ASK THE EXPERTS: PV Optimizers

Intermediate
The increased energy harvest from using PV optimizers is site-specific, but their additional benefits can be enough to justify their use.

When I took a PV design class early in 2017, DC optimizers were presented, but the economics were not explored. In Jim Riggins’ article (“Heliospiti at 5 Years: Lessons Learned” in HP179), the author’s situation suggests investigating the economics of optimizers before making that decision. One manufacturer’s website explains that optimizers increase the electricity output of the PV modules by up to 25%, especially at shade-challenged sites. One seller’s price for a SolarEdge P320 optimizer, for example, was $80. When used on a 320-watt PV module, this should provide an output increase of up to 80 watts (25% of 320).

That’s $1 per watt. My question is, why would I pay $1 per watt (or more) when the retail price for a monocrystalline PV module is about 75 cents per watt? Add in racks and we’re still looking at $1 per watt worst-case, versus a $1 per watt gain with optimizers, best-case. Has the economic window for DC optimizers already closed?

Pete Gruendeman • La Crosse, Wisconsin

The economics of how much extra energy can be gleaned by using optimizers is site-specific, and relies on factors such as partial array shading, varying module manufacturing tolerances, module temperature differences, varying levels of module soiling, and so on. That makes it very difficult to arrive at an estimate of how much additional energy can be harvested.

However, you need to look at the whole package, and consider that the SolarEdge (SE) inverter is less expensive than other grid-tied inverters of the same capacity. For the system I put in about three years ago, buying the SE inverter plus optimizers was close to the same cost as buying a different string inverter of the same size without optimizers.

The optimizer-based system also comes with two additional benefits—module-level monitoring (which I find helpful in identifying individual module problems that would likely otherwise go undetected) and built-in module-level rapid shutdown capability. Rapid shutdown is an add-on that you can purchase with other string grid-tied inverters, but currently it is only at the array-level. However, module-level control, which is discussed in the 2017 NEC Article 690.12, will be required in 2019 (see my article on “PV System Rapid Shutdown” in HP175 for more information).

Justine Sanchez • Home Power senior technical editor

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