Solar Panels??

[Arapiles .]

"Wow. That's a lot of planning. Would be cool if you could post some pictures. Perhaps if we are hijacking this thread we could start a new one in Chaff."

I will post photos once the rain stops and I can take some decent photos.
Re planning, it turns out that I knew what I wanted and we found ethical, practical architects to help. There's also a green home magazine here which has won international awards because it shows homes like ours rather than mud brick or hippy places and I got a lot of ideas from that.

"I installed 3 ceiling fans in our living room. I have a feeling they really don't lower the temperature much, but the circulating air makes it feel cooler. Maybe I will measure it sometime."

That's right, they don't lower the temperature – but because they're moving air over your skin they do cool you down. We have them over our bed and my wife's taken to sleeping under a doona, even when the rooms about 25C. My 2 year old was sleeping under one the other day and her skin, where it was exposed, felt almost cold.

[Kendall Clement]

Mark Ryan,

I just got my Solio Classic that I bought in Gear Swap for $40. I'm excited and I can't wait to try it out. I'll post on this thread my experience with it the first chance I get to use it.

Kendall

[stephan q]

Howdy,
We rely on AA eneloops and solar power while traveling. 2 for the camera, 2 for two zebralights, and two in the charger, for total 6 on board. Batteries are cycled before fully discharged, this way we are" topping them off" instead of trying to "recharge". Our last system was powerfilm based, and was ok. In search of more power, found a thread on WB that got me started.
This is my current mock-up. 3.0 oz. total. Based on this Kyocera mini module rated at 1.4 watts.

Specifications Wired for 6V Wired for 12V
Rated Power (Watts)
1.4 W
Current at Max. Power (mA) 182 mA 91 mA
Voltage at Max. Power (Volts) 8 V 16 V
Short Circuit Current (mA) 190 mA 94 mA
Open Circuit Voltage 10.7 V 20.0 V
Length 6.02 (153mm)
Width
4.64" (118mm)
Depth
.16" (4mm)
Weight
0.20 lbs

Currently using 1n914 diode, which draws 1 volt. My technical questions include…Is this correct diode? And if not, what would be the proper diode for this application? Does this unit produce enough power for charging 4 AA's in short order? We are thinking of adding a Steripen Classic to the mix.

This mock-up raised tired batteries measured 1.1 volt, to fully charged at 1.35 volts in about 4 hours of winter sun, at 37.9N latitude last week. This seems good to me, but is there something I could change to increase charging power?

Thanks

stephan

[Bob Gross]

You say that you are currently using a 1N914 diode. What for? Are you using it as a blocking diode? That would be used to insure that charged battery power is not fed backwards to heat up the solar panel, which would be wasted power. The forward voltage drop across the diode will be closer to 0.5 or 0.7, although there are some diodes with less forward voltage drop.

Your batteries are probably rated for a full charge output of about 2000 mAH each. One general rule of thumb is that you charge a battery at 1/10 of the full charge output, and you charge it for ten times the time, which would be ten hours in this case. Other batteries can be fast-charged, but let's start with the rule of thumb. You seem to be charging the batteries two at a time, so you need enough voltage to drive in 200 mA, and that is into two (1.2v) cells in series, so you need more than 3 volts to do it. You seem to be getting 6 volts out of the solar panel minus a half volt lost in the diode, so that might be sufficient. On the other hand, 6 volts might be significantly high, which might drive significantly more than 200 mA into the batteries, if that were available at the solar panel. I'm guessing that there won't be high current since your data shows 190 mA maximum at short circuit condition. Basically, if you want to speed up the solar charging process, you could double the size of your solar array and double the current available to the batteries.

–B.G.–

[stephan q]

BG

Yes, I'm using the diode for blocking reverse flow. I guess my question revolves around my lack of understanding regarding this diode. I know the voltage drops through the diode, but does the current drop as well? Next sunny day, I will use my multi meter and do some tests. Trying to find best diode that blocks reverse flow and allows maximum charging from one module. Thanks for your help.

stephan

[Jerry Adams]

I charge a battery without blocking diode

Different application – 9 V lead acid battery – but should be the same for small battery

If you remove charger from battery at night, you don't need blocking diode

[Bob Gross]

Jerry is correct that he probably doesn't need a blocking diode. On the other hand, it may or may not hurt much.

Think of a diode this way. It lets the current flow in the forward direction, and it does not limit that. Also, assume that there is a slight voltage drop across the diode that way, usually about 0.5 to 0.7 volt. And the current cannot flow back in the reverse direction. That 0.5 to 0.7 volt is relatively insignificant when you are charging with a big solar panel (with an open circuit voltage of 16 or 17 volts). However, when you get down into low voltage panels like 6 volts, we are talking about a diode drop of about 10% of the solar panel voltage. So, Jerry may have been trying to avoid that.

Current really does not or cannot drop through the diode. However, the current might drop slightly because of the diode's forward voltage drop.

Yes, you can learn some things about your solar system with the use of a multimeter. You will probably get the most result from orienting your panel toward the sun and avoiding any shadows across the panel.

As your current starts to rise, you will get some good out of using slightly heavier gauge copper wires to carry it. But, as long as your current stays down around 200 mA, it doesn't make too much difference. I used a lot of 10 gauge copper on my home installation.

–B.G.–

[Roger Caffin]

Hi Stephan

Bob is right that you do not HAVE to use a blocking diode, but it is generally considered good practice – and a sensible move. It prevents problems when you forget to unhook the charger immediately. Which happens …

You can reduce the forward voltage loss by substituting a Schottky Diode for the 1N 914. It has a lower forward voltage drop, but is a bit more expensive. Make sure you select one with an adequate current rating. 1 A units seems to be readily available.

No, the current will not really drop much with the diode in place: think of it as a backflow valve on a hose.

Solar cells are funny beasts. They can handle the voltage drop due to a blocking diode with very little trouble. They are really limited in terms of current output: they usually have gallons of voltage capacity. Best to think of them as having a current output controlled by the amount of sunlight input.

Cheers
PS: I use a solar charger at times too.

[Bob Gross]

Yes, the Schottky Diode is a little bit of overkill for a low power backpack panel, but you could probably measure the improvement. It could get more important for a higher current lower voltage panel. In my home system, I might have more than 5 amperes flowing for years, so it is nice to get rid of little losses, which is why my charge controller has Schottky Diodes inside and ordinary blocking diodes at the panel. Single crystal solar panels will generally give you a higher open circuit voltage than the amorphous solar panels.

–B.G.–

[Jeremy Malin]

Been reading for awhile and finally decided that I needed to join and take part. I know that this thread is a few days old, but I did want to add a few things. If anyone is looking for a ready to use solar panel charging option, take a look at the GoalZero products. They seem to be pretty well regarded amongst the photography community and have a wide range of options (maybe even light enough for the BPL community).

Jeremy

[Bob Gross]

It seems like some of their panels are single-crystal silicon. That tends to drive the cost up a bit, and it tends to drive up the efficiency.

–B.G.–

[Sean B]

I use the Brunton Solaris 26. This is a fold out 26 Watt panel that weighs 28 oz. It's not light, but in my limited testing it reliably charges smaller electronics (iPhone, AA NiMH Battery Charger). It folds out to 22"x38" so hanging it off a backpack will likely be too cumbersome.

I've found this rule to work: "Find out your max power needs, then buy something that promise at least twice that output." A better rule seems to be to set a budget and try to get as much power output you can afford.

I also charge a Lenovo S12 (a 3lb/12 inch screen netbook) with a 3 cell 11.1V 2.4AH battery off the panel. It's questionable if this is wise since the open circuit voltage on the panel is 19-23V, and the notebook wants 20V (input from those with more electronics experience is *really* appreciated :). On a overcast day, I got about 20 % charge off 2 hours of charging.

Solaris 26 product page:
http://www.brunton.com/product.php?id=420

A great review, by a soldier that used it in Iraq:
http://www.amazon.com/review/RIMTJL8E8W9T8/ref=cm_cr_dp_perm?ie=UTF8&ASIN=B000GEFFBO&nodeID=3375251&tag=&linkCode=

[>> Bender <<]

Sean the open circuit voltage of 19-23v is the voltage under no load. When you plug it into your netbook the voltage will drop. Your netbook has a voltage regulator so it should be able to take a range of input voltages.

[Ken]

I'm working on setting up a 7W powerfilm rollable solar panel to hang on my pack for constant charging of my Android Smartphone, which I use for geotracking purposes and taking short videos in the backcountry.

Amazon link:
http://www.amazon.com/Powerfilm-R-7-Rollable-Solar-Charger/dp/B001QKUK6W

The entire system should weigh less than one pound once I finish modifying the electrical connections between the panel and my device. I haven't placed it on the scale yet :)

I have found a great way to mount the panel to the back of my Osprey Exos 46, where it will hopefully receive enough indirect sunlight during the daylight hours to maintain my battery enough for light use. We'll see how the experiment goes: I'm taking a weeklong trip at the end of June and will be posting pics of the system in the MYOG forum once I've finished my hacking…

[Peter Peters]

They are a great unit, the only thing i think, is that you have to keep folding it out to use it, and also the solar panels cost is it actually worth it, or are there more effective technologies to use. What about the actual backpacks with solar cells built in?

[Brian Strong]

http://www.solarjoos.com/products/

I'm curious to see how well it does in the field.

[Bob Gross]

You are going to carry around 1.5 pound of solar panel to recharge your other batteries with?

I can carry a lot of replacement batteries and stay under that weight.

–B.G.–

[Andy Bryant]

The Joos is mono-crystalline (looks black – single crystal) – which is a rigid panel – although I believe the mono-crystalline panels are the most efficient by area – an important factor if you're looking to mount a solar panel on a rucksack.

If you're trying to power a smart-phone and GPS, then the 'toy' (generally poly-crystalline – looks like lots of little crystals) panels for <$50 are worthless.

I've used a PowerFilm F15-600 (10W) amorphous silicon foldable panel for charging camera battery 12V + GPS (AAs) with success – however the system was cumbersome for backpack mounting. It's perfect for setting up on the side of a tent – however if you're hiking the whole day, your camp-site may not be in the sun for that long.

I've just acquired a Goal0 Nomad 7 (7W) mono-crystalline system, and am testing it prior to a summer trip in the alps. As a rigid system it is heaver than the powerfilm, but the power provided per area is greater – so it will fit well on a backpack.

Once I've completed some comparative measurements I'll post a review.

Andy.

[Brian Strong]

https://powertraveller.com/

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