Going Solar, All In or One Panel at a Time?

John Coen October 12, 2011

When purchasing a home, many people will look for something with ample room, while others will go for a smaller house that has the potential to be expanded. Both of these very same approaches can apply when customers are looking to purchase a solar electric system. Let’s take a look at some of the pros and cons of each.

As a sales representative at altE, I receive many inquiries from customers who are interested in purchasing a solar electric system with available room for future expansion. Essentially, they want a small solar panel array coupled with an inverter (for grid-tied systems) or charge controller (for off-grid or grid-tie with battery backup systems) that can handle a larger array in the future. Typically they are looking to expand their array anywhere from 25% to 100% and beyond, at some point down the road. There are several factors to consider when taking this approach, rather than purchasing a larger system to begin with.

Matching solar panels
Availability of solar panels is always changing, and inventories can fluctuate dramatically from one day (or minute) to the next. In addition, manufacturers are always improving and updating the models they offer. When you decide to buy those extra panels to increase your array, you might find that they are no longer available. Even if you can find similar panels, mixing and matching can reduce the overall performance of your system. A potential positive of expanding on an array at a later date is that panel prices may come down, though this is a bit of a gamble.

Working around existing systems
Many customers who decide to expand on an existing system will encounter limitations that have to be worked around. For example, a customer of mine had an array of 10 210W panels in series, and wanted to add 5 more. Unfortunately, adding them in series would have exceeded the maximum voltage input on their inverter, and a configuration of 3 strings of 5 in series would come in below the minimum input voltage. The customer ended up purchasing one extra solar panel and going with a configuration of 2 strings of 8 in series. Of course, with proper planning, these situations can be avoided, and you can reap the benefits of your system from day one, knowing that you have planned for expansion down the road. Make sure to account for all areas of the expansion, including the combiner box, disconnects, inverter, charge controller, etc. One area that is often overlooked is cabling – make sure that your cabling is sized to handle your future amperage so you do not have to remove it from conduit and replace it!

Running Efficiently
Systems that will be tied to the grid can be sized so that the solar array only uses a percentage of the inverter wattage capability, with the intention to add more panels later. This starting configuration is fairly common, and the only potential downside is inverter efficiency. Most inverters are designed to provide peak efficiency at their maximum wattage rating, and may not perform as well with an undersized array. Certain inverters are designed in stages to increase efficiency over a broad input power range (see Fronius’ MIX concept). Another alternative is micro-inverters, which are installed on a per-module basis, and are an excellent solution when expansion will be needed down the road.

Whether you take the “all-in” approach, or intend to expand over time, it is important to take a careful look at your needs and what you plan to get out of your solar electric system. Keep in mind that solar rebates and incentives are always changing, and right now might be your best time to invest in solar!