Solar Powered Pi's

[jarodium]

Hello there,

I've been diving around the forum and still can't come up with a post regarding solar powered usage with a Raspberry, that suits my needs.

I intend to have a small, personal streaming webserver with the following hardware:

- Raspberry Pi
- A Wifi dongle ( preferently with storage included to hopefully save energy requirements )
- Small pendrive about more or less 32 Gb

I want it to be available 24/7 and I'm thinking of power it with the following:
http://www.thinkgeek.com/product/d0bc/?srp=7

or

http://www.thinkgeek.com/product/c5a7/?srp=4

I would like to know if one of these supplies will suit the project hardware and if there are any foreseeable issues with them. I'm betting my chances on the 2nd product, because the battery is a 2000mAh so I'm expecting that will be enough for all the hardware required.

Thanks in advance
Regards
Pedro

[itimpi]

Neither of those look to have anywhere near enough capacity. If you assume that the Pi is using around 700mA in normal use, then the 2000mA option would kep a Pi running for less than 3 hours - nowhere near the 24x7 you are looking for. In addition using a WiFi dongle and USB drive might mean you need to use a powered hub - and that would push up the power requirements even further.

I would expect that you would need something along the lines of 10000-15000 mAH storage capacity and that is not something I have commonly seen (at least at a reasonable price). That is probably why this is not more commonly discussed.

[Jim JKla]

You should probably be looking at a car battery and the solar pannel from a caravan.

[alexeames]

A small leisure battery (looks like car battery but made to better withstand deep discharge, that car batteries don't like) and a larger than you think solar panel. Add a good switching regulator to get you down to 5V and you're good to go.

I would have thought a 10,000 mAh gel cell, like they use on electric golf trollies would do you if you can get enough solar power charging it.

As far as solar is concerned it depends where you are what size you need. I've tried a 2 Watt solar panel from Maplins to keep a 10,000 mAh gel cell going, but you need much more charging capacity than that in the UK. I ended up giving up and using a cheap 1 Amp Nokia charger. My Pi uses 2-3 watts.

A 10 Ah battery at 12V could theoretically power it for...

10 * 12 = 120 Watt.hours

120/3 = 40 hours.

But then reality kicks in and you realise...

a) you don't get the full 10 Amp hours (say 90%)
b) you will lose at least 15% on regulating from 12V to 5V (say 85% efficiency)

So in reality, you're nearer
40 hours * 0.9 * 0.85 = 30.6 hours

Which gives you 1.5 days with no sun

[Jim JKla]

Use a small model aircraft engine to build a hybrid

I'm shure we could find a methane source

[r4049zt]

I second the comments made in the first reply to this post.
Don't buy products which are too small for 5V 1A rated.

I have got my pi to boot off a block of four 2000mAh NiCAD rechargeables but those only delivered 4.7 Volts at D17 which is 0.2Volts below normal measured operating condition with an rPi approved 5V 1A supply at the ac, so it is no surprise that after startx the mouse was doing nothing. Keyboard was fine, and it booted, from solar power stored in four NiCad batteries.

Expected solar panel size to average 3Watts over a week in uk winter is about 60 to 120 Watts (peak rated, under test conditions), so that is up to a square meter or so. There are some good deals for even bigger panels around now that feed in tariff has been decreased but expect to fit a
1 Amp rated DC-DC converter which can withstand Voc (voltage at open-circuit) of the panel under bright sun on the coldest day of the year.
I tried testing an any-to-5V component but there must have been a mixup with parts as that does any-to-3V into a 6V lightbulb.

I suspect that a used 60Ah car battery could be better value and better Ah than a specially bought 10Ah 12V battery which the 3rd post here correctly advised. I have not proven that yet, but will post when I have.

[alexeames]

I suspect that a used 60Ah car battery could be better value and better Ah than a specially bought 10Ah 12V battery which the 3rd post here correctly advised. I have not proven that yet, but will post when I have.

That's almost certainly correct if you can get one free and as long as you don't need to lug it about. How much does a 60-120 watt solar panel cost? That sounds VERY expensive relative to the cost of the pi and the ~20p a month it costs to power it constantly.

I suppose you might not need to average 3 watts unless it's left on all the time?

Is this sort of thing any good? Costs a bit over 2 Pi.
60 watt solar panel on ebay

[r4049zt]

The 60 Watt panels on ebay look a bit pricey. Better to get a 180 to 240 Watt rated panel at a similar price. I use two KD235-2Pb connected parallel into a pair of car batteries with a 20A pwm regulator from panel Vmp voltage of 25 to 30V to batteries at 23 to 27V and a 28 to 52 Volt rated 350 Watt grid tie inverter to make use of overflow solar power for slight bill reduction of the household ac electricity account. That's not an mcs accredited configuration so there is no point trying to register it for feed in tariff.

Having a couple of full car batteries around can be handy. For example, three 8.5V rechargeables in series are presently on charge, parallel to the 26V or so on the double car battery and with a 100mA 6V filament lamp to limit the charging current in the 8.5V batteries.

More news on getting an rPi to run on solar power stored in rechargeable batteries.
UNCALIBRATED MULTIMETER - FOR INDICATION ONLY
4x 1.3V NiCad 2000mAh
fully charged to 5.4 Volts and connected at D17 on the rPi board
voltage at D17 5.2 Volts
rPi booted but PS2 keyboard did not work

batteries to 5.3 Volts and connected at D17 on the rPi board
voltage at D17 5.0 Volts
rPi booted but PS2 keyboard did not work

approved 5V 1A ac adapter
voltage at D17 4.87 Volts
rPi booted
logged in to Debian6
PS2 keyboard and PS2 mouse worked normally

We'll get there. It seems that getting the exact 5.0Volts at D17 was still not quite right as it has worked better with 4.87 to 4.93 Volts there.

[r4049zt]

This post is writtn from a solar powered raspberry pi.

Four NiCad batteries were charged to 5.4 Volts from solar power and tried.
That did not work and neither did 5.3 Volts.

This try with 5.25V at the battery got 4.98V at D17 and worked.
Both keyboard and mouse coninued to work as battery voltage fell. Now showing 4.22V at D17. Therefore chose your regulator to provide just under 5V and your solar could work. Add some protection diodes to short or overflow anything above 5.2V; I'll use two blue or white LED's for that.

[jarodium]

Thanks for the suggestions.

While browsing this forum I've also found this manufacturer:

http://www.tekkeon.com/products-mypall-specs.html

I really don't have any problems in the Algarve ( Portugal ) because this region has sunlight almost the entire year. Just want a solar panel do charge up a battery and that battery keeps the PI running and portable. Moving around car batteries ir more or less a pain ( but thanks for the suggestion anyway, i'll keep it in mind also ).

Of course I would have issues regarding the rainy/cloudy days, but i'll try first using a simple setup in which I assume I have the sunlight guaranteed.
The PI is intented to be properly encased and sealed to prevent dampness and direct heat exposure, and then, placed outside my house.

Thank you for your time
I'll be taking a special attention to the suggestions made here in this post and start couting costs for each setup xD

Best regards
Pedro

[holmez]

Perhaps you should have a look at this thread from the Networking and servers forum.

The basic conclusion was that a 14W solar panel + a deep cycle leisure battery might be sufficient.

[jarodium]

Perhaps you should have a look at this thread from the Networking and servers forum.

The basic conclusion was that a 14W solar panel + a deep cycle leisure battery might be sufficient.

Hmmm... Yes. This might what I need. I'll take a careful look at this.

Thank you holmez xD

[alexeames]

Having had a longer look on ebay it seems that the going rate for solar cells is about £2 / watt for the smaller ones at the cheaper end of the scale.

Electricity currently costs me ~ 14p/kWh

I thought it would be interesting to do some costings based on these figures.
£2 / watt small solar panel

for a 30 watt...

£60 / 0.14 = 429

So 429 kWh before it's paid for itself.

Assuming 50% operation and 50% of the time gives, say 8 watts average.

During a year, that's 8 x 24 x 365 = 70.8 kWh (if you use it all)

So it will take 429 / 70.8 = 6.05 years to pay for itself.
Or much sooner if the cost of leccy goes up a lot.

That's all without considering the battery side of things. Add the cost of a substantial car / leisure battery and the numbers change a lot.

[startreksteve]

How about a combination of Solar Panels and a little wind turbine? like the ones you see on caravans?
I have two Maplins solar panels on my shed, and it runs the Baygen radio and charges the shed lights, I get maybe one month a year without power.

[r4049zt]

I'd thought about all this a while back. Costings for a 220 Watt solar panel at 60p/Watt are way too high for the p/kWh used by a small computer alone, so that's why I added an (optional) grid tie inverter to a setup with oversized silicon solar panels, to make use of surplus solar power. It is still not cost competitive against coal burning power stations, but is a nice little setup. New 12V batteries cost as much as solar panels, so that is why I prefer used old ones. The other way to design it is with small batteries and solar for good weather and a relay to power up an ac mains supply at night and in winter. As a rough guide, my 2Ah NiCad set stayed in 4.2 to 5V useful range at D17 on the rPi for about 30 minutes. So bigger batteries and better regulation are recommended, unless you have something else to power it up at night. I like the wind powered setup but that too is intermittent, just at different times to the solar. If you are lucky enough to have a small stream which can be dammed then you can do without much battery capacity at all. Look up what Maccynlleth tried.

[CCitizenTO]

I have to say it's a good example to show how much power our modern conveniences require to operate.

If it takes that much to fire up a RPi just imagine how much your Refridgerator or AC unit is guzzling.

[alexeames]

I have to say it's a good example to show how much power our modern conveniences require to operate.

If it takes that much to fire up a RPi just imagine how much your Refridgerator or AC unit is guzzling.

Looking at differences in consumption figures between when we're away from home (couple of months per year) and at home, it looks very much as if our fridge is nearly half of our electricity usage. (Although we don't use a lot). The next one we buy will be super-efficient Over its lifetime, it will be worth it.

[r4049zt]

Looking at differences in consumption figures between when we're away from home (couple of months per year) and at home, it looks very much as if our fridge is nearly half of our electricity usage. (Although we don't use a lot). The next one we buy will be super-efficient Over its lifetime, it will be worth it.[/quote]

Measured power consumption of my parent's fridge plus freezer was 1.1kWh in 24 hours in average spring weather. It is difficult to get very much better than that unless choosing better insulated and smaller storage volume Cuban/Brazilian specification.

If your household small ac appliances use less than 2kWh per 24 hours then you are doing better than most of us. For example a sky broadband box chomps through more than 1kWh per day.

The raspberry pi could cut 200MW off the national electricity usage if everybody used them for tasks which only need <256,000kB RAM and a couple of GB of file storage.

[jarodium]

Wind turbines and solar together.
I'm about to go off topic but I did thought of this applied to a car. While getting solar power from panels and while the car is moving wind powered dynamos inside the car would provide an extra energy boost...

Now that I'm thinking of this, a childrens pinwheel attached to small dynamos could, I just thinking loud, providing extra juice for recharging the battery...

What do you say?

[alexeames]

If your household small ac appliances use less than 2kWh per 24 hours then you are doing better than most of us. For example a sky broadband box chomps through more than 1kWh per day.

More like 7kWh/day, but nearly half of it seems to be fridge-freezer. I think a new one might be in order. Solar-powered of course - to stay on topic. Maybe I can use a Pi to control it.

[Jim JKla]

Wind turbines and solar together.
I'm about to go off topic but I did thought of this applied to a car. While getting solar power from panels and while the car is moving wind powered dynamos inside the car would provide an extra energy boost...

Now that I'm thinking of this, a childrens pinwheel attached to small dynamos could, I just thinking loud, providing extra juice for recharging the battery...

What do you say?

A fan on a car does not work because the fan itself is driven by the cars motion and the fan only adds drag to the car. (If I remember right thats like the third law of thermodynamics).

[r4049zt]

Whilst you could find a fan to make 8W while the car is moving, for example 0.7A at 12V, that is intermittent and small compared to the alternator. A regulated any-to-5V buck converter off the cigarette socket might be a less intermittent supply and its extra load on the alternator would be less than the extra drag from carrying an 8W dynamo and suitable fan. The car battery provides plenty of storage. An rPi could drain a car battery in 100 to 600 hours so it just might be better to have a separate 12V battery if you think that you might forget to unplug things.

[r4049zt]

Since I was here last, I've done two things. I tried a solar panel advertised as 1.2W 6V, which turns out to do 0 to 200mA at 5 to 7 Volts, and found that OK with four NiCAD batteries, if checked with a multimeter and disconnected when batteries are full. I put a diode on mine so that I don't have to disconnect it at nighttime, at the expense of losing 10% of the power in a diode drop. That is the smallest solar which enterprising schoolkids could try with batteries to get an rPi powered for about an hour per day per panel.

I've spotted any-to-any DC-DC buck converters on ebay for a low price and ordered one just to see what it does. That has no specs or anything - just a screw pot to adjust something, so I'll wait and see whether that can do 5V for raspberry pi. Components look about the right size, so I'll be testing with benchtop DC supply and lightbulbs until I know what it can do.