Solar Sizing Guide for Mobile Security Trailers: How Much Wattage Do You Need?

Undersized solar is the single most common reason mobile security trailers fail in the field. Vendors sometimes quote panel wattage that looks impressive on a spec sheet but doesn't account for real-world load, regional sun hours, or seasonal variation. This guide gives you the math to evaluate any solar spec before you deploy.

Understanding the Load

Every component on a security trailer draws power. Before you can size your solar system, you need to add up the full load. Here are typical power draws for common components:

Example Load Calculation: Standard Construction Site Trailer

A typical mid-range construction site deployment might include:

• 2× PTZ cameras @ 15W = 30W
• 1× NVR @ 25W = 25W
• 1× LTE router @ 12W = 12W
• 1× LED strobe @ 50W = 50W (night hours only; ~8h avg)
• System overhead @ 15W = 15W

Daytime load: 82W continuously. Nighttime load: 132W (strobe active). Over a 24-hour period: (82W × 16h) + (132W × 8h) = 2,368 Wh/day ≈ 2.4 kWh/day total energy consumption.

Solar Panel Sizing

Solar panel wattage tells you the peak output under Standard Test Conditions (STC) — 1,000 W/m² irradiance, 25°C panel temperature. Real world is always lower.

The key variable is Peak Sun Hours (PSH) — the equivalent number of hours per day your location receives full-intensity solar irradiance. This varies dramatically by region:

The Solar Sizing Formula

To calculate required panel wattage:

For our 2.4 kWh/day construction site example in Chicago (winter worst case: 3.0 PSH):

Required wattage = 2,400 Wh ÷ 3.0 PSH ÷ 0.80 = 1,000W of panels

This is why vendors in northern climates typically specify 1,200W solar on their mid-range trailers — the extra 200W provides buffer for partially cloudy days and real-world efficiency losses.

Battery Storage Sizing

Battery capacity determines how many days the trailer can operate without any solar input — your "days of autonomy" for cloudy stretches, winter storms, or shading events.

The standard recommendation is 2–3 days of autonomy for construction site deployments. This provides a safe buffer for extended overcast weather without requiring a generator backup.

To calculate required battery capacity:

For our 2.4 kWh/day example with 2 days autonomy at 48V with lithium:

Required Ah = (2,400 Wh × 2 days) ÷ 48V ÷ 0.80 = 125 Ah minimum

Most vendors spec 200Ah lithium at this load level, providing comfortable headroom. If you're running climate control or additional cameras, step up to 300Ah.

Lithium vs. AGM Batteries

Virtually all modern security trailers use lithium iron phosphate (LiFePO4) batteries, and for good reason:

• Cycle life: LiFePO4 handles 2,000–5,000 charge cycles vs. 300–500 for AGM. At one full cycle per day, that's 5–15 years of life vs. 1–2 years for AGM.
• Usable capacity: LiFePO4 can safely discharge to 80% depth without damage. AGM should only discharge to 50%. So 200Ah lithium ≈ 160Ah usable vs. 200Ah AGM ≈ 100Ah usable.
• Temperature performance: LiFePO4 retains capacity down to -4°F (-20°C). AGM degrades significantly below freezing.

If a vendor is still spec'ing AGM batteries at equivalent wattage to a competitor's lithium system, the effective usable capacity is 40–50% lower than it appears.

Common Solar Spec Red Flags

• "800W solar" without specifying battery type or capacity. 800W panels mean nothing if they're paired with undersized or AGM batteries.
• No mention of charge controller type. MPPT (Maximum Power Point Tracking) charge controllers extract 20–30% more energy from panels than PWM controllers. Insist on MPPT.
• Solar specs listed without panel orientation guidance. A south-facing fixed panel and a north-facing panel of identical wattage will have wildly different real-world output.
• No generator backup port. For long winter deployments in Seattle or Chicago, even the best-spec'd solar system may need occasional generator top-off. Confirm the trailer has a generator input before deploying to low-sun regions.