For a health facility, power is not about savings first. It is about a vaccine fridge that must never warm up, an oxygen concentrator for a child with pneumonia, and light for a delivery at 2 a.m. Many dispensaries and health centres have no grid connection, or one that fails often. Solar with a battery can cover the essential loads reliably, if it is sized for the facility's worst days rather than its average ones.
Step 1: list the loads and how long they run
A typical rural dispensary might use:
| Load | Power | Hours a day | Energy per day |
|---|---|---|---|
| Vaccine refrigerator (average draw) | 60 W | 24 | 1.44 kWh |
| Lighting, 12 x 9 W LED | 108 W | 10 | 1.08 kWh |
| Laptop, router and phone charging | 100 W | 9 | 0.90 kWh |
| Oxygen concentrator | 350 W | 6 | 2.10 kWh |
| Laboratory equipment | 150 W | 3 | 0.45 kWh |
| Water pump | 750 W | 1 | 0.75 kWh |
| Security lighting | 40 W | 12 | 0.48 kWh |
| Total | about 7.2 kWh |
Use the ratings on your own equipment. An oxygen concentrator's real use varies widely with patient load, so log it or ask the clinical staff.
Step 2: separate night from day
About 2.4 kWh of this load falls at night: the fridge overnight, part of the lighting, security lights and some concentrator use. That is the minimum the battery must carry every night.
Step 3: size the battery for critical loads, not just the night
A clinic should also keep its critical loads running through a cloudy day or an outage. Allowing for one day of the vaccine fridge, security lighting and two hours of the oxygen concentrator (about 2.6 kWh) on top of the night load gives about 5 kWh of usable storage. A lithium battery used to 90% depth of discharge needs about 5.6 kWh nominal.
Step 4: size the array for the worst month
Including about 8% lost putting energy into the battery and taking it out again, the clinic needs about 7.4 kWh a day from its panels. On Kenya's average sun, each kW of panels produces about 3.8 kWh a day, so 1.9 kW would do on an average day.
But in July, Kenya's weakest month on average, a kW produces only about 2.7 kWh a day. Sizing for July gives about 2.7 kW, or five 620 W panels (3.1 kW). In July those five panels produce about 8.4 kWh a day; in a typical month about 11.9 kWh, leaving headroom for growth or a second fridge. Check your county's months on the solar by county pages; some areas dip much less.
Step 5: choose an inverter that can start the pump
All the loads together peak at about 1.6 kW, but the water pump can draw several times its running power for a moment when it starts. An inverter of about 3 kW with a good surge rating covers it. Wire the vaccine fridge, the concentrator, the delivery room lights and the security lights to an essential circuit so they are the last to lose power.
A note on vaccine refrigerators
Solar direct drive vaccine refrigerators, prequalified by the World Health Organization, run straight from their own panels and store cold in an ice lining instead of a battery. Where one is available, it removes the most critical load from the clinic's battery entirely. Follow the national immunisation programme's guidance on approved equipment.
Keep it working
- Train a staff member to read the battery state of charge and to clean the panels.
- Agree a maintenance contract with response times; a failure at a clinic is urgent.
- Track performance remotely where possible, so a failing battery shows up before it fails.
- Plan for growth. A new maternity wing or laboratory changes the load; leave space on the roof and inverter.
Plan your facility's system
- The free solar calculator sizes panels, battery and inverter from your essential load and backup hours.
- The battery backup and storage guide explains usable capacity and autonomy in more depth, and the solar water pumping guide covers the borehole.
- StimaPulse prepares decision packs for institutions; see solutions or request an assessment.