Stellar has the following advantages for opensolar:
Fast and cheap payments: Stellar transactions are confirmed within 5 seconds and the transaction cost is low (defaults to 0.00001 lumens or 100 stroops per transaction). Transactions are final once they are in a block thanks to Stellar's Consensus algorithm, removing the need for handling re-orgs as would occur in a Proof of Work blockchain.
Easy asset creation: Stellar makes it extremely easy to create new assets and transfer them between addresses. This makes representing state variables easier and enables the creation of secondary markets where users can exchange one asset for another.
Horizon API: Stellar's Horizon API makes it easy to query and post to instances that are full nodes. The API also gives a good interface to build transactions and do operations that change the state of accounts on the blockchain.
Testnet that mimics mainnet: The Stellar Development Foundation mimics mainnet on a testnet that it runs, making it very easy to test features before deploying to mainnet. It also maintain a testnet faucet to get test lumens from, making the process of creating new accounts easier.