Refurbishing 84,000 Gallons of HTF to Restore 64 MW Solar Farm Efficiency with Zero Downtime

The Challenge

In December 2020, a 64 MW concentrated solar farm in Nevada faced a difficult operational decision. After 23 years of service, the facility’s 300,000-gallon heat transfer fluid (HTF) — a diphenyl oxide/diphenyl (DPO/DP) system — was nearing the end of its useful life. High boiler concentrations (heavy degradation byproducts) had climbed to a risky 10.5%, threatening both system efficiency and Environmental, Health & Safety (EHS) compliance.

With seven years remaining on a 30-year power purchase agreement and no planned shutdowns on the horizon, management had limited options. A full system replacement with virgin fluid ran well into seven figures — cost-prohibitive for a facility in its final contract term. Yet leaving the fluid untreated was equally untenable. What they needed was a solution that could restore the system without ever taking it offline.

Business Requirements

• Manage degradation in a large-scale 300,000-gallon DPO/DP system
• Extend reliable performance through the final 7 years of the contract term
• Reduce HTF high boiler concentrations from 10.5% to acceptable operating levels
• Maintain continuous energy production with zero planned downtime

Project Outcomes

• Replaced 84,000 gallons (28% of total system volume) with high-quality reclaimed HTF — avoiding a full drain and refill
• Reduced high boiler concentrations from 10.5% to below 7%, meeting all technical targets
• Achieved approximately 70% cost savings by using reclaimed rather than virgin fluid
• Maintained uninterrupted plant operations throughout the entire treatment process

Key Takeaway

Aging solar facilities don’t always face a binary choice between expensive full replacement and declining performance. Through a carefully executed “Bleed and Feed” approach — gradually cycling out degraded fluid and replacing it with reclaimed HTF while the plant ran at full capacity — this facility restored fluid health, met its EHS obligations, and saved roughly 70% in material costs. It’s a model worth considering for any long-term solar asset approaching the end of its fluid life.