Solar ESS, Solar Energy for Sustainable Solution

Frequently asked questions

Straight answers
about solar in Thailand.

55 questions on policy and payback, choosing a system, warranty, maintenance, the environment, installation troubleshooting and safety.

Policy & Money in ThailandChoosing Your SystemWarranty & LifespanMaintenance & CleaningEnvironment & SustainabilityInstallation BasicsField Troubleshooting GuideSafety & Protection

Policy & Money in Thailand

Net billing, incentives, payback and price

Does Thailand give net metering to homeowners?
Not true net metering. Thailand uses net billing: the solar power you use yourself replaces grid power at the full retail price, and the surplus you export is bought at a fixed lower rate. Units are not swapped one-for-one.
How much do I get for power I sell back?
2.20 baht per unit (kWh) under the household "Solar for the People" scheme, with up to 5 kW of export per meter. In 2026 the national target was raised from 500 MW to 10,000 MW and the purchase period extended to 20 years. Ask us for the current application status with PEA/MEA.
Is there a government subsidy or tax benefit?
Yes. A personal income-tax deduction of up to 200,000 baht applies to on-grid rooftop systems up to 10 kWp connected between 3 Mar 2026 and 31 Dec 2028 (one system, one meter, e-tax invoice required). The government has also announced a planned cash subsidy for household systems; details are still to be confirmed.
How much tax do I really save?
The deduction lowers your taxable income, so the saving depends on your tax bracket. At 20% a 200,000 baht deduction saves about 40,000 baht; at 10% about 20,000 baht.
How long is the payback (ROI) for a home?
Typically about 4 to 7 years for an on-grid system when most solar is used in the daytime. Higher daytime use, the tax deduction and sell-back shorten it. Batteries lengthen payback but add backup and night-time use.
What makes payback faster?
Using power while the sun shines: air-conditioning, pool pump, water heater, EV charging and home office in the daytime. A system sized to your daytime load pays back fastest.
More people want solar. Will prices go up?
Demand is rising, but global factory capacity has grown even faster, so equipment prices have fallen over the long term. Short-term rises can come from exchange rates, shipping, copper and policy rushes.
More suppliers are entering. Will prices get cheaper?
Hardware may get a little cheaper, but labour, structure, cable and protection devices do not. Very low quotes usually cut quality in those hidden parts. Waiting a year usually costs more in lost savings than it gains in price.
Will electricity tariffs keep rising?
Nobody can promise, but Thai tariffs follow fuel (Ft) costs and move up and down. Solar fixes the cost of part of your energy for 25+ years, which protects you from that uncertainty.
Do I need permission to install?
Yes for grid-connected systems: notification to the regulator (ERC) and a grid-connection approval from PEA or MEA, plus engineer-signed drawings. Rules were simplified in 2026. Solar ESS handles the paperwork for you.
Can I finance the system?
Several Thai banks offer solar loans and 0% instalment plans. In many cases the monthly instalment is close to the monthly saving on the bill.

Choosing Your System

Type, size and what to expect

On-grid, hybrid or off-grid: which one?
On-grid: lowest cost, fastest payback, no backup. Hybrid: adds a battery for night use and blackout backup. Off-grid: for sites with no utility supply; needs larger battery and usually a generator.
Will my solar work during a blackout?
A standard on-grid inverter switches off for safety when the grid fails. You need a hybrid inverter with a battery and a backup circuit to keep essential loads running.
What size system do I need?
We size from your electricity bill and your daytime load profile. As a rough guide, each 1 kWp in Thailand produces around 110 to 130 units per month and needs about 4.5 to 5 m2 of roof.
Is my roof suitable?
Most metal sheet, concrete tile and flat concrete roofs are fine. We check structure strength, age, shading, orientation and waterproofing before quoting.
Does solar still work in rainy season?
Yes, at reduced output. Panels produce from diffuse light too. Annual production figures already include the rainy months.
Do I need a battery?
Not for saving money in the daytime. A battery makes sense if you have frequent outages, high evening use, no permission to export, or want more independence.
Can solar charge my EV?
Yes. Daytime EV charging is one of the best uses of surplus solar. A smart charger can follow the solar output so the car takes only the excess.
Can I expand later?
Yes, if planned. Choose an inverter with spare capacity and a battery-ready (hybrid) model, and leave roof and cable space.

Warranty & Lifespan

What is covered and for how long

How long is the product warranty?
Typical for the Tier-1 equipment we use: panels 12 to 25 years product warranty plus a 25 to 30 year power-output warranty; inverters 5 to 10 years (extendable on some brands); batteries about 10 years. Exact terms are stated per model in your quotation.
How long is the installation warranty?
Workmanship warranty covers mounting, wiring, waterproofing and commissioning. The period is stated in your Solar ESS quotation and contract.
How long will the system last?
Panels 25 to 30 years or more, losing roughly 0.4 to 0.5% output per year. Inverters usually 10 to 15 years, so plan one replacement in the system's life. LFP batteries typically last 6,000+ cycles.
What can void a warranty?
Modification by unqualified people, wrong cleaning (high pressure, harsh chemicals, walking on panels), lightning or surge without proper protection, and ignoring fault alarms.
Who do I call if something fails?
Call Solar ESS first. We diagnose remotely through the monitoring platform, then handle the claim with the manufacturer.

Maintenance & Cleaning

Low effort, but not zero

Is maintenance expensive?
No. Solar has no moving parts. Yearly cost is normally a small fraction of the yearly saving: cleaning plus one inspection.
What does maintenance include?
Panel cleaning, visual check of panels and mounting, tightening terminals, thermal scan of DC/AC boxes, checking SPD and breakers, earthing test, inverter fan and filter, and review of production data.
Does it need much work from me?
Very little. Check the app once a week. If production drops suddenly or an alarm appears, tell us.
How often should panels be cleaned?
Usually 1 to 2 times a year, more often near farms, dusty roads, burning season or bird areas. Dirty panels can lose 5 to 15% of output.
How much does PV cleaning cost?
It depends on the number of panels, roof height and access, and water supply. We quote per visit or as a yearly service package.
Can I clean them myself?
Yes with care: soft brush, clean water, early morning or evening when panels are cool. No high-pressure jet, no detergent, no standing on panels, and never work on a roof without fall protection.

Environment & Sustainability

Honest answers to hard questions

Solar energy is clean. Is solar manufacturing clean?
Not perfectly. Making silicon, glass and aluminium uses energy and chemicals. But a panel repays the energy used to make it in roughly 1 to 3 years, then produces clean power for 25+ years.
How does solar compare with fossil power?
Over its whole life, rooftop solar emits around 40 g CO2 per kWh, against roughly 490 for gas and 820 for coal (IPCC median values).
Do panels create an environmental crisis?
No. A panel is mostly glass and aluminium with small amounts of silicon, copper and silver. Standard silicon panels are not hazardous in normal use and do not leak.
What happens at end of life? Can panels be recycled?
Yes. Glass, aluminium frame, copper and silicon can be recovered, around 90% or more by weight. Thailand's recycling capacity is still developing, so used panels should go to licensed e-waste handlers, never to landfill or burning.
Do batteries cause resource scarcity, child labour or environmental damage?
The main concern is cobalt. The LFP (lithium iron phosphate) batteries used in home storage contain no cobalt and no nickel. Lithium mining still has impacts, so choose brands with supply-chain audits.
What do we do with old batteries?
After 10+ years a battery still holds most of its capacity and can have a second life in lighter duty. At true end of life it goes to a licensed recycler to recover lithium, copper and aluminium.
Are used panels worth anything?
Yes. Panels removed after 10 to 15 years often still give 85 to 90% output and are reused on farms, pumps and small off-grid sites.

Installation Basics

Design and workmanship points

What about shading?
One shaded panel can pull down a whole string. We design around shade, or use optimisers or microinverters on the affected panels.
Why do connectors matter so much?
Mismatched or badly crimped MC4 connectors are the most common cause of rooftop solar fires. We use the same brand on both sides and the correct crimp tool.
Will installation make my roof leak?
Not if done properly. Metal roofs use clamps or sealed screws on the ribs; tile roofs use hooks under the tile. All penetrations are sealed and covered by workmanship warranty.

Field Troubleshooting Guide

Detailed answers on strings, cables, insulation, CT, meter and system control

Panels on different angle/tilt: how should I lay the panels?

Keep every panel in one series string on the same orientation and tilt, and give each roof face its own MPPT input.

In a series string the current is set by the weakest panel, so one shaded or differently-facing panel drags the whole string down.

  • Same direction, tilt differs by under about 10°: can share one string; the loss is small.
  • Different directions (e.g. east and west): separate strings on separate MPPTs.
  • More roof faces than MPPTs: two strings of the same panel count and model may be paralleled on one MPPT even if they face differently, because string voltage barely changes with direction. Check the combined current stays under the MPPT's maximum input current.
  • Never mix panel counts, models or orientations inside one series string.
  • Complex roofs or partial shading: use optimizers or microinverters instead.
Before wiring, confirm each string's Voc at the coldest expected temperature is below the inverter's maximum DC input voltage.
Cable was cut: what if my DC cable is bruised or damaged?

Replace the damaged section with proper PV cable and connectors; never repair it with tape.

A string can carry several hundred volts DC whenever there is daylight, and a damaged cable can arc, start a fire or cause an insulation fault.

  1. Make it safe. Turn the inverter off, open the DC isolator, then unplug the string's MC4 connectors. Panels stay live in daylight, so work early morning or late evening, or cover the panels.
  2. Check how bad it is. Exposed copper, a cut through the outer sheath, or a crushed section all mean replacement. A light scuff on the outer sheath only may be acceptable after an insulation test.
  3. Replace. Replace the whole run where practical. If a joint is unavoidable, use a matching pair of MC4 connectors (same brand and type), crimped with the correct tool. Keep the joint accessible, off the roof surface and out of standing water, never buried inside conduit.
  4. Test before reconnecting. Measure insulation resistance (+ to earth and − to earth) and check string Voc and polarity (see the insulation question below).
  5. Prevent it happening again. Run cable in UV-rated conduit or tray, clip it to the rails, protect sharp edges, and guard against rodents and pinching under clamps.
Insulation issue: how should I fix the insulation issue on cable and ground?

Find the one string, then the one panel, connector or cable that leaks to earth, and replace it; never disable the inverter's insulation protection.

Inverters show this as "PV ISO Fault", "DC Insulation Impedance Failure" or "Low Insulation Resistance" depending on brand.

Common causes
  • Water inside MC4 connectors or a panel junction box
  • Cable insulation cut or pinched under a rail or clamp
  • Cracked panel backsheet or glass
  • Heavy dew or rain (a fault that clears by midday points to moisture)
  • Poor or missing frame earthing
How to find it
  1. Note when the fault happens: mornings and after rain = moisture; all the time = physical damage.
  2. Turn the inverter off and open the DC isolator. Disconnect all strings.
  3. Test each string with an insulation tester (megger) at 1,000 V DC (or 500 V for low-voltage strings): + to earth, then − to earth. Healthy strings typically read well above 1 MΩ.
  4. On the faulty string, split it in half and test each half; repeat until you reach one panel or one connector.
  5. Inspect connectors for water or burn marks, and cable runs for damage.
Fixing
  • Replace the faulty connector pair, cable section or panel.
  • Dry and re-seal junction boxes; use drip loops so water runs away from connectors.
  • Check earthing: every frame and rail bonded to earth, earth resistance measured and within the design value (commonly 5 Ω or less).
  • Re-test every string before reconnecting the inverter.
Problem with CT: can we run the inverter without a CT?

Yes for a plain on-grid inverter that is allowed to export; no for a hybrid inverter or any system that must limit export.

The CT is the inverter's only way to see how much power the building is taking from or sending to the grid.

SystemWithout CTResult
On-grid, export allowedWorksProduces at full power; extra goes to the grid
On-grid, zero export requiredNot acceptableInverter cannot limit export; energy leaks to the grid
Hybrid with batteryWorks poorlyBattery cannot follow the load; it may not discharge at night, or may export from battery
Hybrid in backup / off-grid mode onlyWorksSupplies backup loads; no self-consumption control
If a CT fails, switch the inverter to a safe mode (export limit off only if export is permitted, or reduce output) until the CT is replaced.
What is the impact if we run the CT in the wrong direction or on the wrong phase?

The inverter makes the opposite or a random decision: it exports when it should not, or charges the battery from the grid, and the monitoring data becomes wrong.

MistakeWhat the inverter seesTypical symptoms
CT reversed (arrow wrong way, or S1/S2 swapped)Grid import looks like exportZero-export system exports at full power; inverter curtails while the house is importing; battery charges from grid; load shows negative or impossible values
CT on the wrong phaseCurrent from one phase against voltage of another (120° apart)Readings too low, wrong sign or jumping; export control unstable
CT on the inverter output instead of the grid cableOnly its own outputLoad always equals PV; export never controlled
CT on the neutral, or around both L and NNear zeroInverter thinks the house uses nothing
How to check (known-load test): turn the inverter off and switch on a known load (e.g. a 2 kW kettle). The monitor should show about 2 kW import. Export shown = CT reversed; much less than 2 kW or wandering = wrong phase or wrong cable. Follow the brand's manual for arrow direction, since brands differ. Many inverters also let you reverse the CT direction in settings.
Meter: can we run the inverter without a meter?

Yes, as long as the inverter has a working CT (for models that support a direct CT) or export control is not needed.

A smart meter does the same job as a CT — it tells the inverter the grid power — but measures more accurately and talks to the inverter over RS485.

  • On-grid, export allowed: no meter or CT needed.
  • Single-phase hybrid with a direct CT input: CT is enough; a meter is optional.
  • Models that require a meter for export control (many three-phase inverters): the inverter will raise a "Meter Communication" error and cannot limit export without it.

If the meter loses communication, most inverters either lose export control or cut output to zero for safety; check the RS485 wiring (A/B polarity), Modbus address and baud rate.

When do we need to use a meter?

Use a smart meter whenever accuracy, distance or three phases matter.

  • Zero export or export limit on three-phase systems, or where the utility requires proven export control
  • Three-phase sites with unbalanced loads, so each phase is measured correctly
  • Long distance between inverter and main board, beyond the CT cable length the manual allows
  • Large main breakers that need external CTs bigger than the inverter's supplied CT
  • Several inverters on one site, controlled together through a meter plus a datalogger or export manager
  • Accurate consumption data for customer reports, savings analysis or battery sizing
Power running in reverse: why, and how do we fix it?

Power flowing back to the grid when it should not is almost always a CT or meter installation error, or export limit not switched on.

Exporting without a sell-back agreement means giving energy away free, and may break the utility's connection conditions.

Symptoms
  • The utility meter registers export, or the customer's bill does not drop as expected
  • Monitoring shows negative load, or export while the house is clearly consuming
  • Battery charges from the grid at night
Causes and fixes
CauseFix
CT arrow facing the wrong way, or S1/S2 swappedFlip the CT or swap the leads; or reverse CT direction in settings
Meter L and N swapped, or CT on wrong meter terminalsRewire to the meter's wiring diagram
CT installed downstream of the inverter connection pointMove it to the incoming grid cable, between utility meter and all loads plus inverter
Export limit / zero export not enabledEnable it and set the limit to 0 W (or the permitted value)
Sudden large load switching offShort export spikes of a few seconds are normal while the inverter reacts

After fixing, repeat the known-load test and watch the utility meter during a sunny hour with low load.

3P with the wrong CT: what is complicated about 3P and CT?

In three-phase, each of the three CTs must sit on the same phase as the voltage it is paired with, and face the right way.

There are 6 ways to arrange three CTs across three phases and 8 combinations of directions — 48 possible installations, and only one is correct.

Why it is harder than single-phase
  • Phase matching: CT1 must be on L1, CT2 on L2, CT3 on L3, matching the meter or inverter voltage wires. A swap gives readings 120° out, so power looks too small or negative.
  • Mixed errors cancel out: one reversed CT can make total power look reasonable while each phase is wrong.
  • Unbalanced loads: the house may import on one phase and export on another. If the inverter balances its output evenly, a lightly loaded phase can export even when the total is zero. Use per-phase export limit if the inverter supports it, and check how the utility meter records each phase.
  • Phase rotation: check L1-L2-L3 sequence at the main board matches the inverter and meter.
How to verify a 3P installation
  1. Turn the inverter off.
  2. Switch on a known single-phase load on L1 only. Only phase 1 should rise, showing import of about that load.
  3. Repeat for L2 and L3.
  4. Each phase should show a power factor close to 1 for resistive loads. Negative power on a phase = that CT is reversed; power appearing on a different phase = CTs are swapped.
  5. Turn the inverter on and confirm export stays at the set limit on every phase.
System control: how should the system be set up?

System control is how the inverter decides where solar, battery and grid power go; set it at commissioning to match the customer's goal and the utility's rules, then lock it.

Work modes (names vary by brand)
ModeWhat it doesBest for
Self-use / Self-consumptionSolar feeds loads first, then battery, then gridMost homes and businesses with battery
Feed-in priorityExports first, keeps battery for laterSites with a sell-back agreement
Backup / ReserveKeeps battery at a set SOC for outagesSites with frequent power cuts
Time-of-use (TOU)Charges or discharges at set timesTOU tariff customers
Off-gridRuns without gridRemote sites
Peak shavingUses battery to cap grid importCommercial sites with demand charges
Settings to check at every commissioning
  • Grid code set to the local utility standard (PEA or MEA for Thailand)
  • Export limit / zero export, with CT or meter verified
  • Battery type, charge/discharge current limits and minimum SOC
  • Date, time and time zone (TOU depends on it)
  • Monitoring app connected and showing correct load, PV, battery and grid values
  • Firmware up to date
Good practice: don't change protection settings (voltage, frequency, anti-islanding) without a clear reason; record all settings in the handover document; and give the customer view-only app access so settings are changed only by the installer.

Safety & Protection

Surge, earthing and fire safety

What surge protection (SPD) do you install?
Type II SPD on both DC and AC sides. AC SPD to IEC 61643-11 in the distribution board; DC SPD to IEC 61643-31 in the combiner box or at the inverter DC input.
What ratings should a Type II SPD have?
Tested with an 8/20 microsecond wave. Nominal discharge current (In) 20 kA, maximum (Imax) 40 kA or more. AC continuous voltage (Uc) such as 275/320/420 V AC; DC rating (Ucpv) 600 or 1000 V DC, at or above the string's maximum open-circuit voltage.
Why is earthing important?
SPDs can only divert a surge if there is a good earth. Panel frames, mounting, inverter and SPDs are bonded to an earth electrode with tested low resistance.
Is rooftop solar a fire risk?
Very low when installed to standard: correct cable and connectors, DC isolators, fuses or breakers, SPD, and inverter arc-fault and insulation monitoring. Yearly thermal scans catch hot spots early.
Is it safe in storms and lightning?
Yes. Structures are designed for wind load, and SPD plus earthing protect against induced surges. Buildings with a lightning protection system need the solar array coordinated with it.
Type II SPDAC sideDC side (solar PV)
StandardIEC 61643-11IEC/EN 61643-31
Test waveform8/20 µs8/20 µs
Nominal discharge current (In)5 to 20 kA (20 kA common)20 kA
Maximum current (Imax)40 to 80 kA40 kA or more
Where installedSub-distribution board / MDBCombiner box / inverter DC input
Continuous voltage (Uc / Ucpv)275, 320 or 420 V AC600 or 1000 V DC, at or above string Voc

Policy figures as of October 2026. Rates, quotas and incentives change; savings, payback and warranty figures are typical ranges, not guarantees. Your quotation states the exact terms for your system.

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