More reliable, but more costly, too; this solar price comparison is skewed if you don't also include the cost of said batteries / battery capacity. Of course, comparing with coal is also missing the environmental impact.
Also note that there are cheaper energy storage methods than batteries. Compressed air, pumped water, flywheel and the recently discussed Ares gravity-rail systems have various price points for storage (kWh) and delivery (kW). Here is the ARES discussion:
