Solar That Really Works!

Solar that Really Works! covers the design, installation and use of solar in cabins, camper trailers, caravans, fifth wheelers, campervans and motor homes.

eBook versions

Paperback version

The book retailers set their own prices which can vary substantially. We'll aim to keep a selection of the better prices above.

Any bookshop, whether online or bricks and mortar, can order copies of Solar That Really Works!  Just ask.
ISBN: 978-0-6483190-3-0

The Camper Trailer Book

Fourth Edition

by Collyn Rivers

The Camper Trailer Book was first published in 2006. Camper trailers and usage, however, changed so fast it has been updated several times.

This book has not yet been converted to an eBook format and is not yet available as a paperback. While printed copies of previous editions may still be available, we have decided to publish this new edition of The Camper Trailer Book on this website.

Each week we will add a new section.  Over time the complete book will be available on this site. As each section is added it will also be completely searchable.

If you own or are interested in travelling with a camper trailer you will find this book invaluable.  It covers every issue you are likely to encounter and then some.  We trust you will find this helpful and useful.

The Camper Trailer Book – Chapter 20: Example Systems

System 1

Basic system with three-way Chescold (chest) fridge

DeviceAmps (each)Hours/dayAmp hours/day
LED lights (2)
Water pump (12 V)
Fridge (gas)
Total demand2.5
Plus system losses of 12.5%0.3
Total daily draw (amp hour)approx 3.0
Total daily draw (watt hours) approx 36

Earlier editions of this book described a number of actual owners’ systems but this proved less practical as prices fell. The example systems on the next five pages are hypothetical but based on that which camper trailer owners typically do. They are updated between editions.

This example is a basic cheap and reliable system with very low energy draw. A 120 to 130 watt solar module and sealed lead acid deep-cycle battery of about 50 amp hour enables staying on site as long as desired (at least until the fridge’ gas cylinder/s need refilling) almost regardless of weather.

A more versatile version would be to have the battery charged from the tow vehicle’s alternator. That battery would power the system for about seven days – and could be close to fully recharged after an hour or two’s driving. The Chescold fridge would run from the car alternator whilst driving, and gas at all other times.

Adding even a small solar module suffices. A single 50 watt, 12 volt solar module produces about 3.0 amps – or about 144 watt hours/day at 4 PSH when mounted flat – and 30-50 watt hours/day when overcast. But as solar is now so cheap, one might as well use 120-130 watts and have a totally bullet-proof system.

That, plus a basic 10 amp solar regulator and a similar 50-100 amp hour battery, is all that is required to provide adequate power much of the time with only barely visible sun.

Solar monitoring could be included, but is far from essential. A multimeter is handy for checking the system in case of any problems.

System 2

Basic system with 12 volt, 40 litre compressor fridge (optional solar)

DeviceAmps (each)Hours/dayAmp hours/day
LED lights (2)
Water pump (12 V)
Fridge (see main text)30-45
Total demand(realistic maximum) 50
Plus system losses of 12.5%approx 5.5
Total daily draw (amp hours/day)55
Total daily draw (watt hours/day)660

This is much as System 1, but has an electric fridge. It can be set up in various ways – including via solar. It shows the major increase in electrical energy required.

A 40-60 litre fridge is likely to draw 30-45 amp hours/day. If it substantially exceeds that, check the installation and/or usage as something is wrong. This example assumes about 45 amp hours/day.

This system can be powered by the alternator charging an auxiliary deep-cycle battery of about 110 amp hour to store and provide the electrical energy.

Given three or so hours driving at least every third day, the system should allow two to three days on site in temperate climates, and two days in hot ones.

Optional solar

As the current draw is relatively low, and solar capacity now cheap, it makes sense to add solar to have the system be fully self-sufficient – excepting for mid winter down south.

Two 120-130 watt modules should suffice. Increasing battery capacity to 150 amp hours enables the system to run for a day or two before needing solar or alternator charging. The system should then be self-sufficient much of the year, excepting for extended periods of rain. Even then the fridge should be fine if its thermostat is adjusted so that it maintains 5-60 C instead of the recommended 40 C. If using a fridge-freezer it is advisable to have three by 120 watts of solar capacity.

As a general guide, with any system where solar is to be used, have at least 120-150 watts of solar for every 100 amp hours of battery capacity (ideally twice that). It is pointless to have more battery capacity if the energy to charge it is not there.

System 3

Basic system with 60-litre fridge/freezer

LED lights (2)0.533.0
Water pump (12 V)
Fridge/freezer (see main text)50-90
Total demand55-95
Plus system losses of 12.5%approx 7-16
Total daily draw (amp hours/day)62-105
Total daily draw (watt hours)750-1260

Fridge/freezers (unless used in a rig that is driven some hours each day, and thus has considerable alternator input) may introduce problems because their energy consumption can be almost all of that drawn daily, and varies over a wide range.

Well made fridge/freezers have thicker and/or more effective insulation than fridge-only units. Those that are well heat insulated use only marginally more energy. A major cause of variation, however, can be usage – particularly the weight and initial temperature of anything placed in the freezing section. Cooling and freezing freshly-caught fish hugely increases energy draw.

For camper trailer usage, the lower total consumption figure (above) can be handled by solar but needs a lot of capacity. Anything over can only be handled by a generator, or fuel cells if/when the latter are available at a more affordable price. Some form of back-up power is essential unless you are prepared to scrap the food in the event of a extended overcast cloud or rain.

If doing so via generator, huge savings on fuel can be made by using its 230 volt ac output to drive a big (multi-stage) battery charger and AGM battery bank. This will enable the generator to run at close to full power (and thus higher efficiency) for only a few hours a day – rather than on part load 24/7.

A worthwhile approach for DIY enthusiasts is to consider building your own fridge/freezer. Kits are available for the working bits – from Engel, Waeco and Smartfrost. (See page 69 re this.) If that is done using (say) 150-200 mm insulation, or hi-tech thinner equivalents, energy usage will be lowered in proportion to insulation thickness, and/or effectiveness.

Cooling many kilograms by 300-400 C inevitably uses a lot of energy, but once that cooling is achieved, a really efficient freezer hugely reduces the energy losses of keeping it cooled.

System 4

Medium sized system – three-way 120 litre fridge

LED lights (4)0.5 (each)3.06.0
Water pump (12 V)
Fridge (see text)0
Laptop computer3.01.03.0
Plus 12.5% for losses1.2
Total daily draw (amp hours/day)11.2
Total daily draw (watt hours/day)135

Many caravans and motor homes, but few camper trailers, have a three-way (gas, 12 volt dc, 230 volt ac) fridge as standard, or optional extra.

These are excellent devices but must be competently installed for them to work as well as they can. With camper trailers, this will almost certainly necessitate it being installed in that camper trailer (as with the Ultimate) or possibly (under cover, but well ventilated) in the tray of a ute. They need a cold air inlet and provision for hot air to exit. This is difficult, but not impossible, in the rear of a 4WD if at least some air can flow to the base of that fridge.

Three-way fridges must be run on LP gas whilst camping. Their electrical draw is far too high to run from solar or a large battery charged by the alternator.

Providing this is done, even a modest solar system will provide almost bullet-proof electrical power for all other realistic camper trailer needs. A single 130 watt module, basic solar regulator, and a 85 amp hour battery should then be adequate to run this system even in a Tasmanian or NZ mid-winter – and almost anywhere in Australia regardless of weather. It enables campers to stay on site for a month or more. Increasing solar input to two 120 watt modules virtually guarantees it.

The choice of fridge climate rating is vital. Use a ‘T’-rated fridge such as the 120 litre Dometic. It costs a lot more than an electric compressor fridge of the same size but savings on solar and battery chargers more than compensate.

Three-way fridges are fine for typical camper trailer use but not for serious fishers.

Installation, where feasible, is not hard to do, but must be well done. Page 65 shows how.

System 5

Large system with a 160 litre fridge-freezer

LED lights (6)0.539.0
Water pump (12 V)
Microwave oven1300.565
Plus 12.5% for system lossesapprox 22-29
Total daily draw (amp hours/day)194-261
Total daily draw (watt hours/day)2328-3132

This is a typical example of what many newcomers to camper trailers attempt to do. Despite the substantial daily draw, some owners then try to run the whole lot from solar. If planning to be where there is adequate sun, solar assists but it is not likely to provide more than 40-50 amp hours a day – and cannot be relied upon. Typical usage of that microwave oven alone may consume the daily input from two 120 watt solar modules.

The tow vehicle alternator will cope whilst driving, and assist to charge the trailer’s battery bank, but the only way to power systems like this for more than a single overnight away from grid power is via a 2 kW to 3 kW inverter generator. That generator will need to be run for some hours each day whilst on camping, and particularly if attempting to freeze newly caught fish.

As explained on page 34 the generator is best used to charge the necessary minimum of 300 Ah of AGM or LiFePO4 batteries (via a 30-40 amp charger) from the 230 volt outlet of the generator. That generator will still need to run four to five hours a day, and even longer if camping in tropical areas, except in winter, but the battery bank alone will cope at night.

As many an auto-electrician will confirm, examples like this are far from uncommon. They not only cause electrical problems, but (even with LiFePO4s) battery weight can be an issue.

Collyn Rivers is a semi-retired automobile research engineer.  He is the author of seven books, five of which are about making RVs and solar work optimally.

Solar That Really Works!

Solar that Really Works! covers the design, installation and use of solar in cabins, camper trailers, caravans, fifth wheelers, campervans and motor homes.

eBook versions

Paperback version

The book retailers set their own prices which can vary substantially. We'll aim to keep a selection of the better prices above.

Any bookshop, whether online or bricks and mortar, can order copies of Solar That Really Works!  Just ask.
ISBN: 978-0-6483190-3-0