Modernizing Legacy Energy: How to Extract SCADA Logic Without a 24-Month Rewrite

The most dangerous assumption in energy grid modernization is that you can simply "read the source code" of your legacy SCADA system. In reality, 67% of legacy systems lack any meaningful documentation, and for many utilities, the original developers retired a decade ago. You aren't looking at a codebase; you’re looking at a black box that controls critical national infrastructure.

When a utility provider attempts to modernize a legacy HMI (Human-Machine Interface) or SCADA front-end, they typically default to a "Big Bang" rewrite. The statistics for this approach are grim: 70% of legacy rewrites fail or significantly exceed their timelines. In an industry where $3.6 trillion in global technical debt looms over aging grids, spending 18 to 24 months on a manual rewrite is no longer a viable strategy. It’s a liability.

TL;DR: Modernizing legacy energy systems requires moving from manual code "archaeology" to Visual Reverse Engineering, reducing screen migration time from 40 hours to 4 hours by using video as the source of truth.

The SCADA Modernization Paradox#

Energy and utility companies face a unique challenge. Their legacy systems are often air-gapped, proprietary, or built on defunct frameworks like Silverlight, Flash, or early Java Applets. These systems manage high-stakes workflows—load balancing, substation monitoring, and fault detection—where a single misunderstood business rule can lead to a localized blackout.

The "manual" approach to modernization involves an army of business analysts and developers sitting with operators, taking screenshots, and trying to guess the underlying logic. This process takes roughly 40 hours per screen. For a standard utility dashboard with 50+ views, you are looking at a year of discovery before a single line of production-ready React code is written.

The Cost of Tradition#

From Black Box to Documented Codebase#

The future of modernizing legacy energy infrastructure isn't found in digging through 20-year-old COBOL or C++ binaries. It’s found in the UI. The UI is the only place where the business logic, user intent, and data structures converge in a human-readable format.

By using Replay, we shift the focus to "Video as the Source of Truth." Instead of manual auditing, we record real user workflows—an operator acknowledging an alarm, a technician adjusting a transformer load—and use AI-driven extraction to generate documented React components and API contracts.

💡 Pro Tip: Don't start with the database schema. Start with the operator's workflow. The UI reveals the actual functional requirements, whereas the database often contains "ghost columns" and legacy cruft that no longer serves a purpose.

Step 1: Visual Capture and Workflow Recording#

In a regulated energy environment, you cannot always grant external developers access to live SCADA environments. Replay allows internal operators to record their standard operating procedures (SOPs) locally. This recording captures the state changes, data inputs, and visual outputs of the legacy system.

Step 2: Automated Component Extraction#

Once the workflow is captured, Replay’s AI Automation Suite analyzes the visual layers. It identifies recurring UI patterns—gauges, toggles, alarm grids—and maps them to a modern Design System (The Library).

Step 3: Logic and Contract Generation#

The most critical phase is extracting the "invisible" logic. If a gauge turns red when a value exceeds 500kV, that logic is captured. Replay generates the corresponding TypeScript logic and API contracts required to support the new front-end.

typescript
// Example: Generated React Component from a SCADA Substation Monitor
// Extracted via Replay Visual Reverse Engineering

import React, { useState, useEffect } from 'react';
import { Gauge, AlarmList, Card } from '@energy-ds/core';

interface SubstationData {
  voltage: number;
  currentLoad: number;
  status: 'nominal' | 'warning' | 'critical';
  lastUpdated: string;
}

export const SubstationMonitor: React.FC<{ id: string }> = ({ id }) => {
  const [data, setData] = useState<SubstationData | null>(null);

  // Business logic preserved from legacy SCADA behavior:
  // Thresholds extracted from visual state changes in recording
  const getStatus = (voltage: number): 'nominal' | 'warning' | 'critical' => {
    if (voltage > 525) return 'critical';
    if (voltage > 505) return 'warning';
    return 'nominal';
  };

  return (
    <Card title={`Substation Unit: ${id}`}>
      <div className="grid grid-cols-2 gap-4">
        <Gauge 
          value={data?.voltage ?? 0} 
          unit="kV" 
          status={data ? getStatus(data.voltage) : 'nominal'} 
        />
        <AlarmList 
          active={data?.status === 'critical'} 
          timestamp={data?.lastUpdated}
        />
      </div>
    </Card>
  );
};

Bridging the Documentation Gap#

67% of legacy systems lack documentation. In the energy sector, this isn't just a technical hurdle; it's a compliance nightmare. When NERC/CIP auditors ask for the functional specifications of a grid management tool, "we're not sure, but it works" is not an acceptable answer.

Replay transforms the modernization process into an automated documentation engine. As screens are extracted, the platform builds:

• •Technical Debt Audits: Identifying which parts of the legacy logic are redundant.
• •E2E Test Suites: Automatically generating Playwright or Cypress tests based on the recorded user flows.
• •API Blueprints: Mapping the legacy data shapes to modern REST or GraphQL endpoints.

⚠️ Warning: Be wary of "Lift and Shift" migrations for SCADA. Moving a 1998 UI to the cloud without re-architecting the component logic simply moves your technical debt to a more expensive server.

Implementation: The 4-Hour Screen#

Manual modernization is slow because of the "Context Switch Tax." A developer looks at the legacy app, tries to find the code, fails, asks a BA, waits for a meeting, and then finally writes a component.

With Replay, the workflow is streamlined into a repeatable factory model:

1. •Recording: A Subject Matter Expert (SME) records a 2-minute clip of a specific task (e.g., "Adjusting Phase Shifting Transformers").
2. •Analysis: Replay identifies the UI components and data structures.
3. •Refinement: An architect uses the Blueprints Editor to map these to the modern React library.
4. •Export: The platform generates a clean, documented React component with 70% of the boilerplate and logic already handled.

💰 ROI Insight: By reducing the time per screen from 40 hours to 4 hours, an enterprise migrating a 100-screen application saves approximately 3,600 man-hours. At an average architect rate, that's over $500,000 in direct labor savings alone.

Security in Regulated Environments#

For Financial Services, Healthcare, and specifically Energy, data residency is non-negotiable. Modernizing legacy energy systems often involves sensitive infrastructure data that cannot leave the premises.

Replay is built for these constraints:

• •SOC2 & HIPAA Ready: High-standard compliance for data handling.
• •On-Premise Deployment: Run the entire extraction engine within your air-gapped network.
• •PII Masking: Automatically redact sensitive grid coordinates or customer data during the recording process.

json
// Example: Generated API Contract for Legacy Integration
// Target: legacy-load-balancer-service
{
  "endpoint": "/api/v1/grid/load-adjust",
  "method": "POST",
  "payload_schema": {
    "substation_id": "string",
    "target_mva": "number",
    "increment_step": "number",
    "safety_bypass_token": "string"
  },
  "legacy_mapping": {
    "target_mva": "MVA_VAL_01",
    "increment_step": "STEP_INC_ADJ"
  }
}

The Future: AI-Driven Grid Modernization#

The next decade of energy will be defined by the transition to renewables and decentralized grids. Legacy SCADA systems, built for centralized coal and gas, are the primary bottleneck. We cannot wait 24 months for a rewrite to support EV charging integration or solar microgrid management.

By adopting Visual Reverse Engineering, enterprise architects can de-risk their modernization roadmap. You aren't just building a new UI; you're finally understanding the system you've been running for twenty years.

Frequently Asked Questions#

How does Replay handle proprietary protocols like Modbus or DNP3?#

Replay operates at the presentation and orchestration layer. While it doesn't "sniff" the wire for DNP3 packets, it captures how the UI interprets those packets. By observing the visual state changes and the data bound to the UI, Replay helps you define the requirements for the modern API gateway that will eventually replace the legacy protocol handler.

What about business logic that isn't visible on the screen?#

While Replay excels at UI-driven logic, it also captures the network calls and state transitions that occur during a recording. This allows architects to see the "cause and effect" of user actions, which is often where the most complex business rules live. For purely "headless" logic, Replay provides a technical debt audit that highlights gaps between the UI and the backend.

Can we use our own React component library?#

Yes. Replay’s Library feature allows you to upload your existing Design System. The AI Automation Suite then maps extracted legacy elements directly to your specific components, ensuring the output is consistent with your brand and architecture standards.

How long does a typical pilot project take?#

Most organizations see their first legacy screen fully extracted and running in React within 48 hours of setup. A full pilot covering a complex workflow (5-10 screens) typically concludes within two weeks.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.