The top of your fountain is still well within Earth's gravity well. That means that as you add more solar panels to generate more power, the power requirements of the fountain rise.
Once a fountain is flowing nicely, the losses needn't be very high... magnetic deflection without trying to bleed off energy is nice and efficient. Someone suggested that losses would be similar to a flywheel with magnetic bearings, or a few percent of the energy stored in the fountain every hour (maybe less with fancy future super tech). The station at the top has a gravitational potential energy $E = WL$ where $W$ is its weight, and $L$ is its altitude. A hundred tonne station at 100km therefore has a potential energy of about 100GJ, and the kinetic energy in the fountain must equal that (or the situation isn't stable). 1% loss of kinetic energy every hour therefore represents ~280kW, or 2.8W/kg. This scales linearly with height and weight (but not mass!)... ten times the altitude, 10 times the power.
Decay of a fountain isn't interesting though. You're putting in more energy than you're losing, so you have to siphon some of it off to stop the space station blowing itself away. Efficiencies of adding power to and extracting power from the mass stream come into play... some of that power you're pushing in will be lost as heat at both ends of the system. Lets say you have a round-trip efficiency of 90%, so for every 1kW you harvest at the top, you get 900W out at the bottom.
A modern lightweight solar cell can exceed power densities of 1kW/kg, but there's quite a lot of infrastructure that needs to go with it... you can't just hook it up to a pair of cables and call it a day. On the bright side, at 100km altitude you need a little over 3W/kg to keep your station aloft, and even quite conservative estimates for the weight of a solar powersat have 20kg/kW, which is an order of magnitude more than you need to simply break even, even with lower power-transmission efficiencies and higher fountain energy loss rates. This suggests your crazy plan might actually work! That's not to say that it is a better powerstation than more easily engineered alternatives, but it does show that a polar space fountain could be a considerable net source of power.
So, now the major technical objection appears to have been removed, all you need to do now is to install a superconducting HVDC cable from the poles, through particularly hostile and inconvenient terrain, with powerstations that have to operate in exceptionally cold temperatures and seriously strong winds (which aren't going to do your fountain any favours, that's for sure) and justify the expense and effort of the whole thing compared to, say, wrapping superconducting HVDC cables around the equator and using conventional terrestrial solar instead. That might be more of a challenge!
Is this better than a conventional solar powersat design? Well, probably not. Powersats scale trivially, and don't require megascale construction projects in some of the most inconvenient and inhospitable places on earth. If you can build space fountains, then low-cost non-rocket spacelaunch technologies are also clearly within your remit and launching power satellites can be cheap enough to be competetive with ground based power systems, even with the many inefficiencies involved in wireless power transmission.
Powersats can retarget their energy supply on demand, more or less, and you don't need a huge joined-up globe-encircling superconducting power grid in order for everyone to take advantage of the power they supply. There's a lot of be said for them once they're cheap enough to be practical. Your power fountain is a neat idea, but unlikely to be economically competetive.