# Solar Panel Size for Electron in SLEEP_MODE_SOFTPOWEROFF

Hi,

I am using an electron and must make a final decision on a solar panel. I calculate my power requirements as follows:

Sending one sms per day (AH) : 20 sec / 3600 * 0.5 A = 0.0033 AH per day
Wait for sms once a week : 180 sec / 3600 * 0.5 A / 7 = 0.0071 AH per day
Sleepmode : 23.98 hours X 100/1000000 A = 0.0035 AH per day

Total per day = : 0.0105 AH or 10.5 mAH

The smallest 5 V panel I could find was a 0.15 W supplying 30 mA. If only half the capacity can be used due to installation problems (15 mA) and only two hour of sun is available the panel size seems more than enough : 15 mA X 2 H = 30 mAH.

Let me ping someone that might be able to help, @rickkas7 or @ParticleD are you able to assist?

There are too many variables to know, but those numbers look low to me.

Since youâ€™re using SMS I presume you are not using the Particle cloud features and are using a 3rd-party SIM card, as the Particle SIM does not support SMS.

In order to send or receive a SMS, however, you will need to at least connect to cellular (blinking green). This can take from 20 to 60 seconds. I presume since you are only sending once per day, youâ€™ll be turning cellular off. You can reconnect to cellular in under a second in standby mode, but cellular standby will use more power.

One thing youâ€™ll need to worry about if you are planning on only being awake for 3 minutes per week is clock drift. Without the Particle cloud time synchronization youâ€™ll need to set up something to reset the STM32F205 RTC, as itâ€™s not particularly accurate.

You also didnâ€™t mention whether youâ€™re using 2G or 3G. 2G takes more power and generally longer to connect to a tower than 3G. And for both, the better the cellular signal, that faster youâ€™ll be able to connect.

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Hi,

We are already testing the firmware over the past three months and it is working flawless thanks to all the help on the forum. The main question is how small can we go with a solar panel in terms of volts and amps ? I have tested a 5 volt 30 mA panel but its seems to small cause the charger did not start charing - no red led light flashing ?

3g

The RED charging LED On the Electron stop illuminating when the charging current drops below 30mA.

You need more power to actually charge the LiPo battery correctly, 30mA is to low to properly charge the chemistry by some recommendations.

I would go with a 1w 5-6v panel at a minimum.

But you could try this panel if your trying to go as cheap as possible.

http://www.newark.com/osepp/sc10072/monocrystalline-solar-cell-100ma/dp/94W9303?MER=bn_level5_5NP_EngagementRecSingleItem_1

And I always recommend these panels for outdoor use since they are built for that but 2w is more than you need and the cost is probably more than you want to pay but this will make sure your battery is always charged.

https://www.voltaicsystems.com/2-watt-panel

I used a custom 2.7w panel for a few months and it worked just fine to keep the Electron online during the cold winter months for publishing every 5 mins.

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