folding solar panels 1 vs 2

hey mate thanks for the advice I will definatly move the controller closer to the battery and might try and get the panels without a controller so I can buy one of my own was thinking the c-tek 20 or 25amp can remember which it is. as this would allow me to easily add more panels later on if I say started with just one. space isn't too much of an issue in the troopie but it is definatly something I hadn't considered and another reason I may start out with just one 120 watt and see how I go

Oops, the other thing to watch is the weight, the 220W set will weigh about 23kg and the 120W ones will be about 12kg each. Keep carrying that weight in a big panel for setting up in mind.

First a question - To make good use of over 200W of solar capacity you'll need a fair amount of battery storage. Do you have 200Ah or more?

Assuming you do, I agree 100% with Boobook - I'd go with two of the smaller panels. Effectively you then have 4 smaller, lighter panels, an extra 10% energy, save a few $$ and spread the risk should a panel get damaged. As suggested, I would certainly remove the regulators from the panels (or bypass them) and instal one larger one close to the battery/s. (You may be lucky and find the ones on the panels will have the capacity to handle both sets of panels.) Both set of panels should be fed through a single controller to the battery, since if there were two controllers they would interfere with each other and reduce charging performance.

This seller quite often receives favourable mention here.

Cheers

John

John, I know there is a common wisdom on this forum that you should match watts with AH, and as a very rough guide that has some merit. However solar watts are like air. If you don't have enough it is critical but if you have too much it doesn't matter. The rule of thumb assumes good, sunny weather.

Consider someone with 100AH of storage with a fridge and a few lights and cloudy / rainy weather. That person may get 1 - 2 days without recharging at all. With 100W of solar they may only harvest 20 -30AH per day if that, lasting them 2 - 3 days. However with 240w they may still get 40 - 60 AH per day under the same conditions, enough to go indefinitely. Spend some time in the High County where hill, tree and cloud shading can reduce your capacity by half or more and this will ring true.

Another different example is that someone with 300AH of battery and 130W could probably go forever with the same power use unless there was a full bad week of weather, or even less solar in central Australia. Or someone using lights only and a 100AH battery could get away with a 20W panel forever.

It's really more complex that a 1:1 ratio of watts to AH as I am sure you know from your other posts and they are not really related. You need to calculate load, capacity and recharge capability (inc shading season and location) as a group.

The only thing you can say for sure, is you can not have too much solar or battery, electrically speaking.

Boobook,

I have no argument with most of what you say. You are right in saying that there is a general view that matching solar generating capacity (W) to battery capacity (Ah) is about the right ratio between generation and storage. I do not subscribe to that simplistic rule of thumb and after a career spent in this sort of stuff I know full well that the situation is far more complex!

The complexity comes not just from the technical or economic aspects, but especially from the individual circumstances arising from local weather, other charging options and of course the user's usage patterns. My comments above were influenced by my own experience - 200Ah of storage, 150W of solar and a 30A dc-dc charger, and rarely relying on solar for more than 2 or 3 days without driving.

One key factor in system sizing is the ratio of generating capacity to storage capacity. Another is the allocation of dollars. Extra storage costs, extra solar costs, a decent dc-dc charger costs. There's little point in having lots of solar capacity if you don't have the storage to complement it. Little point in lots of solar if most charging is done by the alternator anyway. I used to carry more solar, but one panel now stays at home - I carry enough for routine and emergency charging. (I had one trip where the alternator died and solar fed the vehicle electrics, including ignition for the petrol engine!)

Different requirements lead to differences in the balance of expenditure on the various elements. Should you spend an extra $250 on an extra 100 Ah of storage, or on extra panels, or on a decent charger? The OP didn’t indicate how much storage he had. If it was just the usual 100Ah battery, then I reckon part of his expenditure on 200+ watts of solar might be better directed to more storage - depends on his usage patterns. Depending on his travel patterns a dc-dc charger might be a worthy addition rather than lots of solar.

“The only thing you can say for sure, is you can not have too much solar or battery, electrically speaking.” Sorry – can’t agree with that – every 100Ah is another 30 kg, and every solar panel is another fragile cumbersome bit of gear that has to be housed and cared for. Your requirements determine your needs and the ratio of storage to generating capacity. Excess is good, but not too much excess!!!

Cheers

John

I have a deep cycle that's 105 or 110 ah and the starter im not 100% sure but I think its around 80ah so there is a decent amount of storage as the can both be connected or separated as desired and I would much rather have too much solar than not enough so don't mind going a little bit over board as I don't want to have to worry about power when parked for 3+days so I definatly agree with boobook as I want to be covered in all circumstances and don't like to do anything half assed I will definatly run both through through the one controller as stated above

it is great also to hear more good things about this seller as I have heard that some are not entirely honest is it worth me getting another battery I would think that would be sufficient to last over night as long as I had the solar capacity to recharge the batteries the next day?

Hi psychonaught,

Best to avoid using the cranking battery for household purposes - there's always the risk of running it down too far to start the engine, but also it isn't best suited for the job, and it's charging/discharging characteristics aren't matched to the deep cycle battery's. No problem as a short term fix, but not ideal for general use.

Should you add another battery? Depends on your likely usage patterns. If you have 200+ watts of solar and are running a fridge in hot weather plus lights at night, and charging torches, laptops, ipads, cameras, etc etc, and want 3+ days before charging from the vehicle, then another 100Ah would be nice. (In my experience this lot will require about 35-45 Ah per day.) For the sake of your battery/s it's best not to use more than about 2/3 of their capacity before fully recharging. If you strike a run of heavily overcast days your 200+ watts of solar panels probably won't supply your daily needs. If though you are not running a fridge you will not need an extra battery, and probably not the solar panels either! If 2 fridges, or running one fridge as a freezer then another battery would be very desirable to deal with 3+ days of heavy overcast.

Worth noting that, depending to some extent on where your "house" battery is located, it will not be fully charged by the vehicle's alternator. The voltage supplied by the alternator isn't high enough to fully charge a deep cycle battery, especially if it is some distance from the alternator and significant voltage is lost in the long wiring. This is where a dc-dc charger can be so useful - it increases the voltage to suit the battery. If you are buying a bigger MPPT controller for your solar panels suggest consider one such as the Redarc BCDC series or Ctek D250S Dual which provide both a dc-dc charger and MPPT controller in the one unit. Not cheap, but these give you full charging from the alternator and flexibility.

I certainly agree with your intention to do the job properly. It's not a lot of fun when the butter looks like oil, the meat and milk are definitely on the nose and the beer's hot!

You may find our blog Electricity for Camping a useful read.

Cheers

John

Member - John and Val posted:
BIG SNIP

"“The only thing you can say for sure, is you can not have too much solar or battery, electrically speaking.” Sorry – can’t agree with that – every 100Ah is another 30 kg, and every solar panel is another fragile cumbersome bit of gear that has to be housed and cared for. Your requirements determine your needs and the ratio of storage to generating capacity. Excess is good, but not too much excess!!! "

I think we are in violent agreement, I specifically said 'electrically speaking' given the original context of the question and replies, and agree about weight considerations as I commented earlier. That comment was to dispel the impression some may get that there is some fixed relationship between the AH and watts.

If you used the newer flexible solar panels for example you could have over 300W of solar capacity for around 9kg in a compact storage footprint. The price of these has halved in the past year and make them viable.

Yes Boobook! I agree that we are in violent agreement! Your point that there really isn't a set relationship between generating capacity and storage capacity is well made. The changing prices of panels, both flexible and solid, continues to change how we can optimise our systems.

Cheers

John

that is a fair point about the cranking battery and it would only be used in emergencies and as both can be linked there combined power could be used to start the car in emergencies aswell.

i have a troopcarrier so the battery is located under the bonnet not far from the alternator so I would imagine voltage drop would be negligible and as it is used as a daily driver most of the time I read that dc-dc chargers can actually damage the batteries when they aren't cycled regularily is that correct?

I will most lickley be buying the ctek to regulate the solar panels so there is always the ability to add it to the alternator down the track if I feel it necessary and I will give your blog a read thanks for the link.

if I was to add a second deep cycle battery it would have to be fully contained and stowed in the car some where which I was trying to avoid doing however it might be handy to have one hooked up to a couple of inverters and the fridge leaving the rest for the main battery however how would I go about hooking that up to the solar panels? as it would be hard to get the regulator close to it as it would be in the back of the car and would need to be removable as sometimes I require a completely empty car. would I need a separate regulator for each battery or could the underbonnet supply charge to the one in the car with possibly a dc-dc charger close to the internal battery not sure how it would work

thanks again guys

Psychonaught,

A Troopy owner - man of good taste! A suggestion - If your auxilliary battery is an AGM type, generally speaking it won't like the high temperatures under the bonnet. Suggest provide it with a heat shield to shield it from heat radiated by the engine. Allow some airflow around the battery for cooling too. One of the advantages of a Troopy is that you have space to provide such protection. If it's a wet deep cycle battery, heat shouldn't be a problem.

Can dc-dc chargers damage batteries - yes. At startup, these chargers commence their charging cycle - a constant current stage until the voltage rises to a set maximum, then a constant voltage stage at maximum voltage while the current drawn by the battery drops down to some low value, usually about 1 amp. Then the charger goes to a lower voltage where the battery will draw only a very small current. The problem is that if the battery is already fully charged the charger still goes through the full process at startup (every time the engine starts), and forcing current into a full battery can damage it. For this reason, it is important to have some manually operated switch in the system so that the charger can be turned off when not required.

In your case, with the auxilliary battery right beside the cranking battery, I would NOT consider installing a dc-dc charger. The alternator output will be a bit low for the aux battery, but I wouldn't be too concerned, since your wiring losses will be very small.

If you instal a second aux battery in the back of the vehicle, it will be necessary to wire it in parallel with the original one (positive to positive, negative to negative). It will not be possible to treat one to a charger and not the other - they will function as just one big battery. If it isn't convenient to leave the second one permanently in the vehicle, I'd be inclined to run with just one and see how you go. You may find that one is adequate, given that you will have lots of solar. If not, worry about it all then.

There are a few constraints with having a battery sharing the cabin with you. These are referred to in the blog, but the essence is that you must use an AGM or gel type to avoid having liquid acid inside the vehicle, and obviously the 30 kg must be well secured so as not to become a missile if you have a mishap (not that Troopys have mishaps!) The second constraint is that your aux batteries should have similar characteristics - same type, similar age and history - this can get expensive.

Mounting the regulator close to the battery/s is very desirable. The charger monitors battery voltage and current to optimise charging, and the regulator can be misled by the small voltages that are lost when current is flowing through the connecting wires. Minimising the length of wiring between regulator and battery minimises these voltage losses.

I think if I was setting up my Troopy again (heaven forbid!) I'd run initially with the one aux battery, and see how it all goes. I now have two batteries mounted permanently in the back of the Troopy fed by a dc-dc charger and an MPPT controller sitting beside them - works for me, but took a lot of experience and experimenting to arrive at this
setup. (If you are interested, details of our rig are blogged here.

Cheers

John

Your blog has been such a great read enjoyed every bit of it and give me some inspiration for mine, thanks for the link. I have tried to find heat shields in the past but have never come up with anything that looks decent any suggestions. I am actually about to replace the deep cycle as the old one no longer holds charge and suggestions? was told the yuasa 730 was a good option by the guys at battery world at the Melbourne leisure fest over the weekend they said that was a bit better than the century

good to know I don't need the dc-dc charger means some cash can be spent elsewhere

I think im going to start out with one 120watt folding solar panel and see how I go if I find it inadequate ill get another ill run that through the ctek 25 amp solar regulator mounted close to the battery to reduce voltage drop and give me the ability to expand my solar. ill also just start off with the one battery and see how that goes again I can always upgrade later thanks again

HI
I agree with al that Boobook has said .

AND yes you can connect each panel direct to the battery using it's own regulator , but that may lead to not getting both panels outputting ALL the time

One may cycle OFF before the other reducing the output by50%

So best to have both panels connected to a single regulator ,with the regulator as close to the batterries as pracrtically possible!


PeterQ

that is a good idea and I will definatly make sure I have somewhere to stowe them the weight is not too much of an issue but im thinking it might be a good idea to start with one 120w or even a 140w and see if I need more I can get more

Bit Deals, Peter.

Bob.

that is amazing I would never have thought they were that powerfull and again pushes me towards starting with one smaller panel and upgrading if needed obviously I would get a controller capable of upgrading, however I just don't want to be out camping and realise I should have gotten more solar cause then its too late