Solar panel advice please

[Casimir]

I am planning to fit a solar panel on the roof of my van (a Fleurette Migrateur 73LJ) in the near future and would welcome advice from anybody with solar panel experience.

Here's some background information:
I have calculated that a 160w panel should satisfy our needs. Most of our travels are in Spain and France. I have two 110A leisure batteries but these are not connected in parallel as might normally be the case because the batteries are not of the same age. Instead, following advice obtained from this excellent forum some months age I fitted a battery control switch so that I can switch from the first battery to the second battery when necessary. I was going to fit a "duo" solar controller so that both batteries are connected to the system at the same time. However I am now questioning whether this is necessary since only one battery is in use at any one time.

Also, I have noticed that it is fairly easy to find a branded "duo" PWM controller at a reasonable price but this is not the case with MPPT controllers which are claimed to be 20/30% more efficient.

Does anyone have any thoughts on any of this?

[StuartO]

Casimir - 2016-02-15 1:33 PM.....I was going to fit a "duo" solar controller so that both batteries are connected to the system at the same time. However I am now questioning whether this is necessary since only one battery is in use at any one time.

Also, I have noticed that it is fairly easy to find a branded "duo" PWM controller at a reasonable price but this is not the case with MPPT controllers which are claimed to be 20/30% more efficient.

Does anyone have any thoughts on any of this?

 

If you have a switching system which allows you to change over from one leisure battery to another, as long as you make all your solar connections on the motorhome side of the changeover switch (i.e. not between changeover switch and batteries) you should be able to regard your pair of leisure batteries as one, since only one will ever be connected.  You therefore make your choice of solar regulator on that basis. MPPT regulators are worth paying extra for.

 

But the advantage of solar panels is that they charge all day every day when it's sunny, so they are very effective at topping up the connected leisure battery every day, so you have much less need for OTT leisure battery capacity.  Our 130 watt panel system tops up our leisure battery completely every day, so I am in the process of removing one of my (matched, unswitched) pair of leisure batteries, to save carrying unnecessary weight.  With solar panels fitted, you could do the same.

 

[veletron]

I have 200W over a couple of panels, and an EPSolar MPPT controller with remote display (get the newer version, lots of the old ones on fleabay). Nice bit of kit, and fits nicely in the void above the front seat belt.

 

Fit the biggest panel you can cause that 160W panel will do just 4W on a rubbish winters day - enough to overcome the quiescent drain on your leisure batteries though if stored.

 

Nigel

[aandncaravan]

If you are using the Solar Panel in Sunny Southern climes (the Spain and France you speak of) you might not notice much difference between a PWM and a MPPT regulator?

 

The difference in the Solar Harvest between a solar panel in Cornwall and one in Glasgow (both on sunny days) can be 20% less for Scotland.

Travelling from Cornwall to the South of France can improve that by as much as 20% again. See the UK chart on our Solar Page to see a better explanation : http://www.aandncaravanservices.co.uk/solar-panels.php

 

So if you use Solar Power when far South, the difference between PWM and MPPT is small. In the Sahara a PWM might outperform an MPPT reg.

 

 

A PWM type solar regulator effectively applies a big load on the Solar panel to draw off it's power. That works ok until the available light reduces and the Solar Panel output drops.

Under these circumstances the load placed on the panel can cause the available voltage to drop below that of the battery so no charge takes place, even if the Solar panel has half an amp to give.

Obviously the charge voltage has got to be above the battery voltage, so a battery at 12.5v won't get any charge from a 12.4v regulator.

 

What an MPPT regulator does is moderate it's load on the Solar panel to keep the panel voltage at the optimum level. For example if the load it places on the Solar panel drops the voltage, using the above example, to 12.4v, it backs off it's load so the voltage of the panel rises and charging recommences.

 

In a sunny clime the light output should always be high, so the PWM method of just loading the panel to the maximum should get the optimum charge rate.

 

Scotland in Winter is where an MPPT Reg really makes a difference. This can be as much as 30% higher. But then 30% of very little is still not much at all. You would still be lucky to harvest more than 3Ah a day in Glasgow in December?

 

You will probably find that in Spain you replenish the power taken out the night before quite quickly, partly because the Solar gain through the long days will be high and partly because demand on 12v will be so low :

Long days and short nights mean the LED's don't get lit until late in the evening,

No Heater fan draw.

Too nice outside to sit in watching TV.

Too hot inside the van to be in it anyway.

Etc.

 

So Stuart is right you will probably find one battery is all you need? Just wire a duo PWM for Starter + Habitation?

But suggest you get a decent duo Regulator as some just split the charge 50/50, which is obviously not what you need on a full starter battery?

Likewise avoid the ones you have to manually program the balance, like 20/80 as it will never be the right combination.

Look for one that has dynamic control on both batteries, putting power only where and when it is required.

Basically avoid the cheap ones, they are cheap for a reason.

 

 

 

[Casimir]

Many thanks for the feedback.

StuartO - 2016-02-15 2:53 PM

... as long as you make all your solar connections on the motorhome side of the changeover switch ...

I am not sure I understand what you mean by this. I thought that the battery (or batteries) are normally connected directly to the solar controller.

Once I have had some experience with a solar panel, I might consider removing the second battery but in the meanwhile there is a certain satisfaction in knowing that I have a second battery always available at the flick of a switch.

aandncaravan - 2016-02-16 11:25 PM

If you are using the Solar Panel in Sunny Southern climes (the Spain and France you speak of) you might not notice much difference between a PWM and a MPPT regulator?

Yes, this confirms what I have read elsewhere. For my particular purposes a PWM controller might be perfectly adequate.

At the moment I am leaning towards an Epsolar 20A PWM Duo controller (with a remote display). That would enable me set a balance of say 90% for the main leisure battery and 10% for the second backup leisure battery, just to ensure that it is topped up.

aandncaravan - 2016-02-16 11:25 PM
... Look for one that has dynamic control on both batteries, putting power only where and when it is required...

So far I have not found one that does that. Did you have one in mind?

 

[aandncaravan]

Most of the solar regulators we have seen are not primarily designed for a motorhome, as can be seen from their 'features'.

The best place for a Solar Reg is next to the power distribution box which can be hidden away under a Seat/bed or locker. A place where the regulator is often difficult see, let alone read a display.

If you look around at the number with a built in display, it shows what we mean.

 

If you look at those from Motorhome charger manufacturers, none have a built in display, all remote displays showing they know how the thing is going to be used.

 

Most 'duo' units are designed for charging two banks of batteries that require continuous charging.

Not like in a Motorhome where one bank is almost permanently charged up, and just needs the tiniest trickle.

If you use most generic 'Duo' chargers in a Motorhome, the charge rate is often split to charge a Motorhome Starter battery by too much, drying it out.

 

A dual charger, i.e. two totally independent chargers in a single casing, not one charger being split into two, has two completely autonomous chargers. So if one is looking after a 'fully' charged battery, it will take none of the available power. The other charger either does the same or takes all the power.

You can see that if they are truly independent Solar Chargers, there is absolutely no 'tie' between the two and they operate as two separate entities charging their own battery bank exactly as it needs. One does not know about the other.

 

So if you have a 'duo' regulator that you have to program the split, what is that telling you? More likely to be one charger with two outputs and there may be a battery bank crossover effect when charging.

 

The term 'Duo' is being misused to suggest the regulator is a dual regulator, when it is a single split charger.

The single charger with split outputs is a lot cheaper to produce than the type with two chargers in one casing, so avoid the cheap units.

 

If you find a dual regulator it will charge both your 'independent habitation' batteries exactly as they need as you switch between whichever is the primary one at the time.

 

No sorry can't recommend anything.