I'm thinking of making a RaspberryPi solar powered smart "green house", with LED lights, water pumps and a few sensors. I would like to point out the "green house" would be about 6ftx2ftx2ft - more of a tool shed. I also live in the UK so sunny days aren't guaranteed. Can somebody please help me work out the correct solar panels and battery I might need?

My main concern is the LED lights I will be using. They come with a 12v 5A power supply. Am I right in saying they would use 60w?

According to another post on here a 12v 40ah car battery would power a 50w water pump for 9.6hours. Using the same maths this means I should be able to power the lights for 8 hours, correct?

My question is: What size solar panel would I need?

Is it as obvious as a 60W panel?

There is also the amount of power the Rpi would use and the small 3v water pumps I've bought, these will only be used once every day or so for a short period of time.

Any help would be appreciated.

  • \$\begingroup\$ The power supply should be rated higher than needed. So the LEDs may use less than the power supply indicates. Sensors can require anything from almost no power at all to a lot of power, depending. If just moisture ones, probably not so much. The water pumps may require a peak power you need to be aware of, and not only average power, when asking such questions. Finally, solar panels are rated for noon sun at the equator in clear skies. So... well, you won't be getting anywhere near that from them all day long. So you need battery storage. \$\endgroup\$
    – jonk
    Dec 30, 2018 at 1:13
  • \$\begingroup\$ How many 60W lights total? If you live in northern hemisphere and it's often not bright out, you may wish to investigate types of solar cell that operate better in low light conditions and or adding wind power to your setup. You need to find out how much power you can generate compared to the actual ratings of the panels, take into account how long the night and/or other periods of insufficient light for charging are. You need to figure how much power is needed to run the system for the expected downtime, add losses, then you can use the actual generation of the panels to find bank size. \$\endgroup\$
    – K H
    Dec 30, 2018 at 1:34
  • \$\begingroup\$ Please provide a link to the datasheet for the LED lamps you are using, as well as their power supply. It's not clear to me whether you are specifying power input or power output. You also need to provide an estimate of how much sunlight you will be receiving..."sunny days are not guaranteed" is not enough information to do a proper design. \$\endgroup\$ Dec 30, 2018 at 2:59
  • \$\begingroup\$ Thanks for the feedback, @KH here is a amazon link to the LED's I've been looking at amazon.co.uk/gp/product/… unfortunately I can't find much more info on the lights other than what's in the description. According to Google between May - Aug we get an average of 200 hours a month of sun, Nov, Dec, Jan and Feb are just above 50 hours and Mar, Apr, Sep and Oct are between 100-150 hours. \$\endgroup\$ Dec 30, 2018 at 17:38
  • \$\begingroup\$ @jonk The only sensors I will be using are soil Moisture, this will only be used in the morning or evening to water the plants if needed. I would like to add wind power or even hydro power as a live very close to running water but its an expense I can't afford right now, unless I can find a cheap DIY idea. \$\endgroup\$ Dec 30, 2018 at 17:39

1 Answer 1


Designing PV system estimatimating the power output is not an easy feat. It depends on many things like your local weather, temperature, angle of your panel local shadings, efficiency of the inverter, Rser of the batteries and it also changes with seasons.

There are softwares out there that can help you, the most used one in industry that I know of is PVsyst which comes at a cost, but they have a demo version you could use, but the region is locked.

You also have some web-based calculator like this one that can give you an estimate although doesn't support batteries.

Once you have a good estimation of your PV system performance, then you can calculate the battery size you would need based on power consumption and operating hours of your lights.


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