Optimizing for Speed in Commercial Rooftop Applications

All the focus and pressure to realize high yields and low costs on an individual project often blinds companies to the benefits of a fast execution and in some cases can really slow things down.

When solar designers think about optimizing a PV system, they typically think of ways they can modify various design parameters to save costs and increase energy production. While these are certainly worthy goals, optimization also includes having the ability to design and build projects with speed. Designers should not lose sight of opportunities to optimize projects by reducing costs and improving the client’s return on investment (ROI). However, optimization is also about reaching your company’s financial goals and getting more megawatts on the ground. Optimizing your company for profitability and continued growth is ultimately what will help the climate and create more solar jobs.

While some of the suggestions presented here may seem counter to traditional thinking about project optimization, optimizing for speed can definitely have benefits at the project level. Accelerating system design and construction can reduce engineering and labor costs. Moreover, the sooner a PV system starts generating energy, the sooner the client starts saving money. Most important, a shorter project life cycle increases the number of projects a company can build with the same number of employees, reducing soft costs and overhead as well as enabling faster growth.

Establish Goals and Priorities

It is difficult to optimize a system design without having clear goals and priorities. Does your client value ROI, reduced up-front costs, or long-term reliability and low maintenance costs? Of course, customers want all of these options, but clearly defining their project priorities will help you identify a preferred design approach.

Company goals are also important. One solar contractor might be focused on hitting annual profitability goals, while another is willing to cut margins to increase market share. These are not just issues for management or project estimators. These different company priorities affect design and construction decisions.

When a company’s sales, engineering and construction teams are all on the same page with regard to the priorities of both the customer and the company, it gives everyone involved the confidence necessary to make decisions quickly.

Invest in Site Evaluation

One of the best ways to accelerate a project schedule and reduce risks is to invest in a thorough site investigation, in some cases even prior to signing the contract. Site investigation is not an area where you should be looking to save money. While there are significant costs associated with more-detailed site evaluation activities—such as a professional survey, electrical evaluation, structural review or underground utility locating service—that initial investment provides a hefty return when you avoid expensive mistakes or wasting time on a system redesign.

Every project should have a detailed schedule outlined in project management software with clear dependencies. This schedule should account for and accommodate site investigation and design activities. If the project managers who typically control the schedule focus too narrowly on construction activities, a Gantt chart may not have adequate detail early in the schedule. Projects often get hung up when issues come up during site investigation. You can keep things moving forward by having a Gannt chart that shows early-stage project dependencies, as this can identify areas where you can accelerate the schedule.

Set Realistic Expectations

Solar contractors must set realistic expectations, both within the company and with outside stakeholders. This is perhaps most evident in the desire to maximize system capacity during the design process. As project capacity increases, the cost per installed watt generally goes down due to the dilution of fixed costs that are independent of system size. Moreover, the client wants to save as much money as possible, while the contractor wants to increase revenue. These factors greatly incentivize installation contractors to put as many watts on the roof as they can to win the deal and theoretically make more money.

Since roof area—rather than ampacity limits or load—often limits commercial rooftop system capacity, it is tempting to cram the maximum number of modules onto the rooftop. That leaves very little wiggle room for locating rooftop electrical equipment, establishing fire pathways and setbacks, or adjusting the array to account for unforeseen obstructions. If the sales team does not provide enough contingency space in the preliminary design, then problems can arise when something does not work exactly as laid out in the proposal—a common occurrence. You risk not only spending more time and resources correcting the issue and resetting customer expectations, but also incurring unanticipated costs as you try to satisfy those unrealistic expectations.

Such expectations can undermine project optimization goals in several ways. To meet inflated kWh targets, the design team may have to utilize roof areas where the solar resource is suboptimal due to shading, locate modules in roof areas subject to higher wind loads that require additional ballast materials or roof attachments, or add a small subarray on another roof area or even a different building. While each of these design responses will increase production, the cost per kWh will also increase.

Similarly, if the initial proposal overestimates project ROI or underestimates costs, the sales team will set unrealistic expectations internally in terms of project profitability and margins. Management may then apply pressure on the project team to drive down costs. As a result, the project team has to spend a great deal of time analyzing alternative design options, which can slow the project and increase soft costs.

Standardize Products and Procedures

Standardizing your company’s offerings on a small set of products and vendors should be a no-brainer. To provide vendors with the volume commitments necessary to drive down unit costs as much as possible, every solar company should work with a select few partners for modules, inverters and racking. Having a standard set of products also allows everyone to learn how to efficiently design and install projects utilizing those products. (See Table 1, “Low-Slope Mounting System Vendors,” for an overview of commercial mounting system product lines.)

To work faster and reduce errors, each solar contractor should be working toward standardizing its drawing templates, sheet notes, details, specifications, contracts and scope-of-work documents. It is also beneficial to standardize basic design parameters such as tilt angle and row spacing for similar projects. The sales team can standardize on the amount of roof area held for contingency. Companies may even want to establish standard practices for equipment locations and ac collection strategies, or for when to upsize conductors. Though standardization is not a substitute for design optimization, it is important to optimize the system design as much as possible before sending out proposals.

Create Value Engineering Guidelines

Pair standardizations with clear guidelines for determining when it makes sense to spend time and resources on value engineering activities, as well as metrics for evaluating different design options. As a guideline for the project team, consider putting a value on project time as a means of determining when to invest in value engineering. Placing a value on time, and making sure the project team understands how to use that number as a guideline for devoting resources to value engineering, is a simple way to align the project team with company goals.

For instance, imagine that a project manager hears of a new wire management system that she thinks can save $4,000 in material and labor for a 1 MW project. After a quick review, the design engineer determines that it will take one engineer about 4 days to establish whether the solution is viable and to integrate it into project specifications and details. If the value of the electricity generated by the PV system is $600 per day and the burdened cost of an engineer is $800 per day, then the cost to integrate the new wire management system into the project is $5,600  ($1,400 per day times 4 days). This review suggests that even though the new hardware option could reduce project hard costs, it is not a wise investment, as the savings ($4,000) are less than the costs ($5,400).

The team also needs easy-to-follow and relatively accurate metrics and rules of thumb for estimating cost savings for design alternatives. Make sure the design team has access to simplified per-unit cost estimates—for equipment, conduit, wire and labor—and knows how to use them quickly. These metrics can help prevent the dreaded “analysis paralysis.”

Do Your Due Diligence

It is critical to meet with permitting officials early. Never assume that it is better to ask for forgiveness later than to seek permission in advance, or that a new AHJ might not have the same concerns you have encountered in other jurisdictions. Do not hesitate to ask questions of building or fire officials, even if you are afraid of drawing their attention to a disputed code interpretation. It is far better to get their opinion early on than to have them find something they do not like late in the game.

This is especially true when dealing with fire officials on commercial roof-mounted PV projects. In spite of the best efforts of industry stakeholders, including the Solar America Board for Codes and Standards (solarabcs.org), a number of areas in the fire codes remain open to interpretation, such as whether to apply commercial or residential setbacks to a sloped roof at an apartment complex. Moreover, fire officials have every right to ask for something that goes above and beyond minimum code requirements if they believe it will improve safety. Some fire officials object to pathways that dead-end, even if the pathways terminate at skylights or mechanical equipment. Others insist on straight pathways, even where the design requires a jog to keep the access path over a structural member. You can expedite project timelines by clarifying these types of issues before starting on a design.

Streamline Construction

To help the construction crew get in a flow and move fast, use simple repetitive patterns in the array layout and string wiring. While you may be able to better utilize a roof area with oddly shaped arrays or reduce wire costs with unique string-wiring practices, it will come at the cost of additional field labor.

It is also important to consider roof access, work coordination, staging and layout. On the one hand, a mounting system with a 5° tilt may allow you to pack more kW on a roof; on the other, it could slow the project down if the installers cannot even walk between the rows. Fall protection is another consideration. The fire codes allow 4-foot setbacks on small commercial flat roofs that are less than 250 feet in length in either direction. If the roof does not have a parapet, however, OSHA guidelines require a warning line located 6 feet from the roof edge and fall protection (harnesses, ropes and anchors) for anyone working beyond this perimeter. The extra labor costs required to meet these OSHA requirements may not justify placing modules and electrical equipment beyond the perimeter of the warning line.

Foster Open Communications

Clear and transparent communications are the most effective way to foster an atmosphere of shared goals. It is especially important to be clear, open and honest with project team members when things are not going as expected. Strong relationships built on trust help you not only get the information you need to save money on projects, but also get it fast. This is true whether you are trying to obtain cost estimates from a subcontractor to evaluate value engineering options or spending approval from management to gather valuable site investigation data.

By building trust, clarifying priorities, and providing the right guidelines and resources to the project team, you can accelerate project schedules without increasing costs or risk. Reducing design and construction timelines while putting less pressure on the project team to reduce costs or increase yields after contract signing also better aligns the activities of the project team with the goals of the company and the client.


K. Randy Batchelor, PE / Sol Rebel Power Systems / Alameda, CA / solrebel.com

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