Rethinking Hail Resilience: Key Insights from GroundWork’s October Webinar
Rethinking Hail Resilience
In October, Colin Sillerud (Director of Engineering, PV Test Lab) and Travis Morrison (Product Engineer and meteorologist) shared a groundbreaking, comprehensive hail solution that challenges how the solar industry manages hail risk and reduces project uncertainty to deliver a 6x ROI in the field.
The Discovery: Stow Isn’t as Effective as We Thought
After testing hundreds of modules at various stow angles, GroundWork found a critical discrepancy: modules break at lower kinetic energies than current models predict.
The traditional approach models stow benefit using the kinetic energy equation (½mv²) modified by the cosine squared of the stow angle. But this doesn’t account for complex surface interactions, including tangential energy transfer, vibration, deformation, and heat, adding 1 to tens of joules of energy that current models miss.
Stow absolutely works. It’s just not as effective as we’ve been calculating. And that gap matters when you’re making multi-million dollar insurance and module selection decisions.
The New Model: Coefficient of Restitution
GroundWork proposes incorporating the coefficient of restitution—the same physics concept that explains why a basketball bounces differently than a steel ball. By modeling both normal and parallel plane components of kinetic energy, the approach accounts for module-specific behavior at different stow angles that the simplified cosine-squared model overlooks.
This underscores a key point: module-specific testing is essential. Generic models can’t capture how your particular technology responds to hail at stow.
Real Impact: A Texas Case Study
The value of GroundWork’s integrated approach is already proven in the field. A 500MW portfolio in Texas used the combination of module testing and sensor deployment to negotiate with insurers:
- Deductibles reduced by ~50%
- Premiums reduced through lower loss expectations
- 6x ROI on testing and sensor costs
- $500,000 annual savings
- 8-month payback period
By providing insurers with both lab data on module resilience and field measurements of actual hail events, developers can negotiate meaningfully lower insurance costs—often enough to justify selecting hail-hardened modules that might otherwise seem too expensive.
GroundWork’s Complete Solution
The integrated approach combines four elements:
Preparing: Our team of Advisors reviews and compares portfolio-level resilience measures against industry standards and ensures the site’s risk is minimized.
Testing: Test-to-failure methodology quantifying glass fracture probability, cell fracture probability, stow benefit at multiple angles, and long-term performance risks from cell damage without glass breakage.
Monitoring: Dual Eyewitness hail sensors (one at normal incidence, one on tracker) measure actual impact energy and validate real-world stow effectiveness—not just theoretical models.
Analysis: Spatial heat maps show exactly which parts of a plant experienced damaging hail, enabling targeted O&M response instead of unnecessary full-site inspections.
Module Technology Insights
Testing reveals important differences:
Standard modules: Glass and cell breakage curves overlap—cells and glass break at similar energies, reducing concern about hidden damage.
Hail-hardened modules: Glass withstands much higher impacts, but creates a regime where cells can crack before glass. The overall resilience improvement is substantial with stow, but requires different post-event assessment protocols.
Beyond Radar: The Ground Truth Gap
While radar remains essential for stow activation, it has critical limitations for damage assessment. Radar operates at altitude, measures estimated max diameter (not impact energy), and can’t capture the dramatic variation that occurs over short distances during a hailstones flight time.
On-site sensors provide the ground truth needed for data-driven decisions about which areas actually need inspection.
Key Takeaways
- Module-specific testing is non-negotiable—certification testing alone doesn’t capture real-world hail behavior
- Stow benefit is real but overestimated by current models
- Field monitoring pays for itself through insurance optimization and targeted O&M
- Different module technologies need different strategies for post-event assessment
- Integration is everything—testing + monitoring + advisory deliver the value
Watch the full webinar recording →