I recently got a blog post regarding expanding small systems and how it was prohibitively expensive. There was a lot of misinformation, so I thought I’d let you all know the options. If you’re putting in a “grid tied” system to supplement your power and reduce your electric bill, the minimum size system to make a difference is about 12 panels. You can put in fewer, and expand later at minimal cost if you use the Enphase M190 micro-inverters. These units DAISY CHAIN – i.e. they connect in series, one to the other until you reach a maximum of 15 per BRANCH CIRCUIT. So, you can start with say, 5 panels, and then add as many as you like, as often as you like, till you hit 15. Then, you have to run another branch circuit (Romex 3 conductor with ground) to your breaker box. I’ve actually taken this approach with my little house in the woods. Started with 5, then added 3, then 2 more, then 1 and I plan on just 1 more very soon for a total of 12 panels. The racking system can be extended by using “splice kits” and it takes about 20 minutes to add a panel, start to finish. With excellent 235 and 240 watt panels now selling for $1.09/watt plus shipping, it doesn’t really take a lot of money to add a panel and micro-inverter to an existing array. And the best part of all, you DON’T need to be a licensed electrician to plug in the 2 DC connectors from the panel, or the 240VAC connector to the last micro-inverter in your chain!
If you want your system to be BACKED UP BY BATTERIES when the grid goes down, your micro-inverter style GRID-TIED system can still be used!! Using a technique called “AC COUPLING” you can connect a Magnum MPS4024 inverter/charger and 24 volts worth of 700 AmpHour Rolls batteries and have 4KW of backup power at your disposal when the next storm takes out the power. It’s not cheap, but it CAN be done, and you have the best of both worlds, without getting stuck with a STRING/CENTRAL INVERTER that MUST have a FIXED NUMBER of solar panels for best performance, and involves handling HIGH DC VOLTAGES.
Since this original blog post, Enphase has introduced the M215 series. It is a more powerful microinverter, and it is NOT compatible with the older M190. The M190 is still available though, to those system owners who have them and want to easily expand! My original setup with 5 panels, has expanded 3 times. 1st to 8, then 10, and finally 12 total! The old system can daisy chain up to 15 inverters on one circuit, so still have room for 3 more! Gotta love that Enphase system. Perfect for folks on a budget!!