My reply is based upon the following facts. 1. There is no connection from the local power grid to your cabin. 2. The person that originally wired this cabin, followed the standard practices of the trade and the work conforms to the electrical code, including.......proper grounding of all aspects of the system. 3. And that the existing wiring system in the cabin was set up to receive 120/240 volt AC grid power at some point in the future, if it became available. The way I see it, you have two choices. You can either use a "whole house" transfer switch that will allow you to choose between the existing solar power supply or the genset. OR...... you can simply disconnect the wires from the solar power supply and tape them off inside the main panel for your cabin (fuse box/breaker box). You don't need to actually remove the wire from the fuse box itself. This would allow you to easily reconnect the solar power supply system in the future, should the need arise. The purpose of a transfer switch is to provide 100% isolation between two differing sources of power. So, one way or the other, this isolation must take place. IF you don't isolate the solar system from the genset, then the genset will feed power back into the solar supply. Damage may be done but even if it does not do damage, the solar system is a potential loss of wattage from your genset and you could also have a fire and electrical hazard. Once you disconnect the wires from the solar supply unit, you can install the correct wiring between the fuse box and wherever you are placing the genset. If your panel is a standard residential fuse or circuit breaker panel, then it requires 240 volts plus a neutral wire to connect to the genset. You also need to make sure that all grounding issues are taken care of. Some how, your genset must be grounded to the cabin's system. If you are not sure of how to go about this, then hire a licensed electrician to perform the work. Better to be safe, than electrocuted. You also need to consider that many gensets use about a gallon of gasoline per hour of run-time. If it was me, I would be looking at a diesel genset so that I could install a lockable fuel oil tank in the 250 to 500 gallon size on the property. The thought of transporting several five gallon cans of gas in my car wouldn't thrill me. No matter how hard you try not to, you will spill fuel from those containers. Gasoline is a highly inflammable and explosive fuel. You don't want those fumes inside your vehicle. Having a permanent tank that is refueled by a company with a tank truck has many benefits. Plenty of reserve fuel that is far more stable than gas and no worries about refueling a hot engine.

Totally apart from the technical issues, where is your landlord on this, given that it's not your property, and you are, I presume, not a licensed electrician? Building codes generally demand that licensed electricians do the work on any multi-family dwelling. And then there is the issue of the insurance ramifications if the building burns down....

A 120 V circuit is safer than a 240V one. The main advantage of 240v over 120v is that it requires only half as much current to deliver the same watts into a resistive load, therefore, the wire can be smaller. In the US, single phase residential voltage comes from a center tapped transformer. The center of the winding is the neutral while the two outer ends are the two voltages supplied to the distribution box (circuit breaker or fuse box). Both 'hot' lines measure 120v with respect to the neutral, but since these two hot lines are opposed by 180 deg, they measure 240v with respect to each other. With this system, 240 power can be supplied with lines that are at only 120v with respect to the neutral. Now for the big surprise about ac motors. For motors larger than a few horsepower, the current does not vary lineraly with the load! As the shaft load increases, the current does increase some, however, the big change is the phase angle between the voltage and current. Power delivered is voltage x current x power-factor. When the current is 90 deg to the voltage, power is zero; When the current is in phase with the voltage (0 deg), power factor is 100%. So it is possible to have considerable motor current in the wires with little power output. Fractional horsepower motors have a goodly amount of resistance compared to their reactive component and because of this have greater resistive losses. The debate between 50 and 60 hz can go on forever and from a practical sense, has existed since the dawn of electric power. 60 hz has an advantage over 50 hz in that the cross section of the iron in a transformer can be a little smaller for delivering the same power. Hysteresis losses in magnetic materials is a positive function of frequency, thereby increases with frequency. But, at the same time, the peak magnetic flux required to transmit the same power increases with decreasing frequency. Aircraft systems uses 400 hz to reduce weight. Europe tends to use 50 hz while the US and Canada uses 60 hz. Sometimes it seems that this difference is maintained to make it more difficult to apply products from one side of the ocean to the other - e.g., trade protectionism.

The following is a very general discussion and may not apply to this situation. As Pete said, you've provided rather little detail. If you have a 120 volt motorized timer, it may be possible to rewire it so that the timer motor is powered by 120 volts and the contacts switch a 240 volt load. BUT, there are some concerns. 1. If the timer isn't rated for 240 volts, using its contacts at that voltage would be a code violation, if not outright dangerous. 2. If the timer has a single pole switch, only one hot leg would be opened, making a proper separate DPST disconnect essential if it's not already there. 3. If you have only 120 volts at the remote location, you probably have only two current-carrying wires and a ground. You can't (safely) derive both 120 volts and 240 volts from this combination. It might be possible to use a small transformer to operate the timer motor, but the cost would probably be nearly the same as replacing the timer with a 240 volt model. Bottom line is - you're better off to either get a 240 volt timer to match this pump, or a 120 volt pump to match this timer. Again, this is based on the limited information you provided. You may wish to offer more.