From system voltages to string optimizers, Managing Editor Kathie Zipp spoke with Mark Kanjorski of Ampt to get his insight into trends for 2015. Here are some highlights.
Trend 1: Moving toward 1,500V
“Companies are looking for ways to reduce the levelized cost of energy (LCOE), which essentially compares the expected lifetime costs of a PV power plant with its expected lifetime energy generation in cents per kilowatt-hour. This can be done by lowering the upfront cost of the system or increasing system performance. Raising system voltages helps lower the upfront cost of the system by lowering component cost. For example, moving from a 1,000-V system to a 1,500-V system allows 50% more modules to be connected in a series. This reduces the number of parallel connections and associated hardware by almost a third. Increasing the system voltage also allows the inverter to operate at a 10% to 40% higher power.
There are some challenges to higher voltage systems. Right now there are a limited number of components rated for 1,500V. Those that are available aren’t priced at an optimal point for project cost savings, yet. There are also some unknowns with regard to reliability of 1,500-V systems, mainly on the modules and inverter side. Lastly, there’s uncertainly around when different markets will adopt relevant electrical codes.
All together, the promise of moving to higher voltages is there, but doing so right now is a significant undertaking.
An alternative is using DC power optimizers in 1000-V systems, to deliver the equivalent economic benefits of a 2,000-V system. These benefits can be realized today using widely available 1,000-V rated components. DC string optimizers allow designers to double the string length. With 100% longer strings, the cost of combiner boxes and wiring for the system decreases by 50% while the inverter’s rated output power increases by 40% to 70%.”
Trend 2: Using more string inverters in large projects
“LCOE is the metric of merit when evaluating the economics of solar. An example where efforts to lower LCOE are primarily focused on improving performance can be seen in the recent trend of using string inverters in large-scale PV power plants in the 10-MW range.
String inverters increase the resolution of maximum power point tracking (MPPT) in the field (focusing in on fewer modules at a time) compared to central inverters. A higher resolution of MPPT allows the system to recover more energy that would otherwise be lost due to electrical balances—also known as mismatch. Although systems using string inverters cost more per watt than those using central inverters, the difference is now reaching the point where the performance advantage can be worth the added expense, even on large systems.
So, if you’re looking at performance, using string inverters instead of central inverters can achieve a lower cost of energy. But, you are still paying more for the system on day one, so it is a benefit that is realized over the lifetime of the system.”
Trend 3: Using string optimizers along with central inverters
“Another option to achieve higher system performance in larger projects that saves cost from day one is using DC optimizers with central inverters. Like string inverters, the optimizers help increase the performance through using MPPT, but do so at an even higher resolution (focused on as few as every 10 modules, compared with every few dozen or hundreds with string). Plus, DC optimizers enable the central inverters to achieve a higher rated output power, which lowers their cost per watt. So, a system with optimizers offers the best of both worlds by performing better at a lower cost on day one.
Lowering LCOE is the goal. However, we may short change ourselves when we focus on either cost or performance instead of both. It is possible to find innovative solutions that deliver a true spend-less, get-more value proposition. In doing so, we accelerate the adoption of solar.” SPW
To hear the full podcast interview with Mark, listen here.