannot be installed on the ground there.  Lastly, the utility drop and any easements on the property are off limits for solar, so stay away!

The ground and substrate material needs to be considered if you are making ground penetrations/footings, solid rock or dense clay may require specialized groundwork equipment to install your system.  You should be noting what grading or groundwork may be required in any case, so when the install happens the site is properly prepared for the solar array.

BOS (Balance of System)

BOS is the rest of the solar equipment needed for an installed system to function properly.  For the purpose of this post, BOS is AC inverters, disconnects, and meters.  The first thing to look for on the outside of the building is the location of the Main Distribution Panel and Billing Meter.  After that, start looking for working space for all of your electrical equipment.  Usually, there will be a solar inverter or subpanel, a single throw safety switch, and a meter socket that all need to fit on a single wall.  Things that need to be avoided are gas lines, water canales and spigots, AC units, existing electrical equipment, and doors and windows.  Additionally, the southern and western exposures should be avoided if possible.  These building faces soak up the sun during the hottest part of the day and can adversely affect system performance by reducing voltage and efficiency of the wiring.

Most AHJ’s/utilities will have specific requirements for BOS location and placement, follow their requirements above all else. Many of these requirements have to do with equipment line of sight to the billing meter/point of connection and accessibility of equipment for utility workers.  Couple these requirements with avoiding gas and water lines, and you can find yourself with little to no space to install your BOS on some jobs.  In those cases, you may have to make an external “equipment rack” out of metal strut to mount your solar equipment, an expense that has to be accounted for.


The tools you should bring to a site visit can change based on the type of roof and nature of the solar project.  For most any job, you’ll want a measuring tape or two to quickly dimension areas and locations of equipment.  A ladder and a way to quickly secure it to your vehicle are needed for any roof mounted project (sometimes two ladders are needed for large/tall roofs, make sure you have enough!).  It may not seem like much, but having a screwdriver or two is a big help for opening stubborn electrical panels.  For electronics, a camera is your safest bet for gathering effective site information.  A calculator is good to have, and if you can get one an Inclinometer is perfect for measuring roof pitches and drainage slopes.  Most of these can be found in modern smart phones and internet enabled devices, they are one of your best tools on the roof.  Finally, no discussion on site analysis would be complete without talking about the Solmetric Suneye.  If you can afford one, nothing is better at providing a comprehensive snapshot of nearby shading issues for the solar array.

Customer Interaction

This is the big one, the one that can differentiate you from the competition and make your customer’s solar installation experience one they’ll remember fondly.  The customer has been talking to their salesperson about a solar system, and now there’s a stranger at their house on top of their roof and poking through their electrical boxes.  Many times what was sold to the customer does not match up with what can be installed on their building, and it’s your job to help guide them to the final design and show them how it will work.  They’re paying thousands of dollars for an elaborate electrical system that they may not fully understand, so you have to be prepared for their requirements and suggestions.  Start by reading the customer, seeing how picky they are and how they respond to your installation plan.  Any reasonable suggestions or requirements they make should be followed as long as they are happy with the finished product and it follows local requirements.  If you can’t meet their requests, try to manage their expectations and explain why you have to do it a certain way.  As long as you are courteous and respectful, your point should be well-received.

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