Solar Air Conditioning in Ghana: System Design and Running Costs

Start with the room and the cooling load

Record the room dimensions, ceiling height, window area, roof exposure, insulation, occupancy and heat-producing equipment. A sun-exposed room under a poorly insulated roof can need a different cooling solution from a shaded, well-sealed room of the same floor area. A qualified air-conditioning technician can estimate the cooling capacity in BTU/h or kW; avoid selecting a unit from floor area alone.

Check the AC nameplate and manufacturer data for rated input power, maximum input, starting behaviour and recommended circuit protection. An inverter-driven compressor generally varies its speed after startup, so actual consumption changes with outdoor conditions and the set temperature. Measure or log the unit’s energy use where possible.

Estimate energy before sizing the solar array

Energy is power multiplied by time. As a simple upper-bound illustration, a unit drawing 1 kW continuously for six hours would use 6 kWh before system losses. Real use may be lower as the compressor cycles or modulates, but hot conditions, poor maintenance, open doors and a very low thermostat setting can raise consumption. Use the expected daily kWh—not just the AC’s advertised cooling capacity—to estimate the PV array.

The array must be sized for the local solar resource, shade, orientation, temperature and conversion losses. A qualified designer should use realistic site-specific sunshine assumptions and account for other daytime loads. The inverter’s permitted PV voltage and current, MPPT range, maximum PV power and string limits must all be respected.

Decide whether cooling must continue after sunset

Daytime cooling can often be supplied directly by PV while the system is producing energy. If the AC must run in the evening or through an outage, the battery must deliver the required energy as well as the instantaneous power. Battery sizing should account for usable depth of discharge, conversion losses, temperature, ageing and the manufacturer’s current limits.

For example, a six-hour night schedule is an energy requirement, not a promise that a battery of a particular nominal kWh rating will provide six hours. Compressor cycling, indoor temperature, battery reserve settings and other loads change the result. Ask for the estimated AC runtime under stated conditions.

Match the inverter and electrical installation

Confirm continuous output, surge capability, phase and voltage, transfer behaviour, backup output rating and compatibility with the AC. The inverter must also support the battery voltage and battery-management communications, if used. A system can have ample PV energy yet still trip if inverter output, surge capacity, wiring or protection is inadequate.

Use correctly sized conductors, isolators, breakers, residual-current protection where required, earthing and surge protection. Have the installer verify the AC circuit and follow the inverter and air-conditioner manufacturers’ instructions. Do not bypass protective devices or connect an AC to an output that is not designed for it.

Improve efficiency before adding equipment

Choose an efficient unit that is correctly sized for the room, seal air leaks, shade sun-facing windows, keep filters and coils clean, and use a moderate set point. These steps reduce the energy the solar system must deliver. Keep the outdoor condenser clear of obstructions and arrange routine maintenance.

A useful proposal should state the estimated daily AC energy, expected solar production, battery usable capacity, assumed operating hours, backup duration and the loads excluded from backup. Compare like-for-like designs and ask what happens during cloudy weather or unusually hot periods.

A practical site-assessment checklist

• Photograph the AC nameplate and note the exact model and supply requirements.
• Record desired operating hours and whether cooling is needed overnight.
• List other loads that will share the inverter and identify motor-starting loads.
• Check roof or ground space, shade, cable route, ventilation and equipment location.
• Request a written design showing PV string limits, battery settings, protection and commissioning.