Solar energy
Using solar energy exclusively to operate a 12.000 BTU air conditioner for 12 hours a day is technically feasible in Brazil, but requires rigorous planning, precise calculations, and adaptation to local solar conditions, according to simulations conducted for five Brazilian capital cities.
For many consumers, a 12.000 BTU air conditioner is seen as an intermediate option for small bedrooms and living rooms, combining high cooling capacity with wide availability in the national market.
This model delivers about one-third more cooling capacity than 9.000 BTU units, an increase that is directly reflected in daily electricity consumption.
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In practice, most equipment in this range consumes between 1,2 kW and 1,4 kW, especially inverter versions, which are now predominant in Brazilian residential sales.
Considering 12 hours of daily operation, the average energy consumption is close to 16 kWh per day for air conditioning alone, not including other appliances.
The scenario considered assumes that half of the consumption is met directly by solar generation during the day, with the other half supplied by stored energy.
According to engineer Rogers Demonti, the excess energy needs to be stored to allow for continuous nighttime operation of the equipment.
“If it’s possible to use air conditioning every day using only solar energy, we should also think about energy storage for nighttime use,” explains Rogers.
For the calculations, 400 Wp photovoltaic panels, a system performance factor of 0,75, and a battery efficiency of 85% were adopted.
The maximum depth of discharge for the batteries was also considered to be 80%, a limit necessary to preserve the lifespan of the storage system.
Another determining factor is the peak sunshine hours, the daily period of greatest solar intensity available for photovoltaic generation in each city analyzed.
In Fortaleza, the average considered was 5,5 hours per day, a value higher than that observed in other capitals in the comparative study.
Brasilia averages 5,0 hours of sunshine per day, while Manaus registers approximately 4,5 hours of full sun per day.
São Paulo has 4,0 daily peak hours, a number lower than that of the capitals in the North and Northeast regions analyzed.
Curitiba closes the list with approximately 3,5 hours of sunlight, reflecting the lowest average solar incidence throughout the year.
To compensate for system and storage losses, the project needs to generate approximately 17 kWh per day exclusively for air conditioning.
In Fortaleza, this equates to approximately 4,3 kWp of installed capacity, corresponding to 11 photovoltaic panels of 400 Wp each.
Brasília would require approximately 4,7 kWp, which results in about 12 panels to sustain the projected daily consumption.
In Manaus, the system increases to around 5,2 kWp, requiring approximately 13 photovoltaic modules.
São Paulo would need approximately 5,7 kWp, equivalent to 15 panels, reflecting lower average local solar efficiency.
Curitiba presents the most demanding scenario, with approximately 6,7 kWp installed and a need for close to 17 panels.
While a 9.000 BTU model may require between 8 and 13 panels, the 12.000 BTU model increases the range to between 11 and 17 modules.
“Sometimes the result is startling because it gives us so many panels, but it’s correct,” Rogers emphasizes when commenting on the calculations presented.
The engineer points out that the high power consumption of the equipment and the current technological limitations of the panels explain the numbers obtained.
For nighttime operation without mains power, approximately 8 kWh of usable power per night would be required, necessitating roughly 12 kWh of gross battery capacity.
The recommended hybrid inverter should have a continuous power output greater than 2 kW, with enough margin to handle compressor start-up peaks.
Rogers also points out alternatives to reduce consumption, such as raising the set point by 1°C, saving up to 6% of energy.
Other relevant factors include shading, tilt, orientation, panel maintenance, and choosing more efficient inverter models.
Overall, while technically possible, maintaining a solar system dedicated solely to air conditioning ends up being economically unfeasible in most cases, making it more rational to plan an integrated system for the entire residence.
With information from Canal Tech.
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