You are planning your off-grid camping setup and wondering: “What battery capacity do I really need to be self-sufficient with solar for several days?” The wrong sizing quickly leads to empty batteries – or to oversized, expensive and heavy systems that you cannot fully utilise. This is exactly where this guide comes in: you get a detailed lookup table for 50 to 400 watt solar panels, tried-and-tested rules of thumb, step-by-step calculation examples and concrete storage recommendations for LiFePO4 and AGM batteries. Electronicx provides you with all the tools to perfectly size your solar battery – for true self-sufficiency, even in bad weather.
What to expect on this page: The complete 2026 solar panel table with daily yields, a bad-weather factor calculation, three fully worked camping setups and eight common planning mistakes that you will reliably avoid. All data is based on real measurements with MPPT charge controllers and our LiFePO4 and AGM batteries – no marketing blurb, but solid figures for your planning.
The complete solar panel watt (50-400W) table 2026
The following table shows you at a glance what charge current you can expect from your solar panel, how many amp-hours you harvest per day in summer and winter – and which battery capacity we recommend for it. The basis is a 12V on-board system with MPPT charge controller (maximum power point tracking) and an alignment of the modules to the south with 30-45 degree tilt. The winter values already include the real bad-weather factor of 0.3. Use the table as a quick introduction to roughly size your system – fine-tuning is then done with the rules of thumb and calculation examples further below.
| Solar panel (watt) | Charge current MPPT (A) | Daily yield summer (Ah) | Daily yield winter (Ah) | Rec. battery min. (Ah) | Days of autonomy at 40 Ah/day | Storage recommendation |
|---|---|---|---|---|---|---|
| 50 W | 4,2 A | 21 Ah | 6 Ah | 50 Ah | 0.5 days | AGM 50Ah / LiFePO4 50Ah |
| 80 W | 6,7 A | 34 Ah | 10 Ah | 75 Ah | 0.9 days | AGM 75Ah / LiFePO4 80Ah |
| 100 W | 8,3 A | 42 Ah | 13 Ah | 100 Ah | 1.3 days | AGM 100Ah / LiFePO4 100Ah |
| 120 W | 10,0 A | 50 Ah | 15 Ah | 120 Ah | 1.5 days | AGM 120Ah / LiFePO4 120Ah |
| 150 W | 12,5 A | 63 Ah | 19 Ah | 150 Ah | 1.9 days | AGM 150Ah / LiFePO4 150Ah |
| 180 W | 15,0 A | 75 Ah | 23 Ah | 180 Ah | 2.3 days | AGM 180Ah / LiFePO4 200Ah |
| 200 W | 16,7 A | 84 Ah | 25 Ah | 200 Ah | 2.5 days | AGM 200Ah / LiFePO4 200Ah |
| 220 W | 18,3 A | 92 Ah | 28 Ah | 220 Ah | 2.8 days | AGM 220Ah / LiFePO4 230Ah |
| 250 W | 20,8 A | 105 Ah | 32 Ah | 250 Ah | 3.1 days | AGM 250Ah / LiFePO4 280Ah |
| 280 W | 23,3 A | 117 Ah | 35 Ah | 280 Ah | 3.5 days | AGM 280Ah / LiFePO4 300Ah |
| 300 W | 25,0 A | 126 Ah | 38 Ah | 300 Ah | 3.8 days | AGM 300Ah / LiFePO4 320Ah |
| 320 W | 26,7 A | 134 Ah | 40 Ah | 320 Ah | 4.0 days | AGM 320Ah / LiFePO4 340Ah |
| 350 W | 29,2 A | 147 Ah | 44 Ah | 350 Ah | 4.4 days | LiFePO4 400Ah |
| 380 W | 31,7 A | 159 Ah | 48 Ah | 380 Ah | 4.8 days | LiFePO4 400Ah |
| 400 W | 33,3 A | 168 Ah | 50 Ah | 400 Ah | 5.0 days | LiFePO4 460Ah |
The values are based on an average solar irradiation of 5 kWh/m2 per day (summer, Germany) and a system efficiency of 85 percent with MPPT charge controller. The winter yield only takes into account 30 percent of the summer sun as well as shorter day lengths. The recommended battery capacity follows the rule of thumb "battery Ah = solar watt", which is explained in more detail in the next section. In the storage recommendations, AGM batteries are listed as a cost-effective option and LiFePO4 batteries as a premium solution with higher cycle stability and lower weight – both are available from us in suitable case sizes and ready to use.
Important rules of thumb for selection
This value is calculated conservatively and applies to a well-aligned 100-watt module with MPPT charge controller in the months from May to September in Germany. With suboptimal alignment or partial shading, the yield drops by up to 30 percent. Our table above shows 42 Ah, as we calculate with 5 full sun hours – the 30-Ah rule of thumb gives you a safe planning basis for variable conditions. Remember: if in doubt, calculate with 30 Ah, then you have a buffer.
From November to February you must expect dramatically less solar power. Short days, low sun angle and frequent cloud cover reduce the yield to about one third. Anyone wanting to camp off-grid all year round should triple the battery capacity or install larger modules. With a 200W module you harvest 84 Ah in summer, but only around 25 Ah in winter – that is enough for a frugal consumer day, but no reserves can be built up. Without an additional charging source (shore power, alternator), pure solar self-sufficiency in winter is hardly feasible unless you massively oversize.
For Central European conditions, we recommend sizing your battery so that it can cover your daily consumption for three full days without any solar yield. At 50 Ah daily consumption, you therefore need 150 Ah of usable capacity. Since LiFePO4 batteries may be discharged to 80 per cent, 190 Ah nominal capacity is sufficient for this (190 x 0.8 = 152 Ah). AGM batteries should only be discharged to 50 per cent, so you need 300 Ah. The 3-day rule protects you from warm fridges and flat smartphones, even if it rains for three days in a row. In sunny regions such as Southern Europe, you can reduce this to 2 days.
This golden rule ensures a balanced system: for every 100 Ah of battery capacity, install 100 watts of solar power. A 200 Ah battery therefore gets 200 watts on the roof. Why? Because this allows you to bring the battery from 20 to 80 per cent charge on a sunny day – while at the same time covering your daily consumption. With a 200 Ah LiFePO4 battery and 200W solar (84 Ah yield per day) and 50 Ah consumption, 34 Ah net remain each day, which go into the reserve. After three sunny days, you have rebuilt your 100 Ah reserve. Deviations are of course possible, but this 1:1 rule has proven itself in thousands of camping installations.
PWM controllers (pulse width modulation) are inexpensive, but they give away valuable power. An MPPT controller adjusts the voltage dynamically and gets up to 20 per cent more current out of your module – especially in cold weather and at a low battery state of charge. With a 200W module, that is around 5-7 Ah more per day that you would otherwise be missing. Do not overestimate this advantage: the extra yield is real, but with small systems under 100W or in Southern Europe it is not decisive.
Calculation examples step by step
Example 1: Compact camper with 200 Ah LiFePO4 and 200W solar
Initial situation: A Ducato conversion with a compressor cool box (25 Ah/day), LED lighting (5 Ah/day), smartphone/laptop charging (10 Ah/day) and water pump (5 Ah/day). Total consumption: 45 Ah per day. Desired self-sufficiency: 3 days without mains power even in bad weather. Available or planned: 200W solar module on the roof, MPPT charge controller, 200 Ah LiFePO4 battery (usable capacity at 80% DOD: 160 Ah).
- Step 1: Determine base consumption and reserve. Daily consumption = 45 Ah. Bad-weather reserve for 3 days = 3 x 45 Ah = 135 Ah. These 135 Ah must still be in the battery after three rainy days, otherwise it becomes critical.
- Step 2: Calculate solar yield. According to the rule of thumb, 200W solar delivers about 60 Ah per day in summer (conservative, our table shows 84 Ah – we calculate with 60 Ah for safety). Of this, 45 Ah go directly into consumption, leaving 15 Ah net for the reserve.
- Step 3: Simulate reserve development. On day 1 (sunny): consumption 45 Ah, yield 60 Ah, surplus 15 Ah. Battery starts at full charge with 160 Ah usable. On the evening of day 1: 160 - 45 + 60 = 175 Ah (capped at 160, as full). No net reduction. On day 2 (rain): yield only 8 Ah (winter/bad weather), consumption 45 Ah, deficit 37 Ah. Battery in the evening: 160 - 37 = 123 Ah. On day 3 (rain): deficit again 37 Ah, battery falls to 86 Ah. On day 4 (rain): deficit 37 Ah, battery falls to 49 Ah – still above the deep discharge threshold of 20 per cent (32 Ah).
- Step 4: Interpret the result and choose the battery. The 200 Ah LiFePO4 battery therefore lasts three full rainy days without being damaged. On the fourth day, sun or mains power would be essential. With an AGM battery (only 50 per cent DOD, i.e. 100 Ah usable), the calculation would look different: the reserve would already be used up on the second rainy day. LiFePO4 is therefore the clear recommendation here. Our Electronicx LiFePO4 200Ah with current BMS fits perfectly.
Result: 200 Ah LiFePO4 + 200W solar = 3 days of bad-weather self-sufficiency at 45 Ah daily consumption. The system is well balanced and meets the 3-day rule.
Example 2: Family caravan with high consumption
Initial situation: A large caravan with four people, compressor cool box (40 Ah/day), parking heater with fan (30 Ah/day in winter), two tablets and laptops (20 Ah/day), television (15 Ah/day), various small consumers (10 Ah/day). Total daily consumption: 115 Ah. Goal: 3 days of self-sufficiency in spring/autumn with bad-weather reserve. Planned: 400W solar on the roof, MPPT charge controller, battery sought.
- Step 1: Determine base value. 3-day reserve = 3 x 115 Ah = 345 Ah usable capacity. Since we recommend a LiFePO4 battery, we calculate with 80 per cent depth of discharge. Required nominal capacity = 345 Ah / 0.8 = 431 Ah.
- Step 2: Check solar yield. According to the table, 400W solar generates 168 Ah per day in summer, but only 50 Ah in winter. In spring/autumn we assume an average of about 100 Ah. Consumption is 115 Ah, so even in spring there is a deficit of 15 Ah per day. This means: without shore power or alternator, the battery would gradually discharge each day.
- Step 3: Calculate allowance for deficit. For 3 rainy days with no yield at all: 3 x 115 Ah = 345 Ah deficit. In bad weather with still 20 percent solar (20 Ah per day): 3 x (115 - 20) = 285 Ah deficit. The battery must therefore deliver at least 345 Ah usable – which again leads to a nominal capacity of 431 Ah.
- Step 4: Round the result and select the battery. We recommend a 460 Ah LiFePO4 battery (368 Ah usable) or two parallel 230 Ah LiFePO4 batteries (460 Ah, 368 Ah usable). This puts the reserve just above the required 345 Ah. Alternative: save power by switching off the parking heater overnight or using a diesel heater. Battery recommendation: Electronicx LiFePO4 460Ah Marine Pro with integrated heating system for low temperatures.
Result: 460 Ah LiFePO4 + 400W solar = 3 days of bad-weather self-sufficiency at 115 Ah daily consumption only with additional power discipline or occasional shore power. Year-round self-sufficiency would be better solved with 600W solar and 600 Ah.
Example 3: Minimalist van life bus with 100 Ah and 120W solar
Initial situation: A VW T4 bus with a frugal setup: thermoelectric cooler (15 Ah/day), LED light (3 Ah/day), phone charging (5 Ah/day), occasionally a small fan (5 Ah/day). Total consumption: 28 Ah per day. Available: 120W folding solar panel (mobile setup), MPPT charge controller, battery needed. Desired self-sufficiency: 2 days during a festival weekend even in rain.
- Step 1: Determine base value. 2-day reserve = 2 x 28 Ah = 56 Ah usable. With LiFePO4 (80% DOD), nominal capacity = 56 Ah / 0.8 = 70 Ah. With AGM (50% DOD), it would be 112 Ah. The weight and space disadvantage of AGM is significant in a small bus.
- Step 2: Calculate solar yield. 120W solar = 50 Ah yield per day (table). In festival weather with mixed conditions (sun/clouds), we halve it to 25 Ah. Deficit in bad weather: 28 Ah consumption minus 25 Ah yield = 3 Ah – almost balanced.
- Step 3: Reserve simulation. On day 1 (cloudy): battery starts full (70 Ah LiFePO4). Consumption 28 Ah, yield 25 Ah, deficit 3 Ah. Battery in the evening: 67 Ah. On day 2 (rain): yield only 5 Ah, deficit 23 Ah. Battery in the evening: 44 Ah – that is still 63 percent, well above the critical mark of 20 percent. No problem.
- Step 4: Result and battery choice. The 70 Ah LiFePO4 is sufficient for the festival weekend. You can even add a third day as long as it does not rain continuously. Recommendation: Electronicx LiFePO4 100Ah Slim – slightly larger, but future-proof in case an additional consumer is added. Weight: only 12 kg, fits under the seat.
Result: 100 Ah LiFePO4 + 120W solar = comfortable 3-day self-sufficiency in a minimalist setup. The investment is low, the gain in freedom enormous.
Practical tips
- Always mount the MPPT charge controller directly at the battery: Longer cable runs between controller and battery cause voltage drop and falsify the charge termination voltage. The cables from the solar panel to the controller may be longer, but please use a sufficient cross-section (at least 4 mm2 for 200W).
- Use battery temperature sensor: AGM batteries require temperature-dependent charge voltages (temperature compensation), otherwise overcharging in summer or undercharging in winter may occur. Our LiFePO4 batteries have the BMS internally, but an external sensor on the charge controller still increases safety.
- Never place solar panels directly over a heated roof hatch: The heat of the stagnant air under the panel reduces efficiency by up to 15 percent. Ensure rear ventilation or mount the panel on a support with distance from the roof. With flexible panels on curved roofs, the adhesive may otherwise come loose over time.
- Do not fully utilise battery capacity on the very first day: New LiFePO4 batteries only reach their full capacity after 5 to 10 charge cycles. Plan a conservative discharge for the first trip (maximum 50 percent DOD), then the BMS will settle in.
- When connecting multiple batteries in parallel, all batteries must have exactly the same state of charge: Never connect a full and an empty battery in parallel, as this causes extreme equalising currents that can overload the BMS electronics. Charge both individually beforehand – or buy a suitable large battery from our range straight away.
- Think about the quiescent currents: Many campers forget that the parking heater, radio memory, gas alarm and USB sockets also draw power when stationary. In newer vehicles this can be 2-5 Ah per day – over a week that adds up to 35 Ah that you had not otherwise planned for. Measure your quiescent current before sizing the system.
- Do not underestimate the power consumption of a compressor cool box: In high summer at 35 degrees inside the vehicle, the box runs almost continuously and easily consumes 40-50 Ah per day. For trips to southern Europe, plan for 20 per cent more consumption than the catalogue figures.
Common mistakes when choosing - and how to avoid them
- Battery too small because only the daily consumption is considered: Many think: “50 Ah consumption, I'll buy a 55 Ah battery and that's fine.” Three rainy days later the battery is deeply discharged and ruined. Solution: always apply the 3-day rule and take into account the usable capacity range (50% AGM, 80% LiFePO4).
- No MPPT controller for larger systems: From 150W solar upwards, a PWM controller is no longer any fun – the wasted power adds up and the charging time increases.
- Expectation of “winter self-sufficiency” with too little solar: Anyone who wants to camp reliably self-sufficiently in January with 200W solar and 100 Ah will be disappointed. Solution: either adjust the expectation (mains power every 2-3 days), or triple the solar area – more realistic is a combination with alternator charging or a portable generator.
- Modules mounted flat instead of tilted: Modules mounted horizontally collect snow and rain in the winter half-year, and in summer they lose up to 25 per cent of yield due to the shallow angle of incidence. Solution: use tiltable mounts or mobile modules that you can align towards the sun.
- Battery and charge controller too far apart and connected with too thin a cable: At 20A charging current and 2.5 mm2 cable over 5 metres, you lose around 0.3 volts – enough to prevent the battery from ever being fully charged. Solution: choose the minimum cross-section according to the table, at least 6 mm2 for 200W.
- Not charging the battery fully on a regular basis: AGM batteries must reach 100 per cent at least once a week, otherwise they sulphatise and lose capacity. LiFePO4 batteries are more tolerant here, but they too like regular full charges to synchronise the BMS. Solution: if you have no sun, connect the battery to mains power every 5-7 days.
Frequently asked questions (FAQ)
What Ah do I need for 200W solar and 3 days of self-sufficiency?
With typical camping consumption of 40-50 Ah per day, you need around 120-150 Ah of usable capacity for a 3-day bad-weather reserve. With a LiFePO4 battery (80% DOD) that is 150-190 Ah nominal capacity, i.e. a 200 Ah battery. With AGM (50% DOD) you need 240-300 Ah, which corresponds to a 250 or 300 Ah battery. The rule of thumb “200W solar = 200Ah battery” fits exactly here and reliably covers your needs. If you have higher consumption (e.g. 80 Ah/day), increase to 300 Ah LiFePO4 or install a second 200W module.
What happens if the battery is too small?
An undersized battery will constantly be discharged too deeply. With AGM batteries this leads to irreversible capacity loss through sulphation after just 20-30 deep discharges – the battery “dies” within a few months. With LiFePO4 batteries the BMS does protect against dangerous deep discharge below 2.5V per cell, but here too the service life shrinks from the usual 3000-5000 cycles to under 1000 cycles if you regularly go into the red zone. On top of that, you constantly worry about power: no reliable fridge, no parking heater – that spoils any camping trip.
Can AGM and LiFePO4 batteries be combined?
No, that is not a good idea. AGM and LiFePO4 batteries have different charging characteristics: AGM requires 14.4-14.8V end-of-charge voltage, LiFePO4 only 14.2-14.6V. An MPPT charge controller can only ever run one profile. If you connect both in parallel, either the AGM will be overcharged (voltage too high) or the LiFePO4 will never be properly full. They also have different internal resistances, which can lead to unequal currents and thermal problems. Decide on one battery type and size it correctly. If you must combine both worlds, use a DC-DC converter between the systems that charges independently.
Why is MPPT better than PWM for solar?
A PWM controller simply switches the solar module directly onto the battery as soon as the voltage is right. This means that an 18V module is pulled down to 12-14V and the surplus voltage is dissipated as heat in the module. An MPPT controller converts the surplus voltage into additional current – with the same module output you get up to 20 per cent more current into the battery. The effect is greatest at cold temperatures (in the morning in spring) and with a low battery state of charge. Specifically: from a 100W module a PWM controller draws about 5.5A, an MPPT controller 7-8A. Over the day that is 6-8 Ah more – in a week you have gained an extra day's ration of power.
Which charge controller suits my solar system?
That depends on the module voltage and the charge current. For standard 12V systems up to 200W an MPPT controller with 20A rated current is sufficient (e.g. Victron SmartSolar 75/15 or Electronicx MPPT 20A). At 300-400W you need a 30A controller (Victron SmartSolar 100/30 or Electronicx MPPT 30A). If you connect modules in series at 24V or 36V, you need a controller with a higher input voltage (e.g. 75V or 100V max PV). Our controllers are explicitly optimised for charging LiFePO4 batteries and offer adjustable profiles, temperature sensors and Bluetooth monitoring. The controller should always have about 20 per cent reserve at maximum current so that it does not go into overload on cold days.
What is the benefit of a battery heater for LiFePO4?
LiFePO4 batteries must not be charged below 0 degrees Celsius, otherwise lithium dendrites will grow and destroy the battery. They may be discharged down to -20 degrees, but with reduced capacity. An integrated battery heater (as in our Electronicx LiFePO4 Marine Pro) warms the cells to about 5 degrees via a heating resistor before charging. A small part of the solar current or charger current is used for this (about 30-50 watts for 20-30 minutes). After that, charging is enabled. For winter campers planning a skiing holiday with solar and LiFePO4, the heater is indispensable – otherwise the battery literally stays cold. Our models with heater cost about 15 per cent more, but are the right choice for all-year users.
How many Ah does a battery lose per month without use?
LiFePO4 batteries have an extremely low self-discharge of about 2-3 per cent per month. With a 100-Ah battery that is 2-3 Ah per month, so after 6 months of storage still 80-85 per cent charge. AGM batteries discharge at 5-8 per cent per month, i.e. 5-8 Ah – after 6 months they are below 50 per cent and must be recharged, otherwise they will sulphate. That is why LiFePO4 batteries are the better choice for seasonal campers who put their vehicle away over the winter. Simply store at about 70 per cent charge, switch off the main switch – and in April it is ready to go again.
Can I charge my battery via the alternator while driving?
Yes, this is even recommended. However, you need a charge booster or DC-DC charger for this, which raises the voltage of the alternator (often only 13.8-14.2V)