SOLAR PANELS
OR
 WHY MY BEER WON’T STAY COLD AT PANDANUS
or whilst I'm camping in the middle of nowhere

 







Power, or the lack of it to run 12 volt car or camping fridges seems to be a recurring problem for those who camp at Pandanus Park. Indeed it is not just Pandanus or Veterans who are affected by this problem it besets all campers other than those who choose to camp at the polar ice caps or in Victoria where there is no need for a fridge. Yet this need not be the case.  If we all understood solar power generation and the demands/operation of a car fridge then purchased a battery/solar system to cope. Being properly equipped is the difference between arriving at a campsite fully prepared and appreciating the difference between realistic expectation and dreaming.

                                                                                    In other words, your beer can stay cold - if you are properly equipped and know what to expect. 

The first thing to appreciate is that ALL car fridges and their attendant solar/battery power supplies are required for one purpose only and that is to keep one's beer cold.

Furthermore the solar/battery power supply must do this by day and by night, regardless of the number of times the fridge is accessed, the duration the lid is left open as we grab a cold 'un,   the number of hot beers placed in the fridge, the outside air temperature or even if the ‘beer fridge' is left in the sun or in a hot enclosed car. Clearly the efficient operation of one's car fridge is paramount and we all expect it to be efficient, to work wonders ALL of the time. And why not? After all the salesman told you that this was the best fridge on the planet, used bugger all power and would do all you ever asked of it under all conditions.

Now if you had a decent solar/battery system and the sun was always high in a clear blue sky on each and every day then this would be almost achieveable but far too often the fridge/solar/battery combinations brought to Pandanus or indeed to any other bush camp deliver well below expectations, well below what the salesman claimed and the problem is always the same. Too few solar panels, too small a battery, lousy weather, an old battery and too much current draw by the fridge.  

Understanding Car Fridges.

All 12 volt car fridges are powered by either:
Car Batteries
Extra Batteries
Solar Panels
Portable Generators
12 to 240 volt invertors
Caravan park 240 volt power supplies through a convertor, or
all of the above.

Most 12 volt fridges run a small Danfos compressor that, depending on its size uses 8 amps to start up, then anywhere between 3 and 6 amps in cruise mode. How often the compressor cycles on and off is dependent on many factors, the most importnat being the outside air temperature, efficiency of the 'box', the amount of stuff in the 'box' and age of the motor/compressor plus of course and most importantly, how many times and for how long the fridge is accessed. 

Unfortunately only one of the above mentioned power sources is able to provide a reliable 24 hour power supply and that is a 240 volt mains supply though a portable generator running all the time will be in the same category. Now though the portable generator will do the job it will be expensive and fiddly to run and could be noisy plus annoying to fellow campers. Added to that will be the need to keep fuel up to the genny which, with the nearest service station being four hours (return) drive from Pandanus Park can be a problem. As for 240 volt mains power I don't know of any bush camps that have this luxury. Sensibly then a mix of all of the above is the best solution.


Unfortunately many veterans arrive at Pandanus with just a car battery and a single, small, solar panel then wonder why their system will not cope. Worse, and this happens often, they wonder why their favourite 4WD will not start in the morning because the battery is dead flat. Even more distressing is that far too often this happens after just the first night of camping at Pandanus!

Naturally the mongrel solar panel cops the blame yet it is not the guilty bastard - it is in fact the owner who is at 'fault' because he was not prepared, but in fairness to the owner it is usually due to a lack of knowledge on how to properly set up a small scale solar system. This lack of knowledge is understandable for few of us are qualified electronics technicians wise in the ways of solar power.

This brief then is designed to help improve your knowledge of solar/battery power supplies as they apply to 12 volt car or camping fridges.

Firstly, and importantly there is no need to generate truckloads of power, that is far more power than you can realistically use therefore there is no need to line the pockets of the solar power retailer when you make your purchase of a system.   

 To understand what you need and the reasons why,  here is a Mugs Guide to Electronics and Solar Power.

The Power You Need

 

You need 12 volts or thereabouts at about 8 Amps to both run one car fridge and charge a battery.

 

How Do I Get That?

You will need a 12 volt car  battery, a solar panel array, a couple of fuses and a voltage regulator.  The solar panels feed via fuses into the regulator which feeds into the batteries which via a fuse powers the car fridge.

 

Why all that?

 

Battery stores the power for night time or when its cloudy.

Solar Panels provide power from the sun to keep the battery charged and to help run the fridge by day.

Fuses save this expensive gear from being damaged if something goes wrong.

Regulator ensures that only the power you need goes from the solar array to the battery and fridge. It prevents the gear from cooking.

Electronics - The Basics.

 

Voltage – Even though you require about 12.5 volts for your battery and 12 volt fridge to be happy the higher the solar panel voltage the better provide your regulator can take care of the surplus.  

 

Amps –    This is a measure of the squigglies or the current that flows into and out of a device. The higher the figure the greater the flow. Amps are often referred to as Current, just like the current in a river. The greater the volume of flow or current the more power generated by the river. Floods have lots of current and are powerful whereas trickling streams have bugger all current and are less potent. Electrical current is the same, the greater the flow (Amps) the more oomph.

 

Amp-Hours – This is the measure of the amount of Amps or current that flows into or out of a device averaged over a one-hour period. Again, the higher the figure the greater the flow whether it be used or generated.  

                      IMPORTANT:          HIGH AMP-HOURS GENERATED by solar panels IS GOOD.

                                                        HIGH AMP-HOURS USED by a load e.g. a car fridge IS BAD.

 

Watts – This is also known as Power and is a measure of Voltage x Amps. Power or wattage is only useful if you wish to work out why you can't get 5 amps out of a 85 watt solar panel etc.  It is generally used as the measure of capacity or output of solar panels and for the non-technical camper (that is just about everyone) it is best to ignore Watts. Instead I find Amp-Hours to be  a far more practical measure when assessing or reviewing how much your solar system provides and how much you are using.

This means that when purchasing solar panels one needs to look at the  voltage and amps (maximum out) of a panel rather than its wattage.   

 

Now that you are aware of the basic terminology here are the main formulae you may wish to fiddle around with when considering your system.  

Watts = Voltage x Amps; 

Amps = Watts divided by Volts, and
Volts = Watts divided by Amps.

Amp Hours = Average Amps x hours.

Now to the nitty-gritty.

 

Solar Power

 

 What types of Panels are there?

Essentially there are five types, Mono, Multi and Poly Crystalline, Amorphous and CIGS or thin film technology with even more sophisticated types becoming available over the coming years.   The cheaper panels are now as efficient as the more expensive brands with Polycrystalline often being cheaper because these crystals are cheaper and quicker to 'grow' or manufacture. They are slightly less efficient at high panel temperatures though not by a significant factor. Amorphous and CIGS are less efficient but much lighter.

That said most modern generation panels are close in performance, reliability and warranty and despite the brand name most are now made in China where solar technology is highly advanced, labour costs cheap and their research and development is advancing in leaps and bounds.   

What will a Solar Panel give in the way of power?

 

 A typical modern solar panel achieves around 10% to 15% power conversion from the sun with the theoretical maximum efficiency of a silicon cell (the ones most of us have in our solar arrays) being just 21%. That however is in full sun, clear skies, with a new and perfect cell and with the panel set at the correct angle etc. In the bush camping situation you will rarely, if ever achieve this 21%, you wil get far less efficiency, so the important thing to note is that you cannot get the world from a solar array no matter how good it is.
The biggest consideration for users of solar is of course the sun or more correctly its brightness and the amount of hours per day that thge bright light hits your cells at the optimum angle.
                                                    NOTE: Solar power does not work on heat from the sun. It is conversion of light to power indeed the hotter the panels are the less efficient they get.

The marketed power of a panel can be deceiving.

An 85 Watt panel is sold on the premise that it produces 85 watts of power with this figure arrived at as follows: 17 volts x 5 amps = 85 watts. The 17 volts is the output voltage produced by most of the smaller solar panels. So how come my battery works on 12-13 volts you may ask? Well this where the regulator comes in. It regulates or lowers the output voltage and curent to match the needs of your battery. Yet if you regulate (reduce) the voltage you also reduce the current so suddenly your 85 watt panel is not that powerful. In fact most 85 watt panels produce an actual output of around 4 amps at 12-13 volts, sometimes less.  

 

IMPORTANT: Whilst most small solar panels put out 17 volts in an unregulated state some have built-in regulators which limit their output to 12 volts.  On the other hand the modern high performance panels, the large 220 Watt, or even greater, panels that are used in home solar installations put out 36.83 volts at a nominal current of 7.93 amps. Whilst this seems great and ideal for panels mounted on the roof of a carvan you need to be wary because many small regulators have a maximum input voltage of 24 volts. There are a few that are rated to 45 volts but only if you run the output at 24 volts which for caravan, camping car use is not practical.    

 

How much power from the solar panel will go into my battery?

 In simple terms:
  • ·        Not as much as you would like, and
  • ·        Certainly not as much as most salesman will tell you.
If you do not use any of the solar generated power to run your fridge then all of the regulated output will go into your battery. However if like most campers you have a fridge connected to your battery then the fridge will take most if not all of the solar power. If the fridge runs at say 5 amps then only the curent above 5 amps will go into the battery. On the other hand if you have an 85 Watt panel that produces just 4.5 amps then nothing will go into the battery, in fact the battery will always be helping run the fridge. 

As a rule of thumb a single perfectly aligned 85-watt solar panel should have a peak output of about 4.5 amps under perfect sunny conditions. However on most CLEAR days you will only get this maximum output for four hours (around midday). For the rest of the day you will get far less especially in the winter months when the sun is less bright.  

 Furthermore for those camped in the bush the total daily output will become much less due to shade, intermittent cloud cover, smoke haze, dirty panels and the inability to have a clear line of sight to the view of the sun from sunrise to sunset. 

Watts vs. Amps and Voltage

Though you are buying a solar panel to connect to a 12 volt system it is important to note that common small capacity solar panels produce around 17 volts (with no load) and it is this figure on which the nominal current or power is based, not the 12 volts you hope to utilise. Furthermore due to inconsistencies in the silicon cells not all solar panels with the same nominal wattage produce the same current. To check your individual panel output got to the sticker on the back of the panel. It will list the theoretical or lab tested current generated by that panel.

Angle of your solar array

 To work at peak efficiency the panels must be perfectly aligned to the sun and unless you have an automated tracking device fitted to your solar array (no one I know has) then your best bet is to continuously move your panels so that they always directly face the sun. However this is time consuming, impinging on drinking time therefore it is impractical. The alternative then is to place your array to always face NORTH at midday with the panels inclined at an angle to the sun that is equal to the latitude of your campsite. At Pandanus this is 15 degrees, not the near vertical that most Pandanus campers seem intent on using. Under ideal conditions a variation of up to 15° will not make a great deal of difference in the performance of the panels though it is measureable. Outside of this tolerance the losses can be immense so the right inclination and direction are crucial. Flat mounted panels (eg those on a caravan roof) are never as efficient before they are never at the correct inclination and being flat mounted they collect dust (plenty of that at Pandanus) which when combined with the heavy dews experienced at Pandanus keep the panels dirty and thus less efficient.

   Solar Panel  Ideal panel angle at Pandanus Park = 15 degrees
In summary, place your panels so that their surface faces either north or the midday sun and are tilted at 15 degrees (for Pandanus Park). The panels should also be kept clean and most certainly out of the shade.  To guage if your panel faces north wait until midday then check the shadow that a piece of wood casts on the panel or better still, place a beer can in the middle of the panel. Both should cast a shadow down the centreline of the panel.  Solar panel 2 Checking the midday alignment

Cloudy Days and Shade

 Solar panels work on light so the brighter the light the better. For this reason cloudy days are never solar panel friendly with shade, even broken shade, their number one enemy. However, it is possible to get some power even with 8/8ths overcast provided the cloud is not dark, black, thick and heavy. Pandanus Park gets many cloudy days - for example most of the 2010 season was cloud covered all day every day - yet for much of that time solar power was being generated albeit at a much reduced rate.
Now here is a twist. On total cloud cover days the best results are achieved by lying the panels flat so that they collect the maximum diffused light.

Obviously the more solar cells (panels) that you have you have the more light you capture and thus the more power you generate. To allow for cloudy days you need to add even more cells or panels than are required for perfect conditions hence my claim that a minimum of 240 watts of panel is required for most camping applications. On consecutive cloudy days even that will not be enough.

    Neither of these situations are a solar Dream

Shade is a solar panels worst enemy. Shade is equivalent to virtually no sun so the panel will be all but useless even though it will have soem output due to the diffused light it collects. That output though will be two tenths of stuff all.

How many hours per day will my panel work?

 

 Not many. The winter sun in the southern hemisphere (Pandanus season) is well north of the equator and even though Pandanus is not much more than a day’s route march from the equator there is no more than a maximum of 9 hours useable sunlight per day at Pandanus.  Worse, this figure is reduced if your panel does not see the sun from sunrise to sunset. For most campsites at Pandanus this is the case. Even more effective hours are lost if the sun spends some time behind clouds or your panel is shaded for part of the day. 
NOTE: Of the 81 days that I spent at Pandanus Park during the 2010 season only four days had no cloud at all whilst just 17 had less than half cloud cover so 2010 season was not a good solar year. 

Now even if you are fortunate enough to generate some solar power for all of these 9 hours in the day but use power in excess of that which your panels generate then simple mathematics indicates that you will be on a losing streak and for most days this is the case because there are another 15 hours in the day when you have an operating fridge and no solar power. This is why the smaller systems are of little value, draining your battery to make up the difference. Hence the need for alternate or supplementary power sources such as a generator.

Where then does all the solar power go?

 

 Sadly not all solar panel power goes into your battery.  The output of your solar panel goes both to your battery and, if connected as most are, into your car fridge. Howver it is not distributed equally or uniformly. For some of the time you may have nothing going into the fridge whilst at other times nothing goes into the battery.
When the fridge is running your battery gets only the surplus current, the stuff your fridge does not need.  Thus if your panel is generating 4 amp-hours and your fridge is taking 4 amp-hours then nothing is left to go into the battery. That is why a single 85 watt panel will not run a car fridge and charge a battery at the same time. 
When the fridge is not running all the solar output goes into the battery.

Clearly your solar array needs to generate more power than you use if you wish to run the fridge and at the same time recharge your battery.  This is why I state you need lots of solar capacity, at least 230 watts of panel and in case of a number of continuously cloudy days, a backup generator. 

Charging Batteries.
In an ideal world all batteries would charge identically however we don't live in such a world.
If you have one battery then this unit will take all the charging current however if you have two or more batteries connected in paralell (as most 12 volt systems are) then not each battery will equally share the charging current. One battery is bound to be more efficient than the other, one will take more charging current than the other with the worst combination being a mix of old and new batteries, even if they are of the same type. To add to the multiple battery woes the more batteries that you have the more charging current or surplus solar power you will need to top each up battery. Thus you will need to have more solar panels for a twin battery system than a single battery system.
Furthermore you need even more charging voltage and current to charge Deep Cycle batteries as opposed to the more common lead-acid types.

Twin car fridges.

Whilst dual batteries require more power so too do dual (or more) fridges. As a rule of thumb, if you try to run more than one fridge on solar you will need at least double the number of panels that are required for a single fridge setup - plus some! For dual fridges and dual batteries plan on a 500 watt solar system! Anything less will be a waste of time.

Wiring up your Solar Panels.

This really is a case of bigger is better, indeed the thicker the wire the better. Voltage drop along a length of wire can be considerable especially with thin wire and this in turn results in less power or current to the battery and fridge.
To come to grips with this concept think of the wire from your solar panel as a garden hose. If you want more water to flow quickly at the end of a long run of hose you use a larger diameter hose. If the hose is thin then like most of us, only a dribble comes out the other end and as we all know that is not good. The thin hose restricts the flow. For this reason select large diameter wire and multi strand cable, that is use thick copper cable with multiple strands of wire, not thick insulation. The compromise has to be the space to carry the cable and the weight of the cable plus of course the cost. For most solar installations for campers 3mm battery cable is ideal. 5mm is perfect but costly and heavy.

Multiple Solar Panels

Mutliple panels are almost always needed because most single panels have too small an output to run your fridge and charge your batteries, though as technology improves the panels are getting bigger with 240 watt panels now available however the larger panels output a much higher voltage, too high for most camp regulators. Multiple panels provide the extra power or current that you need and can be joined together in many mutliples to give the capacity you need (and your bank balance can afford). However they must be of the same type, that is all mono or multi or polycrystalline etc. DO NOT MIX panel types.

Not all panels have to be the same wattage though it is best if they are matched but they must be the same voltage that is nominally 17 volts or thereabouts. Onvce you have selected your panel size you can keep adding panels until the cows come home providing your regulator can hack the current and voltage. What is important is that ALL these panels MUST BE wired in parralell when connected to a 12volt system and their total Amps must be less than the maximum input Amps accepted by your regulator. (Check the regulator specifications). The following diagram illustrates Parralell wiring of panels - all the positive terminals are connected together and all the negative terminals are connected together .  Employ CAUTION when using multiple panels as they can generate high current or voltage which can be dangerous.

NOTE: Household solar arrays are wired in series to gain a high voltage as opposed to higher current. Do not use this method of wiring for a 12volt sytem.

How much voltage will my panels give?

Most small to medium size solar panels supply a nominal 17 volts in full sun. Lead acid batteries generally charge to no more than 13 volts therfore the 17 volt panel will cope with ease. On the other hand NiCad batteries or Deep Cycle batteries charge at a higher voltage (often 16 volts) which gives a smaller voltage differential (the difference between 17 volts and 16 volts) and for that reason these batteries will charge much more slowly. Furthermore because of their characteristics Deep Cycle batteries discharge slowly and recharge slowly. Most Deep Cycle batteries are unsuited to solar systems unless the solar array is capable of producing a huge power differential and high charging current.  That is you have a large number of panels.

The larger household power systems have panels that produce 36 volts and around 7.8 amps per panel. These panels are physically large (1metre x .8metre) and usually too powerful for off-road or camping type regulators. Until the small size regulators match the output of these panels avoid using the houshold size panels. 

 

How many Amps will my panel produce?

The output of a solar panel depends on the available sun. The Amps each panel nominally gives is marked on a decal on the back of the panel. In general an 80 Watt panel will give about 4.5 amps, a 120 Watt panel about 7 amps.  A 230 watt panel about 7.5 amps but at double the voltage (36 volts). 

The theoretical outputs of common panel sizes are;
40 watt     2.3 amps
65 watt     3.7 amps
75 watt     4.3 amps
80 watt     4.5 amps
110 watt   6.5 amps
115 watt   6.7 amps
125 watt   7.2 amps

How do I know my panels are working?

The simplest way to check a panel output is to use a multimeter to measure the voltage at the panel junction box and then with the panel connected to the battery, at the battery . If you do not own a multimeter then ask around. There are many campers at Pandanus with them and they will be only too happy to help, though at twenty dollars for a multimeter you really should have your own.

A more accurate and instananeous reading is available on a continuous basis when a good electronic solar panel regulator is fitted between your panels and your battery/load. These units provide a digital display of the actual voltage and current being generated as well as being used at that very moment. They also provide a running total of the daily amp-hours in and amp-hours out amongst other readings. These units are far better value than the simpler and much cheaper, plug 'em in and hope for the best regulators and though they cost around $200.00 it is money well spent.

Self-Regulating Panels

These are mongrel things. Self-regulating panel have fewer cells (standard panels have 36 cells) so the voltage produced is generally less than with a standard solar panel which in turn means that the self-regulating panel puts out less power and that means your battery does not charge as quickly. Indeed the tail-off in charging rate starts at around 50% of battery charge and drops to very little in the 70% to 100% range which is where most batteries sit most of the time. 

This situation gets worse on cloudy days when self-regulating panels may cease working altogether whereas a standard panel will still produce a reasonable charging current. Because of this drop-off in performance the wattage rating of a self-regulating panel can be misleading.

Most knowledgeable solar installers will recommend you stick to standard panels wired to a quality brand electronic regulator.

Solar panels with Fitted regulators

Some solar panels are sold with a small electronic regulator fitted at the back of the panel. These panels produce an output that is regulated to 12 volts maximum, regardless of the demands of the battery. Thus if your battery is capable of charging to 13 or more volts (eg deep cycles and most car batteries) then you are out of luck because the solar the panel via its built-in regulator can only deliver 12 volts. 

Again  it is advisable to purchase standard (non-regulated) panels that can be wired into a quality brand regulator.

IMPORTANT: Do not mix regulated and unregulated solar panels.

Note: All standard panels will have a black plastic junction box at the back. This is not a regulator. It is the junction box for the wires to the panel and the location for the battery or load wires to be attached. There should also be a reverse current diode wired across these terminals. Do no confuse this wiring or terminal box with a 12 volt regulator.

Batteries.

Unless you are driving for quite a few hours each day (and thus charging your battery) or turn your electric fridge off at night (not using power) then it is best not to use the cars battery to run your fridge. This will avoid avoid flattening the car battery.   

Instead it is wise to fit a second or auxilliary battery to your 4WD vehicle. This battery is usually mounted in the engine bay and must be connected to the vehicle alternator via a 'power splitter' which is a small cigarette packet sized black box that ensures the main car battery is charged first followed by the second battery and only the second battery is used to power external loads such as fridges. Though second or auxilliary batteries can be fitted anywhere on your vehicle avoid having them in the cabin because batteries can and do explode. The second battery does not need to be the same size as the main car battery though ideally it should be. However it MUST BE the same type, that is lead acid. DO NOT mix battery types.

 

Note: Lead-acid batteries cost about half the price of a Deep Cycle and last longer as well as being better suited to the charging rate of solar panels. Moreover they discharge gradually.

On the other hand Deep Cycle batteries hold their peak voltage for longer but when they reach the tipping point (the cliff) they drop both voltage and current rapidly. They then take ages to recharge, far longer than the hours of sunlight per day and thus the output of most solar systems. Once fully discharged they require extremly long recharge times.

 

DO NOT mix battery types: Deep Cycle batteries have a different charge/discharge cycle to Lead-Acid batteries.  

Sealed or 'No Maintenance' Lead-Acid Batteries can however be used alongisde the older style 'top 'em up with water' Lead-Acid Batteries.

 

Simple Solar Panel Calculation.

Solar panels on their own will only power frideges etc when the sun shines and usually only for a few hours each day. Therefore to ensure 24 hour power supply the solar array must be mated to a 'base power' source which for most will be a battery. This means that your solar array must produce enough power to:

a.     power your fridge when the sun shines brightly,

b.    charge your battery at the same time, and

c.    do so for most of the daylight hours with the longer this charging period the better.

Then, once the solar output drops below about 4 amps (for most car fridges) your battery system must be capable of running the fridge. Furthermore, because full sunlight and thus solar power is not assured on every single day you should plan on two to three days without solar power being available to recharge your battery and run your fridge. This is when the battery suffers most.

 

Now most car fridges consume between 3 and 6 amps when running and up to 8 amps each time they ‘kick-in’ or cycle on.  Now assume that the fridge is cycling at 50% ON and 50% OFF though more realistically most fridges tend to be ON for much longer periods especially on hot days or when accessed regularly. From experience and day long monitoring of my fridge the following is more realistic - 25% power OFF and 75% power ON. This gives a power consumption of 6 amp-hours.

 

Now we can work out how much power you will need and thus how many solar panels you will require. 

 

The car fridge uses 6 amp-hours for a full day i.e. 24 hours x 6 amp hours = 144 amp-hours per day.

Now hook up a single 85-watt solar panel which on an exceptional day  provides 10 hours sunlight x 4.5 amp-hours  = 45 amp hours (Ah) per day.

 

From the above you will note that the average 85 watt panel has no hope of keeping up i.e. 144 Ah used  less the 45 Ah generated = 99Ah deficiency.

 

Put simply even under perfect conditions your car fridge is draining hell out of your battery even when everything - fridge, solar panel and battery are working at their optimum efficiency which of course is rarely the case. The immediate thinking would be to add another 85-watt panel yet even that will not be enough.

 

 2 x 85 watt panels will generate 2 x 45Ah or 90Ah. This still leaves a 54 Ah deficiency and whilst this does not seem a lot you are always on a losing streak so on each and every day your battery is going backwards -getting flatter. Add a couple of cloudy days and you are in trouble and this is why many Pandanus visitors have battery/fridge problems after just a couple of days. 

 

The solution is simple:

Buy a solar system that copes under most conditions.  This means you will need enough solar panel capacity to easily run a car fridge PLUS charge your battery on virtually every day, noting though that it is impossible to cater for day after day of stuff all sun and thus very little solar power. This means that using the above calculations a 200 watts solar system might go close to breaking even whilst :-

          a 240 watt system will or should cope because it will provide around 12 amps or more for most of the day, more when the sun is highest and less during the late afternoon and early morning.

         a stress-free system would be one that has three 125 watt panels connected to a 30 amp regulator. For those with a caravan this should be the minimum system because your panels are flat mounted and thus less efficient. 

 

Diodes.

 

Solar panels can work in reverse, that is they will discharge a battery when the sun is not shining (night time) or whenever the solar voltage is less than the battery voltage. To prevent this, every solar panel must be fitted with a reverse current blocking diode. Many solar panels come with these fitted in the terminal box but in case they are not there I suggest you purchase a few of these diodes, some as spares because they do fail. The diodes you need must be rated at 10 amps and cost around 75 cents each.  Fit one to each panel using the terminals in the panel junction (terminal) box, connecting them as shown below. I don't normally recommend suppliers however in this case because these diodes can be hard to source I suggest you visit a Jaycar dealer or  a dedicated solar panel supplier.  

 

The diode will be about 10mm long, 4mm diameter, black and will have a 'tail wire' at each end. It will also have a white band at the negative end. Fit the diode as per your solar panel instruction sheet or the instructions on the decal on the reverse of the panel. If these are missing then the diode should be fitted as follows:

 

  • on the solar panel +ve terminal connect the diode +ve tail wire.

  • The other end of the diode, that is the end with the white band or the -ve tail wire then goes to the terminal block connection that is used to connect the solar panel to the battery +ve terminal.  The solar panel -ve terminal is connected directly to the battery -ve. See below.

  • Take care when soldering diodes because they do not like lots of heat.

  • Do not reverse this diode connection otherwise it will not work - it will act as a conductor not a blocking diode.

Charge Controllers.

 

A solar panel can be connected directly to a car battery and it will charge the battery and to an extent the battery will regulate the solar charge rate, however at full power the panel will be putting 17 volts across your battery which is enough to boil most batteries - this stuffs the battery. 

 

To avoid this outcome ALL solar arrays must be connected to a battery or batteries via a reputable brand electronic solar panel regulator. Regulators come in a variety of current ratings with 10 amp being the smallest and cheapest however experience has shown that most campers end up adding extra solar panels until they have the output they need so I suggest purchasing a regulator with a higher current rating than your initial purchase needs. Furthermore as I have already shown a minimum of 15 amps is required to charge a battery and run a fridge so you need at least a 15amp regulator - my suggestion is either a 20 or 30 amp unit as this will be a one off cost, with no need to upgrade.    

 

I also recommend solar regulators or controllers that have digital readouts that show the actual voltage and current being produced by the solar panels, the battery voltage and current in and out the current being drawn by the fridge. Most of these regulators will also give a multitude of other readouts but those above are the most important. Regulators with LED lights work but can be confusing because you have to remeber how to interpret the lights. Nothing beats having the ACTUAL readings in front of your eyes. 

 

Conserving power.

 

No matter how efficient or large your system you will need to be mindful of the need to conserve power, if for no other reason than to cope with cloudy days. The simplest way to conserve power is to become a Pom and drink warm beer. If this is not to your liking then add a generator (about $1,200) to your list of must haves but if this breaks the budget then try turning the car fridge OFF during the cold part of the night. This will dramatically reduce the power draw on your battery and most car fridges will stay cold if  UNOPENED overnight.

 

The five worst enemies of a car fridge and thus the causes of high power use are:

  • Leaving the fridge in the sun
  • Opening the lid often often and dawdling with the lid open
  • Wind
  • Leaving the fridge in a closed vehicle
  • Running the fridge with it less than full.

 

Avoid all five and there will be fewer frayed nerves.

 

Solar panel brands and sizes.

 

There are many variables in solar panels and increasingly there are as many brands of panel. Some are extremely good whilst others are average. In previous years the Chinese manufactured panels were viewed with suspicion because they were cheap due mainly to much cheaper production costs. Nowadays almost all panels are manufactured in China then rebranded and Chinese solar panel technology is up there with the very best. Unfortunately it is hard to get truly impartial advice so search the internet and ask for feedback from those with solar panels.

The list of manufacturers or brands of solar panels is growing rapidly and with production costs decreasing the panels are getting cheaper. Technology is also advancing in leaps and bounds which both widens the choice in panel size and manufacturer. Not so many years ago a 65 watt panel was the norm, now they are becoming rare and in 2011 you can buy a 230 watt panel for the same price as we used to pay for the 65 watt panel. 

 

When buying a panel or panels it is worth contacting a long standing home solar system installer to get a price. These installers have a large throughput so their prices are often cheaper.

As far as the capacity of the system you purchase it depends on your budget, your need and your ability to carry the panels. The larger the panel capacity the greater cost and physical size but the less cost per watt.   Suggestion: Buy as large a capacity system and regulator as you can afford. It will save on upgrade costs. And I can assure you, you will never have enough solar power capacity.

 

There is now an Australian Standard for the solar panels to be fitted to household solar power systems so all these brands are worthy of consideration. 

 

 

Caravan,  not car or camping Fridges. - A word of caution.

 

The three way fridges that are fitted inside caravans, regardless of their size, are notorious for flattening batteries when run on the 12 volt setting. Furthermore they can flatten a fully charged battery quicker than you can drink a stubbie. 

 

Even though these fridges have a 12 volt operating option, they do not operate on the same principle as your 12 volt car or camping fridge. Your 12 volt car or camping fridge/esky has a small compressor to generate the cold and this uses around 4 amp-hours. On the other hand the three-way fridge in your caravan works on a heat exchanger principle with the heat element using 30  amp-hours (often more) and for that reason most User Manuals advise NOT to operate the caravan fridge on 12 volts when the vehicle is not running. Equally you should NOT use a caravan fridge when connected to a solar/battery power supply.

If you wish to run your caravan fridge on a solar/battery mix then you will need around 600 watts of solar panels plus a couple of very good, fully charged, batteries to keep the fridge running at night and even then the batteries are unlikely to last the distance. Run your caravan fridge on gas or 240 volt generator.

 

 

The above information is based on research and practical experience gained over years of camping both at Pandanus Park and other camp locations throughout Queensland and New South Wales, and always in the warm months.

It is not intended to be exhaustive and is provided for guidance only.

The author makes no recommendation as to brands of solar panels, batteries or solar regulators. 

 

The author is a qualified electronics technician.

 

Further, impartial advice can be obtained from the Internet. 







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