There's more than one way to make it.

Almost all of the ammonia produced today comes from Haber-Bosch synthesis out of its constituent elements, whereby the total production quantity grows continuously (e.g. 1980: 70 million tons per year; 2000: 105 million tons per year). Although the main raw material for ammonia production today is natural gas (especially methane, CH4) via a steam cracking process and hydrogen as intermittent product, ammonia can also be produced from any other source of hydrogen. Especially regarding hydrogen economy, renewable sources like water, wind or solar energy via electrolysis could be considered (minimizing the CO2 problem). Being produced in very high quantities, ammonia is of very low total cost ($ 1,20 per kWh; for comparison: methanol: $ 3,80; hydrogen: $ 25,40) [1].

And it has lots of uses.

Pure ammonia is used today as fertilizer, most commonly it is applied directly to the soil from anhydrous ammonia tanks. Also, ammonia is widely used in various branches of chemical industry as catalyst, neutralizing agent or reactant in rubber, plastic and textile industry, ammonia-soda (Solvay) process, fertilizer industry (nitrate, phosphate …), metallurgy… One gram of ammonia absorbs approx. 1,4 kJ of heat when vaporizing, therefore it is also frequently used as cooling agent in air-conditioning systems, ice skating rinks and refrigeration (especially in bigger ships, therefore many harbors are equipped with ammonia fueling stations).

The infrastructure already exists.

Due to that wide use, the infrastructure as well as standards for the use of ammonia is well established. It is either transported in cylinders at -33 deg.C (~ -27 deg.F) at ambient pressure or at approx. 8 bar (120 psi) at ambient temperature. In addition, pipelines for ammonia exist all around the world.

Even the downside is sort of up.

Ammonia has a very specific and strong odor. Very often considered to be a disadvantage, leaks in the system can easily be detected by the strong smell before dangerous situations arise (compare with the not smellable and highly explosive hydrogen). Ammonia is flammable within a small range when mixed with air (15 to 34 vol.%). In contrast to methanol, ammonia is not an environmental poison, because it serves as nutrient source for plants and bacteria. It is lighter than air end evaporates fast. As being part of the natural nitrogen cycle, it is recycled naturally in the environment and therefore does not last long there. Once released to air, it is rapidly removed by rain or snow, or by reaction with other chemicals in the air, especially acids.

To a certain extent ammonia is toxic. However, the lethal amount is more than one thousand times higher than the limit of perception

There are concerns about eutrophication of water bodies due to excess nutrients though. Still, it seems a far more benign substance than current carbon fuels in several important ways.