Hey there! I totally get your dilemma - you're looking at that 15-year-old S7-300 system and wondering whether to go all-in with a complete S7-1500 replacement or take a more gradual approach with edge computing add-ons. Let me break down both options for you.

For the complete S7-1500 replacement, you're looking at a 30% efficiency gain from faster processing and Profinet connectivity, plus future-proofing with modern TIA Portal integration. The migration can be done systematically, and you get long-term support that's no longer available for S7-300. The downside? Higher upfront costs and production downtime during the switchover.

For incremental modernization with edge computing, you can add OPC UA servers or Industrial Edge platforms to your existing S7-300s. This gives you immediate IIoT capabilities, data analytics, and cloud connectivity without replacing the core PLCs. It's cheaper upfront and causes minimal disruption, but you're still stuck with aging hardware that might fail soon.

To justify ROI to finance, focus on these key points:

1. For S7-1500: Calculate the 30% efficiency gains in production output, reduced maintenance costs (S7-300 parts are getting scarce), and energy savings from newer hardware. Include the cost of potential unplanned downtime if S7-300 fails.

2. For edge add-ons: Show immediate data visibility benefits - predictive maintenance savings, quality improvements from real-time monitoring, and the ability to start digital transformation without major capital expenditure.

My recommendation? If your S7-300s are still reliable and you need quick wins, start with edge computing to prove the value of digitalization. But if you're seeing frequent issues or planning major production changes, the S7-1500 replacement gives you a solid foundation for the next 15 years. Either way, present it as a strategic investment in operational resilience, not just a cost.