Can you have too much solar?

[grizzlyj]

Hi folks

In the past it seemed that since solar was pretty expensive it was as well doing a best guess calculation on I have this amount of current usage, I want to be parked up for this period of time, therefore I need this many watts of solar.

Solar is still not cheap, and semi flexy panels made in Europe are really expensive, but my current thinking is to cover the whole available roof with solar. Is that stupid?

The old truck in question has a high wading depth as originally designed, and the (too small) 35 amp alternator is below that, so is waterproof and has a dedicated venting system. If I swapped it for a new high power version it risks being damaged because its right next to the tyre so lots of crud, and if I do wade it won't like it. The engine bay is tighter than a tight thing so no room for a second, or moving the first. I will have a small genny, but am fully aware of how anti social that will be.

There won't be a huge demand for power but there will be a compressor fridge and a diesel hydronic heater. More than a bit of driving from a small alternator can provide.

I realise if I stayed around the tropics then maybe less than 200 watts total would work, but if I went to Iceland for instance is a case of a roof full of solar will do so little its not worth having?

Is there a tipping point so that at a certain point, up north in the winter, you may as well just leave it as a couple of hundred watt panels for when the sun is shining and fire up the genny almost every day is as good as it will get? A football field of solar and you still won't get much on an average day to day basis?


(Kind of unrelated, but an advantage to lithium batteries is the huge charging current they can happily soak up. So its possible to feed in pretty every amp that a 240 volt 13amp plug can throw at it at 12 or 24v, so fully recharged via a small genny may only be 30 minutes every few days. Maybe )

Cheers for any guidance

Jason

 

[Martyn]

Not all solar panels put out the same amperage in low sun light. This is really the test that should be done to differentiate good panels from average panels. In full sunlight most panels perform well. So the first order of business is too select a panel, I'd suggest a manufacturer like Carmanah or Aspect Solar.

Next I would calculate what my power requirements were based on the longest time you would be not moving in a base camp.

Battery selection is important because this is your power reservoir. You will be banking power during hours of sunlight, power in from solar minus power usage during day, and then you will be using power from your reservoir during hours of no sunlight. Your reservoir has to be big enough to get you through the hours of darkness without drawing the batteries down below there lowest limit. So in a sense if you have too much solar and not a big enough reservoir the solar power will go to waste.

Power to your auxiliary battery from your alternator or starter battery will in a large degree be controlled by the size of wire and the length of the wire. As your alternator has a low output I would suggest using at least 4 gauge wire and using a dual battery set up like the National Luna Dual Battery System. That way your starter battery will be charged first and then the power switched to the auxiliary battery. This avoids you trying to charge both batteries at the same time.

Hope that helps. Call us if you need parts.

 

[IdaSHO]

For argument sake, Ill assume the "too much" = detrimental in some way.

When doing the calcs for solar, your actual needs dictates a lot.
So does your type of travel.

With that said, I think you can more easily have "too much" battery than solar.
As every time you add AH, you add a good deal of weight and capacity that you very well do not need or will use.

As mentioned above, having too little battery is of significance as well.

Ideally, you want your battery bank to have the ability to accommodate your power needs,
and the panels need have the capacity to replenish those needs on a regular (daily) basis.

So assuming you have the battery bank to accommodate your power needs, you really have to try to have "too much" solar.
Near the point of being silly. Many people's attempt at solar is based upon a best case scenario.

I say, figure best and worse case, and find a happy place in between, while leaning a bit more towards worse case.

 

[grizzlyj]

Hi

Thank you for the replies
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The last camper had 255Ah at 24v with two I think 120watt panels. Round the Med we didn't need to drive, batteries full all day every day. Northern Scotland in winter the solar may as well not have been there. We did go to Iceland and took a little genny, but that's a bad example because although all except one campsite ended up being closed they ALL left their hook up power on for everyone to use for free
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So at times we couldn't charge as much as we needed to. At times if we had more capacity that would have tied us over until we could maybe plug in and recharge.
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New camper may end up with more battery capacity, and could have of the order of 1500 watts on the roof. Someone who should know tells me that's daft because even half those panels will be too much. I suggested Northern Scotland in winter and relying on solar would be ideal, he said there won't be enough power in the sun to make any solar worthwhile so stick to "conventional" sizing and have a genny. All fixed flat though, none of this tilting swivelling malarkey
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I suppose when it gets marginal a good day and it will work, a rubbish day and it will hardly do anything. So other than the £$€ aspect I may as well fill the roof up?
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Jason

 

[dlh62c]

If your not going to calculate your power needs, a good starting point is 200 watts worth of panels and a 200ah battery bank. If you need more, go from there.

Locate and place your panels and batteries to give you room to add more as needed.

You don't have to place ALL the solar panels on the roof. It's nice to be able to park the vehicle in the shade and place the panels out in the sun.

 

[rayra]

Angle of incidence matters a great deal with solar. A smaller surface area kept perpendicular to the rays of the sun will yield more power than an array 2-3-4x larger that is laying flat.

Also matters if you need roof space for anything else, storage or penetrations for light or ventilation or a rooftop AC. You very quickly run out of usable area with current panel designs.

There really needs to be a modular panel design that works like floor tiles. Which you click together on the edges to form a larger field. With smaller tiles 6"-1' on a side, you can more readily fill an odd-shaped usable area.

Even with my Suburban, I figure I can only use two 'standard' panels, laying flat in a semi-permanent fixture. Even adding spring-loaded pivot pins in an L-channel frame, such that I can unpin one side and tip a panel up at an angle, I've still limited to 2 panels.

I'm considering other designs like a triple stack of panels that unfolds into a larger 3-panel array, or has two of the panels slide out as trays with the topmost being permanently exposed as a battery tender. Or just fabricating a suitcase design that is latched shut and to the roof for transport, but is taken down and ground-deployed,

Truth be told, I want flexibility, portability. I want the resources sunk into a solar system to be readily used in other ways other locations.

And it just comes back to the set angle of the panels. laying flat on a vehicle roof is just a poor solution, and worse so, the higher your latitude.

 

[ikk]

Unless your at the beach or the desert stationary panels can be blocked my trees and other objects. I have a roll-able 70 watt cell that I use that I got pretty cheap that I can lay or hang just about anywhere. I see a lot of people on this forum seem to like the fold-able 100 watt ridged solar panels. You can pull it out, open it, and angle it towards the sun and your done.

 

[LeishaShannon]

Short answer = No

We have 1200W fixed with 400W portable and there are days where more would be handy. All our of cooking is AC powered so when its overcast we modify our eating to suit. In 10 months full time "boondocking/freecamping/whatever you want to call it" we have had to idle the truck to charge using the alternator a handful of times. We usually stay in one spot for a week or longer but If you're driving every few days the alternator will probably keep them topped up anyway.

Lithium will help you harvest the most sunlight as they don't need wasteful absorption charging like LA, they'll accept whatever current is available until they're full. They're also helpful if you are forced to use an alternator/shore power/genny as the run time will be minimised due to the higher acceptance rate. We can charge at > .5C and the batteries don't even get warm