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NFE metering strategy + Glen STREET-EMS (overview)

Purpose

Orient the team on NFE's metering + behind-the-meter control strategy: where it came from, what runs today, and Glen's custom open-hardware "STREET-EMS" that is the next step. Compiled 2026-08-09 from the BOM sheet, the July 25 and June 2 check-ins, and the meter evaluation. Sections marked (to confirm with Glen) are inferred from the BOM/one-line diagram and need his sign-off before they are treated as design.

The evolution (three generations)

  1. Calin / Kalin Chinese prepaid meters (early pilot). Claimed prepaid + postpaid, but the vendor did not expose meter data directly: you had to go through their proprietary cloud middleware API. That caused reliability issues, token-lockout problems (needing overseas tokens just to unlock a customer's meter), slow support, and MOQ pressure. Abandoned.

  2. CHINT DDSU666 postpaid meters (current, since March 2026). Locally sourced, postpaid-only, expose data directly via RS-485 / Modbus into a Raspberry Pi (the pi2 logger), internet via modem. This removed the vendor dependency and the token risk, and gave direct data. An OpenEMS plugin reads the meter usage in real time. The meters are physically clustered in one PDU, so wired connectivity is practical for this dense, apartment-style site (would not suit dispersed rural). This is what feeds billing today.

  3. Custom "STREET-EMS" (Glen's build, in procurement). Instead of buying meters that only measure, build an open-hardware unit that meters AND controls each customer, integrated with OpenEMS. This is the next generation.

Division of labour (agreed direction)

  • OpenEMS = monitoring: meters, battery/inverter, solar. (Already has the meter plugin.)
  • MPM (EnAccess) or the NFE billing engine (MBE) = business: billing cycles, invoicing, payment links, customer/account management.
  • The edge meter/EMS = measure + control at the point of supply. The principle from the EnAccess call: integrate, don't rebuild. Battery/solar data that affects billing is the gray area to model carefully.

Glen's STREET-EMS (to confirm with Glen)

A cabinet-mounted, multi-tenant meter + controller. From the BOM + the July 25 one-line diagram review (multi-channel metering, residual-current monitoring, relays/contactors, EV charging):

  • Metering core: CircuitSetup Expandable 6-Channel ESP32 Energy Meter (main + add-on boards), ATM90E32-based, CT current sensors per tenant/phase + voltage reference. Open hardware (ESPHome/Arduino).
  • Controller: ESP32-S3 / ESP32-P4 on a custom 9x15cm EMS PCB, with RS485 (isolated + non-isolated), SD card, Ethernet (Wiznet W5500), 18650 battery backup.
  • Per-tenant control: RCBO Type-A breakers + modular contactors + 8-channel SSRs for remote connect/disconnect (postpaid enforcement); phase-transfer contactors.
  • Safety: residual-current monitoring (RCM/RCB) with leakage-sensor CTs per phase.
  • EV charging: Etek EVSE charge controllers (Type 2, 32A, Mode 3) + Type 2 cable.
  • Enclosure: FRP/NEMA-4X IP66 cabinets. Custom power-supply PCBs (Myrra 230->9V, XP Power / HiLink 5V).
  • Sizing: each cabinet serves ~3 tenants equipped, wired for up to 9, 3-phase.

Net: a ~$100/EMS open unit that meters each customer, can disconnect them for non-payment, adds EV charging, and speaks Modbus/Ethernet to the NFE stack, replacing per-unit commercial smart meters.

Procurement (from the BOM sheet)

  • Total ~$2,377 for the first batch. Ordering waves: Aug 7 = 5 EMS + 1 cabinet (3 tenants, 3-phase, ready for 9); Aug 14-21 = 10 EMS + 2 cabinets.
  • Logistics split: China-side items ship AliExpress -> Kenya (Nairobi); small PCB parts hand-carried by Glen, who arrives ~4 days early and prebuilds the 3-phase PSUs on site. Albert places the orders.

Open questions / actions (from July 25 check-in)

  • Finish the Kenyan smart-meter provider investigation (pricing, product, contact) - build-vs-buy is still an open comparison against Glen's custom unit.
  • Review the one-line diagram legend + component labels (clarify RCM vs RCB, feeder labels, meter-channel assignments); send consolidated questions to Aaron for the designer.
  • Nansana field issue: cable heating under inverter/EV load - schedule on-site tests, collect temperature data (temperature gun).
  • Grant/partner work: GreenVoter / Regenerate Africa panels; Women-in-Business grant (needs company-ownership legal change).
  • Power Africa 2026 workshop participation (sponsorship, travel, equipment shipping; possible Kigali follow-up).

Gap

Glen's detailed design (the one-line diagram, channel map, firmware behaviour) is NOT yet written up here - the "Behind the Meter Connection" page is empty. This overview should be confirmed with Glen and expanded into a real design page (schematic, channel assignments, firmware, OpenEMS integration).

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