Clean supply and resilience
On-site solar and storage can cut carbon and cost, but a hospital's essential electrical system comes first. Reduce demand, then add supply, with the resilience design done together.
Last reviewed: November 5, 2026. Informational guidance written by Tariq Khurshaidi; see the terms of use.
Matching tools: solar PV, life-cycle cost, toolkit solar sheet, toolkit thermal storage sheet.
Who owns it
The facilities or energy director owns the program, with the electrical engineer of record, the utility, the authority having jurisdiction, finance for the business case, and the emergency power and life safety owner for anything that touches the essential electrical system.
Data you need first
- Interval load data (15-minute kW) for a full year, to see minimum daytime load and demand peaks.
- Roof and site capacity: usable area, structural capacity, shading, and a helipad or equipment clearance review.
- Tariff structure: energy, demand, export or net-metering rules and interconnection limits.
- Single-line diagram of the essential electrical system, generator capacity and transfer switches.
Sequence
- Reduce demand first, so solar and storage are sized against a smaller, flatter load.
- Check the grid constraint early. Interconnection capacity, protection settings and export rules often set the real size limit, not the roof.
- Estimate yield with a recognized tool (NREL PVWatts) and enter it in the solar calculator. It shows output, bill savings and avoided carbon in the first year and over a longer view.
- Design storage with the critical power architecture. Batteries can add resilience and reduce peaks, but they do not replace code-required emergency power, and the system must be designed so it never compromises the essential electrical system.
- Compare options on life-cycle cost with the same assumptions: NPV, savings-to-investment ratio and simple payback, including maintenance, degradation, tariff risk and financing.
- Contract clean power where on-site generation is limited, and prefer additional capacity to unbundled certificates where possible.
Worked example
A 1,000 kWp rooftop array with a specific yield of 1,500 kWh/kWp-year produces 1,500,000 kWh in year 1. At the U.S. national average grid factor of 0.348 kg/kWh that avoids about 522 tCO₂e a year, if all of it is used on site. Use the solar calculator for the multi-year view with degradation, then test the project in the life-cycle cost calculator before any procurement.
The usual failure
Sizing solar to the roof instead of to the daytime load, so surplus is exported at a low price. Counting batteries as a replacement for generators. Ignoring interconnection timelines, which can be longer than construction. And claiming net zero from on-site solar: a verified inventory and independent assurance are required for any such claim.