SOLAR POWER

For caravans and motorhomes

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Solar, wind or generator power?

Firstly I should warn you that I am not a solar-power guru or an electronics expert. I know what I know about this subject from wiring up my own systems and playing around with various types of power generation for more than 18 years. Over time I have found out what works for me and this is just an attempt to pass on some of what I have learned.

What kind of power system is best for your caravan or motorhome? Do you choose just one or a combination?

To use solar and live any kind of 'normal' life on the road you will need lots of solar panels, a big sine wave inverter, a good re-charging system for the time the sun won't shine and lastly big, heavy, expensive deep cycle batteries. If you have deep pockets then this is the way to go. Solar is after all, free once you have paid for all the gadgets and batteries and it is a silent system so your neighbours in the bush will all love you.

Petrol generators are a cheaper alternative BUT they are noisy, are not allowed in all campsites and have on-going running costs. Wind power is quite expensive, takes time to set up and can be unreliable. So what do you choose?

This article will look at each system in detail and hopefully will help you to determine what system will work best for you.

12 or 24 volt?

No matter what charging system you use, your whole power system for your caravan or motorhome will be based on batteries. There are basically 2 main types of battery systems, 12 volt and 24 volt.

12 volt is normally a number of standard deep cycle batteries wired in parallel (Ie. all + terminals are connected to each other and all - terminals are connected to each other).

24 volt systems still use 12 volt batteries but they are wired in series (Ie. sets of 2 x 12 volt batteries wired + to -)

There are far fewer 24 volt systems in motorhomes than there are 12 volt. The main reason for this is the availability of appliances.

Technically a 24 volt system is much better as you do not need the heavy wiring required for 12 volts. A 12 volt system, especially from the panels to the regulator and batteries, needs 6mm wire. (That's 6mm of actual internal wire and does not include the outer plastic insulation.)

The main problem with 12 volt systems is voltage drop due to resistance in the wire. This is why you need short very heavy wire for 12 volt power.

Even so, 12 volt is by far the most popular because most commercially available low voltage appliances are based on 12 volts.

There are different types of deep cycle batteries which is something we will look at further on in this article.

SOLAR PANELS

Working Out Solar

How much solar power you need depends on what appliances you are going to run and how long you want to run them for.

If you want to live on the road full-time then 'more = better'. The cost of solar panels has dropped dramatically in the last few years. A 120 watt panel cost us $1200 in 1999 and in 2012 the same size cost just $399. This means that you can now put a system together far more cheaply.

Our bottom line for a solar system that will allow you to live on the road would consist of 700 watts of panels, a big regulator (60 amps), a 1000 watt continuous sine wave inverter, 800 amp hours of deep cycle batteries and some way of recharging the batteries if the sun refuses to come out.

If you are only travelling part-time for a few weeks each trip then you can get away with a much smaller system.

One of the big determining factors will be the type of fridge you use. A three way (or gas fridge) will mean that you don't need anywhere near as much battery power, so this will be an important factor in working out how many solar panels and batteries you will need.

A solar system that will really work for almost every conceivable situation would (as of 2013) cost the following amounts:

$ 2400 for 6 x 120 watt panels. (half the price it was just 6 years ago)
$ 1300 for a 1000w sine wave inverter.
$ 450 for the 60 amp regulator.
$ 2513 for 800 amp hours of deep cycle batteries.
$ 1300 for a decent motorised 50 amp battery charger.
$ 7963 TOTAL

Add to this the cost of mounting the panels and wiring and you won't get much change from $8.5k.

This system should continue to work well for around 10-15 years before you need to start replacing components but it is a very expensive outlay up front.

You may not need such a large system but this setup will run whatever you want for just about as long as you want.

The trick with a solar system is to have enough panels to quickly charge all your batteries and enough batteries so that they don't run too far down over night. It is a balancing act that is influenced by all sorts of external factors like how many hours the sun shines, what time of year it is, where you are etc.

It is not widely known, but heat adversely affects solar panels. Most solar panels are rated at 25C which sounds reasonable. That is until you see that this is the temperature of the panel surface NOT the ambient temperature. For a panel to have a surface temperature of 25C in full sunlight it is likely that the ambient temperature will be less than 10C.

How many panels will you need?

First you need to work out what your power consumption will be per day. To do this you need to know exactly how much each appliance uses and how many hours it will be running for.

All appliances will show their power consumption in watts and all you need to do is make a list like this:

As you can see a 12 volt fridge will be the biggest power draw for your system as it operates all day. The reason we have shown 12 hours use instead of 24 is that the fridge will turn itself on and off at different intervals and 12 hours with the motor running is just an estimate.

Because we are talking about a 12 volt system here, you now divide the total watt hours by 12 to give the total amp hours of power you will need. 888 watt hours divided by 12 volts = 74 Amp hours.

The following table will give you some idea of how much daily power you can get from solar panels at different times of the year.

There are a copule of methods used for calculating what power you can get from your solar panels over the period of a day. One that we have seen is to say that there are 5 peak hours of sunlight over any given summer day and 4 over a winter day. The method we used was 'real world'. We measured the output of panels from dawn to dusk taking a reading each hour. We added up the total for each hour and then divided by the number of hours to get an average for the day. What we found was that you can simply halve the rated watts of a panel and multiply it by the number of hours of daylight and you will get a fairly accurate assessment of power generated for the day.

For the table above we have used 8 hours for summer and 6 hours for winter and figures are based on a cloudless day. If the weather is overcast then you can lose more than half your expected power coming from the solar panels and this needs to be taken into account.

To work out the number of solar panels needed we divide the total watt hours needed (in this example 888) by the worst case daily winter power generation for your preferred panel size.

Let's say we want to use 120 watt panels, you can't simply divide 888 by 360 (remembering that 360 watts is the least amount of daily power you expect to get from this size panel on a clear winter's day) because the weather might be cloudy. You have to halve the power from the panel and then do the calculation. 360 watt hours divided by 2 is 180 watt hours. This is our absolute worst case scenario for the power coming from a single 120 watt panel on a cloudy winter day.

888 divided by 180 is 4.9, round this up to give the number of 120 watt panels you will need. Remember this is WORST CASE (winter) scenario and means you should NEVER need another charging source to keep your system going.

If this isn't complicated enough, when we start to look at batteries things will get even more complicated.

Recently I worked out the actual figures from our latest solar system. The following table shows how everything currently looks.

Types of Solar Panels

Solar panels basically stop working when it is heavily overcast. From an array of panels that can put in 20 amps you may get just 3-5 amps on a heavily overcast day. This is why you may have to have a backup power source like a generator.

Heat and Shade resistant panels

At one time the only heat and shade resistant panels available on the market were made by Uni-Solar. Many people with large roof spaces used these panels but it is very important to keep the panels clean. Unlike glass panels these ones attract dirt and dust and if left without regular cleaning they will gradually lose their effectiveness.

Other types of shade tolerant panels have gradually become available and this is one feature to check for when you look at buying a solar system that you may want to mount permenantly on the roof of your vehicle.

Mono and Multi crystalline glass panels

By far the most common panels are glass based. They do not like to get too hot and should be mounted with an air space underneath. If only part of the panel is in shade the whole panel stops working but they are still used in greater numbers than the shade resistant models because they self clean during rain. There is really nothing to choose in performance between mono or multi crystalline panels as they both seem to have about the same performance. Multi crystalline are the more modern design.

Due to improved performance in solar technology the amount of power generated for a given surface area is gradually increasing and has resulted in panels getting smaller over the years.

Solar Blankets

A fairly recent entry into the world of solar power are the solar blankets. These are semi-flexible folding solar panels that can easily be transported and are easy to set up when you arrive at your destination.

They are still more expensive than glass panels but they are gaining in popularity due to their portability and ease of use.

They do not replace the fixed glass panel style but can be a useful alternative when travelling.

Panel Grades

Solar panels have a grading system depending on the manufactured quality. It isn't important to know exactly whet the grading system is based on but it is important to only buy grade A or grade B. Anything lower than that is a waste of money.

BATTERIES

How many batteries will I need?

A battery is another strange thing. It is only really happy when it is fully charged and if you leave it alone and don't use it and only have a trickle charger going to make up for any natural current loss.

Batteries do not like to discharge power and they will actually be damaged if you discharge too much power too often.

The reason your 'house' batteries (Ie. Those used to run your electrical appliances) need to be deep cycle batteries is that ordinary vehicle starter batteries are not designed to handle constant charging and discharging.

It may be useful to think of a solar systems in terms of a water tank. The tank represents your batteries, the water coming in the top represents the power coming in from your solar panels, wind generator, or charger, and the water going out the bottom is the power being used by appliances.

The trouble is, there are all sorts of things that interfere with the flow coming in and the flow going out and left to itself the amount in the tank (batteries) gradually leaks away over time.

The analogy is a little simplistic but it does explain a few things about battery power.

The tank (or battery bank) cannot hold more than its given capacity. In the case of batteries this is measured in Amp hours. Once the tank is full no more should be put in. Forcing more in will damage the batteries (they will actually boil). Unlike a water tank, the excess input will keep trying to get in and won't simply overflow. This is why you need a regulator. (More about regulators later).

Running a water tank dry will not damage the tank but that does not apply to batteries. You MUST NOT run your batteries down below 50% and should not run them down below 75% of their maximum capacity.

Because we do not want to draw our battery bank below 75% of its fully charged state, we have to (using the example above) have enough batteries to supply 74 amp hours of power while keeping all the batteries at or above 75% of their fully charged state.

A single 100 amp hour battery supplying 74 amp hours of power would be drained to about 25% of its fully charged state. This WILL damage the battery.

Because you can ONLY safely use 25% of any battery's charge, you have to multiply the amount of power you need (in this example 74 amp hours) by 4 to get the total size of the battery bank you will need.

In this case we multiply 74 amp hours by 4 to give a total of 296 (round up to 300) amp hours.

So for the example of estimated power use given above, you need a battery bank with at least 300 amp hours capacity.

More about batteries

Until recently most people were still using lead acid batteries. This has rapidly changed as lead acid batteries need constant checking of acid levels, will spill if tipped and produce dangerous gases.

Gel-cell and AGM batteries don't require the same maintenance and they were much more expensive. That has now changed and so most people using house batteries have made the switch to AGM of gell-cell.

Some basic rules about battery banks:

DO NOT mix Gel-cell and lead acid batteries in the same battery bank. ALWAYS use the same size batteries in the battery bank. Ie: use 4x130 amp hour batteries instead of 2x100 ah and 2x130ah. Why? Because if you use 2x100ah and 2x130ah in the same bank then you have wasted your money buying the 130ah as all the batteries will run as if they were 100ah.

One of the big problems with any battery system is that if one battery dies you should replace all the batteries in that bank as your batteries should not only be the same size, they should be the same age. A battery bank is only as good as the weakest battery in that bank.

It is usually easy to tell when a battery is 'on the blink' as your regulator will constantly stay in 'boost' mode and your battery bank will never get in 'float'. The only way to really tell which battery has failed is to disconnect all the batteries and test them individually by measuring voltage drop over a long period of time. If the batteries are in good shape they should read around 12.6v. The dud battery will usually read less than 12v.

The voltage level of a battery is meaningless unless the battery has been unused for several hours (and is only really accurate when the battery has been unused for two or three days). This means that the voltage levels you see while appliances are on do not represent the actual state of the battery.

This can be quite a problem when your batteries are in constant use and can be frightening when you see voltage levels of 11.5 volts as this would normally indicate a seriously flat battery.

The only way we are able to get a true reading of voltage is to turn everything off (usually in the very early hours of the morning) and leave things off until first light when we can then read the voltage and get a good idea of how the batteries are doing. A multi meter is not a good indicator of battery state either, as a surface charge of 12 volts or more can be maintained by a battery that is otherwise useless. To see exactly how well your batteries are doing you need to constantly monitor the battery level over several hours, then place a heavy load on the battery for a few minutes and then check the voltage again. if it dropped significantly then the battery is not holding its charge and should be disposed of.

Your 12v batteries should charge up to a maximum of 15 volts during the day and should not drop lower than 12.32 volts overnight. This can be checked by using a monitoring regulator like the PL 20.

Lead acid batteries that are constantly in use will lose electrolyte (acid) fairly quickly and fluid levels should be checked monthly and topped up with distilled water - don't add more acid just use distilled water.

WARNING: Always remember that lead acid batteries produce highly explosive hydrogen gas as they charge. They must be stored in a well ventilated compartment and kept away from sparks or sources of flame. Lead acid batteries contain highly corrosive acid that will damage most things (including you) that it comes into contact with.

Gel Cell or AGM batteries.

When they first started to be available both Gel-cell and AGM batteries were very expensive. They are now the default standard for house batteries and the price has come down to what lead acid batteries used to cost.

Lithium

Lithium batteries are still very expensive but they will gradually take over from Gel and AGM batteries.

The key things to remember about litium batteries are that they are faster to charge, do not suffer anywhere near as much from deep discharge so that you have more power available for daily use and they weigh about half as much as other types of battery.

There are many new developments coming in battry technology but for now, lithium are the fastest growing sector of the market.

Lead acid batteries are now all but dead as 'house batteries' so there is no longer a need to worry about the old style. Just keep your batteries charged at the right levels, don't discharge them too deeply and they will last for many years. We have seen at least one installation of gel-cells that lasted around 15 years!

REGULATORS

Regulating the charge

Because we now know that overcharging your battery bank will destroy it, it is obvious that some means must be used to slow or stop charging when the battery bank is full.

This is done with a solar power regulator.

A good regulator will have some sort of digital read out that tells you the voltage of your batteries as well as other useful information like the number of amp hours used, the number going in and the maximum and minimum voltages.

As the batteries get closer to fully charged the regulator starts to cut down on the power coming in from the panels and as the batteries drop lower the regulator will let more power in.

You can find your self with panels that are able to put in 20 Amps but with a full battery bank you will see the regulator only allowing 1-2 Amps in if all your appliances are off.

The job of the whole system is to get your battery into what is called 'float' as quickly as it can. Many regulators have a 3 or 4 step charging system that includes:

Boost - All available charge is put into the battery during this phase.

Equalisation - Levels the charge between the cells of your batteries by overcharging for a short period of time. This is usually only done on rare occasions, not on a daily basis.

Absorption - As the battery nears a fully charged state charging gets reduced to avoid over gassing the batteries.

Float - During this state the battery is fully charged and more charge is only let in as it is used by appliances.

Any good regulator will have a low voltage cut off that stops power being taken out once the battery voltage drops to a certain level (usually around 11.2 volts). This is an absolute requirement to stop your batteries getting damaged by over discharging.

Regulators vary in price and quality from around $85 all the way up to several hundred dollars.

You MUST match your regulator's capacity to the capacity of your solar panels. A good rule of thumb for 12 volt solar panels is that 20 watts will produce 1 amp. For example. A 120 watt panel produces about 6 amps of power. If you have 3 x 120 watt panels then they can produce 18 amps. You then have to match a regulator to the total ability of all your panels to produce amps. In this case you would use a 20 amp regulator. Always use a regulator that has slightly larger capacity than the total output of your panels so that it is not running at 100% capacity most of the time.

If you use a regulator that is rated less that the total output from your panels then you will burn it out very quickly. You may want to buy a larger regulator than required to allow for future expansion.

There are many brands of regulators available today but if you want something that is easy to use and is very good quality then think about Plasmatronics.

NON-SOLAR

Going non-solar means using a generator of some sort and this means lots of fuel unless you have a lot of batteries and a high end motorised charger that can quickly bring the batteries up to full charge.

We started off with no solar panels but quickly realised that it was not the best (or easiest) way to do things.

Generators are noisy and many people don't like them. The other problem is that some campsites will not allow a generator at all.

A non-solar system will cost less in the initial outlay (around $4-5000) but it will cost much more to run and with the way fuel prices are going that may mean $5 a day or more depending on how long you need power for.

Even with the larger system we used to have we paid $20-30 a week for fuel to run the generator at night.

The new inverter generators are almost twice the price of non-inverter models but they do produce nice clean power that will run any 240 volt appliance. We have seen people buy a cheap generator to run a $1500 Engel fridge only to have the fridge stop working after being forced to use very 'dirty' power.

If all you want to do is run lights and a TV then you might be able to get away with a GMC, Scorpion etc. but if you want to run a computer, charge batteries etc then think about a better quality unit like a Honda or Yamaha.

Note: If you opt for a generator then it is vital that you use the recommended oil and change the oil and spark plug at the intervals nominated in the generator's manual. If you ignore these things you will wear the generator out very quickly.

Clean power

Generators and inverters come in two basic types, those that produce clean power that is equivalent to mains power and those that do not.

The difference between the two - besides that fact that dirty power can kill your appliances - is the cost. As with most things, the better the quality, the higher the price.

Pure sine wave generators and inverters will run all your appliances but modified square wave models (also incorrectly called modified sine wave or quasi sine wave) run the risk of destroying some electrical appliances either very quickly, or over a period of time thus reducing the life span of the appliance.

We run a pure sine wave generator but also did run a good quality modified square wave inverter for several years. This ran most things without trouble but is not suitable for sensitive equipment like computers and we were always a bit wary about plugging new appliances into it just in case.

Now we use a 1000w pure sine wave inverter and that runs everything we want it to including the washing machine, without a single problem.

Wind power

Portable wind generators are being seen more often on camp sites these days and they can be very effective if you are staying in one place for any length of time.

The main problem with them is the amount of time required to set them up as most models have to be on a high pole away from people as they spin very quickly and the blades are very dangerous.

They may not be too popular with your neighbours either as they can be noisy. There are some models (notably the Rutland 913) that are very quiet, although they are said to deliver a maximum of around 18 amps (we have only seen a maximum of 9 amps to date) as opposed to the noisy ones (Air-X) that are supposed to deliver up to 50 amps.

They are not a cheap alternative with most types costing around $1500 or more. By the time we had finished buying bits and pieces to make up a mounting pole for our Rutland, we had spent just over $1800. With the falling cost of solar panels, wind gens are rapidly becoming too expensive to consider.

Our experience with the Rutland 913 to date is that, once you have the mounting kit sorted out, it is relatively easy to set up and in windy areas it delivers around 72 amp hours a day. This allowed us to virtually stop using the petrol driven generator and saved us about $30 a week. (Once we replaced the bushes on this wind gen we have been getting 96 amp hours plus per day from it.)

Don't believe the hype about maximum amp generation on wind gen brochures, they generally do not deliver anything like their rated maximum capacity. In even the strongest winds the Rutland has so far only managed a maximum of 15amps.

The main thing about win generators is that they deliver power as long as the wind is blowing (about 10 knots for the Rutland) or more and they do it all day and night if the wind keeps blowing. In most cases they are not a stand alone solution for power generation and need to be augmented by a solar system. The model we chose to go with is about the equivalent (in power generation) of 2 x 120 watt solar panels and on latest solar panel prices that is only 2/3 of what you will get from solar power for the same price.

Power leads and wiring.

A word needs to be said about power leads as the regulations have recently been changed.

It is no longer acceptable to join two leads together to reach a power point.

Leads need to be a single length (30 metres we believe is now regarded as the maximum allowable) and must be 15 amp rated.

The wires of your solar system are like the pipes to and from the water tank. If the pipes are too narrow then not enough can get either in or out. Unlike water pipes, electrical wires that are too thin on 12 volt systems run the risk of overheating and shorting and may eventually lead to a fire. If your wires are not heavy duty enough then the power can't get in properly from the charging system or out properly to the appliances.

Solar systems are not really simple to understand. There are all sorts of factors that influence how much power goes in and how much goes out.

Wiring up your solar system correctly is very important. If you have a 24 volt system then you can get away with much thinner wire but if (like most people) you have a 12 volt system the wires between your panels and the regulator and from the regulator to the batteries should be 6mm thick (that is the copper part of the wire and does not include the insulation.)

Try not to have too many joins in the wire and try to keep the length of wire used as short as possible. Make sure all joins are properly soldered rather than crimped. (Good advice that I still need to take for my own system!)

INVERTERS

An inverter allows you to get 240 volt power from your 12 volt batteries but it will use power on its own and therefore adds between 1 and 2 amps to the power consumption of any appliances plugged in to it.

When connecting your inverter make sure the + lead is attached to one end of the battery bank and the - lead to the other end of the bank. The same thing applies to chargers, solar panels, win gens etc. This is done to make sure that any charge or draw is evenly distributed over the battery bank.

There are two basic types of inverter.

Modified square wave inverters.

This is the older style of inverter and while good quality models can run everything except highly sensitive electronics like computers and phone chargers, the power they supply is not identical to that you get from the mains.

Modified square wave models are of concern because you can never be sure when plugging in an appliance for the first time, whether they will be damaged or not.

Pure Sine wave inverters.

Sine wave inverters provide the same quality of power that you can expect from mains power. They are therefore safe to use with all your electronic appliances but they do cost more than the modified square wave models.

Any inverter should have a low voltage cut off system and a high voltage cut off system to protect your batteries from damage.

Better quality inverters will also have monitoring ability and will tell you the voltage being produced, the amps and watts being consumed as well as the charge state of the battery etc.

The recharger

Some other way of recharging your batteries when the sun won't shine is an absolute necessity. There are a number of alternatives.

Charging from your vehicle's engine

Standard alternators are usually too small to be of much use in charging your vehicles 'house' batteries. They are also designed to stop charging when the charge level reaches about 70%.

Many people replace their vehicle's standard alternator with a more heavy duty model and use smart chargers to ensure that charging can go all the way up to 100%.

One particular problem we have seen in some setups is that the vehicle alternator is detecting the state of charge of the vehicle battery and NOT the state of charge of the house battery. This causes the alternator to drastically reduce charging and means the house battery never gets charged properly. It is due to poorly set up systems being wired incorrectly and is something you need to be aware of if you are getting someone else to wire up your system.

Generators

Some generators can supply 240 volt power as well as 12 volt DC power for recharging batteries. The number of amps they supply for battery recharging is limited from about 2-6 and they are not an ideal method of recharging on their own.

The main advantage of a generator (especially when teamed with a 240 volt charger) is that they will run all your appliances at the same time as they re-recharge the battery bank. This means that you can do more or less what you want with your appliances and take no extra power from the batteries.

There are some appliances that you simply SHOULD NOT use with a battery based system. These include any electrical appliance that is used as a space heater, water heater or cooker and other power hungry items like air-conditioners. If you want to run energy hungry appliances like these then you will need to get a decent sized generator. 2kva is about minimum.

On the minus side, generators are noisy and have on-going costs including fuel, oil, spark plugs and servicing.

240 volt chargers

A 240 volt charger can be combined with a generator to get your batteries back to full if they are getting low.

Don't waste your money buying the cheapies you will find in many auto shops. A decent charger should be able to put in at least 16 amps but really you should be looking for models that can supply 20 amps or more.

Petrol driven chargers

There are petrol driven battery chargers available by companies like Christie Engineering but they are expensive and noisy. Some models can put in 50 amps or more and they are a very quick way of getting your batteries charged.

Unfortunately quick charging batteries can overheat them and is not the best way to bring them back to full if done on a regular basis. Trickle charging a battery is far better for longer life.

Inverter / chargers

These are a combination of an inverter (see above) and a 240 volt charger that requires a generator to run. They are universally expensive but they can be a good alternative to buying a separate inverter and charger.

What do we use?

Our power system has evolved and changed over time and since we changed from living full-time on the road it is now quite different.

Our full-time power system consisted of:

2 x 40 watt BP solar panels
2 x 80 watt BP solar panels
1 x 120 watt solar panel
PL20 regulator
4 x 100 amp hour North Star gel cell batteries
Rutland 913 wind generator and 20 amp regulator
Honda Eu20i generator
700 watt sine wave inverter
Workshop 20 amp rms 240 volt battery charger (charges 12 or 24 volt).

Our part-time system included:

4 x 60 watt solar panels
4 x 100 amp hour North Star gel cell batteries
1 x 100 amp AGM battery (separate to the gel cells.)
15 amp regulator
Honda Eu20i generator (Never used these days)
700 watt sine wave inverter
16 amp 240 volt charger

The big difference between this and the system above is that in the full-time system was needed to run two 12 volt fridges whereas the part-time system has a gas fridge and we need much less 12 volt power.

We have now changed again and the new system is mounted on our Coaster bus.

DC - DC charger for the Coaster batteries
3 x 90 watt solar panels (fixed)
2 x 60 watt panels (fixed)
1 x 130 watt solar blanket (portable)
3 x 120 amp hour BOSCH AGM batteries
30 amp regulator for the fixed panels
20 amp MPPT regulator for the portable solar blanket
Honda 3kva generator.
1000 watt sine wave inverter (Coaster)
300 watt inverter (Trailer)
240 volt battery charger

We are now back to running 2 x 12 volt fridges and this system works perfectly for the power needs we now have.

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