There are many steps involved in designing a PV system—do your homework to make sure you cover all of your bases. Site-specific variables will dictate your system’s type, size, and location, and several other variables will dictate the components you’ll need.
Evaluate your situation and goals to specify the system type. First, observe your site closely to make sure there’s a good solar window at your proposed array location (ideally from 8 a.m. to 4 p.m., but 9 a.m. to 3 p.m. is acceptable). Sometimes, that “open” solar window is not on your roof, but in the yard, making a ground-mounted system optimal. Or perhaps you want a 4 kW system, but your shade-free space can only accommodate 2 kW. Then there are the myriad individual equipment requirements with which you will need to be familiar. For example, if you found a good deal on a specific inverter, your site’s high and low temperatures and the module specifications will play a role in how many modules you can string in series to connect to that particular inverter.
To comply with and pass your electrical inspection, you will need to be aware of all the various NEC requirements that pertain to your installation. Local requirements may also come into play. For example, while many inverters offer integrated DC and AC disconnects, your local authority having jurisdiction (AHJ) may require additional disconnects. In addition to the NEC, local fire codes can affect your installation. For instance, some mandate 3-foot setbacks on roof-mounted arrays to provide pathways for firefighter access and smoke ventilation.
Performance factors also need to be considered. Do you have enough know-how to optimize the system’s design? For example, even minimal shading of a PV array during the prime solar hours can significantly reduce your system’s output. Also, PV module output declines with increasing temperatures, necessitating a design with good airflow around the modules. The list of considerations goes on and on. That’s why folks seek professional assistance—to ensure that their investment in a PV system isn’t undermined by trying to save a few bucks on installation costs.
When it comes to buying equipment for your PV system, don’t buy cheap! We mean this on two levels. First of all, buy quality equipment. Most of us are accustomed to having reliable grid electricity. If you want to have a reliable solar-electric system, you’ll need high-quality gear. Find out what suppliers are selling the most of and what installers are buying. Be wary about a new product being sold only from one source. Wait until the pros in the industry start trying it, using it, and praising it before you spend your money.
Don’t automatically go for the dealer with the lowest cost. Too often, DIYers end up with a low level of support along with a low price. Especially if you’re installing your first system—you will need some hand-holding. Buy your gear from someone who can help you during and after the installation, and expect to pay more to include that level of support and service.
Second, if possible, try to buy locally. Being able to develop a relationship with your supplier is priceless. There’s nothing like being face to face when it comes to a clear understanding of design, and when it comes to resolving issues with an order, product, or system.
Consider collaborating with a local, professional RE installer, if there is willingness. Buy your components through a local company, giving them their profit margin. Perhaps even hire one of the technical people at the company to review your design before purchase, and again before inspection. This can be a great partnership that will serve your system well. If you do run into problems during design, installation, or operation, you’ll have someone to turn to who has walked the path before.
Don’t buy discounted equipment and then go looking for an installer. These folks make their living selling and installing PV systems. They know the ins and outs of the equipment they prefer to install, and they know how to install it. They also need to mark up the equipment to make their living, just like all businesses. Trying to get something for nothing will most often result in hard feelings and poor relationships—and not the help you’re looking for. If you do find a pro willing to install equipment you already bought, expect to pay top per-hour electrician wages—most likely eliminating the savings realized on the inexpensive equipment.
Most manufacturers are global companies that have little interest or dedicated resources to handle technical questions from homeowners, and this may include warranty claims and issues. So don’t expect to call the manufacturer of your inverter for help with string sizing, or get the footing requirements for your ground-mounted array from the mount manufacturer, for example.