Off-grid power is usually discussed as a product question — which generator, which panel, which battery. It is more useful to treat it as an architecture question, because the same architecture turns out to serve a surprisingly wide range of duties, and the differences between those duties are mostly numbers rather than concepts.
This article sets out that architecture, then walks through seven applications where it is doing real work, with the load profiles and configurations that go with each. It is written from the standards, the physics and published manufacturer data. Where a figure comes from a manufacturer datasheet, it is attributed.
The problem, stated properly
A great deal of industrial equipment draws very little power and sits a long way from a supply. A camera and its radio link might average 15 W. A pipeline RTU with a transmitter might average 8 W. A water-level station with a satellite uplink might average 25 W. A digital radio repeater might average 60 W.
These are small numbers. The difficulty is not the wattage — it is the product of wattage and time with nobody present. Fifteen watts for a year is 131 kWh. Getting 131 kWh to a hilltop with no road is an entirely different engineering problem from supplying 15 W in a building.
Three conventional answers exist, and each has a characteristic failure:
- A small diesel or petrol generator has ample power but must be refuelled every few days, serviced on engine hours, silenced, and defended against theft. Its availability is governed by whoever last visited.
- Solar alone is maintenance-free until it is not. Because it must be sized for the worst consecutive stretch of low irradiance in the year, and because in Thailand that stretch is a monsoon week or more, the array and the battery bank are both sized by an event that occurs once a year. The result is a large, heavy, expensive installation that is oversized for 51 weeks.
- Batteries alone convert an energy problem into a logistics problem: a vehicle, a driver, a lifting operation and a swap cycle that never ends.
The hybrid architecture
The fourth answer keeps the parts that work and deletes the part that does not. A battery carries the load, because batteries are excellent at delivering small power continuously. A solar array charges that battery whenever there is sun, because solar energy is free. And a fuel cell charges the battery whenever the solar array cannot — because the one thing solar cannot do is guarantee a floor.
The critical move is that the fuel cell is a battery charger, not a power source in the circuit. It is asleep almost all of the time. It wakes on battery voltage, runs at its rated output until the battery is charged, and stops. This is why the architecture changes the sizing arithmetic so completely:
- the solar array is sized for a typical week rather than the worst week
- the battery is sized for a night plus a margin, not for a fortnight of cloud
- the fuel cell is sized for average load rather than peak load, because the battery absorbs the peaks
- the fuel is sized for the number of unattended days required
Each of those four is a smaller, cheaper component than it would be in a single-source design. That is the whole economic case, and it holds regardless of which segment the site belongs to.
Why methanol occupies this band
At this power level the choice of fuel is decided by energy density and by handling. Published comparative figures from SFC Energy, for the mass and volume needed to deliver the same energy:
| Store | Mass | Volume |
|---|---|---|
| Methanol, direct-methanol fuel cell | 8.5 kg | 10 l |
| Propane, solid-oxide fuel cell | approx. 27 kg | 7.5 l |
| Hydrogen, PEM fuel cell | approx. 70 kg | 60 l |
| LiFePO4 battery | 100 kg | 12 l |
| Lead-acid battery | 270 kg | 140 l |
Source: SFC Energy AG industry presentation.
Methanol is a liquid at ambient conditions. It requires no compression, no pressure vessel and no cryogenic handling, and a sealed cartridge has an indefinite shelf life. Hydrogen wins decisively higher up the power curve — above roughly 2.5 kW the cylinder logistics stop being a penalty and the higher output matters more — but in the tens-to-hundreds-of-watts band that unmanned equipment occupies, methanol in a cartridge is difficult to beat.
Consumption is a flat 0.9 litres per kWh across the EFOY® range, which makes fuel planning arithmetic rather than estimation. A 10-litre cartridge holds 11.1 kWh; a 28-litre cartridge holds 31.1 kWh; a 60-litre tank holds 66.7 kWh.
Seven applications
1. Security and mobile CCTV
A camera tower or video trailer typically needs to run a PTZ head, illumination, a recorder and a 4G or 5G link. Average draw lands between 10 and 40 W depending on how much the PTZ moves and how hard the illuminator works at night — and night is exactly when solar contributes nothing.
This is one of the most common duties for the architecture, because temporary security sites are by definition placed where infrastructure is not: laydown yards, construction perimeters, substation compounds, port fence lines, remote assets. SFC publishes reference cases in this class, including mobile surveillance trailers running an EFOY Pro 2800 with a single 210 Wp panel and two M28 cartridges for roughly 20 days of autonomy with no sun at all, and autonomous CCTV towers running an EFOY Pro 2800 with 800 Wp of solar and an MT60 tank for year-round autonomy.
2. Traffic and roadside systems
Counters, classifiers, radar, variable message signs, road-weather and temporary signal control. Loads are small and duty cycles are predictable, but the sites are linear and numerous — a highway programme may have a hundred of them spread over hundreds of kilometres, which makes the cost of a site visit, not the cost of the equipment, the thing that governs the design.
Here the relevant number is not watts but days between visits. An EFOY Pro 1800 holding a 50 W average load with no solar at all runs 26 days on one M28 cartridge; with a Fuel Manager FM4 and four cartridges it runs 104 days; with an FM8 it runs 208 days. Add a modest panel and a maintenance round becomes annual.
3. Rail and level crossings
Lineside equipment, crossing protection, trackside monitoring and temporary works power. Rail sites are often close to a railway but a long way from a distribution board, and the traction supply is not available for auxiliary loads. The attraction of a fuel cell here is that it is silent, has no rotating parts to inspect and produces no exhaust plume near a running line, so it can be left in a relay room or a lineside cabinet with the off-gas ducted out.
4. Remote sensing and environmental monitoring
Water level, rainfall, air quality, noise, seismic, and meteorological masts, including LiDAR and SoDAR wind measurement. This is the application where the monsoon argument is sharpest: the measurement that matters most is often the one taken during the weather event that destroys solar yield.
These stations are also frequently in places where a service visit costs a day. SFC publishes reference cases of environmental stations running nine months unattended, and of Arctic field stations operating year-round. The Thai equivalents are canal and reservoir gauging, upland rainfall stations, coastal air-quality monitors and flood-warning telemetry.
5. Telecommunications and critical infrastructure
Repeaters, transmitters, digital trunked radio and microwave relays, plus extended backup for sites that must survive an outage well beyond what a battery string alone can cover. Loads here are larger — 50 to 150 W is common, and a clustered installation or an EFOY Pro 12000 Duo at 500 W covers a small site.
The specific value in a backup role is that autonomy is stored as fuel rather than as battery capacity. Extending a battery-only site from 8 hours to 72 hours means a battery room roughly nine times the size. Extending a fuel-cell-hybrid site means adding cartridges.
6. Oil, gas and pipelines
SCADA and telemetry, valve actuation, leak detection, flow computers and cathodic protection along a right-of-way. Two things make this segment distinctive: the sites are linear and remote, often with no road access at all; and there is frequently a classified area to consider, so the equipment location and any ducting have to be resolved against the area classification at design stage rather than assumed.
Cathodic protection in particular is a long-duration, low-power, high-consequence load — the kind of duty where an unnoticed power failure is discovered later as corrosion.
7. Special-purpose vehicles
Survey and broadcast bodies, command vehicles, mobile laboratories and instrumentation platforms that must run a payload with the main engine off. Idling a vehicle engine to hold up a payload is loud, expensive, bad for the engine and in many locations not permitted. A fuel cell charging the auxiliary battery removes the reason to idle.
Monitoring is part of the architecture, not an accessory
An unattended power system that cannot be interrogated is an unattended power system that will be visited. EFOY® units report over secured MQTT to EFOY Cloud — status, history, fuel level, e-mail alarms, remote configuration and firmware updates — and expose Modbus TCP so that the power supply appears as a point on an existing SCADA system rather than as a separate island with its own login.
In practice this changes operations more than any hardware feature. A fuel level that is visible from an office turns refuelling from a discovery into a schedule, and a fault that raises an e-mail turns a multi-day outage into a same-day callout.
Where the architecture stops
Three honest limits are worth stating, because they define the boundary of sensible use.
Power. A single methanol unit is a 40 to 500 W device. Clustering reaches roughly 3 kW. Anything with a motor start — a pump, a compressor, an air conditioner — is outside the band, and the correct answer is a hydrogen system, which starts at 2.5 kW and scales to 50 kW and beyond, or a conventional generator.
Cost of energy. Fuel cartridges are a consumable with a real per-kWh cost. Where a reliable mains connection exists or can be run at reasonable cost, mains wins, and no amount of architecture changes that. The case for a fuel cell is made by the cost of the alternative — the trenching, the service visits, the generator maintenance — not by the cost of the kilowatt-hour.
Siting. The reaction products are water vapour and carbon dioxide, which is benign but not nothing: inside an enclosed space the off-gas must be ducted out, and in a classified area the installation has to be resolved against the area classification rather than assumed compatible.
Fuel handling in practice
Methanol reaches site in sealed single-use cartridges, which is what makes the logistics tractable. M5, M10 and M28 cartridges are shipped as UN 3473, fuel cell cartridges, class 3; the 60-litre MT60 tank is shipped as UN 1230, methanol, class 3 (6.1), packing group II. All are UN-approved for sea, road and air transport. Storage and operating range is −20 to +50 °C. The M10 is kept upright; the M28 may lie on its side with the valve uppermost.
Operators planning a fleet of sites should settle three things early: where cartridge stock is held, how that store is set up and managed, and how empties return. Those three answers, rather than the fuel cell specification, are what determine whether a hundred-site programme runs smoothly.
How to size one, in four numbers
Any credible conversation about an off-grid site starts with four figures, and a supplier who does not ask for them is guessing:
- Average load in watts, measured or calculated over 24 hours — not the nameplate rating of the equipment.
- Site location, which sets the solar yield and the worst-case low-irradiance stretch.
- Required days between visits, which sets the fuel quantity and therefore the enclosure.
- What happens if it stops, which decides how much redundancy is justified.
With those four, the rest is arithmetic: average load times 24 hours gives daily energy; daily energy less the expected solar contribution gives the fuel-cell duty; fuel-cell duty times 0.9 litres per kWh times the required days gives the litres of methanol; and the litres decide the cartridge configuration and the box it lives in.
SATU Innovative is SFC Energy’s authorised distributor for civil products in Thailand, and supplies EFOY® fuel cells, enclosures, hybrid design, commissioning, cartridge supply and after-sales service. The appointment covers SFC Energy’s civil (non-military) products only. If you want a site sized, send us the four numbers above.