A solar sit survey is the first step in planning to establish the objectives, required materials and the general expectations and requirements of a pv system. A survey of the site conditions including the condition of the mounting surface if it is to be placed on a roof, the surrounding structures that could cause solar shading issues, and even the ground conditions for a ground mount array system must all be taken into account as well as potential array locations, and measurements. The site survey will also include electrical infrastructure capability and requirements. A home energy audit may also be performed. All this information is put together to provide a plan and proposal. The proposal should include system size, components, solar energy performance estimates, as well as estimated revenue if the system is a feed in grid system. A time line of installation to the up and running state should also be added in the proposal. The site survey is the preliminary guideline that influences all of the rest of the system design.
The Customer
A solar customer could be a residential house owner, a business owner, or an agent acting on either of their behalf. The process of putting together a system may and likely will include a structural engineer, architects, electrical engineers, roofing experts, environmental engineers, electrical safety authorities, and installation experts. In smaller jobs particularly residential jobs the home owner may be directly involved. It should be noted that any hands on people who will be involved in the install know their responsibilities. All solar professionals and especially the salesperson must identify the customer’s needs, desires, concerns, and expectations. Some customers will be quite knowledgeable while others may need explanations and taught the various requirements and systems and costs associated to make an intelligent decision. The cost of the system and financing if needed are the primary concerns. Financing of a system may be addressed by government incentive programs at various levels and the customer should know about any and all programs. Scheduling the system install should have some flexibility built in to allow for weather problems, and any other issues that can arise. Guarantees and warranties on roofing and all materials and components should be addressed as well as any routine maintenance required so that there are no surprises down the road.
Geographic Area Evaluation
The area the pv system will be installed should be investigated for the amount of available solar radiation and desired tilt angles. Environmental conditions affect the amount of collected solar energy in ways that include temperature, precipitation, humidity, and seasonal weather such as snow or being close to water can cause more solar radiation than expected from reflective radiation. Wind is always a factor that can cause issues with a solar array and must be taken into account. Temperature and humidity affect the solar panel output greatly while humidity causes corrosion on metals. A geographic location may have different building codes and electrical standards that a solar designer must know in order to complete a job and get it approved. One other factor that could come into play is the solar panel array might be used to shade an area on purpose. An example of this would be a parking lot.
Utility Grid Connection Systems
For Utility Grid or feed in systems the customer is usually required to enter into an agreement with the local utility through a government authorized program and receive payment at certain amount per kilowatt. There may be special consideration given to insurance requirements, system labelling and electrical approvals.
Safety
PV system installers should be well versed and trained in the safety requirements of fall prevention and protection when doing a site survey that involves working at heights. Proper protective clothing such as hats, sunglasses and sunscreen to help with too much exposure from the sun are wise to implement. Hard hats and proper safety shoes are necessary in many places. When checking out a site to be installed on a roof, ladder safety, full body harnesses, lanyards, and solid anchor points should be utilized to reduce the potential of injury.
Equipment Requirements
A sun path calculator that identifies shading as well as the amount of solar radiation is the beginning of the solar site analysis process. For system installation a multimeter is needed to check voltages, load currents, and continuity. Tape measures, protractors to measure angles of roofing and tilts are needed both in the initial site analysis and during installation. An electronic stud finder and infrared temperature measurement devices are needed during installation to pinpoint site features. Chalk lines, stakes for ground mounting layout, flags, string and paint may be used to figure out the positioning of arrays.
Exposure and Sizing
The entire site survey comes down to one very important and critical factor. There must be a southern exposure to put solar panels on. Because solar panels by their nature are considered low density power they need a large surface area to produce a decent amount of power. How much surface area you have available if it’s a roof may be the limiting factor as to how large a system could be installed. Figuring out the array size and power output can be approached through the use of the following mathematical formula.
Area = peak array power in kw dc______
1kw/m squared x module efficiency
Example:
What is the estimated size of an array using 12% efficient modules that should produce 10 kw at the peak sun ?
A = __10________ = 84 meters squared
1 x .12
There should also be some excess area added to take into account any spacing between modules and rows. In some locations local building codes specify that modules must have certain space around the array on the roof for access and safety reasons. Other reasons could be ground mount protective fencing requirements. A 10% area increase is typical for sloped roofs and in ground mounts it could be as high as 50%. Each site will require a custom evaluation.
There are two kinds of arrays used no matter if it’s a ground mount or roof mount. Sun tracking arrays constantly change position as they follow the sun across the sky to optimize their energy capture. Stationary arrays rely on one specific orientation to gather in energy. If a residential roof has a limited or no southern exposure it isn’t likely a good candidate to put a solar installation on. The measurement of the slope of the roof is another concern that must be factored into a site survey and must be measured for the calculation of total power output estimates. There are a number of ways to do this but probably the easiest is to have an angle finder that is just laid on the roof and provides a measurement very quickly. Using a steel square on the side of the roof and measuring the rise and run will also work. You take the rise and divide the run into it and the arctan of that value is the slope in degrees of the roof. See below.
slope in degrees = arctan ( rise )
run
We must also figure out the azimuth orientation of the roof which is how directly south it truly is by taking a compass and using it at the site then look up the magnetic declination and correct accordingly. A sun path finder has a built in compass and has the ability to adjust for magnetic declination. There are maps available on the internet that will give the magnetic declination for any given area in the world.
Shading Analysis
Solar Shading causes an array to be less efficient the more shading there is. In some cases depending on the module orientation be it horizontal or vertical can cause a large energy capture loss. Evaluating the amount of shading may cause an installation to move to a micro inverter system to limit the impact shading has on the array. Micro inverters limit the shading to one module instead of affecting an entire string of modules. There are two methods of design regarding how the dc energy will be transformed into ac energy suitable for sending to a grid. A solar system that employs one or two larger inverters that have strings of panels hooked to them are more susceptible to shading because the panels are set up in strings. Sometimes these strings can be 12 panels in series or more. If one panel is shaded the entire string is shut down and limited. If you employ the micro inverter electrical system each solar panel is an island to itself and dc energy is changed to ac energy right at the solar panel. Ac power is easy to combine together and therefor each panel is not affected by the other that might be shaded. It is preferred of course to have panels installed where no shading occurs, but site conditions may not allow this to happen. Sometimes shading can be removed if it is a tree or other obstruction able to be taken down or removed. Best results are achieved with a solar array if it has an unobstructed solar window from 9 am to 3 pm in the summer.
Accessibility
The site survey should also take into account the site accessibility for installation, inspections, proximity to the electrical system for interconnection to the grid or residence.
Roofing Evaluation
For roof mounted systems it is wise to have a look at the condition of the roof and the remaining expected life it has left. If you’re going to install a solar system that will anchor to the sub frame rafters it will be in the way if you need to replace a leaky roof after 5 years as an example. If the roof is an asphalt roof it is wise to install a new roof if the roof is any older than a couple of years. Other types of roofs you need to look at the wear and tear on them. Concrete, clay, or slate roofs should be checked for cracking and alignment. For metal roofs rust is the determining factor. If a metal roof is the place where a solar array will be mounted the site assessment should evaluate the underside structure to see if the metal is mounted on a substrate that can support installers. Membrane and gravel built up roofing are commonly found on commercial roofs or low sloping roofs. It is wise to consult a roofing specialist for these types of roofs to determine the life expectancy.
Structural Support
For every installation there will need to be a structural engineering evalutation performed by a professional structural engineer. During the site survey notes should be taken to point out any concerns that may require further investigation. Sagging roof structures are generally a concern to look into. A taunt string will expose any sagging if it is stretched across the roof. The survey specialist should walk across the roof carefully checking for any spongy areas. The specialist should look for any structure modifications, repairs, and other problems that can occur such as dry rot, leaks, bird nests, bee nests etc. all of which could become an issue upon installation.
For ground mounted systems evaluate the terrain, any hills, soil conditions, errosion, seasonal flooding, and small trees that could become shading issues in the future.
Electrical Assessment
The analysis must include a look at the existing electrical system and evaluate if it needs upgrading to accept the extra power of a solar interface. There are many things to consider such as conductor sizing, electrical box ratings, circuit breaker ratings, transformers etc. If a battery back up system is required there will need to be a service panel installed and some space required for that. All system components should be identified and determined as to where their location should be. It is wise to locate equipment as close as possible to each other to limit the size of conductor runs and thus limit voltage drop energy losses, and extra materials that could otherwise be saving money. Accessibility is also a consideration for all pieces of equipment for maintenance and inspection. Each site will dictate it’s own areas that equipment could possibly be placed.
Inverters should be installed in a cool dry area and never in direct sunlight. There should be adequate air flow around it to help keep it cool. Large inverters can be very heavy and will require strong mounting brackets that must be installed to support structure that can support it. Never just mount an inverter to drywall using plugs.
Batteries should be placed in a well ventilated area that is away from any living quarters. Areas such as garages, utility rooms, air conditioned outdoor spaces, or buried container rooms are typical locations. Planning should include racking and foundation that can support the weight of the batteries.
Drawings
The site analysis should have a drawing for array placement. This drawing should include all structures and measurements between all components as well as identifying all components. Photography always helps to supplement the site information and a list of notes that will affecting site installation.
Compiling the Site Analysis
The site analysis will be used for the purposes of developing a site proposal. The site proposal will include cost estimates with an installation timeline. A performance estimate and revenue expectation for a grid tie system will most certainly be necessary for a customer to make a decision on going ahead with the purchase of the system.
The proposal should also include a value assessment for return on investment.
Three should be a schedule of installation and date of completion.