Quick Summary (TL;DR)
You can monitor an entire home in Home Assistant without sending electricity data to a manufacturer’s cloud. The most straightforward packaged choice for many single- or three-phase installations is a Shelly EM-family meter or Shelly Pro 3EM, using Home Assistant’s official local Shelly integration. For a wired, vendor-independent measurement path, choose a properly specified Modbus RTU electricity meterAliExpress price with a USB–RS485 adapter or a suitable locally managed Ethernet gateway. An ESPHome-based meter, particularly a purpose-designed metering board using an ATM90E32, provides more flexibility, but shifts calibration, electrical integration and maintenance responsibilities to you.
Local-first is not synonymous with outage-proof. A meter may measure while the internet is down yet lose Home Assistant history when your LAN, broker or server is unavailable. An on-device cumulative kWh counter, known reconnect behaviour, local buffering and reliable backups matter at least as much as protocol choice. Never assume a device with Ethernet or Wi-Fi exposes a local API: Emporia says its standard Vue products do not.
For most buyers, start by identifying the electrical measurement boundary (grid connection, solar feeder or separate circuits), the number of phases, and whether you need separate import and export energy counters. Ask your installer to confirm physical space, safe CT placement, wiring requirements and compliance before ordering. This is a buying and architecture guide, not a live-panel wiring tutorial.
What ‘without cloud’ actually means
Vendors and reviews use local, offline, no subscription and cloud-free as though they were the same specification. They are not. At least four independent questions determine whether your installation behaves as expected.
| Test | What you need to establish | Why it matters |
|---|---|---|
| Data path | Does the device send measurements directly to Home Assistant by supported LAN protocol, serial link or local broker? | Data should not have to pass through an account or external server. |
| Commissioning | Can the exact firmware be configured and reconfigured without an online account? | Some products may use cloud onboarding even if later local control is possible. |
| Outage behaviour | What keeps accumulating while the internet, Wi-Fi, gateway or Home Assistant is down? | A sensor returning after an outage does not prove that missing intervals were preserved. |
| Operational ownership | Can you update, back up, restore and replace the meter without relying on a vendor service? | Long-term reliability includes maintainability, not just today’s data feed. |
A local API means a documented or otherwise accessible interface on the device that a controller can query or subscribe to inside the property. Local broker means a service such as Mosquitto MQTT running on your own LAN. Locally hosted Home Assistant stores its recorder database on your own machine, subject to your backup and retention choices. It does not force every connected sensor to be local: the device integration still decides where the readings originate.
Three deployment patterns are worth distinguishing. LAN-local, vendor-supported describes the official Shelly-to-Home Assistant path. Protocol-based, locally polled describes a standard Modbus meter read via serial or network. Owner-managed firmware describes an ESPHome device you build and maintain. Community cloud integrations and reverse-engineered firmware are separate categories, even if somebody demonstrates them working offline.
The best hardware architectures at a glance
| Architecture | Typical equipment | Home Assistant data path | Strength | Limitation |
|---|---|---|---|---|
| Packaged local CT meter | Shelly Pro 3EM with compatible CTs | Official Shelly integration over local Ethernet/Wi-Fi | Practical three-phase whole-home installation; per-phase readings | Correct electrical installation, model-specific CTs and LAN health still matter |
| Packaged single-phase or two-channel CT monitor | Exact Shelly EM model suitable for the job | Official local Shelly integration | More focused measurement at one or two boundaries | Verify generation, channels and energy import/export capabilities for the SKU |
| Wired industrial-style meter | Modbus RTU Eastron/other documented model | RS485 to Home Assistant or Modbus gateway | No vendor cloud; documented registers; wired data | Integration work, bus termination, meter variant and register mapping |
| Owner-managed multi-channel meter | ESP32AliExpress price + ATM90E32-based metering hardware | ESPHome native API or local MQTT | Fine-grained circuits; firmware and calibration control | More design, testing, long-term support and safety assessment |
| Utility-meter local reader | Compatible P1/DSMR reader or local optical interface | Local UART/ESPHome/other protocol | Can reflect the utility meter’s measurement boundary | Only where meter and utility access actually support the reader |
| Cloud-managed multi-circuit monitor | Standard Emporia Vue | Vendor cloud and supported/community integration route | Multi-circuit view in its own ecosystem | Not an appropriate stock-firmware choice for a strict no-cloud requirement |
These are architectures, not a claim that every meter in each family has the same specifications. Verify the exact suffix, current rating, energy counter behaviour, regional approvals and firmware before purchase. A meter described merely as “Modbus” could be RS485 Modbus RTU, Modbus TCP, or a separate interface variant; M-Bus is not Modbus.
Option one: Shelly Pro 3EM as a locally integrated whole-home monitor
The Shelly Pro 3EM is a DIN-mounted, CT-operated three-phase energy meterAliExpress price with Ethernet and Wi-Fi connectivity. Shelly documents standalone operation on a local LAN and support for local mechanisms such as HTTP/RPC, WebSocket and MQTT; it also documents per-phase electrical values and accumulated energy. The device’s cloud capability is optional for this use case. The Home Assistant Shelly integration uses local communication, with generation 2 and newer Shelly devices using RPC; for an ordinary Pro 3EM installation you do not need to build an MQTT bridge just to read the meter. Shelly device documentation and Home Assistant’s Shelly integration detail those paths.
The Pro 3EM is a useful starting point when you have three-phase supply, a three-phase solar connection, or a desire to see each mains phase independently. It can also be used for supported single-phase applications according to the manufacturer’s diagrams; do not assume every installation topology or CT wiring arrangement is interchangeable. Shelly’s published material describes a 120 A-class per-phase configuration for a particular Pro 3EM product and a separate 3CT63 variant with different transformers. These are not generic CT inputs: the sensors must match the device and approved part number.
If your priority is one or two single-phase measurement points, inspect the exact Shelly EM-family product rather than paying for capacity you will not use. The names Shelly EM, Shelly EM Gen3 and Shelly Pro 3EM designate different hardware. Confirm the CT input count, supported clamp choices, whether the unit measures import/export separately and whether you need Ethernet rather than Wi-Fi.
A key trade-off is dependency versus observability. The Shelly may measure locally while the internet is absent, but your Home Assistant charts depend on successful delivery to its recorder and, where supported, on-device history and recovery logic. Shelly documents stored historical measurements for Pro 3EM; do not assume the official Home Assistant integration automatically backfills every missing minute after any outage. Test your exact firmware and integration if complete archival records are important.
Recommended local setup checklist
- Have a qualified electrician identify the grid boundary, phase conductors, meter mounting position, CT orientation and protective arrangements. Obtain the correct Shelly model and matching CT set.
- Connect the meter to a reliable LAN. Prefer Ethernet where the distribution board and installation instructions permit it. Allocate an IP address predictably, commonly via a router DHCP reservation.
- Commission the meter using the manufacturer’s local interface. Confirm real voltage and current values, sensible per-phase signed power, and cumulative energy counters before using them in automations.
- In Home Assistant, open Settings → Devices & services, add Shelly, and select or enter the device’s local address. Confirm that entities update while the WAN connection is unavailable.
- Locate suitable grid import and export kWh entities. Do not select a live W sensor as if it were accumulated kWh. Check whether the device or integration provides already-split import/export counters.
- Record the final settings, installed CT types, phase labels, firmware version and what happens during network and Home Assistant restarts.
A supported local RPC API is useful for diagnostics, but an elaborate custom polling script adds work without obvious benefit when Home Assistant’s official integration already exposes the needed measurements. Limit RPC access to trusted networks; do not open an unauthenticated meter interface to the public internet.
Option two: a wired Modbus electricity meter
A Modbus RTU meter on RS485 can remove Wi-Fi reliability concerns and avoid a vendor cloud. The meter reports values through a documented register map, while Home Assistant communicates through a USB–RS485 adapter, a supported serial device or an RS485-to-Ethernet gateway. The protocol is local by design, but the quality of integration depends on the meter’s registers, data types, byte order, polling interval and gateway configuration. Home Assistant offers a native Modbus integration and recommends checking for a suitable device-specific integration first.
For example, the Eastron SDM120/SDM630 family includes products commonly used in Home Assistant projects; some carry Modbus RTU interfaces, while other related variants differ in their communication options. SDM630-Modbus, SDM630MCT and SDM630 M-Bus should not be bought solely because their names look alike. A direct-connected meter and a CT-operated meter have different electrical installation requirements. Check the exact model’s manufacturer’s datasheet, register document and certifications.
A gateway may be Modbus TCP to RTU translating, or it may merely transport serial RTU frames over a TCP socket. Home Assistant treats these differently (tcp versus rtuovertcp or a serial connection); selecting the wrong type can produce timeouts even when the IP and port are reachable. The manufacturer’s documentation, not the gateway’s marketing label alone, must determine the setting.
What a Modbus purchasing list actually includes
| Component | Purpose | Decision to make before ordering |
|---|---|---|
| Meter | Measures voltage, current, active power and energy | Single-/three-phase; direct-connected/CT; import/export; documented register map |
| CTs, if required | Sense current at the relevant conductors | Correct ratio, physical aperture, polarity, output type and approved meter match |
| RS485 adapter or gateway | Carries data between meter and Home Assistant | USB compatibility or Ethernet gateway mode; supported isolation where appropriate |
| Cabling, protection and enclosure space | Makes a compliant permanent installation possible | Electrician to determine routing, termination, power supply and safety requirements |
| Local Home Assistant host | Polls and records sensors | Stable power, network access, Recorder configuration and backup |
| Documentation and commissioning time | Maps the meter registers to meaningful entities | Signed versus unsigned values, scaling, word order, counters and reset behaviour |
The cheapest meter on a listing is not necessarily the lowest-cost system. Installer labour, enclosure alterations, a certified meter where one is required, and a properly documented gateway can outweigh the hardware price difference. Equally, a documented local register interface can make the system less dependent on the original vendor’s cloud policy over time.
Why you should not copy arbitrary Modbus register YAML
Modbus sensor examples online are often specific to one model and firmware. A 32-bit floating-point power register cannot be copied to a different meter with a 16-bit scaled integer register. Even when the register number matches, the address notation can be zero-based or one-based, and the values may be in W, kW, Wh or kWh. Sign convention for import/export may differ. Use the exact manufacturer’s table, verify with a known normal load, and inspect plausible minimum and maximum readings before adding anything to the Energy dashboard.
For additional site-specific context, see our existing ESP32 Modbus energy-meter guide and our energy-monitoring methods comparison. These articles focus on implementations; this guide focuses on removing cloud dependencies from the entire system.
Option three: ESPHome and an open metering board
An ESP32AliExpress price running ESPHome can expose readings to Home Assistant over the local ESPHome native API without a cloud account. A board built around the ATM90E32 can provide multiple CT channels and, where the hardware implements the required voltage measurement, active power and directional energy data. The official ESPHome ATM90E32 component documentation covers supported parameters, phase association, current and voltage calibration, and forward/reverse energy measurements.
This is attractive for owners who need several circuits, want to retain their own configuration, or already maintain ESPHome nodes. It is not equivalent to clipping a bare sensor onto a wire and expecting a calibrated kWh meter. True active-power measurement requires a suitable voltage reference and correct phase relationship. A current reading multiplied by an assumed constant voltage is only an approximation and may be especially misleading for poor-power-factor loads, variable voltage or mixed-phase circuits.
Use a purpose-designed, appropriately insulated metering board with documented electrical design and enclosure provisions. DIY sensors that share or derive a reference from mains require a competent safety assessment. Avoid improvised mains interfaces, exposed high-voltage modules, and unsupported CT wiring inside a live consumer unit. A qualified person must handle anything involving the distribution board.
ESPHome advantages and responsibilities
| You gain | You also take responsibility for |
|---|---|
| Device configuration and local API | Keeping firmware, board pinout and YAML compatible |
| More channel layouts on suitable boards | Correct CT/voltage pairing and safe signal wiring |
| Ability to add local logic | Confirming the logic behaves sensibly on reboot |
| Integration without vendor account | Reliable power, network placement and encryption keys |
| Access to source configuration | Calibrating measurements against a suitable reference meter |
For the majority of homeowners buying a one-off whole-house monitor, a packaged locally supported meter is easier to maintain. ESPHome becomes much more compelling when custom channels or integration logic are the real requirements, not merely because it uses an ESP32AliExpress price.
Our ESP32 CT clamp energy monitor guide gives useful implementation background; the official ESPHome documentation remains the authority for current configuration details.
What about Emporia Vue, cloud-to-local firmware and community integrations?
The standard Emporia Vue is a capable multi-circuit monitoring concept, but it is the wrong default recommendation for a buyer whose non-negotiable rule is no vendor cloud. In its March 2026 developer-access guidance, Emporia states that its products, including Vue monitors, do not provide direct local device data access and that all standard device data flows through its cloud. The vendor also describes its cloud architecture in its own how Vue works documentation. Emporia’s developer-access statement is a better source than assumptions based on the presence of Ethernet or integrations marketed as real-time.
You may encounter community Home Assistant integrations which query a cloud account, and third-party projects which replace or modify firmware on certain hardware revisions. Neither makes the stock device a manufacturer-supported local API product. Flashing hardware may bring loss of warranty, safety issues, incompatible revisions, reduced features and difficult recovery; do not base a consumer recommendation on it unless you have verified the exact hardware, project support and risks. Cloud integrations are valid choices when remote convenience is the priority, but that is a different design objective.
The same scrutiny applies to smart meters marketed with a local dashboard that actually depends on an external login. Check whether raw instantaneous data, energy counters, configuration and historical data are separately accessible without WAN, rather than accepting a broad “works locally” claim.
Prefer Ethernet, RS485 or Wi-Fi?
Ethernet: fewer radio uncertainties
For a fixed distribution-board installation, Ethernet can be the sensible preference if the device provides a genuine local service and the cabling can be routed safely. It avoids signal attenuation around metal enclosures and reduces reliance on a congested 2.4 GHz network. It does not protect against a failed router, switch, local power supply or DHCP problem. Keep the energy meter on a trusted local subnet reachable from Home Assistant; restrict unneeded outbound traffic only after you have established that commissioning, time synchronisation and local integration continue to function.
RS485: useful where physical determinism matters
RS485 is robust for properly engineered wired multidrop installations. It is not Ethernet, and it is not a substitute for proper bus design. Addressing, cable characteristics, topology, bus bias/termination where specified, electrical isolation, grounding strategy and gateway mode all matter. Leave electrical installation and any wiring inside a distribution board to a qualified installer. Where long-term operational independence is paramount, a well-documented meter and standard register map can remain maintainable even if a manufacturer’s app disappears.
Wi-Fi: often sufficient if you test it
A strong and stable 2.4 GHz signal can be adequate for a Shelly or ESPHome energy monitor. Survey signal strength at the proposed installed location, not merely in the hallway. Avoid building your only measurement path around a flaky connection. Reserve stable addresses, keep mDNS or relevant discovery traffic possible on the required segments, and confirm that inter-VLAN policies permit actual device-to-controller traffic. Discovery failure is different from data-path failure: many integrations can be set up manually by IP even when discovery broadcasts cannot traverse subnets.
A local-first reference architecture
An uncomplicated architecture looks like this:
Electrical grid boundary → CTs or metering terminals → local meter → Ethernet/RS485/Wi-Fi → Home Assistant → local Recorder database → dashboard and automations.
Optional additions include a local MQTT broker where the chosen device requires it, a small UPS for the router and Home Assistant host, a separate local storage/backup destination, and a secure remote-access mechanism such as a VPN. Those components should be budgeted, but MQTT is not compulsory. For Shelly Pro 3EM, the built-in Shelly integration is typically the cleaner route. For Modbus, use an appropriate integration or register mapping. For ESPHome, use its native API where possible.
What must survive each type of outage?
| Failure | Meter reading | Home Assistant history | What to verify |
|---|---|---|---|
| WAN/internet connection fails | Should continue for genuine local meter | Should continue if LAN/server are healthy | Cloud access really is unnecessary for runtime |
| Wi-Fi AP or Ethernet switch fails | Local device may keep measuring | Live updates stop until path returns | Which counters persist and whether gaps can be recovered |
| Home Assistant reboots | Meter can often keep measuring | Recorder has a gap unless later reconstructed | Persistent cumulative counters, reset and restore semantics |
| MQTT broker fails | Device-dependent | MQTT entities can become unavailable | Broker restart, birth/discovery and retained data design |
| Power cuts to meter | Measurement stops | No energy is measured during meter outage | Whether device restores or resets lifetime kWh counters |
| Router/NTP unavailable | Local measurement may continue | Timeline and timestamps may be impaired | Timekeeping and history timestamps after reconnection |
Offline test: after commissioning, record the live power and cumulative energy; disconnect only the internet uplink, not the LAN, for a controlled test; keep a known load running; confirm the values continue updating locally. Restore the uplink. In a separate, supervised test, restart Home Assistant and inspect whether its cumulative counters and historical trends resume correctly. Never disable safety systems or interrupt power to critical appliances just to test an energy dashboard.
Energy boundaries: the mistake that ruins otherwise good local installations
A measurement can be fully local yet wrong for the user’s purpose. Decide whether the CTs or meter are measuring the utility grid connection, home loads, solar inverter feeder, battery inverter, or a named circuit. A utility-grid sensor should distinguish electricity imported from and exported to the grid. A solar inverter’s total generation reading is not automatically a grid-export reading, because some PV energy is consumed immediately by household loads.
For a simple home with solar and no battery, one instant might show 4.0 kW solar output, 2.5 kW household demand, and 1.5 kW grid export. The solar has generated 4.0 kW, but the grid meter shows export of just 1.5 kW. If you instead feed a solar power sensor into the grid-export field, your Home Assistant Energy dashboard will be misleading. With a battery and multiple inverters, pay close attention to the separate charge/discharge paths, sign conventions and double-counting across meter boundaries.
Three-phase systems need another decision. The house can import on one phase and export on another at the same instant. A meter and tariff may use an algebraic net total or separate per-phase import/export accounting. Use the device’s documented energy counters and confirm local metering conventions with the supplier; do not blindly add absolute values or reuse a CT channel intended for a separate load as a second copy of grid consumption.
| Entity | Typical unit | Home Assistant expectation | Common wrong substitute |
|---|---|---|---|
| Instantaneous grid power | W or kW, often signed | device_class: power, typically state_class: measurement |
Lifetime kWh counter |
| Grid imported energy | kWh cumulative | device_class: energy, state_class: total or total_increasing as appropriate |
House total consumption or unseparated signed net power |
| Grid exported energy | kWh cumulative | Distinct export entity with proper semantics | Total solar production |
| Solar generated energy | kWh cumulative | Inverter or metering counter at generation boundary | Export-only grid counter |
| Battery charging/discharging | kWh counters where supported | Separate charge/discharge flows according to HA dashboard needs | State-of-charge percentage |
| Appliance monitoring | W plus cumulative kWh | Individual device, without counting it a second time as grid import | Adding all appliance readings to grid-total reading |
For the dashboard setup itself, see Home Assistant’s official electricity-grid setup guide and energy FAQ. The site’s existing Energy Dashboard troubleshooting guide covers common missing-entity and statistics problems.
Data retention: a cumulative counter is essential, but not magic
A W reading is a snapshot of current power. A kWh reading is accumulated energy. Home Assistant may calculate energy from sufficiently frequent power readings using integration, but if the recorder missed data during an outage, a simple power-to-energy integration can undercount the missing interval. A meter that maintains a durable, cumulative import/export counter is generally a better foundation. When Home Assistant reconnects, it can observe the counter increase over the gap, subject to the semantics of the integration and its statistics handling.
There are limits: the late arrival of a total does not reconstruct the exact time pattern of energy used during the outage. A reset counter may be misinterpreted if its state_class is wrong. A firmware upgrade that changes units, naming or scale can corrupt statistics. If detailed historic load profiles are important, prefer a meter with retrievable timestamped history and verify that your chosen collector actually imports it, not merely that the manufacturer advertises local storage.
Home Assistant’s recorder and long-term statistics are local capabilities, but still require consistent sensor states and a backed-up database. Check Recorder exclusions, disk free space, database backups, and whether the device supports native cumulative counters. Define your required granularity: monthly billing estimates are easier to preserve than a second-by-second load-tracing archive.
What should you back up?
Keep a record of the exact meter model and firmware, CT part numbers and ratio, electrician’s circuit/phase labels, Modbus register documentation, static IP or DHCP reservation, Home Assistant integration configuration, ESPHome YAML if relevant, MQTT topics if used, and any calibration records. Store backups on a separate device and test restoration. Local-first should make the installation easier to recover, not simply shift the dependency from a cloud account to one unbacked-up SD card.
Total installed cost: compare systems, not shelf prices
Price quotations change by country and time, so a defensible comparison is a bill of materials and work, not a made-up “typical installed price”. A Shelly Pro 3EM needs the correct CT set and electrical commissioning; a Modbus meter may need RS485 hardware and integration time; an ESPHome build can demand an enclosure, power supply, metering board, CTs, calibration equipment and maintenance. Where the board lacks safe DIN-rail integration, its low component price can be particularly misleading.
| Cost category | Shelly local meter | Modbus meter | ESPHome multi-circuit meter |
|---|---|---|---|
| Core device | Branded energy meter; verify included CTs | Direct/CT model, exact Modbus variant | Controller + metering board + compatible sensors |
| Installation | Approved panel mounting and CT installation | Panel wiring, protection, bus connection | Safe enclosure design, power and sensor installation |
| Communications | Existing LAN/Wi-Fi, perhaps Ethernet cabling | USB–RS485 adapter or network gateway | Local Wi-Fi/Ethernet and ESPHome maintenance |
| Calibration and checking | Verify phase/CT assignment, sign and reference readings | Verify scaling/registers, phase wiring and accuracy | More extensive reference calibration likely |
| Long-term software | Firmware and official integration compatibility | Register mapping, gateway replacement and Home Assistant | ESPHome configuration, board support and updates |
| Service and subscriptions | No vendor subscription needed for stated local path | No vendor subscription needed for standard local Modbus | No vendor subscription needed for local API |
Get a line-item quotation from a qualified electrician, especially for three-phase boards or solar/battery systems. In the UK, Ireland and EU, ask for the relevant equipment ratings, declarations and any metering approvals that apply to the intended purpose. MID certification can matter for regulated or contractual submetering, but a general Home Assistant hobby meter does not automatically become a billing-approved meter. Do not assume that any product can replace your utility’s sealed revenue meter.
Buying recommendations for five real situations
A normal household with a three-phase supply
Choose a suitable Shelly Pro 3EM if the specified device, CT set and board layout are compatible. It is a practical packaged option with official local Home Assistant support and Ethernet. Consider documented RS485 Modbus when your network architecture or preference favours wired industrial protocols. An electrician should validate panel space, the correct mains measurement boundary and the proposed CT placement.
A single-phase home that wants only grid import/export
Compare a correctly sized Shelly EM-family meter with an appropriate Modbus single-phase meter. You probably do not need a large multi-channel build. Confirm whether the meter’s local API exposes the required cumulative import/export readings and whether the sensor arrangement fits the conductor size. If a compatible P1-style port is already available on the country’s utility meter, that can be an elegant alternative because it reads near the billing boundary; check access conditions and supported standard first.
A home with 10–20 circuits to analyse
A purpose-designed multi-channel ESPHome metering board or a properly documented multi-circuit local commercial platform may be justified. Budget for installation time and channel calibration, not just CTs. Decide whether your aim is monitoring selected circuits or ensuring they reconcile to the grid total. Avoid using a cloud-centric multi-circuit device if strict offline operation is required; likewise, don’t assume a single three-channel meter can directly provide sixteen independently measured circuits.
A solar-equipped house with batteries and EV charging
Start with grid import/export quality and sign conventions, then separately integrate the solar inverter and battery where an official local integration exists. If you will automate an EV charger, confirm whether its fail-safe local load-balancing functionality exists independently of Home Assistant. Energy monitoring is observability; it is not a substitute for the charger’s own protective and regulatory controls. Three-phase PV/net-metering arrangements need special care so per-phase totals are interpreted correctly.
A privacy-oriented installation with no permanent internet
Prefer a documented RS485 Modbus meter or a manufacturer-supported local Shelly installation, after verifying the exact unit can be provisioned and recovered without vendor service. Use a locally hosted Home Assistant host with local backups. Do a controlled WAN-disconnection acceptance test before committing. If you are willing to maintain firmware, ESPHome can be a strong owner-managed option. Do not select an Emporia Vue on stock firmware expecting it to become cloud-free merely because a community project mentions Home Assistant.
Twelve-point pre-purchase checklist
- Identify grid, solar, battery and circuit measurement boundaries on the electrical single-line diagram.
- Confirm whether your supply is single-phase, split-phase or three-phase, and what the meter supports in your country.
- Calculate realistic maximum current by phase and select compatible rated CTs or direct-connected equipment.
- Confirm local read access to live power and cumulative kWh, not merely app display access.
- Verify how import and export are represented, including sign convention and phase aggregation.
- Read the exact hardware’s data sheet, firmware notes and integration documentation.
- Verify whether commissioning, device restarts and firmware recovery work without cloud login.
- Check Ethernet/Wi-Fi coverage or RS485/USB gateway support at the actual installed location.
- Ask what happens to counters and timestamped history when Home Assistant is down.
- Confirm local legal/electrical compliance, enclosure space and who will carry out the installation.
- Budget for CTs, gateway, cabling, labour, host storage, UPS if justified, and backups.
- Run an acceptance test before depending on the system for tariffs, automations or reporting.
Common questions
Will a Shelly Pro 3EM still measure if the internet is disconnected?
The manufacturer documents local LAN operation, and Home Assistant’s Shelly integration communicates locally. In a properly commissioned local configuration, loss of the WAN should not require the measurements to transit a cloud service. Your exact firmware, network settings, clock behaviour and recorder’s available history still deserve an offline test.
Is Modbus faster or more accurate than Shelly?
Not inherently. Modbus describes a communications protocol, not the metering chip’s measurement accuracy. A poor meter does not become accurate because it uses RS485. The effective freshness depends on device sampling, register updating, polling and network design; accuracy depends on meter specification, correct sensors, calibration and installation.
Can I use a bare ESP32 and a single CT clamp to measure kWh accurately?
A bare ESP32 does not constitute a calibrated electricity meter. Current alone cannot reliably determine active energy for arbitrary loads. You need a suitably designed and safe voltage/current sensing approach, phase information, metering computation and reference calibration. For grid-level use, favour proper certified equipment and qualified installation.
Do I need MQTT for offline monitoring?
No. The official Shelly integration and ESPHome native API can run without an MQTT broker; Modbus can connect directly to Home Assistant over a serial adapter or documented network interface. Use a local broker when it offers a real benefit for the actual devices, not as an assumed compulsory layer.
Can a local monitor replace my utility electricity meter?
Ordinarily no. A home energy monitor is valuable for insight and automation, but the utility’s approved/sealed meter remains the billing authority unless a regulated arrangement expressly says otherwise. Compare your totals over meaningful periods and investigate differences in phase aggregation, timing, calibration or load boundaries.
Is an on-device history buffer the same as Home Assistant backfilling?
No. A device might keep samples internally yet an integration may resume from current readings without importing the missing individual intervals. Persistent cumulative counters help with energy totals but do not guarantee complete minute-by-minute historical reconstruction.
Final recommendation
For a homeowner who wants local Home Assistant monitoring with the least custom engineering, start with a suitable Shelly EM-family meter or Shelly Pro 3EM, depending on phase count and measurement points, because the official local integration and device documentation reduce integration risk. For wired, system-independent monitoring, prioritise a correctly specified Modbus RTU meter with published registers and an appropriately configured adapter or gateway. Choose ESPHome plus metering hardware when multi-channel design control genuinely justifies the extra commissioning and maintenance workload.
The decisive tests are not marketing badges or protocol names. They are whether the correct boundary is metered, whether genuine cumulative import/export energy is available over a supported local path, how the system behaves when pieces go offline, and whether you can maintain it ten years from now. Install safely, validate the data, keep backups and let the dashboard reflect the actual electrical system rather than an assumption about it.
Sources and further reading
- Shelly — Pro 3EM technical knowledge base — supported local operation, electrical interfaces and measured values.
- Home Assistant — Shelly integration — official local integration and RPC data update mechanisms.
- Home Assistant — Modbus integration — RTU versus TCP, gateways and register configuration.
- ESPHome — ATM90E32 power sensor — board-specific measurement and calibration guidance.
- Home Assistant — ESPHome integration — native local communications.
- Home Assistant — electricity grid energy setup — energy entity and meter-boundary expectations.
- Home Assistant — Energy Dashboard FAQ — sensor attributes and troubleshooting.
- Home Assistant — long-term statistics — recorder and energy-history behaviour.
- Emporia — developer access and future integrations — manufacturer’s current position on local access.
- Emporia — how Vue works — standard Vue’s cloud data path.
Editorial note (October 2026): This article is based on published manufacturer and platform documentation, not claimed independent laboratory testing. Regional hardware versions, firmware features, certification, commissioning requirements and service availability can change. Verify the exact part number and current documentation before purchase or installation. No retailer quotes, savings claims or affiliate URLs have been invented.