Design PV Systems with Confidence: Data-Driven Sizing Using Shelly Pro 3EM
The Problem with Single-Number Quotes
Most residential PV installation quotes are built on one figure: the customer's average monthly electricity bill. That single number hides everything - daily load profiles, seasonal variation, peak demand events, time-of-use patterns. The result is a system designed on a guess, and a customer who may question your methodology before the contract is even signed.
Shelly Pro 3EM changes that dynamic.
What Shelly Pro 3EM Captures
Installed at the main distribution board, the Pro 3EM measures all three phases at 1-minute resolution and streams data to the Shelly Cloud (premium subscription). Over a profiling period of two to four weeks, you collect:
Data Point | Value for System Design |
|---|---|
Peak demand (kW, per phase) | Inverter sizing, grid connection rating |
Baseline load (night floor) | Battery minimum useful capacity |
Time-of-day usage curves | Self-consumption optimisation, tariff matching |
Weekday vs. weekend delta | Storage dispatch strategy |
Phase imbalance | Single- vs. three-phase inverter decision |
The Installer Workflow
Initial visit - Mount the Pro 3EM on the incoming phases. No wiring interruption required. Commission the device to the customer's Wi-Fi in under 20 minutes.
Profiling period - Two to four weeks of passive data collection. No follow-up visits needed.
Data review - Pull the 1-minute CSV export or review the cloud dashboard. Apply your load analysis tooling.
Proposal - Present a system design justified by actual consumption data: panel count, inverter model and rating, battery capacity and chemistry, expected self-consumption ratio and payback period.
Building the Customer Relationship
The profiling visit is a low-commitment, high-trust entry point. You can frame it in two ways depending on your commercial model:
Subsidised visit: Charge a nominal fee for the installation and profiling report. The customer keeps the device regardless of their decision.
Conditional offer: The profiling and device are included in the project price if the customer proceeds with you. If they choose another installer, a small retrieval fee applies.
Either way, you are the installer who used real data. That is a differentiator no brochure claim can match.
Technical Integration Notes
Compatibility: Works with any grid configuration. Supports TN-C-S, TN-S, and TT earthing arrangements.
Data export: REST API and MQTT available for integration with your design or CRM tooling.
Cloud retention: With Shelly Premium, 1-minute data is retained for 12 months.
Expansion: The Pro 3EM can remain post-installation as the production and consumption monitoring device, feeding data to the inverter management system or a home energy management system (HEMS).
Summary
The Shelly Pro 3EM profiling bundle gives you a structured, repeatable process for converting uncertain prospects into well-specified projects. It reduces design risk, shortens the sales cycle, and positions you as a data-driven professional in a market full of rule-of-thumb estimators.