Good question, I had a similar application last year where client wanted solar lights to illuminate some trees rather trench across 2 acres of back garden lawn (dont think cost of actual trenching/cable would have been a problem, just didnt want his lawn wrecked - discounted mole due to roots).
I couldn't find anything from a reputable manufacturer powerful enough for his needs (unless risky Chinese products)!
His gardener said he could get some so we lost out there but still not sure what he ended up with or if did the job)
