For the most part, installing a larger solar power system is not that different from installing a smaller one but there are a few things that you should consider for larger systems.
First, a system this large is most likely being installed on a commercial facility and not a residence. If it is a residence, it is likely to be a very big residence with a high power draw so it would be using the same electrical equipment you would typically find in a commercial building. It does still make a difference if it is classified as a one or two family dwelling versus a commercial building and we will get into those differences as we go through this.
One of the things that may be different is the service voltage that is fed to the building by the electric company. Typically, a house or commercial building with a very large power draw will get three phase power from the electric company instead of single (split) phase power that is typical on residences. When it comes to solar, three phase power means using three phase inverters.
When choosing a three phase inverter, it is important to identify what type of three phase power is coming into the building. Most three phase power is 120/208 or 277/480 Volts but other voltages are possible like 240 volt three phase with a high leg. Once you have identified the voltage you have to determine if it is 3-wire or 4-wire (hint: 4-wire has a neutral conductor and 3-wire does not). You also need to know if it is wye or delta configuration. If there is a neutral, it is usually wye, but not always so you may have to do some voltage testing to determine the configuration. If there is no neutral, it usually delta but there is no way to know for sure even with voltage tests so you will have to ask the utility company to be sure about the configuration.
Sometimes when planning the large commercial system, you run into the issue of not having enough roof space for the solar panels. If you have room for a ground mount, this may solve your problem and you can check out our article “Tips for DIY Ground Mount Solar” for some good installation advice. Another option may be to use solar canopies. These are great because they can provide a shaded parking area or shade for animals if the installation is for a farm.
One of the big differences between the three phase inverters and the single phase residential inverters is that the three phase inverters can take a higher DC voltage. This means that you can put more solar panels in a string but this is where the building classification matters. Per NEC Code, a one or two family dwelling is limited to a maximum of 600 volts. It is possible that you would be installing three phase inverters on a large house so you would have to make sure they will operate with a DC input of less than 600 volts. Most of them can work with the lower voltage with just a small efficiency loss but you can check the minimum DC voltage requirements on the datasheet to be sure. If it is a commercial building, you are free to go up to 1,000 or even 1,500 volts based on the maximum voltage the inverter and solar panels can handle.
Another thing that is often an issue on the larger solar installations is the rating of the main service panel. A 30 kw system on a 208 or 240 Volt main service panel rated for 200 amps is going to be very awkward because of the 120% rule which states that the inverter output x 1.25 plus the main service breaker rating must be equal to or less than 120% of the busbar rating. You can see our previous article “Evaluating You Main Service Panel for Solar” for more details and some math examples on the 120% rule.
Larger systems also mean larger conduit. There are likely to be more string or branch circuit conductors from the array and larger conductors for the inverter output. While a typical residential system can be installed with ¾” or 1” conduit. The larger systems often get into 1 ½” and larger conduit. If you are using EMT, this larger conduit will be more difficult to bend by hand so you may consider using pre-bent conduit pieces and LBs or you could buy or rent a commercial conduit bender.
Finally, you should also consider that there might be more hassles in permitting and net metering paperwork because cities, counties and utility companies treat commercial systems differently than residential. They often require more documentation to approve the permit or net metering agreement. This is one of the reasons why you should make sure you purchase your do it yourself commercial solar kit from a full service company like GoGreenSolar.com who will assist you with all the paperwork necessary to get your project approved.