Because of the vast distances from the sun New Horizons will operate at Solar power is impractical. At the elliptical orbit of Pluto the strength of the sun varies from 0.0012 to 0.0004 times what we get on Earth.
Instead of trying to collect the tiny amount of sunlight available New Horizons uses a Radioisotope Thermal Generator (RTG). Specifically, a General Purpose Heat Source — Radioisotope Thermoelectric Generator (GPHS-RTG) manufactured by General Electric Space Division (now part of Lockheed Martin).
The GPHS-RTG that New Horizons carries is actually a spare from the Cassini mission. It provided about 250W at launch, and the decay of the Plutonium causes the power output to drop by approximately 5% every four years, meaning that by now the RTG should be providing about 200W of power.
This graphic shows the position of the RTG on New Horizons.
For some more reading on New Horizons power systems see The Pluto-New Horizons RTG and Power System Early Mission Performance, Geffrey K. Ottman and Christopher B. Hersman. (source of the above graphic)
Until someone solves the N-body problem every spacecraft needs some kind of propulsion to correct its course during the mission. New Horizons uses a Hydrazine based propulsion system including four 4.4 N main thrusters and twelve 0.9 N attitude control thrusters. Its 77 kg fuel tank allows a total post launch delta-v of somewhere over 290 m/s (650 mph).