C&I solar design decisions that have a big impact on PV bankability | The Buzz

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The commercial and industrial (C&I) solar segment often requires the same lead sentence: So much rooftop space with so much opportunity, but a variety of challenges keep holding it back. On the latest episode of The Buzz, we chatted about the role of solar design in easing those challenges with Paul Grana GM of helioscope at Aurora Solar. We discuss:

  • 0:12 – What are commercial solar installers saying about the market?
  • 1:10 – When are projects won and lost in the design process?
  •  3:45 – How do we avoid overpromising and under-delivering?
  • 5:27 – The problem of under voltage vs. over voltage
  • 6:56 – How do EVs and storage change proposals?
  • 9:06 – Process efficiencies to tighten up C&I design
  • 11:20 – What’s the next crucial advancement in C&I solar?

Watch the full 14-min video right here or read part of the transcript below.

Crowell: One bright spot that I’ve written about even before the IRA passed was how financiers were getting more comfortable with mid-market solar projects and I’m curious how much of a role front-end design plays in improving the bankability end of things?

Grana: First is just using a good model. All through a project life cycle, there are decisions being made — including just whether to engage with up with a potential customer or not, which sites are attractive or not, which technologies are attractive on those sites — and one of the things that’s most important is you want to make sure that you’re using the core fundamental math all the way through the project cycle.

Now, the requirements of the model that you’re using are going to change. Early on, you need something that can be used everywhere, that can be updated quickly, that is quite transparent, and that has only enough knobs to get you through the funnel. At the very end stage, you want something that can be really dialed in, and that has many more knobs because now you’re looking to dial in impacts on the order of a tenth of a percent.

This is why we still see PVsyst used for the final step, and that’s totally fine and understandable because it’s really a fundamentally different tool from what people need in the early stages when you’re actually engaging with the customer, when you’re figuring out how to answer all your biggest uncertainty.

And as far as we’re concerned, that’s where most of the value is created in the solar industry and where most of the pain exists in the solar industry. The biggest source of uncertainty, risk and loss happen in the early and mid parts of the funnel. That’s where things are won and lost.

And especially for the medium to small size to C&I projects: the smaller you get, the less it makes sense to roll a truck and do a really good, comprehensive site walk, drone survey, etc. So, LIDAR plays a really nice role in giving you a set of data. It might not be the only set of data, but once again, what we’re really talking about is a multi-step process, with multi-steps of a funnel, and it’s playing out over multiple months.

Having that LIDAR data early to get to a fatal issue earlier — moving a fatal issue up from step six to step one —  is huge in terms of saving you time and is just a way to give you a second set of data.  You might be doing a drone survey later, but now you have something to compare and contrast that drone data with, to dig a little further.

Crowell: One of the core issues that can plague a C&I project is under performance, lost revenue. We often tie that to operations and maintenance, and keeping things going long term, but … what needs to be done in the design phase to make sure that we aren’t over promising and under delivering?

Grana: Being really aware of what resource you’re using. Both weather source, weather vendor within the source and what flavor of the actual resource you are looking at — P50 or P90 or something else.

Another element where design can kind of help is designing for maintainability. I only flag that because … in C&I generally speaking, you want to pack as much power density on the roof as possible … but after tiling the whole roof, how are we going to actually maintain this thing?

Let’s assume there’s going to be an issue. How are we going to access that issue? How are we going to diagnose and troubleshoot and resolve it? There is a way in which the maintenance requirements are somewhat at odds with the general economics because, again, the bigger you get, the better the economics are of that system. You’ve got fixed costs. So, if you can make the system 20 percent bigger, all of your fixed costs are roughly 20 percent less expensive on a per Watt basis.

So, bigger is better, but there are some real trade-offs in terms of O&M.

Crowell: Do you have any more examples of a less considered issue here that could impact a system long term?

Grana: Think about under voltage issues. It depends on the module technology, but in many cases, module degradation happens in voltage not current.

To the extent that it happens in voltage, if your string voltage is going to be falling over time, then you don’t want to be hitting the lower end of your inverters’ voltage range. Undervoltage at the string level can have significant impact on energy production, more so than overvoltage.

If you’re driving the voltage higher than the inverter wants … the impact on power is actually a relatively soft part of the IV curve. But IV curves are very steep when your string is too low and the inverter can’t follow your string voltage down.

If you’re starting out at the design stage in the low end of the inverter’s voltage range, and then the modules degrade, you could see fairly material impact on system performance.

And keep in mind that this is going to happen at the peak part of the day. The hotter it gets, the more voltage sags. If you’re having an undervoltage issue, not only is the curve’s slope very steep, but it’s happening at the hottest part of the day, which obviously is also going to be the sunniest part of the day.

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