This guide covers what radar changes: a load profile weighted toward the modem, mounting shared with a structure over open water, sizing that holds through the flood-season peak, and the power kit our partner factories typically ship for this configuration.
Why Radar Gauges Change the Power Design
A non-contact radar gauge measures water level without touching the flow, and that single property reshapes the entire power system built around it. The sensor, data logger, and solar panel all mount on one structure positioned above the channel, such as a bridge rail or cantilever arm, rather than sitting apart on the bank next to a stilling well and its intake pipe.
Non-contact measurement removes a list of civil-works problems tied to older float and pressure-transducer setups. There's no stilling well or intake pipe to build and periodically de-silt, no sensor fouling from sediment and debris buildup, and no wading crew needed for sensor swaps or calibration checks. That combination is a large part of why radar has become the default choice for new flood-warning stations in many monitoring programs.
What non-contact adds is a different job for the power designer: station hardware concentrates on one structure over the channel, and panel placement, cable runs, and service access all inherit that location. The module itself behaves the same as anywhere else — the fundamentals in DOE's photovoltaic technology basics (tilt, orientation, shading loss) still govern the panel wherever it sits.
The general math behind sizing a station's power system stays the same, and it lives in our water level station power design guide. What changes here is where every component sits and what the worst month of the year looks like for that mounting location, which is covered next.
The Radar Station Load Profile
A radar water level station's load profile is a short measurement burst a few times an hour sitting on top of a continuous telemetry draw, and the telemetry side sets the panel size. The radar head and logger barely register against a full day's budget, measured in watt-hours (Wh) per day. Telemetry choice is where the sizing decision actually lives.
- Radar head: pings the surface for a fraction of a second, then idles. Milliwatt-class average draw, roughly 1–5 Wh/day at typical 5–15 minute intervals — duty cycle, not peak power, is what matters.
- Data logger: runs continuously to timestamp readings and manage the radio, drawing a few Wh/day. Steady background load; rarely changes the panel size on its own.
- Telemetry — the decision that sizes the panel: a 4G modem averages a typical 3–6 W continuous, landing at 72–144 Wh/day, usually more than everything else combined. A LoRaWAN link to a shared gateway cuts the station's own radio budget to a fraction of that, if coverage reaches the site. Charge regulation follows the split: the 4G tier pays for MPPT, the smallest LoRaWAN stations can run simple PWM.
| Telemetry path | Typical draw | Typical Wh/day | Panel class | Choose when |
|---|---|---|---|---|
| 4G modem (direct to network) | 3–6 W continuous | 72–144 | 40–80 W | No gateway nearby; single or scattered stations |
| LoRaWAN node (to shared gateway) | Fraction of 4G | A fraction of the 4G figure | 5–10 W class | Multiple stations within gateway range |
Reporting interval is the buyer's biggest free variable. A station that reports every 5 minutes during flood season can drop to hourly reporting in the dry season, and that firmware schedule change moves daily Wh meaningfully without touching a single wire. It's a standing lever, not a one-time setting.
Mounting Over Water: Bridge Rails, Cantilevers, and the Panel
The radar head has to hang over the water, but the solar panel usually does not. The best panel position is on the bank end of the structure, above flood stage and clear of the bridge's own shadow. Running conduit an extra few meters back to solid ground costs less than fighting shade all day.
A bridge deck or parapet can shade a rail-mounted panel for hours at a time, depending on orientation and time of year. Walking the site in the morning and again in the afternoon, or checking a sun-path chart for the structure's bearing, is standard practice before fixing the panel position. Doing that walk-through is cheaper than resizing the array after commissioning turns up a shortfall.
Public bridges add three constraints beyond shading:
- Vandal and theft exposure — mount the panel as high as the structure allows, use tamper-resistant fasteners, and treat visibility from the roadway as a risk factor when picking the exact spot.
- Permission — attachments to a bridge usually need sign-off from the road authority, and clamp-on mounts that don't penetrate the structure clear that approval faster than anything requiring drilled anchors.
- Cable discipline — the run from panel to enclosure to radar head gets conduit, drip loops at every entry point, and IP67-rated glands, with IP68-rated connectors on any splice below possible flood stage.
Coastal and estuary structures add salt exposure on top of everything above — see tide gauge coastal power design for how that changes the enclosure and hardware spec. Where no bridge or other structure exists at the gauging point, the fallback is a bank-side pole with the radar mounted on a cantilever arm reaching over the water, which puts the design back on the standard river gauge station power pattern.
Sizing for Flood Season: The Worst Month Is the Whole Point
A radar flood-warning station is sized for its worst month on purpose. The storm weeks that starve the panel are the exact weeks the station exists for, and a gauge that browns out mid-flood is worse than no gauge at all, because someone downstream is trusting the number it reports. Size for the average month instead, and the station works nine months of the year, the nine months nobody needed it.
Storm season brings more cloud cover, shorter effective sun hours, and a station that may switch to its fastest reporting interval at the same time rainfall spikes and river levels start climbing. Demand peaks exactly as supply bottoms out. That correlation is why flood-critical stations carry 5 days of autonomy as the common baseline, often 7 in typical practice, and why sizing runs on worst-month peak sun hours, never an annual average.
The worst-month check takes three steps:
- Pull the worst-month peak sun hours for the site, with any bridge or valley shading factored in.
- Apply the flood-season load profile (fastest reporting interval, not the dry-season schedule).
- Size the panel from those two numbers and the battery from the autonomy requirement — then leave both alone in the dry season, when the surplus is the margin you paid for.
In El Niño seasons, Pacific-facing basins tend to see flood-monitoring demand and cloud cover rise together, and stations sized for a normal year start running tight margins right when call volume is highest. Agencies planning ahead with forecast services such as NOAA's National Water Prediction Service are commissioning gauges on exactly this correlation, a pattern worth running through the El Niño monitoring readiness checklist before the wet season starts.
Highland catchments add one more variable: clear, cold nights push the LiFePO4 battery toward its 0 °C charge cutoff, so cold-climate battery behavior needs a heater pad or charge lockout spec'd from day one, not retrofitted after the first frost.
Procurement: The Radar Station Power Kit
The cleanest way to buy power for a radar gauge program is as a complete station kit — panel, MPPT charge controller, battery with low-temperature protection, enclosure, and structure-specific mounting as one line item per station, not five vendor relationships per site. One supply chain means one QC record per unit, not five mismatched invoices to reconcile after a failure.
Four things belong in the kit spec before a quote goes out:
- The station's daily Wh draw and worst-month sun hours for the deployment latitude.
- The mounting interface (bridge rail clamp, cantilever, or bank pole) with rated load specified in Pa or psf and material grade in writing; rooftop variants in North America fall under UL 2703 racking rules.
- The battery's charge temperature range and whether a heater option is needed for winter sites.
- Compliance documents to request: IEC 61215 module qualification, CE/RoHS declarations, UN38.3 transport certification for the lithium pack, and the factory's ISO 9001 certificate.
Kits through our partner factories start at MOQ 10 sets, a natural fit for a gauge network rollout rather than a single test site. A single pilot unit is quoted per configuration first, and custom-built samples typically run 7–14 days. Orders ship with a pre-shipment QC photo and video report and one proforma invoice per shipment, so a multi-site order settles as a single transaction.
The panel, controller, and battery in this kit are the same components covered in our complete remote solar power system configurations.
Radar Water Level Station FAQ
What size solar panel does a radar water level sensor need?
The radar head alone needs almost nothing to run. Station size comes down to the telemetry, not the sensor: a 4G-reporting station typically lands in the 40–80 W panel class with battery to match, while LoRaWAN-linked stations run on a fraction of that.
Can the panel mount on the bridge with the sensor?
Yes, it can, but the better default is the bank end of the structure, above flood stage and clear of the deck's shadow. Bridge attachments usually need road-authority approval, and a non-penetrating clamp mount clears that review faster than a permanent fixture would.
How many days should the battery last without sun?
Five days of autonomy is the common baseline for flood-warning stations. Flood-critical sites often spec seven days instead, because storm weeks starve the panel exactly when reporting intervals speed up and battery draw increases, precisely when a gap in reporting is least acceptable.
Can I trial one station before fitting the whole network?
Yes, that's the normal path. A single pilot kit is quoted per configuration and deployed through one storm season, and the fleet order (MOQ 10 sets through our partner factories) follows with the pilot as its reference build, so scale-up isn't a guess.
The bottom line: size for the modem and the worst month, mount for the structure, and pilot before the fleet. A flood-warning program is not the place to guess — pilot one station this season, and if the numbers hold, the fleet ships to the same spec. To get started, request a pilot station quote for your first site.
