What your generator costs to run
In Puerto Rico a generator stopped being a luxury a long time ago. What almost nobody has a clear number for is what it costs to run, and the answer isn't on the label: it's in how much you put on it.
Fuel use follows the load, not the size
A generator doesn't burn the same idling as it does running the fridge, a fan and a water pump. Gallons per hour climb with load, which is why two neighbors with identical units can spend very differently in the same week.
Spec sheets usually quote consumption at half load and at full load. If you only have one number, it's almost always the full-load figure, and using it when you're barely running a couple of appliances gives you an inflated cost.
Measure your own burn rate once
The most reliable figure is yours. Fill the tank, note the time, run the unit with your usual load, then note how many gallons it took to refill and how many hours passed. Gallons divided by hours is your real gallons per hour.
Measured once, that number beats any catalog estimate, because it includes your appliances, your usual load and the condition of your machine. Save it on your phone and use it every time.
What an outage costs
With gallons per hour, the rest is multiplication: hours running times gallons per hour gives gallons, and gallons times the price of gasoline or diesel gives the cost. The generator calculator does that and also tells you how many tank refills you're in for, which is the number that actually organizes a long outage.
Knowing how many refills you need tells you how many cans to have ready before the power goes, and how many trips to the gas station are waiting if it drags on. After a hurricane, that line is the scarce resource, not the money.
If the outage stretches out, compare that weekly cost against what you normally pay for power using the electricity calculator. Seeing the difference in dollars is what turns the solar-or-battery conversation from abstract to concrete.
Before you start it
Cost isn't the only thing to plan. Carbon monoxide from a generator kills with no smell and no warning: the machine goes outside, away from doors and windows, never in the garage or an enclosed balcony, no matter how hard it's raining.
Stored gasoline degrades within months, so a tank saved since last season is less good news than it looks. Rotate your fuel, keep it in approved containers, and let the machine cool before refueling.
And add up the load before you plug anything in: if what you switch on at once asks for more than the unit can carry, the problem stops being the fuel bill and becomes the equipment.