Always a bit late to the dance, but here is my input on this topic, since we just had a short power outage.
I have a B7300 with a 2 speed rear PTO. I think they are 540 and 950 or something like that. PTO HP is rated at 12.5HP. I also have a WINCO 10KW PTO generator connected to the house with a double throw switch, so at 2HP per KW, I may get 6KW plus from the genset at full power/RPM.
Over the years, on another forum, there has been much discussion about small tractors, gensets, a 2-3speed PTO's.
After having a discussion with my Kubota dealer before buying the genset, and having talked with many local dairy farmers who depend on PTO generators during power outages, here is what I have learned and experienced.
I use my PTO genset for back up power during outages. During outages, I consider just having power a luxury. I do not need to run the dishwasher, electric range/oven, clothes dryer, etc. I do like lights, my furnace, fridge and freezer.
No matter what your PTO speed selection, you are going to adjust the engine throttle to attain the proper voltage output on the genset. I adjust to 120VAC on the meter. On my little tractor 2900RPM engine/540RPM PTO, I can get the maximum 6KW out of my generator, but run times are less due to fuel
consumption. I only use this setting when I have heavy electric loads in the house, such as during meal times.
During periods with less load requirements, I can set the engine throttle to about 1700RPM and the PTO to 950 RPM and I still get the 120VAC on the genset meter. Granted, if I tried to run a heavy load item, like the stove/oven, that would put a heavy draw on the generator, and the tractor engine, so I do not do that. But under normal, low load requirements, the furnace, freezer, fridge, lights all work well with little to no noticeable affect on the tractor/engine with this setting.
Does it work? In a word, YES! Back in 2011, when hurricane Irene came through our part of the country, we were without power for 3 days. As I had never used my setup for any extended period of time, I was prepared and committed to try it. The end result was, with using the above stated power selections, I made it through that period, running the engine all day, and only used a bit under 12 gallons of diesel. Did I need to run all that time? Maybe not, but I had the luxury of having both house lights, fridge, freezer, computer, Internet (for my home business at that time) and had no problems.
In the future, in the summer/warmer months, I might not run the engine for the full time. However, in colder/winter months, I probably would run it full time as you never know when a call for power will be needed. Again, I would probably run the engine at 1700RPM/PTO at 950RPM, and go for the low load options. During meal times, we can/could get by heating foods in a microwave, which has not been a problem for the setup.
As for those who 'debate' using a tractor for the genset, I generally look at it this way. I have a loader bucket, PTO snowblower, and a PTO Genset. During an outage, what are my priorities. If I need to clear snow from the drive, I can temporarily disconnect the genset, and plow the drive with the bucket, or quickly remove the genset and connect the snowblower. Either way, it is only a few minutes of downtime and the job is done. My diesel engine has never failed to start, even in the coldest Vermont weather. My very first gas generator, 30 years back, I cannot say the same for that. That gasoline engine was very hard to work with in cold weather. Plus, my diesel engine is maintained and run all the time.
What would I do different? Probably not much right now. If I had an opportunity to upgrade anything, I might go for a tractor with 25HP, thus being able to get the full potential from the genset.