Welcome to the segment on site surveys for residential grid-tie design. We'll begin this segment with looking at a site survey kit. A site survey kit is very useful when going on a proposed site, so you have all the tools needed in one place. Your typical site survey kit would include a site survey checklist or unified permit, along 100 foot or 30 meter tape measure, as well as a shorter 25 foot or eight meter tape measure. A solar pathfinder sole metric SunEye with compass, a camera, notepad, pen, a ladder, a flashlight, screwdrivers, and a magnetic protractor or angle finder. There are links in the module readings to some examples of site survey checklist, as well as some unified solar permits. Once you get to a site, the first thing that you want to do is take measurements and photos of the exterior space. We'll focus on a residential site in this lesson. You should also take photos of the front-end side of the building as well as use the tape measure to record the length and width of the building. It's also important to know the azimuth of the building and relation to the solar, array, and the sun. The next step would be to look at the roof structure itself. Now, you can use you climb up a small ladder or look from a distance to see any deterioration that might exist on the roof, as well as note the type of roof material that's used, the metal, tile or shingle, are typical. You can look under the eaves and oftentimes see the thickness of the sheathing, as well as make sure that there's appropriate area for the solar array installation. Generally sheathing for roof should be about a half inch thick or thicker. If you're unsure about the quality of the roof in terms of age and strength, you are the homeowner should consult a professional roofer for inspection. While you're up on the roof, this is also a good time to do a quick shade analysis using the solar pathfinder. The next important step is to determine the size of the actual roof space. There are a few ways that you can calculate the length and width of the roof. With newer asphalt shingles, you can count the number of shingles on a roof slope because each shingle has a 5.5 inch exposure in the United States, and you can use that to determine the length of the roof. You can determine the width from the exterior site measurements that you took before. If there's not a shingle roof or you cannot see the top of the roof, another way to do this is to use an angle finder and then do some trigonometry. The roof itself would be considered the hypotenuse of a triangle, and you can measure that angle by taking a picture and then applying a protractor or using an angle finder, and rest on the rooftop to determine the angle. As long as you know the angle of the rooftop, angle a in this case. You can take the cosine of angle a, and divide it by the adjacent length, which is X. The resulting value is the hypotenuse, which is the total length of the rooftop or the rise of the roof. For example, consider a roof angle of 27 degrees and the building width of 60 feet. Splitting that width at the peak of the roof, equals 30 feet. The resulting hypotenuse or rise of the roof becomes 33.7 feet. Once the roof size is known, the next step is to go inside the attic space and assess the roof structure. Once you get into the roof the first in the attic, the first thing you want to do is take some pictures of all the spaces, but especially make note of where the roof is constructed of rafters or truss systems. If we look a little bit closer, trusses are more modern method of roofing, and they are very strong. But it's important that trusses are not altered in any way or compromising the structural integrity of the whole system. In older style roofing, uses rafters with color ties, where the rafters go from the attic floor up to the peak of the roof. Either system can be used for mounting photovoltaic arrays, but that's why it's important to follow international building code and consult an engineer. You may be required to provide additional reinforcement for the dead load associated with a photovoltaic system on that rooftop, especially in areas that have high snow loading. The next stop on the site survey is to consider whether or not the system will be used on grid or off-grid. While we're planning for on grid design in this course, if you consider batteries they require a stable warm location and must be placed no further than 20 feet from the inverter, according to National Electric Code. Generally, this means looking in a basement area to determine where the inverter will be located, generally some wall, and finally, a floor space for that battery bank. Electrical Code also requires that any battery be placed in a sealed box with venting. The inverter and any battery charge controller need to be mounted in a space that's accessible and clear from any obstructions. This typically means a clear area on an exterior wall in a basement. So, you want to take a look at the basement area or wherever the system will be, and see where the inverter and other electronics can be placed. The final piece to look at in the site visit is the breaker box or fuse box. It's important to record the size and brand of that circuit box, also known as the load center. Record how many circuits are available, as well as the bus bar amperage rating on the breaker panel. The bus bar rating indicates the maximum current that's allowed to flow through load center. You'll have a better idea of why this current value is so critical once we talk about site design in installation. Note that, at minimum, at least to breaker locations need to be open for a photovoltaic system to be installed. The site survey will be later used to develop the site design as well as develop a project proposal for the customer, and apply for a municipal permit. In the next few lessons, we'll look at designing and wiring a photovoltaic system. Then, how to match that to an inverter for a photovoltaic project.
