Solar – bringing it all together
This and several following sections show how the various electrical bits and pieces need to be installed (or should have been installed) to work as a reliable system. They explain what’s required and help to estimate costs.
Earlier editions of this book were written when solar capacity was costly, batteries were cheaper, lights and fridges less efficient. Now, batteries are expensive, solar is cheap and lights and fridges more efficient. Whilst compromises are feasible this book now suggests two main approaches, each modifiable to suit individual needs. Choose whichever best fits.
Driving most days: this suits a quick ‘Around Australia’ but is hard on batteries and typically limits staying away from grid power to only one day and night (two days tends to flatten the battery). It is that approach used for rental RVs, many camper trailers and basic caravans. An originally full charged auxiliary battery (of 100-120 amp hour) provides for that day and night. It then relies on being recharged by driving at least five/six hours on the following day.
Trak Shak’s solar module mounting also provides partial shade. Pic: Trak Shak.
It is inflexible, and gives the batteries a pounding – but is cheap and easy to set up.
This approach works well for those doing a fast, long trip that requires four or five hours driving each day. It is just possible to stay two nights on site, but is then likely to need a full day’s driving or a night in a caravan park recharging from a 230 volt supply. If this is to be the only or main usage it is the cheapest approach. Battery life is unlikely to exceed a year, so a cheap deep-cycle lead acid version will suffice.
Electrically self-sufficient: this is the preferred option where you have at least 3.5 PSH/day: e.g. most of Australia from September through to May – but not Australia’s south coast in mid-winter. It allows for horizontal solar module mounting, LED lighting, an efficient post 2014 TV, and an efficient 60-80 litre compressor fridge or fridge-freezer.
It must be done properly, but, if it matches your needs, is 100% recommended. Tens of thousands of owners do so and find it works. The downside is that it costs more initially.
No single approach needs following exactly, but unless you really know what you are doing it is best not to depart too much from that described. Also, before getting in too deeply, check what you are planning is physically possible. Is there room for that second battery? If not where can it go? Is there enough space to mount the solar modules? It is essential to have enough solar capacity to enable the battery/s to reach full charge by noon on almost all days. This provides back-up during days of little sun – when irradiation may drop below 20%.
Given the above, with rare exceptions of solar blanked by bush-fire smoke, or long periods of totally overcast sky, it enables you to stay on-site as long as you wish.
If a compressor fridge (and particularly a sleep apnoea machine) must be relied on, carry a 1 kW quiet Honda, Yamaha or Dometic generator, and use it to recharge the battery via a three stage mains battery charger running from the 230 volt ac outlet as a back-up. See page 34. This will fully charge the battery in an hour or two during the day – and not disturb others nearby at night. This should also be used during mid-winter in the far southern parts of Australia and New Zealand.
As the fridge typically draws 70% or so of a camper trailer’s daily energy input, a viable alternative (that needs far less solar) is to use a Chescold or similar chest-opening three-way fridge running from the alternator whilst driving and LP gas at all other times: a 9 kg cylinder typically lasts 3-4 weeks if run full time on gas.
Determining the demand
The table below shows the typical energy draw of the main RV electrical items. Fridges tend to be by far the major energy users. Most cycle on/off, drawing energy during the ‘on’ cycles. Cycling times vary from brand to brand but daily draw depends mostly on usage and installation. Some run constantly, varying motor speed and current draw as they do.
|Fans (12 volt)||1-2|
|Lights – 12 volt LEDs||0.3-0.5|
|Microwave (800 watt)||115-130|
|TV small (LED) (230 V via inverter)||approx 4.0|
|110 litre and less||10-15|
|Above 170 litres||20-30|
From known data, or the average data above, prepare your own version of the table below. For each item in column A, enter amps draw in column B. In column C enter the hours you expect to use each device per day, allowing for multiple lights etc. on at the same time. Multiply each entry in B by the entry in C. Enter the result in D.
Column D’s total shows total daily use. To this needs to be added 12.5%-15% for charging/discharging losses. The result is the minimum energy needed each day.
If the system is to be self-supporting, to cope with exceptional usage and speedy recharging, it is strongly recommended to add a further 30%-50% or more solar input, but not necessarily to add more battery storage.
|Devices||Amps draw||Hours ‘on’||Amp hours/day|
|Lights LED-(3-5 watt x 4)||0.3-0.5||3.0||6.0|
|Fridge (60 litre electric)||2.5||12||30|
|Add 15% for charging/discharging losses||6|
|Final Total||Approximately 50-55|