The success of any cryptocurrency hinges on just one fact: how many people adopt it. Bitcoin and Litecoin were adopted merely because they were novel. And Ethereum was adopted because it is a platform on which hundreds of other cryptocurrencies could be built. But what is the trick to get any of the other coins adopted by the masses? Well one idea is to just airdrop the coin (or give it away for free). The CommunityCoin project tried to do this back in 2014 and initially they demonstrated early success. They gave a way a large portion of their coins in three different payouts over the course of several weeks. If you didn't touch your wallet after the first payout, then you would be eligible for the second payout, etc. But then what happened after the three large airdrops? It started to die very early on, and today nobody knows what CommunityCoin is. So one must ask: why did this CommunityCoin die? And the best answer I can come up with is because they failed to continue to attract enough new users to reach a point of sustainability. Secondly, CommunityCoin was completely free during the airdrop period. Nobody had to invest or buy anything at all to receive it. And when a coin is completely free (without any other established form of value backing it), then mass adoption is extremely difficult if near impossible.
So this is one thing that sets SolarCoin apart. While SolarCoin is technically given for free, the solar user receiving the grant had to first make a monetary investment in solar power. Thus SolarCoin is backed by something very valuable: energy. Furthermore, the goal with SolarCoin is to distribute the coins over a 40 year period and not over a month period. To those who produce solar energy, the coins are distributed every six months. There is no reason for a user to leave the SolarCoin network as long as they continue to produce solar power. The end result is an established strong foundation on which to grow a huge community.