Check out these LED Solar Anchor Lights

http://www.premiermaterials.com/Prem...s/model501.htm

Unfortunately, the only one I really think would be adequate is the
largest and most expensive.

The English company that actually makes them has a less expensive
version than even the 501 but it has a max range of 1 km, not enough.
It might be good for long term mooring but not as an anchor light.

For now, I do not think the solar cells are efficient enough to really
power an anchor light. maybe in 5 years it will be practical.