What is common targeted cost of green H2 production till 2030?

There have been long-term natural cycles of about 1,000 years with it having been warmer in Roman times and also in Medieval times than the peak we are starting to pass through before about 500 years of cooling. No valid physics exists that can be used to prove so-called "greenhouse" gases warm the planet.  In fact, they cool it, water vapor by a few degrees, but carbon dioxide and methane by less than 0.1 degree.

The correct physics in my peer-reviewed 2012 paper "Radiated Energy and the Second Law of Thermodynamics"* explains why the claims made by climatologists are based on nothing but fictitious, fiddled physics. 

It is now proven that cosmic rays assist cloud formation and thus affect surface temperatures. It is also proven that an increase in sunspot activity enlarges the heliosphere which in turn then shields Earth against more cosmic rays.  There is also a superimposed natural cycle of about 60 years which appears to correlate with the alignment of close planets, the fields from which probably alter the paths of cosmic rays.

Correct physics in my paper "Planetary Core and Surface Temperatures"* explains for the first time anywhere in world literature just exactly how the required thermal energy gets to the surfaces of planets and even to the core.  Planets are not cooling off from some far hotter initial state.  Rather, they were originally formed by clumps of matter from cold (<2K) inter-stellar Space coming together in orbit around our Sun because of their own gravity, whereupon energy from the Sun warmed them to current temperatures right down to the core. Thus, melting occurred, and spherical shapes formed as a result.  Dare I quote: "The Earth was formless and empty" (Genesis 1:2)   

* https://ssrn.com/author=2627605

$1USD/kg is too expensive considering the logistics issues associated with hydrogen. Currently, green hydrogen is not being produced in the US, or at best small-scale. Thus, the estimates of current costs of $5-6/kg, really mean natural gas reformation, not wind/solar electrolysis. The green hydrogen estimate is on the plus side of $10/kg.

Why is $1/kg too expensive? For transportation, only hydrogen use long-haul heavy-duty trucking is still being discussed, since short-haul HD and light-duty will be EVs. However, the pipeline and fueling infrastructure logistics just kill the business case for long-haul hydrogen. Anybody can build a scaled-up hydrogen fueling station for heavy-duty trucking . . . if they have $20M. Build one of those every 100 miles on the thousands of miles of US interstates and you're running into serious money. That's just CAPEX, which is the easy part. Find an investor with too much spare money, say $100B, and you're fine. It's the OPEX that nails you. Let's say you could buy green hydrogen for $1/kg. By the time you pipe it to your fueling station in Iowa (if you could build a pipeline with the right material . . . and don't even talk about trucking hydrogen, especially liquid hydrogen), you've lost 25% due to leakage at the compressor stations and along the way. Also, the compressor stations will eat you alive with another 25% efficiency loss (new, high efficiency compressors). Then, you have the O&M costs of the fueling stations themselves. For safety reasons, someone has to operate the fueling stations. Also, hydrogen is an unforgiving gas. I know. I used to work on a hydrocracker in a refinery. If you think you had line and efficiency losses associated with the pipeline compressors, the fueling station compressors are an order of magnitude worse. The pipeline compressors only need to boost to 200-300 psig. The fueling station compressors need to boost to 12,000 psig so that they can feed a truck at 10,000 psig (~700 bar). That $1/kg hydrogen at the wind farm just became $3-5/kg hydrogen going in to the truck. Of course, you can't get $1/kg hydrogen, but you might get $5/kg green hydrogen some day . . . which ends up as $8/kg hydrogen going into the truck. As a parting thought, from me as a chemical engineer, hydrogen is great for hydrocracking, hydrogenation, and hydrodesulfurization. It's also great for making fertilizer and in a few other niche applications. These are the traditional uses of hydrogen. It's possible hydrogen will find an application beyond these, but it's not obvious what that is. Hydrogen is a nasty little critter.

Globally engineering firms discuss arround 3 / 5 USD/kg , for agencies they aim around 2.5 / 4.5 USD/kg