vopi181
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How many solar panels would i need to power

Sun Jan 26, 2014 10:29 pm

Hi, i have 5 6V 120mA Solar Panels. How many of those solar panels would i need to power the pi and what would be the best way, IE hooked up to a battery. What would be the best battery etc

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mahjongg
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Re: How many solar panels would i need to power

Sun Jan 26, 2014 10:56 pm

you cannot just compare a solar cell with a battery, solar cells have an optimum Voltage versus Current point, (at which they have a reasonable efficiency) one that also differs depending on the amount of light it receives. Simplest solution would be to charge actual batteries with solar cells, then use the batteries to power stuff.

A PI needs a stable 5V (with 5%), and consumes about 450 to 600mA depending on what it is doing.

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CopterRichie
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Re: How many solar panels would i need to power

Sun Jan 26, 2014 11:12 pm

mahjongg wrote: A PI needs a stable 5V (with 5%), and consumes about 450 to 600mA depending on what it is doing.
Please, may I ask how is the USB port powered? Meaning, it is tied to the GPIO Pin 2 or is it powered by some other means?

Thank you.

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redhawk
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Re: How many solar panels would i need to power

Sun Jan 26, 2014 11:15 pm

Bad idea, what if it's a sunny day and then suddenly you have a solar eclipse or the weather suddenly gone cloudy your Pi wouldn't last very long running purely on solar panels. :D
As mahjongg suggested you'll need rechargeable batteries in the mix, I would also suggest you throw in a switch mode regulator to ensure that the Pi is getting the correct voltage from the batteries.

Richard S.

vopi181
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Re: How many solar panels would i need to power

Sun Jan 26, 2014 11:23 pm

Thanks for the replies, I am no means new to electronics but when it comes to power, I dont know anything

plugwash
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Re: How many solar panels would i need to power

Sun Jan 26, 2014 11:49 pm

Ok well the first thing to learn about solar power is that panel manufacturers are highly optimistic.The headline figures they give you are what the panel will produce when pointed directly at the sun in strong sunlight. Even during the daytime you are unlikely to get the headline figures most of the time (unless perhaps you live in the desert) and of course at night you will get nothing. It's not uncommon to find that for reliable operation the nominal output of the panel has to be 10 or more times larger than the power consumed by the load.

The second thing to learn about both solar panels and batteries is that the nominal voltages are just nominal. The actual voltages will vary considerablly depending on the operating conditions. A "12V" lead acid battery will require more like 13-14V to charge and may be as low as 10V when fully discharged.

You need to make sure your panel produces enough voltage to charge the battery but not so much as to risk damaging it. You also need have at least a diode between your panel and your battery to stop the battery discharging into the panel. Ideally you would have a smart charge controller between panel and battery to hold the panel voltage at the level that maximises output power independent of the current battery voltage but on a system sized to power something like a Pi the cost of a smart charge control system would probablly outweigh the benefits.

Lead acid would probablly be the battery technology most people would go for. It's cheap enough that one big enough to get you through several days of bad weather is affordable and it's reasonablly tolerant of abuse.

The Pi wants a good clean 5V supply. In general the easiest way to do this is to make your solar/battery system work at a considerablly higher voltage than the Pi runs at. You would then use a step-down switching converter to power the Pi.

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Re: How many solar panels would i need to power

Sun Jan 26, 2014 11:52 pm

Have a llok at the Pi 100% powered by solar:

http://pi.qcontinuum.com/project.html

Image

and check the homepage for downtime (even with that big panel winter give insufficient light) http://pi.qcontinuum.com/

with solar you always need much much bigger panels than you first think to get any useful power out,
the above pictured one wasn't enough !
Last edited by mikerr on Mon Jan 27, 2014 9:33 am, edited 2 times in total.

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Tage
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Re: How many solar panels would i need to power

Mon Jan 27, 2014 1:59 am

vopi181 wrote:Hi, i have 5 6V 120mA Solar Panels. How many of those solar panels would i need to power the pi and what would be the best way, IE hooked up to a battery. What would be the best battery etc
my guess is that you will need at least a 60W solar panel, probably more. and you need a large battery if you want to run the Pi continuously. your tiny panels are 6V x 0.12A =0.72W, so you probably need at least 70 of those kind of panels.

edit:
oops, sorry I did not read mikerrs post with the link earlier but it is interesting to see that somebody actually is trying to power the Pi by solar panel. if I understand the text correctly, the 45W solar panel turned out not to be large enough so he doubled the panel size. and the batteries keep going bad probably from being low on charge most of the time.

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mahjongg
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Re: How many solar panels would i need to power

Mon Jan 27, 2014 10:35 pm

To make the most of a solar panel (charging a car battery) you will need something called a "maximum power point tracker", (MPPT) it is what I have hinted on earlier. https://en.wikipedia.org/wiki/Maximum_p ... t_tracking

hannieB
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Re: How many solar panels would i need to power

Tue Jan 28, 2014 9:00 am

I think, you need 12 solar panels for that.

hampi
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Re: How many solar panels would i need to power

Tue Jan 28, 2014 9:37 am

My sketch

https://github.com/oh7bf/RaspiPwr12V/wi ... spberry-Pi

I do not know yet when I will assemble the system. Summer should be good time for that.

nione003
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Re: How many solar panels would i need to power

Wed Apr 05, 2017 10:44 am

vopi181 wrote:Hi, i have 5 6V 120mA Solar Panels. How many of those solar energy led lighting solutions would i need to power the pi and what would be the best way, IE hooked up to a battery. What would be the best battery etc

Hello vopi181,

you can't simply contrast a sun powered cell and a battery, sun based cells have an ideal Voltage versus Current point, (at which they have a sensible proficiency) one that additionally varies relying upon the measure of light it gets. Most straightforward arrangement is accuse genuine batteries of sun oriented cells, then utilize the batteries to power stuff.

mfa298
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Re: How many solar panels would i need to power

Thu Apr 06, 2017 7:57 pm

I'd back what plugwash has already said. Solar can be a tricky beast, you could quite easily need panels rated 10x what you need for an overcast day, Possibly more in winter. but maybe only 3x in summer!

The sensible thing would be to start off working out what power requirements you need for the Pi. How long does it need to be operational (are you trying to go for 24x7, or is it just a couple of hours a day). Also determine what current it draws and whether you have the right model of Pi for your needs. Also think about whether you need it to work throughout the year or just parts of the year.

From that you can start to work out what sort of battery requirements are needed, and what solar is needed to keep those batteries charged up.

Initially it might be easiest to work in Watts (for power) and Watt Hours (for capacity), for instance a Pi3 could be drawing around 8W to run, a 12V, 7Ah SLA would have a capacity of 84Wh (12*7), That would give you around 10 hours of running (84/8) from the battery. You can then scope panels to be able to charge that battery in a suitable time. for example if you had 6 hours of sunlight you'd need to charge at around 14W (84/6).

Note that maths is very simplified, There will be losses in that system as you convert voltages and batteries etc. aren't perfect, but you can get an idea of what's required based on your requirements.

peterlite
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Re: How many solar panels would i need to power

Thu Apr 06, 2017 11:18 pm

Your location?
Sydney, LA, and similar locations get twice the sun compared to London, a city I visited a few years ago for the whole 3 days of their summer. I am looking at powering a Pi Zero W with a 10 watt panel due to that extra Australian sunlight.

The Pi panel will be in a position that is shaded in the afternoon. Four hours of morning sun and a couple of hours of midday sun will charge a battery to run the Pi Zero W for more than 24 hours.

The panels are labelled 12 volts and produce more than 18 volts during the peak time. I run them into a controller with a special connection for a 12 volt lead acid battery. The controller handles any type of lead acid battery. For lithium batteries, you need a completely different controller and the controller must be matched to the exact type of lithium battery or you will end up with the lithium batteries bursting into flames like an iPhone or a Galaxy 7.

Put your panels out in the sun with a volt meter attached. Watch the voltage across the day. Your panel might produce 9 volts, enough to charge a 6 volt battery. 6 volts can run through a regulator to power your Pi.

The electronic controller between the panels and the battery will be the most expensive part. The regulator between the battery and the Pi should be cheap. There are really cheap 12 volt to USB adaptors for cars. There might be something equivalent for 6 volt.

You could also look at wiring panels in series, if they are identical, to use 12 volt electronics.

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