To upgrade your Solar Tower ruin, you need Solar Tower Shards.
With each upgrade, you need more Solar Tower Shards.
Below is a list of possible ways to gain these.
Gems
You can purchase Solar Tower using gems.
1 Solar Tower Shard = 15 Gems
10 Solar Tower Shards = 125 Gems
100 Solar Tower Shards = 1,154 Gems
1000 Solar Tower Shards = 10,000 Gems
Chest
You can purchase a chest using guild coins to have a chance at
gaining extra Solar Tower Shards.
To purchase, click bag, click chests, click the third icon on right hand side.
The chest is called Magical Shard Box and costs 22,500 Guild Coins.
It randomly gives you 10 shards for any of the ruins or statues.
Campaign Elite Sweeps
You can sweet elite campaigns to pick up extra Solar Tower shards.
Elite 2-1
Elite 2-2
Elite 2-3
Elite 2-4
Elite 2-5
Elite 2-6
Chests
Chest from the VIP daily clan gifts (Sunsingers city) gives Solar Tower shards too.
VIP Daily Clan Gifts
You can collect 3 Solar Tower shards per gift from daily VIP Clan gifts (Once you have level 25 diplomacy for this city).