While most are a scam, Arcadia does not have a separate rate. They use the BGE or whatever other rate you already have and just give you solar credits from their community solar farm. No extra charges and they even cover credit card fees when you pay your bill. You can purchase additional solar energy credits but I opt out of it.

Edit: To whoever is downvoting me, please feel free to point me to where you see on Arcadia's website that they are offering a low intro rate to reel you in. You won't be able to. The majority of companies do this but Arcadia does not switch your electric supplier to them. Your rate stays the same. If someone can point to proof that I'm wrong I will gladly retract my comment.