RE: Solar streetlights project

But... how is it possible that solar lights - which need sunlight - work at night when there is no sunlight?^^

Since you're new on Steemit, here are some tips I give to newbies when I see them:

never just copy a text or publish a photo/video without explanation. Always add some text and never forget to add an image to a text.
Never steal an article and if you quote something or re-publish one of your own articles from somewhere else, always add a link to the source.
Always use all 5 tags for more visibility.
here is an interesting site where you can look up the stats for your account and others.
this is another stats site where you can see your reputation and what to do to climb up the ladder. (commenting other posts is very important).
there is even a help site for Steemit where you can find explanations for the site's functionalities
I wrote a post with an explanation of the most important Steemit vocabulary.
if you want somebody to read your article or follow your conversation, mention their username (don't forget the @).
commenting other posts is very important because you get "curation rewards" which means Steem Dollar from the pot for the article as a reward for the interaction.
learn the Markdown styles to format your posts (you can find how it works in a link on the right side below the text box)
A lot of votes on steemit come from bots that you (or others) can pay for a vote. Depending on the bot, you end up with more $$ than you had before.
All bots work pretty much the same way: You go to your wallet and click on the little arrow next to the Steem Dollar amount. Then click on transfer, fill in the name and the amount and add as memo the URL to the article for which you want an upvote. Very simple.
Here is a site where you can compare the performance of difference upvote bots.
There are also resteem bots, but I don't find them too useful and don't know which one is good.
Be careful with your password and watch out for scamming attempts. Several big accounts got stolen and now they try to lure others into giving away their password by posting comments with links to fishing sites.
you have several different passwords. Whenever you have to use a password and it is not stated differently, use the active key and as little as possible your owner key! The latter is the big key to your account and if that is gone, you account is gone.

I will follow you now. (<- always add that to a comment when you intend to follow the person who wrote the article. This way, you increase the likelihood that they follow you as well.)