US vs. international solar installations: a tale of two standards
The difference between solar PV on one side of the Atlantic versus the other
Most of us are probably familiar with differences between American electrical standards and those used in most of the rest of the world through personal electronics. Today’s laptop computers and phone chargers can accept either 110v or 220v so all you need to travel between regions is an adaptor for the plug. But it was not always so, and many electronic devices designed for 110v came to an early death when their owners plugged them into a 220v outlet on their European holiday.
In the world of solar power, there are similar standards that dictate the maximum voltage a photovoltaic (PV) panel can use. Like their consumer-level counterparts, these standards vary between regions.
Outside of North America, IEC standards (specifically IEC 60364-7-712) provide requirements for solar installations. In the US, the National Electric Code (NEC) governs public and private wiring installations (article 960, if you’re interested) while the National Electrical Safety Codes cover power generation, also applicable to solar PV.
It gets even more complicated because NEC standards also specifically require the use of equipment that is compliant with product standards established by Underwriters Laboratories (UL).
So, what’s the difference between solar PV on one side of the Atlantic versus the other?
In a word, it comes down to voltage. US standards cap the operating voltage of a PV panel at 1000v but conventional wiring practices typically mean the voltage is set even lower, at 600v. Meanwhile, IEC systems typically operate at 1000v or even 1500v.
This has some important implications when it comes to overall system efficiency and cost. Higher system voltage allows for:
- A reduced of number of source circuits and a reduced numbers of conductors for a system of the same capacity
- A reduced number of overcurrent protection devices, inverters, disconnectors and a subsequent reduction in labor cost
- Smaller cross-section conductors (i.e., lower materials cost)
- Reduction of wire resistive losses
- Increased efficiency at the inverter stage
- Increased power at the same current rate
These benefits have not gone unnoticed by the US standards bodies, and are at the center of the debate now taking place in anticipation of a revision to the NEC this year. If the codes are changed to allow higher voltage levels, we could see a drop in overall PV system costs once equipment vendors adapt to the new standard. It’s hard to say how much of a reduction the end user will see, but even a small improvement would certainly be welcome.