Find the electricity produced
5 kWp × 4–5 peak sun hours per day × 30 days ≈ 600–750 kWh per month.
Article · Calculate value for money
How much can installing solar PV reduce your electricity bill per month? And how many years will the payback be?
See a simple calculation method. Complete with examples showing assumptions at every step. So that you can evaluate without misunderstanding that every house will be equally economical.
Short answer
How much do solar PV save?
PTH GREEN calculates savings at 100% of the power produced, because the system is designed so you use everything it generates. An example 5 kWp panel kit produces approx. 600–750 kWh per month (5 kWp × 4–5 peak sun hours per day × 30 days). At 4.20 baht per kWh, that saves approximately 2,520–3,150 baht per month, with a payback of about 4–5 years.
These figures assume 100% of the generated electricity offsets your bill, as designed. Actual results still depend on location, orientation, tilt, shading, equipment, and your real electricity rate.
3 formula steps
Calculate savings easily
Count savings at 100%
The system is designed so you use everything it generates, so all 600–750 kWh offsets your bill — no self-consumption discount needed.
Convert to money
600–750 × 4.20 baht = save approx. 2,520–3,150 baht per month
comparative example
How much might a 3, 5 and 10 kWp panel kit save?
| Panel power | Est. monthly generation* | Est. monthly savings** (100%) | Starting investment*** | Est. payback |
|---|---|---|---|---|
| 3 kWp | 360–450 kWh | 1,512–1,890 baht | 90,000 baht | 4–5 years |
| 5 kWp | 600–750 kWh | 2,520–3,150 baht | 150,000 baht | 4–5 years |
| 10 kWp | 1,200–1,500 kWh | 5,040–6,300 baht | 300,000 baht | 4–5 years |
* Assumes 4–5 peak sun hours per day × 30 days, with 100% of generation counted as designed. ** Assumes 4.20 baht per kWh, counted at 100% with no self-consumption discount. *** Estimated starting project value; actual pricing depends on equipment and site survey. All figures are not a guarantee and exclude degradation and maintenance costs.
Payback period
How to calculate payback?
Simple payback period = Net investment ÷ Annual savings
Example: a 5 kWp panel kit with a starting project value of 150,000 baht. Counting savings at 100% as designed, that saves approximately 30,240–37,800 baht per year, giving a simple payback of approximately 4–5 years.
These figures assume 100% of the generated electricity offsets your bill, as designed. Real investment evaluations should also include degradation, inspection and maintenance costs, actual electricity rates, and site-specific conditions.
Why are the real numbers different?
7 Factors that cause unequal savings.
- Does the house use a lot or a little of daytime electricity?
- Is the system size too large for daytime load?
- Direction, angle of inclination, and shade of the roof
- Weather and seasons
- panel performance Inverter and power cord
- The user's actual electricity rate
- Maintenance and cleanliness of the panel
Increase value without adding panels
Shift electricity use to sunny hours
Set the washing time
Move washing and drying to mid-morning to afternoon. When the system is producing power
Pump water and charge the car during the day.
Schedule flexible loads during sunny hours to reduce unused surplus electricity.
Turn on the air conditioner with a plan.
If there are people staying in the house during the day Using the air conditioner during power generation can greatly increase the proportion you use yourself.
Before believing the numbers in the quotation
Ask the installer to complete 5.
- Use electricity usage data for which month and for how many months?
- Assuming the output per kW, how much?
- Assume what percentage of your own electricity is used?
- How many baht per unit does the average electricity cost cost?
- total deterioration Maintenance cost And other expenses?
Credible bidders should be able to explain their assumptions. Don't just give numbers. “Maximum savings”
Want numbers from your actual bill?
Send the monthly electricity bill 6–12 to the PTH GREEN team to evaluate the system size, savings amount, and initial payback period for free.
Read more: Is your home suitable? · How much does each size system cost?