Solar High Mast Sizing (Worst-Month Method)

Off-grid high mast projects fail when sizing assumptions are hidden. This guide standardizes worst-month PSH, runtime, dimming and autonomy terms.

Where This Guide Fits

Quick Takeaways

  • Always size with worst-month PSH assumptions stated in writing.
  • Compare bids using usable battery Wh, runtime hours, autonomy nights, and dimming profile.
  • Require a deliverables pack: datasheet + assumptions + (if applicable) photometrics/spacing plan.

Connect Load, Solar Input and Usable Storage

Start with nightly energy, not lamp wattage alone. Add the actual electrical input power multiplied by operating hours for every lamp at each scheduled dimming stage, then include controller, communications or other auxiliary loads where fitted. State the power basis; a brightness percentage does not by itself establish electrical input power.

Estimate the site’s solar energy input. Array rated watts multiplied by worst-month peak sun hours gives a first-pass daily energy estimate before losses. Use solar data appropriate to the location and panel orientation, then state allowances for shading, soiling, temperature, wiring, controller and storage losses at the relevant points in the energy path.

Compare usable storage with the same load boundary. Battery nameplate capacity is not necessarily the energy available to the lights. State the permitted discharge range, battery-management limits, temperature and aging assumptions, and delivery losses. If quoted usable Wh already includes a reduction, do not apply that same reduction twice. For a no-recharge autonomy check, divide energy deliverable to the loads by the stated nightly load energy; changing the lighting schedule changes the result.

Check normal operation and recovery separately. The proposed array must support the operating schedule and the agreed battery-recharge requirement under the stated worst-month conditions. Daily averages alone do not guarantee performance through a sequence of poor-weather days. Keep the assumptions and model configuration together for engineering review; IES/LDT and lighting simulation address light distribution, not proof of the battery’s energy balance.

Copy/Paste sizing inputs

Project location:
Worst-month PSH (or location so it can be estimated):
Runtime (hours/night):
Autonomy nights:
Dimming profile (time / smart / none):
Target illuminance and area geometry:
Environment (dust/coastal/humid):

RFQ clauses (copy/paste)

  • Supplier must state worst-month PSH assumptions and dimming profile used for sizing.
  • Supplier must define usable battery capacity (usable Wh) and autonomy nights under stated assumptions.
  • Supplier must provide a clear model mapping and deliverables checklist.

Next Steps