Off-grid inverter + ATS (budget hybrid)
The budget “hybrid” many Philippine homes build: an off-grid inverter runs the house from the battery, and an automatic transfer switch moves the house to the grid when the inverter stops on low battery, then back when solar has charged it. The grid never charges the battery here; the MPPT does. A true hybrid inverter does all this in one box.
Open it in the simulator ▸Size it from my electric bill
What is in it
800 W of panels, a 24 V 200 Ah LiFePO4 battery (5.1 kWh), 2,000 W of inverter. 25 parts in all, wired and sized the way the lab's solar studio sizes them.
- Two strings of two 200 W modules, MPPT 40 A, 24 V 200 Ah LiFePO4
The same solar side as the off-grid template: the battery is charged only by the sun. - Off-grid inverter, 2 kW pure sine
It runs the house while the battery lasts and stops at its low-voltage cut-off. It has no anti-islanding, so it must never meet the grid. - Inverter breaker 16 A and main breaker 32 A
An ATS does not protect: each source gets its own breaker in front of it. - ATS 2P 63 A, priority II (the inverter), back after 10 s
Both L and N switch, and the two sides are interlocked, so the grid and the inverter never meet. When the inverter stops, the house moves to the grid in a fraction of a second; when the inverter is back and steady for 10 s, the house moves back to solar. - Loads breaker 20 A after the ATS
The house circuits, whichever source feeds them. - kWh meter, AC SPD, ground rod
The utility side as usual; the SPD at the service, the rod for both SPDs. - Loads: a refrigerator, lights, a fan and a TV
The refrigerator’s compressor runs about 10 hours a day (150 W while it runs), the lights 6 hours, the fan 10, the TV 5: about 3 kWh a day. On a clear day the 800 W array harvests about 4.7 kWh, so the battery ends the day well above empty.
A clear day on this system
The lab ran this exact system through a clear day: 36 hours from 18:00 the evening before. The panels harvested 4.7 kWh and the loads used 5.4 kWh; the battery went between 33 % and 80 %.
Parts and prices
Philippine prices as estimates (about US$1,322 in all at ₱64 per US$). In the simulator, Buy all the parts gives the same list with shop links where we have them.
| Part | Qty | Est. |
|---|---|---|
| Power inverter Pure sine 2000 W · DC 24 V in | 1 | ₱14,000 |
| Solar charge controller MPPT 40 A solar charge controller, PV 100 V · MPPT 40 A | 1 | ₱7,200 |
| Solar panel 200 W · 40-cell mono | 4 | ₱14,400 |
| LiFePO4 battery LiFePO4 25.6 V 200 Ah · 5120 Wh | 1 | ₱37,050 |
| AC breaker 2-pole MCB · C16 | 1 | ₱280 |
| AC breaker 2-pole MCB · C20 | 1 | ₱280 |
| AC breaker 2-pole MCB · C32 | 1 | ₱280 |
| Automatic transfer switch (AC, dual power) Dual-power automatic transfer switch · 2-pole (L and N) | 1 | ₱2,600 |
| DC breaker 2-pole MCB · C125 | 1 | ₱380 |
| DC breaker 2-pole MCB · C40 | 1 | ₱380 |
| Fuse Blade fuse (ATO) in inline holder · 20 A | 2 | ₱90 |
| Fuse Blade fuse (ATO) in inline holder · 60 A | 1 | ₱45 |
| Surge protector (SPD) AC SPD, Type 2, 275 V · DIN-rail module, two pluggable varistor cartridges with a status window each | 1 | ₱650 |
| Surge protector (SPD) PV DC SPD, Type 2, 600 V · DIN-rail module, two pluggable varistor cartridges with a status window each | 1 | ₱950 |
| 220 V bulb A60 E27 · LED 54 W | 1 | ₱90 |
| 220 V desk fan 12-inch desk fan · 40 W | 1 | ₱950 |
| Household appliance LED TV 43" · 100 W | 1 | — |
| Household appliance Refrigerator · 150 W | 1 | — |
| 1/0 AWG battery cable black | 1 m | ₱520 |
| 1/0 AWG battery cable red | 1 m | ₱520 |
| 12 AWG (3.5 mm²) THHN any colour | 5 m | ₱240 |
| 12 AWG (3.5 mm²) THHN red | 5 m | ₱240 |
| 14 AWG (2.0 mm²) THHN any colour | 3 m | ₱105 |
| 14 AWG (2.0 mm²) THHN black | 1 m | ₱35 |
| 14 AWG (2.0 mm²) THHN red | 1 m | ₱35 |
| 8 AWG (8 mm²) battery cable black | 1 m | ₱120 |
| 8 AWG (8 mm²) battery cable red | 1 m | ₱120 |
| 8 AWG (8.0 mm²) THHN any colour | 1 m | ₱110 |
| 8 AWG (8.0 mm²) THHN red | 1 m | ₱110 |
| PV cable 10 mm² black | 9 m | ₱1,260 |
| PV cable 10 mm² red | 9 m | ₱1,260 |
| PV cable 4 mm² black | 2 m | ₱120 |
| PV cable 4 mm² red | 2 m | ₱120 |
| Ring lugs for 8 AWG tinned copper, crimp + heat-shrink | 6 | ₱90 |
| Estimated total | ₱84,630 |
What the safety check verifies
- ✓ Cold-morning Voc inside the MPPT controller's input
- ✓ Hot-noon Vmp stays above the controller’s minimum
- ✓ PV conductors rated for 1.56 × Isc
- ✓ Array-to-controller voltage drop
- ✓ DC disconnect between array and controller
- ✓ MPPT controller set for the 24 V bank
- ✓ Inverter set for the 24 V bank
- ✓ Battery to Inverter protected: Battery breaker
- ✓ Battery disconnect: Battery breaker
- ✓ Battery-to-inverter drop
- ✓ Battery to MPPT controller protected: Battery breaker, Controller fuse
- ✓ Battery-to-controller drop
- ✓ Inverter sized for its loads
- ✓ AC breaker on the inverter output
Questions
How big is this off-grid inverter + ats (budget hybrid)?
As drawn: 800 W of panels, a 24 V 200 Ah LiFePO4 battery (5.1 kWh), 2,000 W of inverter. Every size can be changed in the simulator, and Solar & wiring → My house sizes one from your electric bill.
Does it work in a brownout?
Yes, and it keeps running on solar first: the automatic transfer switch moves the house to the grid only when the inverter stops (low battery), and back when it returns.
Is the wiring diagram correct?
It is drawn from the working simulation: every line is a real connection on the bench, and the safety check passes 23 checks with no fails. It is a design to learn from and adapt: check it against your local electrical code and the manuals of the parts you buy.
On the bench
Open it in the simulator ▸All solar systems and builds
Other systems
Off-grid solar system · Grid-tie solar system · Hybrid solar system · AC-coupled solar with battery · 12 V solar for an RV, boat or small DIY · Three-phase grid-tie solar