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I'm planning a 30 day trek in Nepal. Should I carry extra batteries in the field or bring a solar charging unit?

Details about the trek:

  • Upper and Lower Dolpo.
  • Above 8000ft (2400 m) most of the time, with three passes over 16,000ft (4900 m).
  • Camping, no teahouses.
  • I'm bringing two Sony RX 100 III's.
  • There are about 4 rest days during the trek.
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    How many photos do you expect to take every day. What camera? When you will go (how much sun you will get)? Apr 8 at 15:05
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    What will be the temperature? I realize Nepal is already fairly high altitude, but sometimes when people talk about trekking in Nepal, they are talking extremely high altitude, which correlates to very cold temperatures.
    – scottbb
    Apr 8 at 16:53
  • @scottbb How would you expect the "temperature" to have an effect on this?
    – MrWhite
    Apr 8 at 23:15
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    @MrWhite Battery life is shorter, and batteries produce lower voltages, in colder temperatures
    – scottbb
    Apr 8 at 23:17
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(this answer assumes digital photography)

Carry extra batteries in the field or bring a solar charging unit?

Carry the batteries. juhists answer explains why a solar charger is not practical.

Ration your photos. Don't take 100 photos per day, don't take video or very long exposure night shots. Spend minimal or no time looking at your photos after you take them. If you bring three (sets of) batteries and each can do 500 photos, you can take 1500 photos or about 50 per day. That should be more than enough (around 4 photos per daylight hour), but half of that should work, too. Think/look carefully before you shoot. It will make you a better photographer. I don't shoot film (see also the answer by Bob Macaroni McStevens), but thinking before shooting used to be common sense before the marginal cost per photo became very low with digital photography.

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    note that Lithium batteries discharge themselves very fast so after 2-3 weeks the remaining batteries may have only ~70% remaining capacity
    – phuclv
    Apr 11 at 2:29
  • @phuclv Yes. If it was a 3-month expedition this approach would be not feasible, but 4 weeks should still be doable, I think. And maybe in week 4 people take less photos than in week 1.
    – gerrit
    Apr 11 at 19:00
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If having a solar charger, you should note the limitations of law of energy conservation.

Sunshine at best produces 1000 watts / square meter. However, best single junction solar panels are around 20% efficient so you get out 200 watts / square meter. Add 95% efficient charger (you need DC-DC converter somewhere, you can't just plug a raw solar cell into a raw battery) you get 190 watt-hours of charge per square meter per hour.

A 20 cm x 20 cm square solar panel thus provides 7.6 watt-hours of charge per hour. A Canon LP-E6NH battery is 15.762 watt-hours. To charge it at 95% battery charging efficiency (which is a different thing than DC-DC converter efficiency) you need 16.592 watt-hours of energy. Your 20 cm x 20 cm solar panel produces it in 2 hours 11 minutes. So, not even 2 hours is enough to charge the battery!

If you think a smaller solar cell let's say 15 cm x 15 cm is enough, it needs 3 hours 53 minutes of charging.

To make matters worse, this requires the solar cell placed at an optimal angle towards the sun. Most likely, the sun is at 45 degree angle on the average and your cell at 90 degree angle (you lay it flat on the ground) so the charging time is multiplied by 1/sin(45*pi/180) or the square root of 2. So your 15 cm x 15 cm panel now charges the battery in about 5 and half hours. That's nearly half of the average sunlight hours of 12 hours (of course some seasons have more and some seasons have less sunlight hours).

Is that fast enough for you? Most likely you won't want to spend half of your sunlight hours staying standstill charging one camera battery!

Also note that as is well-known among photographers, clouds can reduce the exposure by 2 stops. This means energy is one fourth of what it is without clouds. So the 5 and half hours in cloudy weather is 22 hours. The trouble is, there's no 22 sunlight hours in a single day.

So, if selecting a solar charger, please do make sure the panel is large enough that the charging time is acceptable. I would say 20 cm x 20 cm is minimum, and even then you can only reasonably use it during sunny hours unless you consider it acceptable a charge takes the whole day. Clouds? No way.

Because you need to consider that there can easily be 5 consecutive cloudy days, you most probably need not just the solar charger but also few spare batteries.

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    On cloudy days, esp. overcast, the light is diffuse which means the panel angle is not really relevant then. If the sky is only partially covered then the solar intensity is only reduced partially on average. The bottom-line is, I think it's not correct to multiply the additional charge time in case of non-optimal angle with the additional time due to lack of solar intensity on cloudy days because that exaggerates the combination of both effects. However, I come to the same conclusion that several batteries are still needed due to unpredictable weather.
    – Matt
    Apr 9 at 8:13
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    The way I did it once with a cheap-ish solar panel (around 10x40 I think) from Aliexpress on a hike was to just attach the solar panel hanging over my backpack charging a battery pack (for phone). Lots of inefficiencies, but by the end of the day it had collected some charge without it costing me much (the weight of the solar panel). It helped that we trekked in the right direction to catch sunlight on my back, although I doubt that over the length of my short hike it was worth it (weight of solar panel vs weight of battery), but I wonder whether at 30 days it might not work out differently. Apr 10 at 21:39
  • @DavidMulder That's about the same size I proposed if the 10x40 are centimeters. However, a phone battery is slightly smaller than a camera battery so it requires only at most about 75% of the time to charge.
    – juhist
    Apr 11 at 8:20
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I trekked for 14 days in nepal. I also bought a solar charger and extra batteries. Buy the highest wattage solar charger you can find and bring like 4 extra batteries. You can get away with charging 2 batteries at the same time.

Also note many tea houses along trekking routes have access to electrical outlets. You will need an adapter though. Below is a picture of my setup/trip:

https://www.facebook.com/media/set/?set=a.10106203663824786&type=3

https://www.facebook.com/photo?fbid=10106203664787856&set=a.10106203663824786

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    Hi Brian, would you mind embedding the photo of your setup in the answer? I think it would add to your answer. Currently people without a logged in FB account have to fend off multiple banners from FB before seeing your photo. Apr 11 at 14:52
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If space is not a critical issue. You should probably bring a few extra batteries as well as a solar charging unit. That way, if you ever run out of battery in your camera while on the field, you can swap batteries and charge the empty one on the go.

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    Maybe you should say "extra batteries", 2, 3, even more. Apr 8 at 15:43
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    In the mountains, if space is not a critical issue, weight usually is. Apr 9 at 3:03
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    Have you tried charging on the go? From what I've read, charging a battery with a panel strapped to a backpack works very poorly.
    – gerrit
    Apr 9 at 7:52
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Depends on the camera. If a DSLR, you can get around 1000 shots per charge. If a mirrorless or some other camera that eats batteries, then 500 shots per charge, perhaps less. I can get by with two battery packs (one in camera, one spare) for 4 weeks in the bush (I don't shoot video). If shooting video, that really drains batteries

I would take extra batteries. I have found when traveling in remote locations electronics break and cables are easily lost and damaged. You could take a solar charger with at least 2 camera batteries and a charger battery pack. The charger battery pack is what you charge on the solar panel. Use the charger battery pack to charge your camera batteries at night.

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  • And of course disable all things like "live view" and similar features as much as possible.
    – jcaron
    Apr 9 at 10:35
  • If you don't use the built-in flash (if any), and use the rear LCD sparingly, you can easily get over 2000 shots per charge on most DSLRs. CIPA ratings are typically around 1000, but the CIPA standard testing methodology does not reflect many use cases well.
    – JohannesD
    Apr 9 at 14:27
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Using a broader concept of cameras, carrying film and a camera that can operate without batteries is also an option.

Small rangefinder cameras with excellent fixed lenses are widely available in the used market for less than the price of a few on brand rechargeable batteries.

It’s not an option for everyone of course. And film will need hand inspection at airports, but otherwise it might make logistical sense. Less fiddling about in camp at the end of a long day. And less to fail.

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My vote is for a solar panel. Assuming you're going during tourist season you'll have bright beautiful days with lots of sun. Sure it will take all day to charge your phone though.

Additionally I would highly recommend bringing a light socket to electrical plug adapter (like this: https://www.amazon.com/GE-Polarized-Adapter-Install-54276/dp/B002DN6QX2). Many tea houses have electricity, but don't have outlets in the guest rooms. They do however have light sockets which you can turn into an outlet to charge your devices. This worked great for me last time I was there and helped to save a few bucks rather than paying to have my phone charged in a common area and risking someone walking away with it.

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    Please not that using light to plug adapters is not up to the technical standards. Wires to light sockets are not build to carry the same current as wires to plugs. So using a 15W charger is probably fine - but don't use it for your water kettle, rice cooker and space heater.
    – Christian
    Apr 9 at 13:42
  • Be aware that as part of the former British empire the most common lamp socklet in Nepal is probably B22. so take that style of lamp socket adaptor.
    – Jasen
    Apr 10 at 13:41
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    Nepal was not part of the former British empire. For Nepal there are three associated plug types, types C, D and M. Plug type C is the plug which has two round pins, plug type D is the plug which has three round pins in a triangular pattern and plug type M has three round pins. Nepal operates on a 230V supply voltage and 50Hz. Source: electricalsafetyfirst.org.uk/guidance/advice-for-you/…
    – nepalipunk
    Apr 13 at 10:30

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