How to Size a 2kW/12V Off-Grid Solar System in Europe with GSIKE: 900W PV, LiFePO4 Battery & 12V Cable Math
Continuous power 2000 W (2000 VA) · surge 3000 VA (1.5×) · pure sine wave 230 V / 50 Hz · 12 V battery bus (12.8 V LiFePO4) · single MPPT 60 A solar charger · max PV 900 W, Voc ceiling 160 V DC · AC charger 80 A / combined charge 120 A · no parallel operation · price EUR 149.99
Short answer: sizing a 2 kW / 12 V off-grid system starts from your daily watt-hours and the night load, not from a catalogue wattage, and on a 12 V bus the single hardest part is the copper — at full 2000 W the battery feed carries about 167 A ideal (179 A at 93% efficiency), which forces very short, very thick cables. For a European camper van, garden office, small cabin or backup circuit that uses about 1 kWh per day, the worked result is a single 12.8 V 100 Ah LiFePO4 block (1280 Wh nominal, 1024 Wh usable at 80% depth of discharge), a PV array of roughly 500–750 W built as three 250 W panels in series, and a 12 V battery cable of 70 mm² kept to a 1 metre run (20–25 mm² only if you accept a 3% volt drop). The GSIKE unit's engineering ceiling is 2000 W continuous with a 3000 VA surge; the storefront name "2.5KW" is a tier label, not a higher power rating.
GSIKE 2.5KW 12V inverter: specs, price and reviewsFirst, the current reality — why a 2 kW / 12 V system lives on very thick copper
The single most expensive mistake in a low-voltage off-grid install is sizing parts to a brochure number instead of to the real simultaneous load. Before any calculation, note that the GSIKE unit runs on a 12 V bus (physically a 12.8 V LiFePO4 block, four cells), not 24 V or 48 V.
The voltage-selection rule repeats across every solar sizing guide: about 1–2 kW suits 12 V, about 2–4 kW suits 24 V, and from roughly 3–4 kW upward you need 48 V. At 2 kW a 12 V bus already pulls close to 170 A, which is why this class is described as a camper, cabin and short-run system — never a whole-house system.
Do the quick current comparison first, because it drives every later choice. At full 2000 W output the current on the 12 V bus is I = P ÷ V = 2000 W ÷ 12 V = 166.7 A (ideal, ignoring efficiency). Peak battery-to-inverter efficiency is 93%, so the real battery-side current the cable must carry is I = 2000 W ÷ (12 V × 0.93) = 2000 ÷ 11.16 ≈ 179.0 A. The surge rating is 3000 VA ÷ 2000 W = 1.5×, available only for short motor starts such as a fridge compressor or a small pump — not for continuous cooking load.
That is the honest ceiling: a 12 V bus at ~179 A is why this inverter class uses busbar-style 70 mm² cables and demands the battery be mounted almost beside the inverter. If your simultaneous peak keeps exceeding 2000 W, the right answer is a 24 V or 48 V inverter class, not thicker 12 V cables on this single, non-parallel unit.
The same five formulas run through every step below. You can drop in your own appliances and re-check the whole system in a spreadsheet.
1. Daily energy [Wh] = appliance power [W] × hours of use per day [h].
2. Battery energy [Wh] = nominal voltage [V] × capacity [Ah].
3. Usable Wh = nominal Wh × depth of discharge (for LiFePO4 we use 0.8).
4. Nominal capacity [Ah] = usable Wh needed ÷ DoD ÷ bus voltage [V].
5. Cable cross-section: A = (2 × one-way length [m] × current [A]) ÷ (κ × ΔV), with copper conductivity κ = 56 m/(Ω·mm²) and ΔV the allowed volt drop in volts.
Solar charge ceiling: the single MPPT charger is rated at 60 A, so the theoretical solar charge power into a 12 V bus is 60 A × 12 V = 720 W (at the 13.5 V float it is ~810 W). Above that, extra panels do not push more charge current — the surplus flows straight to midday loads. This is why a 900 W array is the hard maximum and 3 × 250 W (750 W) is the practical sweet spot.
Step 1 — The watt-hour balance for a camper van or garden office
A 12 V 2 kW inverter is sized for a single-room, mobile or backup load: a camper van, a garden office, a small cabin, a tiny home, a shed workshop, or a home backup circuit of essentials. It is not sized for a whole house. The worked anchor in this guide is ~1 kWh/day — LED lighting, a laptop, a TV or router, a small compressor fridge, phone and camera charging, and an occasional small appliance.
Daily load balance (~1 kWh/day reference build)
| Load | Power | Hours/day | Energy/day | Notes |
|---|---|---|---|---|
| LED lighting (4×8 W) | 32 W | 4 h | 128 Wh | Evenings |
| Compressor fridge (avg.) | 45 W | 24 h | ~450 Wh | Cyclical, not constant; 3–5× startup surge |
| Laptop / phone / router | 50 W | 5 h | 250 Wh | Needs pure sine wave |
| TV / media box | 40 W | 2 h | 80 Wh | Evenings |
| LED kettle / microwave (occ.) | 1100 W | 0.15 h | ~165 Wh | Short burst, near the 2000 W ceiling |
| Water pump / small tools | 300 W | 0.2 h | 60 Wh | Inductive startup surge |
| Miscellaneous always-on | 10 W | 10 h | 100 Wh | Standby, sensors |
| Day total | — | — | ≈ 1000 Wh | ≈ 1 kWh/day |
The number that matters is the night without sun. After sunset the PV array stops producing and the battery becomes the only source. For this 1 kWh build, overnight load (roughly 22:00–07:00) is dominated by the fridge and standby electronics — about 300–400 Wh — which is exactly why a single 100 Ah block with ~1024 Wh usable covers one night with margin.
Remember instantaneous power, not just the daily average. A 1100 W kettle, the fridge compressor starting and a laptop charger at the same moment approach the 2000 W ceiling fast. That is why camper owners stagger the kettle and never run a microwave and a kettle together. The 3000 VA surge (1.5×) is reserved for motor starts such as compressor fridges and small pumps, not for continuous cooking.
Step 2 — Sizing the 12.8 V LiFePO4 battery: DoD 80% and one night of autonomy
The GSIKE inverter pairs with 12.8 V LiFePO4 blocks (four cells in series), with BMS communication over RS485. Lithium iron phosphate chemistry is designed around a depth of discharge of 80% — the range where it guarantees a long cycle life. You never pull more than 80% of a block's energy out in a single cycle.
The worked anchor — 1 kWh/day, one night of autonomy
1. Usable energy needed ≈ 1000 Wh for one night (the fridge and standby keep running overnight).
2. Nominal capacity at DoD 0.8 = 1000 Wh ÷ 0.8 = 1250 Wh nominal. Because only 80% is usable, the installed nominal energy has to be larger than the usable target.
3. Convert to amp-hours on the 12.8 V bus = 1250 Wh ÷ 12.8 V ≈ 97.7 Ah.
4. Practical choice = one 12.8 V 100 Ah LiFePO4 block = 1280 Wh nominal, 1024 Wh usable at 80% DoD. That single block covers the planned 1000 Wh usable target with a small winter buffer.
How long does a 12.8 V 100 Ah block actually last?
| Draw at the 230 V outlet | Battery-side current @12 V (at 93%) | Runtime on 1024 Wh usable | Comment |
|---|---|---|---|
| 200 W (laptop + lights + router) | ≈ 18 A | ≈ 4.7 h | Comfortable all-evening load |
| 500 W (TV + fridge cycle + laptop) | ≈ 45 A | ≈ 1.9 h | Typical evening peak |
| 1000 W (half the inverter rating) | ≈ 90 A | ≈ 0.95 h (~57 min) | Short, staggered use |
| 2000 W (full rating, theoretical) | ≈ 179 A | ≈ 0.48 h (~29 min) | Only brief bursts; 1 h at 2000 W needs ~167 Ah |
Two reference builds that map onto real installations:
| Build | Battery | Nominal energy | Usable @ DoD 80% | Autonomy |
|---|---|---|---|---|
| Camper / garden office (~1 kWh/day) | 1 × 12.8 V 100 Ah | 1280 Wh | 1024 Wh | 1 sunny day + 1 short night |
| Small cabin / backup (~2 kWh/day) | 2 × 12.8 V 100 Ah in parallel | 2560 Wh | 2048 Wh | 1–2 nights, fridge + pump + lights |
Charge-rate check: the 60 A MPPT charger into a 100 Ah block is a 0.6C rate; into a 200 Ah pair it is 0.30C. Both are healthy LiFePO4 rates — a 100–200 Ah 12 V bank is the right match for this inverter, and you should not go below ~100 Ah. Wire blocks in parallel (the bus must stay 12.8 V), run equal-length cables so current shares evenly, and keep the RS485 BMS lead connected so the inverter reads state of charge and temperature limits.
Step 3 — Sizing the PV array: 900 W ceiling, 3 × 250 W sweet spot, single MPPT
This unit has a single MPPT solar charger (one tracker channel, 60 A charge, 50 A input), not dual MPPT. The PV input window is MPPT working range 30–160 V DC, open-circuit ceiling 160 V DC, and the engineering ceiling allows up to 900 W of panels on the array side. That is a ceiling on panel power, not a target. (Some generic marketing text implies a much larger 500 V / 120 A channel, but the linked GSK-2KW-12V-WIFI manual, the spec image and the official PV-selection table all agree on 900 W, 160 V and 60 A — plan to those.)
Across most of Europe the year-round mean of effective peak-sun-hours (PSH) is about 3.0 hours per day — lower in the far north, higher in the Mediterranean. Apply a derate of about 0.75 for temperature, dust, MPPT and wiring losses.
The worked anchor — PV for 1 kWh/day
Required Wp = daily Wh ÷ (PSH × derate) = 1000 Wh ÷ (3.0 × 0.75) = 1000 ÷ 2.25 ≈ 444 Wp. Build a little over that for winter margin, so plan ~500–750 Wp — which sits comfortably under the 900 W maximum.
Why 900 W of panels only feeds ~750 W into the battery
Raw 900 W ÷ 12 V ≈ 75 A would flow on paper, but the solar charge stage is capped at 60 A. Above 60 A the surplus PV simply powers midday loads or is absorbed, it does not charge the bank faster. That is why the practical array is ~750 W = three 250 W modules, exactly the example in the official PV-selection table: each 250 W panel runs at Vmpp ~36 V / Impp ~8.3 A / Voc ~40 V, so three in series give ~108 V working (inside 30–160 V) and ~120 V Voc (comfortably under the 160 V cold ceiling).
| Scenario | Daily use | Theoretical Wp = use ÷ (3.0 × 0.75) | Practical build |
|---|---|---|---|
| Camper / garden office | 1 kWh/day | 444 Wp | 500–750 Wp (2–3×250 W) |
| Small cabin / backup | 2 kWh/day | 889 Wp | ~900 Wp (3×300 W) — at the PV ceiling |
| Hard array limit | — | 900 W panels max (single MPPT) | 900 ÷ 250 W ≈ 3 modules; keep string Voc < 160 V |
String voltage check: keep the winter open-circuit voltage below 160 V. With a typical −0.30%/°C Voc coefficient and a −10 °C roof, apply a ×1.10 cold multiplier to the string Voc. Three 250 W panels at 120 V cold sit around 132 V — safe. Do not stack four panels in series on this unit, or the cold Voc can cross 160 V and the MPPT will refuse to start.
Across a year, 1 kWp in central Europe yields roughly 850–1050 kWh (indicative). A 750 Wp array gives about 650–780 kWh a year, averaging ~1.8–2.1 kWh/day in summer but far less in deep winter — which is exactly why the 80% DoD reserve and the 80 A AC input (grid or generator) matter for grey weeks.
Step 4 — The 12 V battery cable cross-section: 70 mm² at 1 m / 1%, 20–25 mm² at 3%
At full 2000 W output the current on the 12 V bus is 166.7 A ideal, and 179.0 A at 93% efficiency. On 12 V the allowed volt drop is tiny: 1% of 12 V = 0.12 V, and even a relaxed 3% = 0.36 V. Using copper conductivity κ = 56 m/(Ω·mm²), the minimum cross-section is A = (2 × L × I) ÷ (κ × ΔV), where the factor 2 accounts for current travelling out and back along the positive and negative leads. A ×1.2 design margin for temperature and ageing is applied on top.
| Case | Working | Theoretical A (×1.2) | Choose copper |
|---|---|---|---|
| 1 m one-way, 1% drop (0.12 V), 166.7 A | (2 × 1 × 166.7) ÷ (56 × 0.12) = 333.4 ÷ 6.72 | 49.6 → ×1.2 = 59.6 mm² | 70 mm² |
| 1 m one-way, 1% drop, 179.0 A (at 93%) | (2 × 1 × 179.0) ÷ (56 × 0.12) = 358 ÷ 6.72 | 53.3 → ×1.2 = 63.9 mm² | 70 mm² |
| 1 m one-way, 3% drop (0.36 V), 166.7 A | (2 × 1 × 166.7) ÷ (56 × 0.36) = 333.4 ÷ 20.16 | 16.5 → ×1.2 = 19.8 mm² | 20–25 mm² (only if 3% drop is acceptable) |
In plain terms: with the battery beside the inverter (a 1 m one-way run), a strict 1% volt drop at full load demands 70 mm² copper — a busbar-thick cable. If you can tolerate a 3% drop at the terminals (a slightly warmer cable and a small voltage sag at the inverter), the gauge drops to 20–25 mm². This is the single most important install rule on a 12 V bus: keep the battery run short. Every extra metre forces either much thicker copper or a much larger volt drop.
Fuse sizing: place the main DC fuse as close to the battery positive terminal as possible, inside a sealed enclosure. The rule of thumb is 1.25 × maximum line current. At the 179.0 A full-load current that gives ≈ 224 A, so a 225–250 A DC fuse or breaker (with a matching DC isolator) is the standard choice. Crimp copper ring terminals with a proper tool — no intermediate connectors — because on a 12 V bus at 179 A every loose joint becomes a hot spot and a fire risk.
Step 5 — The honest comparison: 12 V vs stepping up to 24 V or 48 V
The fair question every smart installer asks is: "do I really want 12 V, or should I step up to 24 V?" The answer depends entirely on your simultaneous power and how long your cable runs are. At the same 2000 W output, current is inversely proportional to voltage — so a 12 V bus pulls roughly double the current of a 24 V bus and quadruple that of a 48 V bus.
| Bus voltage | Ideal current at 2000 W | Real current at 93% | Cable for 1 m / 1% drop | Best for |
|---|---|---|---|---|
| 12 V (this GSIKE unit) | 166.7 A | 179.0 A | ~70 mm² (20–25 mm² at 3%) | Camper, cabin, garden office, backup essentials, short runs |
| 24 V (next class up) | 83.3 A | ~89.6 A | ~16–25 mm² | 2–3 kW, longer runs, small home |
| 48 V (large class) | 41.7 A | ~44.8 A | ~6–10 mm² | 3 kW+ whole-house, long cable runs |
Choose 12 V when your simultaneous load stays under ~2 kW, your battery can sit within 1–2 m of the inverter, your budget wants the cheapest 230 V outlet for a van or shed, and you already own 12 V leisure batteries. Step up to 24 V or 48 V when your peak keeps pushing past 2 kW, your battery room is metres away from the loads, or you want whole-house comfort. The GSIKE 12 V unit is deliberately compact (358 × 295 × 105.5 mm, 6.0 kg) for the short-run, mobile and backup class — it is not the right tool for a whole house.
Honest limits to plan around. This unit is single-unit only — it cannot be paralleled or stacked. Continuous output is a hard 2000 W (3000 VA surge only for short motor starts). It runs on a single MPPT channel. It has no IP rating — only a detachable dust cover — so plan indoor, van or sheltered installation. Support chat is English, and WiFi monitoring is an optional external add-on.
A complete ~1 kWh / 1-night build on paper
Reference camper / garden-office build: one GSIKE 2.5KW 12 V inverter (engineering 2000 W continuous, 3000 VA surge); one 12.8 V 100 Ah LiFePO4 block (1280 Wh nominal, 1024 Wh usable); three 250 W panels in series = ~750 Wp on the single MPPT (under the 900 W ceiling); a 70 mm² battery cable kept to 1 m one-way (20–25 mm² if you accept 3% drop) with a 225–250 A DC fuse near the battery; a 16 A AC feeder breaker; and the 80 A AC input reserved for grey-week top-ups from campsite hook-up or a small generator.
The inverter itself costs EUR 149.99, shipped free to 15 European countries (handling 1–3 days, transit 2–7 days), with 30-day returns. A comparable 12.8 V 100 Ah LiFePO4 block adds roughly EUR 130–180 separately, so the whole ~1 kWh entry build lands around EUR 300–360 before panels and cabling.
The Bottom Line — keep the 12 V bus honest: short runs, thick copper, a small array
The takeaway: on a 2 kW / 12 V system the win is matching the battery to the one-night load, the panels to the daily energy, and the volt drop to a cable that runs almost no distance. For ~1 kWh/day that is one 12.8 V 100 Ah LiFePO4 block (1280 Wh nominal, 1024 Wh usable at 80% DoD), a ~750 Wp array of three 250 W panels (from the 444 Wp calculation, under the 900 W ceiling), and a 70 mm² battery cable at 1 m / 1% drop (20–25 mm² at 3% drop), plus a 225–250 A DC fuse. Stay inside the hard limits: 2000 W continuous, 3000 VA surge (1.5×), single MPPT, 900 W max PV, no parallel — and remember that 12 V roughly doubles the current a 24 V bus would need, which is exactly why this class of system is built around short, thick copper and small daily loads.
Frequently asked questions
How many Ah battery do I need for a 2000W 12V inverter for one hour?
At full 2000 W the 12 V bus draws 2000 ÷ 12 = 166.7 A ideal, or 2000 ÷ (12 × 0.93) = 179.0 A at the inverter's 93% battery efficiency. So running the inverter at full output for one hour needs roughly 167 Ah at 12 V — in practice about 179 Ah to account for efficiency, and you would divide by 0.8 for the 80% depth of discharge. A single 100 Ah block therefore gives only about half an hour at full 2000 W; for a full hour at full load you need a 200 Ah block (two 12.8 V 100 Ah in parallel).
How long will a 12.8V 100Ah LiFePO4 run a 2000W inverter?
A 12.8 V 100 Ah block holds 12.8 × 100 = 1280 Wh nominal, of which 80% (1024 Wh) is safely usable. At a 200 W evening load (laptop, lights, router) that is about 4.7 hours; at 500 W about 1.9 hours; at 1000 W about 57 minutes. At the full 2000 W rating it lasts only about 29 minutes, because 2000 W is the continuous ceiling and a 100 Ah block is sized for a camper or cabin, not full-power endurance.
What size 12V battery cable do I need for a 2000W inverter at 1 metre?
Full-load current is 166.7 A ideal or 179.0 A at 93% efficiency. Using A = (2 × L × I) ÷ (κ × ΔV) with copper κ = 56: at 1 m one-way and a strict 1% drop (0.12 V) the area is 49.6 mm² at 166.7 A (53.3 mm² at 179.0 A), which with a ×1.2 margin gives 59.6–63.9 mm² — so choose 70 mm². If you accept a 3% drop (0.36 V), the area falls to 16.5 mm² and a 20–25 mm² cable suffices. Keep the run short either way.
Why does a 12V 2kW inverter need such thick cable (70 mm²)?
Because at 12 V, 2000 W is a very high current: 166.7 A ideal, 179.0 A at 93% efficiency. Ohm's law means even a tiny resistance at that current drops a lot of volts and heats the cable. To hold the volt drop to just 1% (0.12 V) over 1 m, the copper cross-section has to be ~60–64 mm² after margin — hence 70 mm². This is the defining trade-off of a 12 V system: thick, expensive cable, but only if the battery sits right next to the inverter.
What is the maximum PV array size for the GSIKE 12V 2kW inverter?
The single MPPT accepts a maximum of 900 W of panels, with an open-circuit ceiling of 160 V DC and a working range of 30–160 V. The solar charge current is capped at 60 A (50 A input). The official PV-selection example is three 250 W panels in series (750 W, ~108 V working, ~120 V Voc), which is the practical sweet spot — extra panels beyond ~750–900 W do not charge the battery faster because the 60 A stage limits the current.
Why is the practical solar array only 750W when the maximum is 900W?
Raw 900 W ÷ 12 V would be about 75 A, but the solar charger is capped at 60 A. Above 60 A the surplus PV does not push more charge into the battery — it only powers midday loads directly. So 900 W is the array-side hardware ceiling, while 3 × 250 W = 750 W is the build that matches the charger without wasting panel wattage. At 60 A × 12 V the theoretical solar charge power is 720 W (about 810 W at the 13.5 V float).
What DC fuse rating protects a 12V 2kW battery feed?
Place the fuse as close to the battery positive terminal as possible, inside a sealed enclosure. Size it at about 1.25 × the maximum line current: 1.25 × 179.0 A ≈ 224 A, so a 225–250 A DC fuse or breaker with a matching DC isolator is the standard choice. Use properly crimped copper lugs and avoid intermediate connectors, because a loose joint at 179 A on a 12 V bus overheats very quickly.
Should I choose 12V or step up to 24V for a 2kW camper system?
Stay on 12 V if your peak load is under ~2 kW, the battery can sit within 1–2 m of the inverter, and you already own 12 V leisure batteries. Step up to 24 V if your peak keeps approaching or passing 2 kW, or if the battery room is metres away from the loads. At 2000 W a 24 V bus draws only ~89.6 A (about half the 179 A at 12 V), which drops the cable from 70 mm² to roughly 16–25 mm² and lets you run longer distances.
How many watt-hours per day does a camper van or garden office actually use?
A compact camper van or insulated garden office using LED lighting, a laptop, a TV or router, a small compressor fridge and phone charging typically draws 0.8–1.5 kWh per day. The worked build here uses ~1000 Wh: fridge ~450 Wh, lighting 128 Wh, laptop/router 250 Wh, TV 80 Wh, an occasional kettle or microwave ~165 Wh, pump 60 Wh and standby 100 Wh. Build your own list by multiplying each appliance's wattage by its hours of use.
Why is the 12V inverter current 167A but the cable current figure 179A?
The 166.7 A is the ideal current: 2000 W ÷ 12 V. The 179.0 A is the real current the battery must supply, because the inverter loses about 7% converting DC to 230 V AC (93% battery-to-inverter efficiency). To deliver 2000 W at the outlet, the battery actually has to push 2000 ÷ (12 × 0.93) ≈ 179 A. For cable and fuse sizing you should design to the higher 179 A figure, not the ideal 167 A.
Sources and figures used in the math
The figures below are the parameter and data sources behind the calculations. Consumption and climate values are indicative for a European-wide mean across the 15 shipping countries.
• GSIKE 2.5KW 12 V product page and the linked GSK-2KW-12V-WIFI manual (2000 W continuous, 3000 VA surge, single 60 A MPPT, 900 W max PV, 160 V Voc, 30–160 V working, AC charge 80 A / combined 120 A, price EUR 149.99): gesike.com.
• European single-phase supply standard 230 V / 50 Hz (EN 50160) and indicative PV yield of 850–1050 kWh per kWp per year across Europe; about 3.0 peak-sun-hours as a year-round mean.
• Copper conductivity κ = 56 m/(Ω·mm²) and the voltage-drop formula A = (2·L·I) ÷ (κ·ΔV); cross-checked against published DC cable-sizing guidance that puts 24 V as the preferred bus above ~2–3 kW and 12 V below ~2 kW.
• LiFePO4 chemistry designed around 80% depth of discharge for long cycle life; block nominal voltage 12.8 V (4S), float charge 13.5 V, overcharge protection 14.1 V.
Guides & comparisons
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