It is usually feasible to run things from solar that do not generate heat over long periods as their main purpose: for that, gas or diesel is a better source of energy. Electric jugs are border-line feasible in big rigs, but not otherwise. Also out are 12 volt incandescent globes (legally banned since 2010 in 230 volt form), older CPAP machines (recent CPAP machines using a heating cycle still need a lot of energy), hair dryers etc.
The main electricity draw (typically 70% of the total) is an electric fridge. Late models use less, but their draw is mainly related to how well they are installed – most are done badly, some appallingly so.
It is also essential to have adequate wiring - again, most is not - and an adequate charging system (if powered also via the alternator). See later in this article re wiring.
If solar capacity is too low, adding more battery capacity makes things worse! It’s like opening a second bank account for the same money paid in. This may seem obvious (once it’s pointed out) but many people who routinely run out of solar power add more batteries. Not only does it not assist, it results in the battery capacity being chronically undercharged. This damages them and they will not last as long. (Batteries are like lead-acid Labradors – they like being fed but are not that keen on strong exercise).
Cost apart, it’s impossible to have too much solar – there is zero risk of overcharging (as that’s caused by over voltage – not over capacity). Having a lot of solar capacity helps on overcast days as there is often only 20% of normal charge coming in. It is also affordable – as solar cost has plummeted since 2010. (Prior to that, most RVs had too little solar, yet many owners have not since added more).
Many commercial RV solar systems are scaled for users who spend most nights in caravan parks. Few will cope with more than one overnight stay away from 230 volt power. Worse, many have only little better than so-called float charging, i.e. that maintain the charge of already well charged battery between uses. They can recharge a deeply discharged battery but as major one supplier advises, if deeply discharged as many are, it takes about 18 hours to recharge a 120 Ah battery recharge to 80% and a further twelve hours to charge from that to close to 100%. One major supplier quotes no less than an overall 70 hours. It is not possible to modify these existing so-called ‘Converter’ systems. This is too major a topic to discuss here.
Solar regulators ensure that charging is speedy and safe, meanwhile protecting batteries against overcharging, and appliances against over-voltage. With a genuinely high quality solar regulator installed (typically $250 plus), it is safe and beneficial to leave batteries on permanent charge - but for those who still use wet batteries (those that need routine topping up with water), it is essential to check their level at least every 8-10 weeks. Some owners claim solar regulators are unnecessary - but it's odds on their system is so badly designed/installed that even omitting the regulator makes little further difference! Or the solar input is very low.
Instantaneous measurement of battery voltage is so totally meaningless it may lead to sound batteries being discarded and worn out ones retained. Why? It is because after 30 minutes engine running, a battery that's almost flat may measure as close to fully charged (12.6-12.8 volts). A close to fully charged battery may measure as close to 'flat' (less than 11.6 volts) after running a microwave oven for ten minutes - a total energy draw some twelve times that of starting a big 4WD diesel engine.
Further, because the energy interaction between a battery’s lead plates and the so called water/acid ‘electrolyte’ is very slow, a reading taken from a big deep cycle battery that is totally off-load for 24 hours is likely to have at least 10% error.
The only meaningful measurement is to check the energy that goes in, and the energy drawn out - deduct a bit for system losses: that which is left is more or less what you've still got. Such energy monitoring is built into upmarket solar regulators, but it can also be done by stand-alone units that, in some instances, can be easier to read.
Without monitoring, you risk wrecking batteries through constant undercharging and/or over-discharging. Over-charging is less common but occurs. It is usually caused by leaving a battery across a poor quality battery charger too long.
An electric-only fridge gobbles 60%-80% of daily electrical draw. Chest-opening types are the most efficient, door-opening types use a few per cent more power. A realistic maximum is 170 litres and that will need three (ideally four) 120-watt modules. (Around 2003, members of a well known 4WD ‘van club poured ongoing forum
scorn on that contention – until they experienced a hot weekend rally - and warm beer).
An alternative is a Dometic Climate Class 'T' three-way fridge. These run on 12-volts whilst driving, 230-volts when available and gas at all other times. The 'T' indicates the fridge is designed to run in ambient temperatures up to 43 degrees C. Use this type of fridge and you may need only 160-250 watts solar (see later for specifics) for everything else.
, Dometic has four or five such in its range, but do not be fobbed off by vendors who claim that all Dometic fridges are T-rated. They absolutely are not – the confusion is probably due to Dometic upgrading all their products in the 1990s – and using the term ‘tropicalised’ for all of them. That company has never claimed that tropicalised implies ‘T-rating’ but not all sales people appear to be aware of that. In the author’s view, if a three-way fridge is used, it needs to be ‘T-rated’ in travelling in Australia
’s North and North West.
All fridges must be installed correctly to work as intended. Most are not - and hence don't, but three-ways will disappoint more than most if ineptly installed. Cooling performance and energy usage of almost any RV fridge can be hugely improved via the simple changes outlined in most of the author’s books.
A microwave oven draws more energy than many assume. The rated wattage is the equivalent heat produced - not the energy drawn in doing so. Via an inverter, a (2013) '800-watt' microwave may draw 1500 watts (around 125 amps at 12 volts). Ten minutes usage may draw a full day's mid-summer output from an 80 watt module. Use a microwave only where there's mains power. But many find long term travelling changes living styles – and that may not use a microwave at all.
[SH]Lighting]/SH]The most efficient lights are LEDs and, but less so in terms of usable light, compact fluorescent globes. Some of the latter have an inbuilt inverter for 12-volt connection. You can use 230-volt fluros via a remote inverter but that necessitates mains-voltage wiring.
LED lights draw little power mainly because their light is tightly focussed. They are good for reading and, (in headband form) for campfire cookery, but have no energy saving advantage for general lighting. Halogen globes use twice the energy of fluorescents at up to 700 degrees C. They can be very uncomfortable if close overhead. They also produce a lot of UV.
Solar is not feasible for major heating applications. Use gas or diesel for cooking and water heating water. Water pumps need to be 12 volts - ditto cooling fans. TVs, VCRs and DVDs are only a problem if used for hours on end. If you really need a computer, use a laptop. Some can also double as a TV.