Well, power basically is flow x drop (pressure)... if you don't have a lot of flow, you'll need a lot of drop and vice versa.. Banjo, from what it sounds like to me, a 10K generator would be WAAAY too big.. I'd look at 1000W max just from the sound of it... I looked into it for our place and we have a 2" line and about 100 PSI (220 ft drop or so) and I figured I could safely make about 1500W, and that's running something like 50 GPM.
Alternators can be used, but the problem with them is they electrical power to make power, and the typical alternator takes about 7 amps to energize, 7A at 14V is 100W just to energize the alternator.. in a bigger system using a 240amp (3kw) alternator it's not that much, but in a small system it's a whole lot. A permanant magnet generator will be more efficient for smaller applications, but they're a bit more bulky for the power they'll produce.
Cow pollinator... Yes, you can get higher output alternators, but they take more power to turn.
I think I've found some online water power calculators through google...
Things to remember with these calculators that there are friction losses in the pipe... the flow must be measured with a restriction at the end (like the nozzle of the turbine would be), and a pressure guage just before it. If the hose is completely open, there will be big flow but no pressure, = no power. completely closed is max pressure and no flow, again, no power... somewhere in between you will have a maximum of flow and pressure, which is where you want to be operating at.
You'll probably want to have at least 1 battery anyhow, and run a standard RV inverter to run everything 110V... that way you can run a skil saw, etc which will take more power than the turbine can produce continuously. If you want to run on 12V, you can get these new LED floodlights for trucks that don't take much power and D@mn are they bright... you could easily light up a reasonable sized barn with 100W generator and these lights if you had a battery that would charge during the daytime. If you want just 200W in AC, I think walmart, napa, etc all have cigarette lighter AC adaptors for laptops, etc that are only about $25, you should be able to run anything except flourescent lights on them with no trouble at all.. some CFL bulbs may work well, but can't say for sure.
The first thing you need to do is get some numbers... Get a pressure guage and see how much pressure you have with no flow, then open up a tap until the pressure drops about 25%, and see how long it takes to get a 5 gallon pail full (make sure the spring can support this flow).. from that you can figure out your GPM at a reasonable working pressure.
