Self-sufficiency in the caravan/mobile home

Reading time 14 minutes

Updated - June 18, 2025

Introduction

Self-sufficiency – a term that quickly loses its meaning in the above context. This article will examine in more detail why and how the greatest possible self-sufficiency can actually be achieved, but will also point out limitations.

On campsites, all is generally still well with the world. However, outside of this type of civilization, things quickly look completely different.

Three main topics are the most commonly discussed:

• power supply
• Industrial water
• sewage
  
  
  

Foreword on the subject of batteries

Every vehicle has a vehicle or starter battery. It serves as a power source for the starter and is therefore vital for starting the vehicle. It is charged by the alternator while driving so that it is as full as possible when the vehicle is parked in order to be able to handle the next start. The starter battery also supplies lights, indicators, horn, ventilation, radiator fan, etc.

A motorhome, on the other hand, has a second so-called body battery that is separate from the starter battery. This battery supplies, for example, the water pump, heating fan, lamps, the toilet flush pump, and the refrigerator.

Anyone who thinks that the built-in battery is an unnecessary luxury runs the risk of only hearing a tired whirring noise when they try to start the car in the morning. During cold seasons and the gas heater was running, the heating fan drained the battery overnight.

In this case, the only thing that can help is a friendly citizen who will give you a jump start, provided a jump start cable is available.

However, if you have a body battery, you are immune to such scenarios because your additional consumption in the living area is supplied by the separate body battery.

Energy supply for the body battery

Of the above points, energy supply is still the easiest construction site to implement.

The answer is “photovoltaic / PV system”. Sure, what else? In most cases there are one or two modules with a total of 100...200 W on the caravan or preferably motorhome roof and a 100 Ah body battery.

In the caravan, this is not charged while driving, unless you have installed a corresponding controller in the vehicle that allows the body battery to be charged via an additional cable from the car to the caravan. However, this usually only charges with a very low current of around 1.5 A.
So this battery is charged either by installed PV modules or a connected power cable at a campsite.

Most motorhomes have a charge controller installed for both batteries. A clear advantage of mobile homes.

Case study for the design of a PV system

The sizing depends on several aspects. In addition to the electricity requirement, the length of uninterrupted downtime and the destination, correlating with the expected hours of sunshine, the resulting yield.

consumption

The all-important question is: How much current is DC (direct voltage) or AC (alternating voltage) required? The worst case scenario (winter) is assumed here, as this is where the highest expected electricity demand occurs.

DC, everything that is supposed to work with 12 V (battery), such as lamps, pumps, fans.

AC, everything that requires the usual socket, i.e. runs on 230 V, such as a hair dryer, razor, microwave and therefore requires an inverter (as well as a UV system that may be installed, more on this in the topic of water treatment).

A list of all consumers (DC - direct voltage and AC - alternating voltage) helps to determine the actual requirement. The respective average duty cycle should also be noted for each individual consumer.

Once the calculated (DC) requirement has been determined, the resulting Ah (Ampère-hours) or Wh (Watt-hours) are added.

Example:

Heating fan 0.3 .. 1.0 A (3.6 W .. 12 W) – running time in winter 24 hours -> 24 x 0.3 = 8 Ah, or 1.0 x 24 = 24 Ah (86 ,4 .. 288 Wh).

2x LED lamp 0.42 A (5 W), running time in winter 8 h -> 0.42 x 8 = 3.36 Ah (2 x 40Wh = 80 Wh)

Depending on the fan level set, the heating fan requires between 8 and 24 Ah per day in winter. With a 100 Ah battery, it is deeply discharged after four days without additional charging, which should be avoided as much as possible. And this without additional consumption for lights, water pumps, etc.

This example clearly shows the quickly reached limit of supposed self-sufficiency.

generation

In March, for example, an average of around 1.5 kWh/d was generated per kW of PV modules installed.

Assuming one(1) installed 100W PV module, you will achieve around 12.5 Ah (150 Wh) as a yield on one day in March.

If you take the consumer example above with a consumption of a minimum of 8 Ah for the heating fan running at the lowest level and 3.36 Ah for two LED lamps, the entire yield, even if the sun was shining a little, has already been used up. The water pump and other consumers then live off the battery reserve, as do every other lamp, TV, etc.

So all in all it's getting tight. And even more so when there is little sunlight. What to do?

More PV modules, or larger ones with more power?!

Selection of PV modules

Over time, the PV modules available on the market become increasingly more powerful (up to currently 400 W for less than 200 euros), albeit with an associated increase in size, while a 100 W module costs just over 100 euros. This makes it more economical to use more powerful modules.

The more modules with the highest possible performance that can be installed on the roof, the more sensible it is.

Please note the V_ok (Voltage open circuit) of the modules, as well as their type of connection (serial or/and parallel). For the 400W Hyundai, for example, this is 46.4 V DC.

A serial module circuit of, for example, two modules of 100 W each at 12 V with 5.6 A adds the voltage (12 V + 12 V = 24 V) with a constant current of 5.6 A, while the parallel circuit adds the voltage ( 12 V) but adds the current (5.6 A + 5.6 A = 11.2 A).

For example, if you want to install 2 modules of 400 W each, you can connect them in series to 38.6 V + 38.6 V = 77.2 V 10.4 A 802 W or in parallel to 38.6 V and 10.4 A + 10, 4A = 20.8A 802W

When connecting in parallel, it should be noted that the modules provide the same voltages; the performance may differ. Since currents add up when connected in parallel, the upper limit of 70 A (better 60 A) must be observed to avoid damage!

A parallel connection causes a multiplication of the resulting current corresponding to the number of modules and thus an increase in the required conductor cross-section! In the case of partial shading, parallel connection has the advantage that more yield is generated compared to series connection.

A mix of series and parallel connection is recommended if a parallel connection would result in a current > 60 A. Modules should then be connected in pairs in parallel and these pairs in series. This leads to an increase in voltage, but also to a reduction in current consumption.

Finally, a note: no, they do not have to be modules specifically designed for mobile use. Any (!) module that is conventionally installed on building roofs is also suitable for this purpose.

Assembly of PV modules

Ideally, modules should be installed together on a frame that can be erected using V2A shutter hinges. In this way, in the event of maintenance, it is possible to set up the modules, making all connections and cabling accessible.

Aluminum construction profiles are more stable than those typically used for PV modules, although they are naturally heavier. They absorb vehicle torsion well while driving, thereby protecting the vehicle body construction and the PV modules equally.

A practical report can be found here.

MPPT controller selection

The MPPT controllers (Maximum Power Point Tracking) ensure the adaptation of the PV voltage (here e.g. 46.4 V) to the system (battery) voltage of usually 12 V without loss of power.

The technical data sheet of the MPPT controller provides information about the maximum system voltage to be processed of 12, 24 or 48 V (12 V for caravans and motorhomes), the permissible current and the PV open-circuit voltage (depending on the number and type the module interconnection, whether serial or parallel).

When choosing MPPT controllers, you should not primarily pay attention to the price, but rather to the data and the manufacturer or their experience. Only then should the price-performance ratio be the deciding factor.

Devices below the three-digit euro limit rarely keep what they promise. And if you have to rely on the warranty, it won't be of any use to you if the worst comes to the worst when you're far from home. MPPT controllers from EPEVER or VICTRON, for example, meet these requirements. When it comes to service and support, short response times are also a quality feature worth highlighting.

Conductor cross section

In order to avoid losses along the line and overheating of the cable connections, cross sections must be selected that correspond to the current intensity. Single-core cables are suitable for higher currents than multi-core cables. It is assumed here that only single-core cables are used.

Attention: If batteries are connected directly to one another, large cross-sections and shortest cables must be used in order to achieve a voltage drop across the cable of < 0.05 V!

The necessary cross-section of copper cables for DC applications can be calculated here, as can the voltage drop. The yellow fields are editable:

Since very large cross-sections are becoming increasingly difficult to handle mechanically, you can also pull two cables with a smaller cross-section.

Example – battery <-> inverter

The required current is 470 A, which means that with a cable length of only 0.5 m per plus and minus cable, a cable cross-section of 70 mm would be required² find use. Instead, for the purpose of smaller bending radii, you would use 2 x 35 mm² (corresponding to 2 x 235 A).

Such current strengths are available, for example, with 12 V inverters with an output of more than 4,000 W.

The following formulas are used to individually calculate the cable cross section (A):

In words: The cable cross-section results from twice the conductor length multiplied by the desired maximum current, divided by the conductance of the conductor material in Siemens/meter multiplied by the permissible voltage drop; For alternating voltage, the meter is also multiplied by the electrical efficiency of the system.

Example MPPT controller <-> battery

500 W PV module nominal power, 36 V PV module nominal voltage -> 13.9 A, MPPT output 12 V, MPPT battery cable 2x 2.5 m

• Total cable length plus/minus cable 5 m
• Current 13.9 A
• Conductivity (copper) 5.8
• Voltage loss 0.5 V

Calculation method

2 x (length) 5 x (current) 13.9 = 139 : (conductivity copper) 5.8 x (voltage loss) 0.5 = 47.9 mm²

Accordingly, the choice falls on the next higher, commercially available value of 50 mm².

Battery storage

The good old lead-acid battery has become obsolete for this purpose. It was supposed to reliably supply the starter with a very high current for a short time and was also charged with a very high current by the alternator. The critical deep discharge voltage is 11.8 V.

The newer AGM batteries (absorbent Glass Mat) do not have any liquid/acid that can evaporate or even leak. It is hermetically sealed and does not require ventilation. They currently represent the most economical product choice. The recommended maximum depth of discharge is 50% and is therefore achieved at 12.3 V. The durability is approx. 350 .. 500 cycles.

Lithium batteries are considered the non-plus-ultra, but are also the most expensive solution. They provide the nominal voltage at a constant level over the entire discharge period, while AGM batteries decrease in voltage as the discharge increases. They have more than 10 to 20 times the number of cycles than AGM batteries. This puts the significantly higher purchase price into perspective.

Inverter operation 230 V

What could be the reason for using an inverter? In addition to the everyday hairdryer, the need for baking rolls is often the reason for using a hot air microwave combination. Also potentially vital equipment whose batteries need to be reliably charged from time to time. Another aspect is drinking water treatment using UV clarifiers.

Not to be underestimated: in order to generate 2,000 watts from 12 V, peak currents of (2,000 W / 12 V =) 166.7 A are to be expected in the DC voltage branch (cable cross section for the - shortest possible - connection between inverter and battery(s)) 50mm² – max. 198 A)! On the 230 V AC side, 2,000 W corresponds to “only” 8.7 A.

A 2,000 W inverter should be able to provide the nominal power over a longer period of time. But this means maximum load - and electronics don't really like limit operation. It is better to agree on around 75% load. 1,500 W would be the moderate load limit for the example 2,000 W inverter.

In terms of costs, a 2 kW inverter costs just under 2,000 euros. At times there are also B-stock products that do not look like a new device, but are technically flawless. Such devices are often offered around 30 % cheaper. They are recommended for the intended purpose in every respect, especially economically.

It should be noted that the inverter produces a true sine wave. Older devices usually only produce a stepped quasi-sine wave, which is not (!) suitable for consumers with a switching power supply.

There are also pure sine wave inverters as a – limited – useful and cheaper alternative, such as this Giandel 4000/8000 for around 700 euros. However, the 4 kW are probably. not to be taken literally. 2.5 kW should be a realistic value for continuous load. The nominally stated 8 kW is only permitted in the range of seconds.

The device has an alternating LED display for battery voltage (V) and output power (W/kW). The following protective circuits are implemented:

• DC under/over voltage
• AC overload
• AC short circuit
• Excess temperature (> 65 °C)

When switching on, the AC output voltage is slowly increased to 230 V, which leads to gentle starting behavior, especially with inductive loads.

As with most of the larger devices, switching on can be done on the device itself or using the included remote control (button with LED function/error display.

Good to know: the DC cables are attached using M10 thread terminals. M10 nuts are not included with the device.

The AC output is implemented via three Schuko sockets and a screw terminal (earth - zero - phase), which is suitable for hard wiring to the on-board consumer network.

The efficiency of the inverter is 90%. For example, if AC 1,000 W is required, AC 1,100 W is effectively required. The body battery must therefore provide 1,100 W / 12 V = 91.67 A. A 95 Ah battery would be empty within an hour!

Practical examples:

• Refrigerator 250W + 25W (10% loss due to efficiency) / 12V = 22.92A
• Hot air oven 1,650 W + 165 W (10% loss due to efficiency) / 12 V = 151.25 A
  (Bake rolls at 170 °C for 16 minutes = 56.72 Ah)
  
  

Space requirement planning

In total, there are a number of devices, fuse holders, switches and cable routes that require a considerable amount of space for - ideally clear - installation.

For the cable routes between the components, depending on the cable cross-sections to be selected, you should also consider that increasing cable cross-sections also require larger bending radii.

Cable ducts for bundling cable harnesses also require space.

It is helpful to first make a 10:1 drawing, on which you can draw the available area as a frame and, similar to setting up an apartment plan, position the components in the intended manner.

It makes sense to mark the cable connections in order to create a laying plan for the cabling as soon as the positions have been determined.

Ultimately, you receive documentation that can be consulted when troubleshooting later.

An example of such documentation can be here can be viewed. It includes devices from the Victron system solution mentioned below.

Victron – The system solution

Anyone who would like to have an all-round solution will soon come across Victron in their search. There is a separate one for this Contribution.

Alternating mains and inverter operation

At home, on campsites or other public parking spaces, 230 V is usually supplied from outside. Since the above-mentioned inverters do not allow grid-synchronous operation (in contrast to inverters that are used in stationary PV systems), a grid priority circuit is still required. Parallel operation is not(!) possible.

The mains priority circuit ensures that the stationary 230 V network is automatically switched off and that the on-board inverter is switched on with a short delay. A suitable device for this is, for example, the H-Tronic MPC 1000 by ELV.

Please note and checkn: In previous board layouts, the connection labels were printed master and Slave reversed. In the voltage-free state, the L connections of the master /Slave terminals against L connection Load Test for continuity with a continuity tester. Is passage between master and Load given, then the print is correct. On the other hand, there is a passage between Slave and Load determine, then the print is swapped and Slave as master, as well as master as Slave consider.

To carry out the internal wiring, the circuit board should be removed from the housing using the four retaining Phillips screws. This means that the screw terminals for master (mains), slave (inverter) and load (on-board network cabling for consumers) can be held in place when screwing the individual wires (L, N, earth) in order to avoid excessive stress on the soldering points on the circuit board.

When commissioning, three LEDs indicate the AC voltage present at the respective connections.

When using this circuit, please note that it is only designed for a maximum permissible current load of only around 1.6 kW!

Consumers who like to be forgotten

The general consumers have already been mentioned, but what about the razor, for example, whose built-in battery is usually equipped with a 230V plug-in power supply? Or the battery charger for photo/film cameras, possibly also a charger for Li-ion batteries?

It helps to look at the printed technical data on plug-in power supplies for these devices, if necessary with a magnifying glass. Usually voltages of 5V, 6V, 7.5V, 12V are shown.

Devices that are powered by a 12V plug-in power supply can be operated 1:1 with the vehicle electrical system. In other words, a multimeter is used to determine which pin carries +12 V on the plug that is connected to the device to be supplied.
The cable is then cut off just behind the output of the plug-in power supply, the two ends are stripped of about 2 - 3 mm and connected to the desired plug (e.g. for the cigarette lighter): the plus line with the center contact, the minus line with the remaining ground contact.

For devices that require voltages other than the standard 12 V, DC/DC converters must be used that reduce the 12 V on-board voltage to the required voltage (step down converter) or increase it (step up converter).

Here, too, you must first check which of the two connection cables is positive: plug the power supply into the socket and determine the plus/minus on the outgoing device plug. Pull the power adapter out of the socket and wait a moment before cutting the cable about 4 cm behind the power adapter.

Strip one millimeter of insulation from both cable ends behind the plug-in power supply and pull them apart a little (usually double wire, otherwise strip 3 cm of insulation from the round outer sheath and then strip one millimeter of insulation from the single wire). Plug the power adapter back into the socket. Use the multimeter to check which of the two wires is positive. The plus wire is usually marked in color or in another way. Unplug the power supply again.

Connect the determined plus line to the corresponding plus output of the converter and the minus line to the minus output.

Converters usually have three connections, rarely four, although two out of four connections may be bridged internally. This can also be determined with a multimeter (continuity tester).

Connect the inputs of the converter to 12 V plus and minus. The new power supply is ready.

Please note: Converters require cooling, especially at higher currents. For this purpose, the converter can be mounted on a heat sink or cooled using an active fan. The metal back of the converter must be covered very thinly (!) with special thermal paste, which ensures a better transfer of the heat produced to the heat sink. However, if it is applied too thickly, it hinders heat transfer and is therefore damaging.

A fuse on both the input and output sides helps to avoid damage in the event of defects. An additional but worthwhile effort.

Conclusion – energy supply

So if you have plenty of financial resources, the solution is clear: 400 W modules or higher output, 2 .. 4 of them, 2 high-capacity lithium batteries (almost 3,000 euros alone) and a decent MPPT controller in total a good 4,000 euros. The all-in, worry-free package for regular use of an inverter.

The moderate variant would consist of 2...3 modules of 400 W each, 2...4 AGM batteries and an equally useful MPPT controller for around 2,000 euros, although, as above, the batteries take up the lion's share of the money. Like the worry-free package above, this equipment already allows the economical use of an inverter.

A minimal version with an energy reserve, even in winter, could consist of 1 ... 2 module(s) of 400 W each, 2 100 Ah AGM batteries and a good MPPT controller for a total of around 1,000 euros. However, economical use of energy is strongly recommended here.

Cables, small parts, brackets, etc. are not included in the above price calculations.

Further suggestions are welcome: just leave them as a comment!

Industrial water

You fill up domestic water at home. True. And later, if not at a campsite? Well, … at the gas station? Possible, but not welcome. In the cemetery with the watering can? Maybe not exactly the best idea. But where then?!

Admittedly, except at the public supply stations, things are tight. However, those who strive for self-sufficiency are less likely to spend time in areas where tap water is available. There is more likely to be a stream, river, lake or similar body of water within reach.

What all such water sources have in common is that they are not suitable for drinking water and are therefore not easily considered drinkable. Nothing works in this self-sufficiency segment without appropriate preparation.

Drinking water treatment

The solution is a drinking water treatment plant. It sounds a bit cliché at first, but it is relatively simple and can be implemented in the price range of around 250 to 350 euros.

As an example, here is one of Purway distributed system can be accepted as it is also distributed by other providers. It works according to the principle of reverse osmosis, as it is presented in more detail in the linked article.

The reverse osmosis system cleans the water from any contamination including bacteria and viruses. Only a few viruses can pass through due to their size being just below the filter pore size.

In order to eliminate this remaining residual risk, a UV clarifier operating at 230 V can be connected downstream.

Additional tank

If you decide to use such a system, it makes sense to plan for an additional water tank. The water to be filtered is filled into this tank.

When water is removed from the drinking water tank, the pump of the treatment system starts (if it is connected in parallel to the pressure pump, as well as the UV clarifier via relay, of the caravan/motorhome). It pumps the water to be clarified through the filters and the UV clarifier into the drinking water tank.
A level switch that can be retrofitted in the drinking water tank can switch off the treatment as soon as the desired “full” level in the drinking water tank is reached again.

If you follow this idea, it is helpful to move the water level indicator that may already be installed from the drinking water tank to the additive water tank. This means you will be reminded in good time to fill up, but you will always have a virtually self-refilling and therefore full drinking water tank available.

Water procurement

... from water reservoirs

The final question that remains to be clarified is how does the water from the available natural water source get into the tank?

Not every water source will be at the same height as the vehicle, nor will it be right next to it. So you will have to overcome differences in height and distances. Since you usually don't want to fill up the tank little by little with a watering can or bucket, a pump has to do this.

Gear pumps, diaphragm pumps, submersible pumps and well pumps are available, among others. With the exception of gear and diaphragm pumps, most require 230 V, but provide considerable suction and pressure heights. The smallest deep well pump creates a pressure height of 34 m at 370 W 230 V. After less than 5 minutes there are 150 liters in the tank. A correspondingly long hose is required, including a connecting cable and a supporting rope.

... from rainwater

Another, perhaps somewhat daring, but conceivable way of obtaining drinking water is - the roof area of the caravan or mobile home.

A border around 5...10 mm high (attention - always no more than half the height of the lower edge of the roof hatch, etc.) glued all around is sufficient. Joints must be sealed watertight. Two or - ideally - four roof ducts are made in the corner areas, similar to a sink drain.

The outlets are connected internally via a hose running around the storage compartments (in the cable duct) and T-pieces and lead into the additive tank. From now on, every rain will fill the additional tank.
Conventional leaf catcher attachments, such as those found in gutter drains, help to keep coarse contamination away.

When the vehicle is stationary, a “puddle” is created on the roof, which constantly empties into the additional tank via the covered drains. While driving, water is predominantly applied to the rear drainage area.

Excess water drains away via a T-piece in the tank ventilation of the additional tank below the vehicle.

If you want it to be perfect, take a coarse filter mat of the appropriate thickness and position it across the entire width of the roof in a depth of around 40 to 50 cm above the rear drains. Aluminum or V4A perforated sheet metal (approx. 5 mm hole diameter) above, fixed at corners and long sides at a distance of approx. 25 cm using spacers. Don't forget to carefully seal any necessary holes/screw connections in the roof area!

In this way, the water does not storm over the roof and its surroundings while driving, but instead gets caught in the filter mat and flows into the additional tank instead of otherwise being lost.

Conclusion – domestic water supply

As always, there are several roads to Rome. Which path you choose remains to be decided individually. Not everyone likes to puncture their roof, has enough weight reserves or the necessary electrical energy available. That's why there is no THE way.

Further suggestions are welcome: just leave them as a comment!

sewage

This is where self-sufficiency has reached its limits. As soon as there are dishwashing liquids, detergents, fats, etc. in the gray water tank, the only option is to dispose of them at public disposal stations.

The only exception is a mixed public wastewater system for rain AND industrial water, which can be disposed of carefully.

If you only wash with clear water, you can recycle your gray water using the reverse osmosis system.

Elimination of the above-mentioned substances usually contained in wastewater is currently not possible in an economical way - the clear end of self-sufficiency - and this contribution.

ps If you need personal support in the implementation for a fee, you are welcome to Ticketing make!