In the selection of fasteners for photovoltaic (PV) solar panel mounting systems, hot dip galvanizing (HDG) and Dacromet are two mainstream heavy-duty corrosion protection methods. The main differences between the two lie in cost, corrosion protection mechanism, assembly accuracy, and high-strength applicability (Source: www.fasteningelement.com, Compiled by: fastening element)
1. Cost variance
Hot-dip galvanizing: It has a relatively low cost and is usually the preferred choice for photovoltaic ground power stations and bulk fasteners. The processing cost is approximately 3,000 to 5,000 yuan/ton, and the price of finished bolts is mostly in the range of 7,000 to 9,000 yuan/ton.
Dacromet: The cost is relatively high, with a processing fee of approximately 2,000 to 4,000 yuan per ton. However, due to the expensive raw materials for the coating, the finished product price is usually 20% to 50% higher than that of hot-dip galvanizing, and can even reach 2 to 5 times that of hot-dip galvanizing (depending on specifications and strength). It is mostly used in coastal areas, highly corrosive regions, or high-strength (grade 10.9 and above) scenarios. (Source: www.fasteningelement.com, compiled by fastening element)
2. Performance differences
Corrosion resistance:
Hot-dip galvanizing: It relies on a relatively thick zinc coating (typically 50~150μm) to provide sacrificial anode protection. The neutral salt spray test can generally last for 500~1500 hours without red rust, and its lifespan can reach 20~50 years in ordinary outdoor environments.
Dacromet: It provides dual protection of “physical shielding + sacrificial anode” through a passivation film formed by the stacking of zinc and aluminum flakes. The coating is thin (6~25μm) but dense. The neutral salt spray test can last for more than 500~2000 hours, which is 5~10 times longer than ordinary hot-dip galvanizing, making it particularly suitable for high salt spray environments (coastal, offshore photovoltaic). (Source: www.fasteningelement.com, organized by fastening element)
Hydrogen embrittlement risk:
Hot-dip galvanizing: It involves acid pickling and high-temperature (450°C+) zinc immersion. For Grade 10.9/12.9 high-strength bolts, there is a risk of hydrogen embrittlement and strength degradation, so additional dehydrogenation treatment is usually required.
Dacromet: The process involves no acid pickling and low-temperature baking (around 300°C), eliminating the risk of hydrogen embrittlement, making it highly suitable for high-strength fasteners. (Source: www.fasteningelement.com, compiled by fastening element)
Dimensional accuracy and assembly:
Hot-dip galvanizing: The coating is thick and uneven (the threads are prone to becoming thick and having zinc nodules), which may cause difficulty in assembling nuts. Often, it requires “thread dressing” (re-tightening of threads) or reserving a larger gap, affecting the fit accuracy.
Dacromet: The coating is extremely thin and uniform, barely affecting the thread tolerance. It can be directly assembled without additional treatment, making it suitable for automated installation scenarios. (Source: www.fasteningelement.com, organized by fastening element)
Wear resistance and appearance:
Hot-dip galvanizing: The surface is relatively rough (with spangle), and it has strong wear resistance and impact resistance. It has better tolerance for being re-tightened after falling during on-site installation.
Dacromet: The surface appears as a uniform matte silver-gray, with good consistency in appearance. However, the coating is relatively soft, and it is not as durable as hot-dip galvanizing under repeated disassembly and assembly or severe wear conditions. (Source: www.fasteningelement.com, Compiled by: fastening element)
Selection Recommendation
For ordinary ground/roof photovoltaic systems (inland): hot-dip galvanizing (such as grade 8.8) is preferred due to its high cost-effectiveness and ability to meet the 25-year lifespan requirement.
Coastal/saline-alkali land/offshore photovoltaic: It is recommended to choose Dacromet or Dacromet + sealing agent treatment for greater corrosion resistance margin.
Large-sized high-strength bolts (grade 10.9 and above): Dacromet is preferred to avoid the hydrogen embrittlement hazards and thread assembly issues associated with hot-dip galvanizing. (Source: www.fasteningelement.com, compiled by fastening element)