Quick Guide To Selecting
The Right Parts For
Your Residential Solar System
Many customers who have decided to go solar, face their first hurdle in selecting the right equipment for their PV system. As with any selection process involving multiple options, you want to be well informed about what each option has to offer. Solar equipment is no exception, but it is a lot easier than you might think. We put together the following guide to help with your selection process of residential solar panels and grid-tie inverter.
Selecting the Right
Choosing the right grid-tie inverter is perhaps the most critical component to ensure the successful performance of your solar system. The job of the inverter is to convert DC power from solar panels into AC power that is compatible with the utility grid. All available inverter technologies offer a high conversion efficiency, so it is difficult to state with authority that one particular technology is better than another. The two main characteristics that help us differentiate between the inverters in a solar system are:
- How the panels in the same string (or branch) perform when a few of them are shaded or have a different orientation
- The ability to monitor each solar panel individually
Grid-Tie Inverter For A
Clean-Cut Solar Array
When you achieve a solar system that is as close to perfect as possible – for example, a single array in which all the panels are facing the same direction – a central inverter would be the most cost-effective option. In this arrangement, the solar panels are grouped in strings, and each string is connected to the inverter.
Central inverters have multiple MPPT channels, usually one per string. To give an example, if you had a ground mount system with a total of 30 panels, you could mount a central inverter at the back of the structure, group the panels in two strings of 15 panels each, and connect each string to an independent MPPT channel.
Note: the NEC requires a Rapid Shut Down System (RSS) for roof-mounted systems. Central inverters do not have an RSS; therefore, we only recommend them for ground-mounted systems.
A central grid-tie inverter provides an efficient and budget-friendly energy solution. The number of parts in the system is significantly reduced. One advantage of central inverters is that the power electronics are not mounted right behind the panels, a location in which higher temperatures tend to threaten their performance and durability.
One limitation of using central inverters, as opposed to, say, microinverters and optimizers, is the inability to monitor the performance of each module individually. With a central inverter, you can only monitor the performance of the system as a whole. Panel-level monitoring is most useful when shading is present in the solar array; and is not always an essential consideration for an open array like the one in the example above.
Pros: simple installation; reduced number of connections; all electronics in a cool, ventilated space as opposed to behind the panels; cost-effective solution
Cons: no panel-level monitoring, limited to ground-mounted installations
Our central inverter recommendation: SMA US-41 Sunny Boy
Solar Optimizers For When
There Is Shading Or Different Orientation
It is rare to have sufficient roof space for a proper square PV array. More commonly, solar panels are distributed in multiple roof faces, with some of them inevitably shaded for a portion of the day. In this scenario, it becomes beneficial to control the output of each solar panel individually; this way, if a few solar panels are performing poorly during a period, other panels in the same string will adjust their output to compensate for the losses.
A great way to do this is with power optimizers (one optimizer per PV panel). They constantly monitor and regulate the output of the panels in the string, sending optimum input to the inverter and facilitating the highest efficiency operation in any given condition. All optimizers in the system communicate with the inverter, additionally offering panel-level monitoring when internet connectivity is available.
Another benefit of using power optimizers is the built-in Rapid Shutdown System (RSS) feature, required by most jurisdictions. If the power is turned down or the AC voltage is lost, the optimizers will bring the output voltage of each panel below 1V, complying with the maximum RSS requirement of 30V.
Pros: panel-level monitoring; built-in rapid shutdown system; shading mitigation; flexible string sizing
Cons: more hardware and connections (not a big concern, however)
Our optimizer recommendation: SolarEdge optimizers plus inverter
Solar Microinverters For
Severe Shading Or Challenging Layout
Just like central grid-tie inverters, the use of power optimizers requires each string feeding the inverter to have a minimum number of modules. There are instances when a particular roof layout demands additional flexibility. For example, let’s say that we have a string of 9 modules with power optimizers on a roof face right next to a neighbor’s home; at 3pm the neighbor’s roofline casts a shadow on 2 of the panels. Given that we need a minimum of 8 optimizers operating in a string, at 3pm that string will not produce power.
The same group of modules in the example above will benefit from using microinverters. These are mounted behind the solar panels and convert the DC voltage of the panels to AC voltage at 240V, ready to be transferred to the utility grid. All microinverters produce energy at the same voltage (240VAC), and each one is considered an independent unit. Within this architecture, it is irrelevant whether the adjacent unit is fully shaded or installed in a different orientation.
Pros: maximum flexibility; panel-level monitoring
Cons: more parts and hardware; slightly higher system cost; power electronics installed on the roof
Our micorinverter recommendation: Enphase IQ microinverters
The Right Inverter For
Small Arrays And Future Expansions
Sometimes there is only enough space for a small solar system. String inverters and power optimizers have a minimum system size requirement, usually around 3,000W of PV power. For a solar system under 3000W, the most feasible alternative is to use microinverters. These allow you to have a solar system composed of only 1 or 2 panels if need be.
With all of the advantages mentioned above, when building a solar system in stages or adding on to an existing system, microinverters often offer the most flexibility.
Pros: System of any size; modular additions
Cons: Higher system cost; power electronics on the roof
Our micorinverter recommendation: Enphase microinverters
Choosing The Solar Panels
For Your System
When it comes to solar panels, the technology has reached a point where all products, as long as they come from a reputable manufacturer, will perform well on your roof. Though there a few options to choose from, the final decision rests on personal preference. We made this Solar Panel Selection Guide to highlight the main differences among PV panels.