Solar panel, battery and payback calculator for Thailand

1Plan name

Where would you like to start?

Start with an electricity bill or your household appliances.

Results update as you change inputs

Average monthly electricity use

kWhFind kWh on your bill. This average is used each month unless you enter all 12 months separately.

Enter the bill amount instead

Monthly bill including Ft and VAT

THB

Daytime use 06:00–18:0060%

Using electricity while the sun shines increases direct solar use.

Hourly electricity profile (optional)

For homes with meter or monitoring data, such as overnight EV charging or time-specific air conditioning. Replaces the daytime/nighttime split.

Use separate weekday and holiday hourly profiles

Utility shown on your bill

Tariff category on your bill

Already on a TOU tariff

Select when your bill already uses TOU. The tariff category above will update to match.

Home electrical supply

Phase count does not directly change the electricity tariff. Read more

12 monthly energy values (optional)

Leave this off if use is similar each month. The average works for both normal and TOU tariffs. Enter separate months when you have a full year of bills or seasonal variation. This sets energy quantity, not Peak/Off-peak timing.

Enter electricity use for each of 12 months

No bill yet? Add up your appliances

Enter average operating power, especially for air conditioners and refrigerators that do not run at full power continuously.

Appliance name

watts

Quantity

hours/day

days/month

Appliance name

watts

Quantity

hours/day

days/month

444.0 kWh/month

Ft and VAT from your bill

Ft adjustment

THB/kWh

VAT

Default Ft: 0.1623 THB/kWh for Sep–Dec 2026 Check rates

Average bill savings฿ 1,941per month in year 1

First loan payment฿ 1,69684 payments · 5% interest

After the loan ends฿ 1,784Average of the first 12 months after repayment

Initial outlay฿ 30,000Total interest฿ 22,470

Sustained payback by cost scope

Installation only6 years 6 months

Installation + annual maintenance6 years 11 months

Installation + maintenance + inverter replacement6 years 11 months

Uses the full installation price of 150,000 THB, offset by bill savings and export revenue. Each measure adds its specified costs and must remain nonnegative for the rest of the horizon. Excludes interest, fees and battery replacement. Charts and net cash flow still include all plan costs.

Cash flow after costs

over25 years

End of year 25 284,502 THB

First-year production 7,300 kWhUsed in the home4,818 kWhUseful energy 66%

View an example January bill breakdown

Item	Without solar	With solar
Energy charge	3,175.00	1,404.97
Ft adjustment	129.84	63.88
Service charge	24.62	24.62
VAT	233.06	104.54
Total bill	3,562.52	1,598.01

THB · Before: 800 kWh / After: 394 kWh · Same tariff category

Figures in THB, except month number
month	Without: bill	With: bill	Payment	Interest	Principal	Remaining debt	Net difference	Net cumulative cash flow	Cumulative savings
Jan (1)	3,562.52	1,598.01	1,696.07	500.00	1,196.07	118,803.93	268.44	-29,731.56	1,964.51
Feb (2)	3,562.52	1,622.80	1,696.07	495.02	1,201.05	117,602.88	243.65	-29,487.91	3,904.23
Mar (3)	3,562.52	1,563.44	1,696.07	490.01	1,206.06	116,396.82	303.01	-29,184.90	5,903.31
Apr (4)	3,562.52	1,588.60	1,696.07	484.99	1,211.08	115,185.74	277.86	-28,907.04	7,877.24
May (5)	3,562.52	1,605.70	1,696.07	479.94	1,216.13	113,969.61	260.75	-28,646.28	9,834.07
Jun (6)	3,562.52	1,664.58	1,696.07	474.87	1,221.20	112,748.41	201.87	-28,444.41	11,732.01
Jul (7)	3,562.52	1,644.87	1,696.07	469.79	1,226.28	111,522.13	221.58	-28,222.84	13,649.65
Aug (8)	3,562.52	1,648.89	1,696.07	464.68	1,231.39	110,290.74	217.56	-28,005.28	15,563.28
Sep (9)	3,562.52	1,668.47	1,696.07	459.54	1,236.53	109,054.21	197.98	-27,807.30	17,457.33
Oct (10)	3,562.52	1,640.85	1,696.07	454.39	1,241.68	107,812.53	225.60	-27,581.70	19,379.00
Nov (11)	3,562.52	1,618.34	1,696.07	449.22	1,246.85	106,565.68	248.11	-27,333.59	21,323.18
Dec (12)	3,562.52	1,590.33	1,696.07	444.02	1,252.05	105,313.63	276.12	-27,057.47	23,295.37

Net difference = bill without solar − bill with solar − loan payment − maintenance/replacement + export revenue • Initial cumulative cash flow: − 30,000 THB • Cumulative savings = bill savings plus export revenue since month 1, before costs

Long-term assumptions and limitations

Simulation horizon

years

Annual electricity price growth

Annual demand change (optional)

%0% = unchanged use each year. Positive means more use, such as additional appliances; negative means less.

Annual panel degradation

Maintenance/equipment inflation

% per year

NPV discount rate

% per year

The model uses representative hourly days, separating weekdays and holidays when enabled. It repeats a 365-day calendar and the same off-peak-day share each month. It does not model actual daily weather, roof position, shared hybrid-inverter power, outages or per-phase electricity. Loan interest is calculated monthly, not daily.

Tariff growth changes energy charges and Ft only; service charges stay fixed. Maintenance is waived for the first1 years, then increases with inflation from installation. Replacement occurs at the start of the year after the specified service life. Excludes salvage value, export-income tax, subsidies and personal tax benefits.

All formulas and calculation methods

Base tariff: MEA / PEA September 2026 · Checked 22 Sep 2026 · Low-voltage residential only · Permit requirements

Is solar worthwhile for your home?

Tariff category on your bill

TOU electricity pricing

Money left after loan payments

Sustained payback by cost scope

Cash flow after costs

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