Solar Payback Period: How Many Years, and Is It Worth It? Calculated on Today's Tariff
The first question before anyone installs solar is “how many years until it pays back”. This page does not answer with a floating number — it gives you a formula you can re-run with your own quote and your own bill, three worked scenarios (5 kW home / 20 kW shop / 100 kW factory) on the current tariff (top-tier energy 4.42 + Ft 0.1623 + 7% VAT), a panel yield of 1,300–1,500 units per kWp per year, and a re-computable table — then what makes your own number faster or slower.
Solar in Thailand pays back in roughly 4–8 years — homes usually 6–8 years, shops and commercial buildings about 4–6, and factories that use nearly all of their power by day 4–6. It all comes from one equation: payback (years) = total investment ÷ electricity value saved per year, where the value saved = units generated × share used on the spot × the tariff you actually pay (home top tier 4.42 + Ft 0.1623 + 7% VAT ≈ 4.90 THB/unit) + any surplus sold at 2.20 THB (program homes only). What moves the number most is “what share of the daytime output do you use yourself?”, not the panel brand. The tables and the do-it-yourself method are below; “what does it cost” lives on the installation cost page and “which system type” on the on-grid vs off-grid vs hybrid page.
How Many Years Does Solar Take to Pay Back?
| Scenario | Output / yr | Self-use | Tariff displaced (incl. Ft+VAT) | Value saved / yr | Investment (assumed) | Payback (yrs) |
|---|---|---|---|---|---|---|
| Home 5 kW (on-grid, surplus sold at 2.20) | 7,000 units | 60% | 4.90 THB/unit (401+ tier) | 20,600 + sale 6,160 = 26,760 THB | 200,000 THB (assumed) | ≈ 7.5 yrs (no sale 9.7) |
| Shop / office 20 kW (self-use, no sale) | 28,000 units | 80% | 4.65 THB/unit (business ~4.18 + Ft + VAT) | 104,076 THB | 400,000–500,000 THB (20,000–25,000/kW) | ≈ 3.8–4.8 yrs |
| Factory 100 kW (TOU, daytime self-use) | 140,000 units | 90% | 4.56 THB/unit (on-peak 4.1025 + Ft + VAT) | 574,980 THB (demand-charge savings not counted) | 2,200,000–2,500,000 THB | ≈ 3.8–4.3 yrs |
Three scenarios (yield 1,400 units/kWp/yr · May–Aug 2026 tariff · investment = stated assumption)
Is Installing Solar Worth It? Check These 3 Numbers First
1) Self-consumption share
Every unit used on the spot saves the full 4.90 THB (homes above 400 units/month); every unit left over earns only 2.20 THB, or nothing outside the program — MEA's own summary is that homes with heavy daytime use (retirees at home, pets, working from home) “pay off and show results fast”. Aim for ≥60–70% self-use.
2) Tariff per unit you displace
Not the oft-quoted 3.95 THB average, but the *top tier* of your own bill: a home above 400 units pays its last units at 4.42 + Ft 0.1623 + 7% VAT = 4.90 THB (the 151–400 tier ≈ 4.69 THB); general business about 4.65 THB; factory TOU daytime about 4.56 THB — the higher the displaced tariff, the faster the payback (all rates on the Thailand tariff page).
3) Installed price per kW
Compare quotes as “baht per kW (or per watt)”, not the total, and check whether installation, the connection filing, the utility inspection and VAT are included — bigger systems cost less per kW (factory systems under 1 MWp sit around 20,000–25,000 THB/kW on our cost page) while small home systems usually cost more per kW — which is why factories pay back faster than homes even on a lower tariff.
How to Calculate Solar Payback Yourself (Formula + 5 kW Example)
You need just 4 numbers: system size (kW) · actual installed price · the top-tier rate on your bill · your daytime self-use share. Five steps:
Estimate annual output
Units/yr = kW × specific yield (Thailand 1,300–1,500 units/kWp/yr per our Thai solar yield page; use 1,400 as the midpoint) → 5 kW × 1,400 = 7,000 units/yr
Split self-used vs surplus units
Work out what share of the output your home uses by day (roughly 09:00–16:00) — at 60% self-use: 4,200 units used, 2,800 units surplus (from your bill/meter, or have the installer model the load)
Multiply by the real per-unit tariff
Value saved = self-used units × (top-tier energy rate + Ft) × (1 + VAT) → 4,200 × (4.42 + 0.1623) × 1.07 = 20,600 THB/yr; if enrolled in the sell-back program add 2,800 × 2.20 = 6,160 THB → 26,760 THB/yr in total
Divide the investment by the yearly value
Payback = investment ÷ value saved per year → with an assumed quote of 200,000 THB: 200,000 ÷ 26,760 ≈ 7.5 years (no sale: ÷ 20,600 ≈ 9.7 years)
Adjust for three realities
(a) panels degrade about 0.5%/yr → adds only a few months; (b) tariffs tend to rise (our tools assume 3%/yr) → payback about half a year sooner; (c) budget for cleaning/maintenance and one inverter replacement around year 10–15 (after payback) — or let our solar calculator do all of this automatically
Re-computable Payback Table: 5 kW Home, Varying Price and Self-Use
Same formula as above, 7,000 units/yr, 4.90 THB/unit displaced, surplus at 2.20 THB — vary only “price paid” and “self-use share” and watch which one matters more:
| 5 kW system price (assumed) | 60% self-use, no sale | 60% self-use + sale at 2.20 | 80% self-use, no sale | 80% self-use + sale at 2.20 |
|---|---|---|---|---|
| 150,000 THB | 7.3 yrs | 5.6 yrs | 5.5 yrs | 4.9 yrs |
| 200,000 THB | 9.7 yrs | 7.5 yrs | 7.3 yrs | 6.5 yrs |
| 250,000 THB | 12.1 yrs | 9.3 yrs | 9.1 yrs | 8.2 yrs |
What Speeds Up or Slows Down Payback (TOU · Ft · Degradation · Sell-back · Tax)
Ranked from largest to smallest effect for typical homes and businesses:
Self-use share — the biggest lever
Shift loads into daylight (laundry, water heating, EV charging, timed appliances) or size the system slightly below the daytime load — every 10% of output moved from “sold at 2.20” to “self-used at 4.90” adds about 1,893 THB/yr on a 5 kW system
Price per kW and design
Compare several quotes, pick the package that fits your real roof and shading (optimizers/micro-inverters cost more but pay off under shade), and skip the battery if night use is small — a battery raises the investment without adding many saved units (see choosing on-grid vs hybrid)
A TOU (time-of-use) meter
A home on a TOU meter pays on-peak (Mon–Fri 09:00–22:00) at 5.80 + Ft + VAT ≈ 6.38 THB/unit — so weekday daytime solar displaces power dearer than the normal rate and pays back faster, but weekend/holiday output displaces off-peak at only ≈ 3.00 THB; judge the whole week, not just workdays
The Ft charge and the tariff trend
The current Ft of 0.1623 THB/unit (May–Aug 2026) is reset every 4 months by the ERC — a higher Ft makes every saved unit worth more and shortens payback; our tools assume tariffs rise 3%/yr on average, which trims a 7-year payback by about half a year (how Ft works: What is the Ft charge)
Panel and inverter ageing
Tier-1 panels really degrade about 0.5%/yr (see panel lifespan & degradation); in year 8 they still produce about 96%, so payback stretches by only 1–2 months; what you must actually budget for is the inverter (10-year warranty per PEA/MEA), usually replaced once in the system's 25-year life, plus yearly cleaning
Selling back at 2.20 THB — helps, but is not the hero
Type-1 homes with ≤5 kW can enrol in the Solar Phak Prachachon program (2.20 THB/unit for 10 years) — in the 5 kW / 60% example the surplus sale adds 6,160 THB/yr and trims payback from 9.7 to 7.5 years, still far less than extra self-use; businesses cannot join (how to apply: sell power back page)
Tax measures for businesses
MEA summarises the government measure (article 18 Jul 2026): juristic persons and individuals (s.40(5)–(8)) may deduct 1.5× the solar investment when the equipment is new, installed and ready by 31 Dec 2028, not combined with BOI privileges, and backed by an e-Tax invoice — for businesses this genuinely shortens payback (confirm current terms with the Revenue Department / your accountant)
Factories & Businesses: Faster Payback Than Homes — and a Route With No Payback to Wait For
About the Author
Compiled by the CapSolar team under Frank Lee (Founder). CapSolar is a commercial & industrial solar EPC/PPA provider in Thailand that computes payback from real bills for factories and commercial buildings as routine work, and publishes every formula and assumption so the numbers can be re-checked.
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