I'm creating an automated irrigation system, using an Arduino UNO.
I decided to use a solar panel to power all the things up; in particular, i have Arduino UNO, a 12v relay to control the 12v pump (19W), an RTC board, and a soil moisture sensor.
I choose a 12V 7Ah battery (lead acid), a charger regulator, and a 18V solar panel.
The pump will stay on for about 20/30 minutes every day (or every 2,3 days, it depends on the soil moisture value). In the remaining time current is only mainteining on all the devices.
My first idea was to stop the current when the system is not operating, but then i realised that a similar circuit would be difficult to make (for me, obviously)
I've done some calculations, and i think 5W are ok for the solar panel. Should i take a 10W one ?
What do you suggest? I should consider other factors?
The output from a solar panel depends on the sunlight intensity -Thr figures for panels are usually the maximum output and you may get considerably less , and will be even lower at some times during the day as the panel won’t be facing direct sunlight .You need to factor all that in to decide .
This JRC website may help you to estimate the solar energy you will collect.
If in doubt get a bigger solar panel. A bigger battery might also be a good idea. It is important that a lead-acid battery should not remain partially charged for long periods. At the very least it should get a very full charge once every 2 weeks, and once every week would be better. That means having a solar panel that can definitely provide more energy than your pump and other equipment consume - even with a spell of cloudy weather in winter.
I've done some calculations, and i think 5W are ok for the solar panel.
Probably not.
The pump consumes about 10 Watt-hours (Wh) every day it is on. The panel supplies 5 W only in full sun, and only when it is perpendicular to the sun. Depending on your part of the world, you can probably count on about 4 hours of full power output on a sunny day, or 20 Wh, for a fixed panel orientation. Derate for cloudy days, obviously.
The battery should be chosen to supply the system for the longest dark, cloudy period it must operate, and it should be underrated by about 50% to account for aging and inefficiences. So call a 12V, 7 Ah battery 40 Wh, or about 4 days of pump operation.
Robin2:
A bigger battery might also be a good idea. It is important that a lead-acid battery should not remain partially charged for long periods. At the very least it should get a very full charge once every 2 weeks, and once every week would be better.
A lithium battery could be an alternative ? Can i find an appropriate charge regulator? Cause the ones i found only work with lead acid batteries...
jremington:
No, they are destroyed very easily, and require very special care, such as overcharge protection, undervoltage protection and overcurrent protection.
I agree 100%.
For this sort of project the robust nature of lead acid batteries is essential.
You may want to monitor the lead acid voltage as well and set up a cut out for when the battery gets down near the lower region of normal use range.( usually around 10 volts)
Lead acid (as with other lipo and lifePo4 batteries) do not like be discharged below a certain value.
