Solar inverter and battery monitoring over a SIM: why the link drops and what to check
A monitoring dongle that shows offline does not always mean the inverter has a fault. This guide sets out what manufacturers' documents say about SIMs, signal and settings, what Eir's 3G switch-off changes, and what to check before you replace anything.
Why monitoring links drop out
Some solar and battery monitoring runs through a small cellular dongle or logger fitted to or beside the inverter. The manufacturers' documents cited here point to a handful of common causes.
- Weak signal at the unit. Victron's installation notes say to place its modem where metal objects do not cover it, and suggest the optional outdoor antenna if the unit sits in a closed metal enclosure. Its troubleshooting table gives one signal bar as the minimum for portal logging [1]. Huawei's dongle guide has a flashing red code for no signal, weak signal or no traffic [2].
- A data plan that has ended. Some dongles come with a fixed-term plan. One GivEnergy 4G dongle is listed with a one-year data plan [3]. Huawei's guide says to check the SIM's tariff and traffic [2].
- Wrong settings. Victron lists an unset APN as one reason a modem registers on a network but does not go online [1]. Huawei ties a dialling light that lasts over a minute to wrong 4G parameters [2].
- Another connection taking priority. GivEnergy's AECC dongle tries a cable first, then Wi-Fi, and calls 4G a fallback only [4]. Victron says its cellular link ranks below Ethernet and Wi-Fi, even when those links are poor or have no internet [1].
A lost link is not always a lost system
SEAI's Code of Practice for domestic solar PV installers requires the inverter to show generation by day, week, month and year. The display can be the inverter's own screen, a web portal, an app or a remote display in the home. That display must give the homeowner a simple indication when the system is not working normally or has failed [5]. So look at the inverter before assuming the array has stopped. If the portal is the only display, a lost link also means a lost warning. That is the practical reason to keep it connected.
Export payments are a separate question from monitoring. ESB Networks says you need a smart meter to be paid for the excess electricity you export, and that the meter records exports [6]. If you are unsure how your export is metered or paid, ask your electricity supplier.
What is changing on Irish networks
- Eir: 3G is being switched off in phases from 1 October 2026, starting in Donegal. GoMo and Lyca Mobile use Eir's network, so their 3G services go too [7]. ComReg's notice of the change says Eir plans to contact customers directly who use 3G-only services, and that for customers with a 4G or 5G-enabled smartphone or device the change is not likely to affect them [8]. A SIM bundled with a dongle may not be in the owner's name, so check rather than wait for a letter.
- Vodafone: switched off its 3G network in October 2024. ComReg says Clear Mobile and An Post use the Vodafone network, so their 3G services are retired too [7].
- Three Ireland: none of the pages used here gives a date, so ask the SIM provider rather than assume.
- ComReg's equipment list includes security and fire alarms, GPS trackers, automated electric gates and heating systems. It does not name solar inverters, batteries or monitoring dongles [7]. That is not proof that none are affected. It means you should check the radio in yours.
What manufacturers' documents say
Models differ a lot. These are examples from the documents cited. Always check the manual for your exact model and region.
| Product | SIM format | Radios stated | Worth knowing |
|---|---|---|---|
| Victron GX GSM | Not stated on the page used | 2G and 3G only | Victron describes it as working on 2G and 3G only, networks it says are slowly being phased out in different countries, and names the GX LTE 4G as its replacement [9] |
| Victron GX LTE 4G | Mini-SIM | 2G, 3G and 4G | APN is set on the connected GX device, only if needed [1] |
| Huawei SmartDongle-4G, EU variant | Mini-SIM | LTE and GSM bands listed; WCDMA not listed | Other regional variants do list WCDMA, so the model code matters [10] |
| SolarEdge Cellular Plug-in (version 1.0 guide, 2019) | Nano SIM | LTE Cat M1 bands listed | Non-SolarEdge SIMs need a minimum inverter firmware version. Check the guide for your region [11] |
| GivEnergy 4G dongle (retailer listing) | Micro SIM | Not stated on the listing | Sold with a one-year data plan, for sites without broadband [3] |
SIM size, APN, PIN and data
- Format and APN. The table shows Mini, Micro and Nano SIMs in use, so check before you order. Victron's manual says some networks need the APN set by hand, especially when roaming [1]. Not every device exposes that setting, so ask the manufacturer first.
- PIN. Victron says a SIM with its PIN disabled works without further setup. Its SIM status list shows “PIN required” when a SIM needs a PIN to unlock [1]. Check for a PIN lock early.
- Data. Monitoring uses little data, but not none. Huawei's guide for its SDongleA-03 4G dongle gives a monthly traffic requirement of 10 MB plus 4 MB per inverter, with small additions for optimisers and power sensors [2]. SolarEdge's guide says its plug-in stays connected and sends the data collected since the last upload every 5 minutes [11]. Look up the figure for your model.
What a multi-network SIM changes
SimFalcon's Irish solar page lists multi-network connectivity as useful for rural rooftops, farm buildings and remote energy sites where one network may be weak, subject to coverage and device capability. It also lists, as a benefit, avoiding lost telemetry when the customer changes broadband provider, Wi-Fi password or router [12]. That is useful, but it has limits.
- It cannot add a radio. A modem that supports only 2G and 3G stays that way, whatever SIM is in it.
- It cannot fix settings. APN, PIN, SIM size and firmware limits still depend on the device. SimFalcon says compatibility depends on the exact model and communications hardware, and asks for the exact inverter, logger or router model before ordering [12].
- Billing. SimFalcon's pricing page says standard plans are billed annually, and qualifying business-volume accounts may be billed monthly, so there are no pay-as-you-go top-up expiry issues [13]. That avoids one possible cause of dropout, a pay-as-you-go SIM whose credit has expired. It does nothing for the other causes above.
Check this before you replace anything
- Look at the inverter's own display or lights. Is it generating, with only the monitoring link down?
- Find the dongle's exact model and region code. Read its manual for the radios it supports. If it supports only 2G and 3G, ask the manufacturer about a 4G model. A new SIM will not add a radio.
- Check whether a bundled plan has ended or a pay-as-you-go SIM has run out.
- Check the SIM is seated, the right size and not PIN-locked. Then read the status page or light code. SolarEdge's guide lists separate messages for a missing SIM, no signal, activation or data-plan settings, and server connection failures [11].
- Check signal where the antenna actually is, not in the house. Try moving the antenna before changing hardware.
- Check which connection the device prefers. On some devices, a poor or dead Wi-Fi or cable link can stop the cellular one being used [1].
- Only then ask the manufacturer or installer about an update or a 4G replacement. Write down what you found.
For the basics, see SIM not connecting, APN setup and weak or no network. The solar monitoring SIM page lists what to send us so we can check a model, and pricing shows the plans. SimFalcon sells IoT SIMs, so read the points attributed to SimFalcon as ours, and everything else as taken from the source listed, which is a manufacturer, regulator or operator or, where the entry says so, a retailer's page hosting a manufacturer document.
Sources
- [1] GX LTE 4G manual, rev 04 (09/2024), Victron Energy. Checked 3 October 2026.
- [2] SDongleA-03 Quick Guide (4G), issue 08, 30 September 2019, Huawei (copy hosted by Europe Solar Store). Checked 3 October 2026.
- [3] GivEnergy 4G Mobile Internet Dongle with 1 Year Data Plan, Segen. Checked 3 October 2026.
- [4] AECC dongle setup guide, GivEnergy. Checked 3 October 2026.
- [5] Domestic Solar Photovoltaic: Code of Practice for Installers, version 2.0 (March 2025), Sustainable Energy Authority of Ireland. Checked 3 October 2026.
- [6] Smart meters, ESB Networks. Checked 3 October 2026.
- [7] 3G retirement, ComReg. Checked 3 October 2026.
- [8] Eir 3G switch-off from October (20 August 2026), ComReg. Checked 3 October 2026.
- [9] GX GSM manual: introduction, Victron Energy. Checked 3 October 2026.
- [10] Smart Dongle-4G specifications, Huawei. Checked 3 October 2026.
- [11] Cellular Plug-in Installation Guide with SetApp, version 1.0 (August 2019), SolarEdge (copy hosted by Rexel). Checked 3 October 2026.
- [12] Solar Monitoring SIM Cards for Inverters, Batteries & Remote PV Sites (Ireland page), SimFalcon. Checked 3 October 2026.
- [13] Multi-Network IoT SIM Pricing (Ireland), SimFalcon. Checked 3 October 2026.
Frequently asked questions
Will the Eir 3G switch-off stop my solar monitoring?
It could, if your dongle or logger can connect on 3G only and its SIM uses the Eir network. ComReg's equipment list does not name solar monitoring, so check the radios in your model's manual. ComReg's notice on the Eir change says that for customers with a 4G or 5G-enabled smartphone or device, the change is not likely to affect them.
Does a lost monitoring link mean the inverter has stopped generating?
Not necessarily. The link and the generating hardware are separate parts, so a dropped link does not by itself show a generation fault. Check the inverter's own display or lights. SEAI's installer code allows the display to be the inverter screen, a web portal, an app or a remote display in the home, so if you only have a portal, you will need to check how else your system shows a fault.
Can a new SIM add 4G to a dongle that only supports 2G and 3G?
No. A SIM cannot add a radio the device does not have. Victron says its 2G and 3G-only GX GSM modem has been replaced by a 4G model, and notes that 2G and 3G are slowly being phased out in different countries.
What size SIM does a solar dongle take?
It depends on the model. The documents cited list Mini-SIM for Victron's GX LTE 4G and Huawei's SmartDongle-4G, Micro for one GivEnergy dongle listing and Nano for the SolarEdge plug-in. Check your manual.
Does a multi-network SIM work with any inverter?
Not automatically. SimFalcon says compatibility depends on the exact model and communications hardware, and asks for the exact inverter, logger or router model before ordering.
Questions about connectivity for your equipment? Talk to SimFalcon or ask Engineer Support.