Why the number of solar components matters. Do you know what is on your roof?

Technical Article

1/15/2020 / Portage

As Solar becomes more mainstream and more residential systems are built, and NEC 2017 comes into effect, we should reflect on what makes a cost-effective and most sustainable building a solar system. One critical aspect here is the number of components a solar system consists of. Common sense tells us that simpler systems with less components on the roofs are better.

solar installation for residential systems

Let's start with the basics.

A PV (solar) system consists of a certain amount of modules, which account for most of the components in a system. Ever increasing power output of modules helps to reduce the number of modules needed for a kilowatt. However, there is now not room for a significant reduction of the number of modules in a system. These modules need to be mounted somehow, so some sort of racking is also inevitable and accounts for the number of components. Then there is of course wiring, which brings us to the power electronic components needed. Different technologies vary widely in regards to the number of components in a system. This becomes especially relevant when thinking about NEC 2017 compliance.

For example:

To highlight this variation, let's have a look at a typical 6 kWp residential system. If the system is designed with DC optimizers or rapid shutdowns, the number of electrical components adds up to 26. There is one DC optimizer attached to each of the 24 modules, and then there is an inverter and most likely some sort of communication gateway. If a string inverter is used, the number of components is only 2 - a Rapid Shutdown Box and the string inverter. This is a significant difference, with a big impact on many aspects of the system. Let's have a closer look on these.

Solar configuration with a string inverter

A string inverter solar system requires fewer components. Here it is shown how a PV system in a NEC 2014 state could look

HARDWARE COST

Every component of a system has a price tag. A higher number of components results in higher initial cost. The upfront cost of a solar system is a crucial buying criteria for homeowners. To make solar more mainstream, cost-reduction must be an industry wide goal.

INSTALLATION

Labor makes about 15-20 % of the initial cost of a typical residential solar system. The time needed to install a system is critical. There is no doubt that less components means less installation steps, less hours and therefore less cost. It must also be the goal to simplify the installation-process, reducing training needs and ensuring quality installations - less components means less potential for installation errors - and more simplicity. Also, the installer can keep inventory costs lower with a simpler string inverter system.

A residential solar home owner

OPERATIONS & MAINTENANCE (O&M)

Every component in a system is a potential point of failure. More components increase the likelihood of a failure in a system. If you think of the example in the introduction (2 components versus 26), the risk is significantly higher - and we are talking about components mounted on a roof, exposed to harsh weather conditions. Imagine the huge number of power electronic components (DC optimizers) that are out there on roofs nationwide. Even a very low failure rate will cause a tremendous number of truck-rolls over the 20+ years lifetime of a system, resulting in tremendous cost and unsatisfied system owners. This is why manyinstallers believe that NEC 2017 can actually lead to unsafe solar systems.

solar monitoring for residential systems

CONCLUSION

A high number of components in a residential solar system has significant downsides on various levels of a system’s lifetime. Starting with initial cost for hardware and labor, through the overwhelming amount of data to O&M challenges over 20+ years. The number of components in a solar system matters, and it must be in the solar industry's interest to simplify systems, make them more affordable and easier to operate and maintain.

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