Can I wire a generator into the house myself without an ATS?

Strongly no. Back-feeding into a wall socket is illegal and can be lethal — power flows up the line and can electrocute a lineworker, and equipment is damaged when mains returns. A licensed electrician must fit a transfer switch (ATS/changeover) that isolates the house from the grid before the generator supplies it. The simpler, safer route is plugging appliances straight into the generator with a suitably rated extension lead.

Inverter vs conventional generator — what's the difference, do I need inverter?

An inverter unit varies engine speed with load and conditions the output into a clean sine wave, so it is quiet, sips fuel at low load and is safe for sensitive gear (PC, TV, inverter fridge). A conventional unit gives less clean power and is usually louder. For just lights/fans/a basic pump a conventional one is fine, but if you have important electronics an inverter is worth it long term.

Frequent city outages — buy a generator or a backup battery?

In a city with short outages (minutes to an hour) and close neighbours, a backup battery/solar system usually fits better — silent, no fumes, switches on automatically. A generator shines for long outages of hours to days or in remote areas, since you just refuel and keep going. Weigh it by how often/long your outages are and your tolerance for noise.

Does a generator need the TISI (มอก.) mark — how do I choose safely?

Choose a unit carrying the TISI (มอก.) standard mark for safety and quality. Read the continuous (running/rated) power, not just the peak, because the continuous figure is what you can actually use; check for a clean sine wave if you have electronics, a low-oil cutoff, and an earthing point. Finally, connecting it to the house must go through a licensed electrician plus a transfer switch (ATS).

Home Backup Power Guide

Home Backup Generator — How Many Watts, Gasoline, Diesel, or Inverter

Name: CapSolar
Address: 429/44 Sukhonthasawat Rd, Lat Phrao, Bangkok, 10230, TH
Telephone: +66 2 124 5414
Price range: $$$$

Before buying a generator, know two things: what you need to keep running during an outage (total running watts plus a margin for the surge when motors start) and which type to pick (gasoline, diesel or inverter). This page sizes it step by step, compares the three types on fuel and noise, weighs it against a UPS, a battery/solar system and when each makes sense, and shows how to connect it safely with a transfer switch (ATS) — fuel and noise depend on model and load, so read the actual spec rather than a made-up fixed number.

9 min readLast updated: 23 Aug 2026Data as of: Aug 2026

Size it from "what you must keep running during an outage", not from the size of the house. Add the watts of everything on at once, then allow for the surge when motors start (a fridge, water pump or air-con draws 2–3× its running watts at start-up). A home that only needs lights, a fridge, fans and phones is fine on about 2 kW; add a water pump, TV or microwave and it moves to ~3 kW; add one air-con and you need 5 kW or more. On type: an inverter unit is quiet, sips fuel at low load and gives clean power safe for electronics; gasoline is cheap and fine for small, occasional use; diesel is durable and fuel-efficient at larger sizes — and never back-feed into a wall socket: you need a transfer switch (ATS/changeover) fitted by a licensed electrician.

How many watts / kW should a home backup generator be?

Add the watts of everything you will run at once during an outage, add the starting surge of the single biggest motor, then leave ~20% headroom. Do not pick by "house size" — during an outage you are not running everything at once; pick by the list of things you genuinely cannot do without.

Sizing example by need

What you need to run	Recommended size
LED lights + fridge + fans + phones/wifi	~2 kW (quiet inverter)
+ water pump / TV / microwave / rice cooker	~3 kW
+ one air-con (~12,000 BTU)	5 kW and up
Whole house / several air-cons at once	7–10 kW+ (consider diesel + fixed ATS)

The watts above are typical running values (e.g. a fan ~50 W; a fridge ~150 W running but a several-hundred-watt surge when the compressor starts; a water heater 3,500–6,000 W; a 12,000-BTU air-con ~1,200 W running) — read each unit's nameplate, or the appliance power guide, then add up what you will actually switch on. Key point: water heaters and air-cons draw a lot and surge hard; if you can drop them during an outage, the generator gets much smaller.

How much fuel does a generator use per hour — how long does 1 litre last?

There is no fixed number — it depends on load and model. A generator burns more as the load it supplies rises, so running it near half-load and choosing an inverter type stretches each litre much further than running it flat out. For the real figure, read the spec sheet (makers usually list consumption at 50% and 100% load).

To estimate run-time per tank = tank capacity ÷ consumption at your load. Small portables have small tanks, so they need refuelling often at high load, while an efficient inverter at low load can run for several hours per tank. To cut fuel cost: drop the heavy loads (water heater/air-con) during an outage and power only essentials — you save fuel and can buy a smaller unit.

Diesel, gasoline, inverter — what's the difference and which to pick?

Gasoline is cheap and fine for small, occasional use; an inverter gives clean, quiet power, sips fuel at low load and is safe for electronics; diesel is durable and fuel-efficient at larger sizes / heavy use. Choose by the size you need, how often you will run it, and whether you have sensitive electronics (PC/TV/modern fridge).

Type	Strengths	Limits	Best for
Gasoline	Cheap, light, easy to start, fuel everywhere	Thirstier than diesel at high load, less clean/steady power, noisier	Small 1–3 kW, occasional outages, tight budget
Diesel	Durable, handles long heavy runs, fuel-efficient at size	Pricier and heavy, more noise/fumes without an enclosure	Big homes/several air-cons 5 kW+, frequent use, fixed + ATS
Inverter	Clean sine wave (safe for electronics), quiet, fuel-efficient at part load, portable	Higher price per kW and usually size-limited (mostly ≤ 5 kW)	Typical homes powering fridge/wifi/PC, wanting quiet clean power

On noise: enclosed/inverter units are clearly quieter than open-frame ones; the dB(A) figure is on each model's spec. If homes are close together or you run it at night, pick a low-noise model and set it well away from windows. Look for a unit carrying the TISI (มอก.) standard mark for safety and quality.

Generator vs UPS vs battery/solar — which should you choose?

Choose by "how long the outage lasts" and "can you tolerate noise/fuel". A UPS bridges a few minutes of flicker for a PC/router — not whole-house backup. A battery/solar system is silent and fuel-free, best for short, frequent outages. A generator runs as long as you have fuel, best for long outages or remote areas.

UPS

Stores energy in a small battery for a few minutes. Its job is to "bridge" flicker/brief cuts for sensitive gear (PC, router, CCTV) so they do not drop suddenly — not to back up the whole house.

Battery / solar

Silent, no fuel, no fumes; powers essentials for hours and recharges from the sun — best for short, frequent outages, though the upfront cost is higher and power/duration are limited by battery size. For the full home-system picture see on-grid vs off-grid vs hybrid solar.

Generator

Runs as long as you keep refuelling, and gives more power per baht than batteries at larger sizes — best for long/frequent outages in remote areas, but it means noise, fumes and maintenance/fuel storage. For businesses costing "downtime per hour", see the B2B view at what a factory outage costs + how solar/battery help.

How do you connect a generator to the house safely (ATS)? Can it charge an EV?

Never back-feed a generator into a wall socket. The power flows back up the utility line and can electrocute a lineworker repairing it, and it damages equipment when mains power returns. The correct way is to fit a transfer switch (ATS or manual changeover) via a licensed electrician so the house is isolated from the grid before the generator supplies it.

More cautions: always run it outdoors with good airflow — never inside a house or closed garage, because the exhaust contains carbon monoxide that can kill · earth it per the manual · refuel only with the engine off and cool. For installation safety follow utility/safety-body guidance and choose a TISI-marked unit.

Can a generator charge an EV? Technically yes, but not recommended as a routine — it must be an inverter unit giving clean power, sized above the AC charger (a ~7 kW slow charger needs a bigger generator), some cars reject unstable power, and the fuel cost per unit is far above grid charging. For what EV charging actually costs, see EV charging cost: station vs home.

Who wrote this page

Compiled by the CapSolar team, a commercial solar provider in Thailand, led by Frank Lee (Founder). The sizing method uses basic electrical principles (running watts + starting surge + headroom); appliance watts are typical values to check against each nameplate, while fuel consumption and noise depend on model and load — so we give how to read the spec rather than a fixed number. Safety points (never back-feed / run outdoors / choose TISI-marked) follow utility and safety-body guidance. As of Aug 2026 — general information, not personal advice; leave the actual installation to a licensed electrician.

FAQ

Enough for a home's essentials plus one air-con — lights, fridge, fans, TV, wifi, water pump and one ~12,000-BTU air-con — provided you avoid several motors starting at once, since the combined surge can exceed the rating. To run several air-cons together, step up to 7–10 kW or more.

Outages hurting the business — want quiet backup with no refuelling?

For buildings and factories, CapSolar designs solar + battery-backup systems that cut the bill and keep power on during outages — free assessment, no obligation.

Talk to CapSolaror call +66 2 124 5414