12 V solar for an RV, boat or small DIY
A van, a nipa hut, a farm shed: a 100–200 W panel, a 12 V LiFePO4 battery, 12 V loads straight from the controller and a small inverter for the odd 220 V tool.
Open it in the simulator ▸Size it from my electric bill
What is in it
200 W of panels, a 12 V 100 Ah LiFePO4 battery (1.3 kWh), 300 W of inverter. 15 parts in all, wired and sized the way the lab's solar studio sizes them.
- One 200 W panel, 2.5 mm² PV cable
24 V Voc, 11 A: a 20 A MPPT with margin. - Controller’s load terminals for the 12 V loads
The controller’s own low-voltage disconnect protects the battery from the 12 V loads; a 10 A fuse protects the thin wire. - 12 V 100 Ah LiFePO4, 60 A breaker
1.1 kWh usable; the breaker covers the 300 W inverter’s 29 A × 1.25 and the controller. - A 300 W inverter on its own breaker
For a laptop or a drill; not for a kettle (that is 1500 W). - DC SPD, ground rod
Even a shed gets lightning.
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 1.2 kWh and the loads used 1.9 kWh; the battery went between 3 % and 80 %. The example loads are more than this array refills in one day: in the simulator, add panels or cut a load and run the day again.
Parts and prices
Philippine prices as estimates (about US$399 in all at ₱64 per US$). 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 300 W · DC 12 V in | 1 | ₱2,500 |
| Solar charge controller MPPT 20 A solar charge controller, PV 100 V · MPPT 20 A | 1 | ₱4,200 |
| Solar panel 200 W · 40-cell mono | 1 | ₱3,600 |
| LiFePO4 battery LiFePO4 12.8 V 100 Ah · 1280 Wh | 1 | ₱10,500 |
| AC breaker 2-pole MCB · C10 | 1 | ₱280 |
| DC breaker 2-pole MCB · C16 | 1 | ₱380 |
| DC breaker 2-pole MCB · C60 | 1 | ₱380 |
| Fuse Blade fuse (ATO) in inline holder · 10 A | 1 | ₱45 |
| Fuse Blade fuse (ATO) in inline holder · 30 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 60 W | 1 | ₱90 |
| DC motor 130-size brushed · ~6 Ω | 1 | ₱60 |
| 12 V Wi-Fi router Wi-Fi router · DC 12 V 1 A in (5.5 × 2.1 mm, centre +) | 1 | ₱950 |
| 10 AWG (5.5 mm²) THHN black | 1 m | ₱75 |
| 10 AWG (5.5 mm²) THHN red | 1 m | ₱75 |
| 14 AWG (2.0 mm²) THHN any colour | 4 m | ₱140 |
| 14 AWG (2.0 mm²) THHN black | 1 m | ₱35 |
| 14 AWG (2.0 mm²) THHN red | 2 m | ₱70 |
| 18 AWG (0.75 mm²) cord black | 2 m | ₱36 |
| 18 AWG (0.75 mm²) cord red | 1 m | ₱18 |
| 8 AWG (8 mm²) battery cable black | 1 m | ₱120 |
| 8 AWG (8 mm²) battery cable red | 1 m | ₱120 |
| PV cable 2.5 mm² black | 1 m | ₱45 |
| PV cable 2.5 mm² red | 1 m | ₱45 |
| Ring lugs for 8 AWG tinned copper, crimp + heat-shrink | 8 | ₱120 |
| Estimated total | ₱25,529 |
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 12 V bank
- ✓ Inverter 300 W set for the 12 V bank
- ✓ Battery to Inverter 300 W 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 300 W sized for its loads
- ✓ AC breaker on the inverter output
Questions
How big is this 12 v solar for an rv, boat or small diy?
As drawn: 200 W of panels, a 12 V 100 Ah LiFePO4 battery (1.3 kWh), 300 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?
There is no grid in it: the battery carries the loads, the panel refills it by day.
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 17 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 · Off-grid inverter + ATS (budget hybrid) · AC-coupled solar with battery · Three-phase grid-tie solar