Finding the Best Fit for Your BESS Project: 5 Key Questions to Ask an Engineering Firm

Arun Ramadass, Vice President of Engineering at Castillo

In just the last few years, BESS systems have become much faster, easier, and more cost-effective to install – leading to tremendous growth and demand for project engineers. While this is great news for the renewable energy transition, easier installations can create a false sense of comfort among well-meaning but less experienced engineers, who may overlook critical due diligence and design steps. 

An inexperienced engineering team can create multiple issues that cause significant project delays and cost overruns. Fortunately, these issues can be easily prevented by choosing an experienced engineering team with a track record of BESS success. 

To help BESS developers make an informed decision, here are 5 key questions to ask a potential engineering partner: 

1. Can you share previous BESS projects designed by your firm? 

Past experience is a bellwether of what’s to come. Look for tangible results and a definable track record, not just a list of clients:

• Case studies with specific challenges, solutions, and outcomes

• Geographic experience relevant to your project locations (regulations vary dramatically by state/AHJ)

• A range of work across BESS types - chemistries, use cases, and discharge methodologies similar to your project’s needs

In addition, ask which services the firm provides in-house vs. outsourcing. Outsourcing specialized services isn’t necessarily a deal-breaker, but in-house services (especially hydrology, civil, and electrical) enable faster coordination, quicker responses to AHJ comments, and streamlined decision-making.

2. How does your team manage due diligence for local & state regulations? 

   
   

BESS compliance is more complex than standalone solar, and often requires much more upfront time (in part because solar has more established regulatory timelines). These approvals can be more challenging than the physical site work itself. 

Since BESS local and state safety regulations vary widely by the authority having jurisdiction (AHJ), understanding and adhering to regulations makes the difference between smooth sailing and overcomplication. The larger the patchwork of these regulations, the more they can increase design complexity and approval timelines. 

In states like California, regulatory requirements are often the biggest hurdle, since project designs must comply with particularly comprehensive environmental and safety approval processes. As California goes, so goes the nation; this approach is expanding nationally, with increased coordination among regulators and local fire departments around battery safety and emergency response. 

What to look for:

• Due diligence happens first - before any design work begins

• Detailed assessment process covers:

  • Local zoning and fire code requirements

  • State-level safety regulations

  • NFPA 855 (Energy Storage Systems)

  • UL 9540 and UL 9540A compliance

  • Environmental permitting requirements

    
    

• Proactive coordination with fire departments and emergency responders early in the process

3. What differentiates your BESS design approach from solar-only projects? 

Since standalone BESS projects have a much smaller footprint than large-scale solar projects, they don’t require as much civil and electrical work to prepare the site. 

This results in a much shorter timeline for BESS projects, which leaves engineers with less margin for error. Design decisions that could be deferred in solar projects, must be locked in upfront for BESS.

What to look for:

• Upfront decision-making - every critical design element is identified and decided before detailed engineering begins

• Integrated approach - civil and electrical considerations addressed simultaneously, not sequentially

• Use case clarity - battery chemistry, capacity, discharge methodology, and application align with project goals from the start

BESS civil scope may be smaller than that for large solar projects, but accuracy requirements are just as stringent. Look for a partner that understands how to manage these compressed timelines. 

4. What are the most common BESS design risks, and how do you prevent them?

The most common BESS design risks are seen in layout, electrical coordination, and incorrect alignment. Experienced partners have effective systems to avoid these problems:

• Poor Use Case Alignment

Battery chemistry must match the application, whether that's frequency regulation, energy arbitrage, or backup power. A design that doesn't optimize for the project's actual revenue model wastes both capital and performance potential.

• Over or Under-Sizing

Oversizing BESS projects drives unnecessary capital costs, higher long-term O&M expenses, and wasted capacity. But undersizing creates revenue limitations, and may not provide enough capacity to meet demand. Right-sizing BESS projects requires a deep understanding of both technical requirements and business objectives.

• Inadequate Battery Protection

Batteries are typically the most expensive project asset. Insufficient protection leads to premature degradation, frequent maintenance, and early replacement – especially in extreme climates. 

• Electrical Coordination Failures

Misalignment between battery specs, inverter capabilities, and grid requirements creates performance bottlenecks and potentially expensive retrofits. Inadequate voltage regulation or power quality controls can jeopardize interconnection approval.

Further questions to ask:

• How do you validate use case assumptions?

• What battery protection strategies do you build into designs?

• How do you optimize sizing for both performance and cost?

5. Which site decisions have the biggest impact on BESS project outcomes?

What to know: Site design decisions cascade through the entire project. BESS engineering challenges are created by sites with: 

• Steep slopes or floodplains

• Extreme temperatures

• Limited site access

• Tight parcel constraints

• Complex zoning overlays

Before choosing a partner, ask them about their approach to these early design decisions: 

• Equipment spacing - affects both safety compliance and future expandability

• Access requirements - maintenance, emergency response, equipment delivery

• Geotechnical assessments - foundation design for heavy battery systems

• Grading strategy - especially on sloped terrain or constrained parcels

• Thermal management - cooling/ventilation needs in extreme temperatures

• Drainage - stormwater management for impervious surfaces

Finally, future-proofing matters more for BESS than almost any other renewable technology. BESS technology is evolving quickly, with much higher storage capacity than just a few years ago. BESS capabilities advance quarterly, and inflexible designs quickly become obsolete.

Augmentation planning should include room for future capacity additions, and designs must accommodate technology evolution. 

Is Your BESS Project Ready for the Future? 

Experienced BESS engineering partners assess regulatory, environmental, and access constraints before design begins. They build in flexibility for technology improvements. They coordinate early with AHJs and first responders. And they ensure that, long after the design is finalized, BESS projects remain flexible enough to adapt to future needs and innovations. 

BESS’ quick growth and technological innovations provide new opportunities and benefits for developers and EPCs – but only if projects are designed right. If you want an experienced partner that can design for success from the start, we’re ready to get started.

Get in touch with our team to learn more about maximizing the benefits of BESS.