This is interesting because it actually gives the critical numbers needed for an evaluation, or most of them.

We have the size of the panels.

We have the efficiency.

We know that it does not use precious metals, although I would like to know also about rare earths.

We have the size of the storage needed.

What we don't have are figures for the assumed solar isolation etc, although they could be found by a bit of digging.

For the US the energy use would be a heck of a lot more, but as against that solar isolation almost everywhere in the 48 is a lot more.

I am cautiously impressed.

OK, taking the solar insolation figures for Brussels from here:
https://www.gaisma.com/en/location/brussels.html

And approximating an average by simply adding together the average monthly insolation figures in KWh/m2/dy then dividing by 12 I get:
32.96/12 = 2.73

Times 365 = 996.45

So 1000 KWh pa

At 15% comes to 150KWh/m2 pa in hydrogen

Or we have at 2.73KWh/m2/dy *15% =0.182KWh/m2/dy

So 1 panels at 1.6M2 = 0.2912 KWh per panel/dy

Times 20 = 6KWh per day in hydrogen equivalent, near enough for government work

That is something like 200 grams of hydrogen.

At 60mpge that comes to around 12 miles per day.

I think they are assuming some very light vehicle etc, as well as a super efficient house.

Unless of course I have messed up the arithmetic, which is always possible!

One of the things I notice on the illustration is that they have built a box structure to do the job, not a panel.

It may or may not be possible to have something thin enough to put on a rooftop.

If not, then extra space is needed, not too practical in a lot of places, and wherever they put the box equivalent it is quite bulky, never mind worrying about the hydrogen storage tank, unless this is it.

This looks like another positive step towards near future clean H2 economy? Roofs and attics could be used to generate and store enough H2 for homes HVAC and FCEVs?

The Toshiba H2One thing appears to be over-sold; it only supplies a 12-room annex to the Henn Na Hotel and I saw nothing about bigger follow-up projects.  I looked up the hotel itself and the reviews were generally poor, though none of them directly referenced the hydrogen system (but the tiny cube fridge and tea pot may be related).

The 4 cubic meter (Volume?) pressure tank @ pressure? = kW/h?

15% efficiency is very impressive obviously when compared to ~ 4% from (20%) solar to H2 electrolysis.
How does this design compare for reducing sunshine in winter. I.E. is it better described as a storage device buffer for night time and winter?
The difficulty as with its advantage is that is is produced specifically for storage so is really a small piece of a functional system . High efficiency P.V. nearer to 30% would way better than half the real estate required for direct consumption is especially relevant for household where battery performance is unlikely to be temperature affected .

This house will stay warm day and night winter and summer in the none too sunny latitude of Belgium.

The uncritical acceptance of claims like this is at the root of the political deadlock between romantic idealists on the one hand and scientists and engineers on the other.

It's past time to inject some reality into this discussion.  First, 4 cubic meters is an ENORMOUS tank; it's over 1000 gallons.  The typical propane "pig" where I live is 500 gallons or less, and it's made of mild steel.  To get decent energy capacity the hydrogen tank is going to have to operate at pressures on the order of 700 bar.  Steel can fail catastrophically and compressed gas at such pressures literally forms a bomb; safety requires fussy and expensive high-strength composites like graphite fiber.

On to energy density.  Propane has roughly 91,500 BTU of energy per gallon, and a 500 gallon tank is filled to 80% full for an energy capacity of 38.6 GJ.  Hydrogen at 700 bar stores a mere 4.7 MJ/liter, so the 4 m³ tank will store just 18.8 GJ; that is not even half the energy held by a propane tank less than half the size.  Can you actually keep a house heated and lit on so little energy?  Depends on the house I suppose, but you are going to have compromises like a small refrigerator.

Next is cost of the tank itself.  This 2016 projection finds that tank cost may drop to as little as $10.54/kWh at high production volume, or $1970 per 5.6 kg tank.  One kg of H2 has 142 MJ/kg, and my cross-check of the numbers is roughly congruent with the cost figure given assuming that the energy is given for the raw hydrogen and not the output of whatever it is fed to.  The 4 m³ tank holds 18.8 GJ or just over 5200 kWh; its cost is going to run something like $55,000!!  Then you have the cost of the hydrogen production panels, the compressor, and your furnace/fuel cell/whatever.

What else could you buy with $55,000?  Well, at a pessimistic $6000/kW you could get something in excess of 9 kW of nuclear power plant.  Assuming it operates continuously from October 1 to March 30 (182 days), that would give you 39,312 kWh or 142 GJ.  That would serve roughly 8 houses as efficient as the one running on the 4 m³ hydrogen tank... oh, and it would heat several times as many if its waste heat was utilized.

Do you understand now why I call it "hypedrogen"?

BTW hydrogen for bulk storage in these sorts of quantities is stored for instance on garage forecourts at 900 bar or more, not 700bar.
If it were at 700 bar there would be no pressure differential to enable the fuelling of the tank in the car.

So the resemblance between these underground structures and the tank in a car is tenuous, and attempting to calculate costs from the latter shows not only a non-existent grasp of the technologies, but is about as sensible as trying to calculate the cost of an oil tanker from that of a 1 gallon can in the back of your car.

Those who think they know it all fall flat on their faces.

For a car weight is important as well as cost, and you don't need anything like the same volume of casing materials for a far larger tank

There you are wrong.  The wall thickness scales linearly with the radius of the tank for a given pressure, so the ratio of wall volume to useful volume is roughly constant.  You may be able to get by with cheaper fibers, e.g. high-strength glass instead of carbon, but you're going to need a great deal of it and the cheap crap won't do when you're literally confining the energy of a bomb.

the resemblance between these underground structures and the tank in a car is tenuous

This, from the guy who just said "I don't have figures to hand for the cost of such large storage tanks".

nor am I about to research it

I gave you my source.  You won't do any research, but you're still certain I'm wrong.  This is rather amusing in a way.  BTW, one of the things I uncovered but didn't use was a commercial source for steel tanks such as are used in welding.  However, they have working pressures on the order of 2200 psig so I didn't consider them valid for comparison.  Also... steel is subject to hydrogen embrittlement and corrosion, so really isn't suitable for use outside a controlled industrial setting.

attempting to calculate costs from the latter shows not only a non-existent grasp of the technologies, but is about as sensible as trying to calculate the cost of an oil tanker from that of a 1 gallon can in the back of your car.

If you had bothered to read the linked paper, you'd see that the price difference between single-tank vehicles and dual-tank vehicles favors single tanks but is quite small.  The big difference comes with production volume.  Larger tanks are going to require bigger winding machinery, curing ovens, etc. and will likely cost more as a consequence.

There's a reason Elon Musk chose 18650 laptop cells for his first few generations of EV batteries:  they were already being produced by the billions and the cost/kWh was unbeatable at the time.

Some would say going nuclear would be a solution but

No buts.  Nuclear and hydro are the only proven solutions we have.  Even biomass causes emissions through land-use change.

regardless the apparently unsolveable concerns surrounding weapons and toxicity (again trust is broke)

Every country that developed nuclear weapons did it BEFORE or WITHOUT having a nuclear energy program.  USA, USSR, China, India, Pakistan, N. Korea... none started with nuclear electric plants.  Those came later or not at all.

practically nuclear does not scale as well with distributed power R.E,s across developing country economies, island grids or remote locations. That is to say it has an industrial rather than human scale.

Hogwash.  When the first oil price shock hit, France's grid was mostly powered by petroleum and made up more than 1/5 of US fossil fuel consumption for electric generation.  Over the next 17 years, France had almost eliminated fossil-fired generation and the US had almost completely replaced petroleum in that role as well.  France de-carbonized at about 2%/year over this period, while eliminating one major source of air pollution.  France became both cleaner and greener.

What's Germany doing with its Energiewende?  Its emissions reductions have stalled out.  We have industrial-scale economies which require industrial-scale solutions.  No country has ever decarbonized with unreliable energy of any kind, and given the lack of serious engineering proposals they never will.  "Renewables" are a front for the fossil fuel industry, to keep them in business forever.

there would appear to be not much point in 'banging on' about virtues compared to R.E.

One would expect the virtue that it's the only proven solution would be worth something, but with idiots who value feelings over facts and pursue romantic visions that cannot be turned into engineering reality we are headed for some very bad times indeed.

In the early 1970s, plutonium breeder reactors which produced essentially free fuel were thought to be the solution for providing more clean, economical energy to a growing U.S. economy.

And that was correct, even if the Clinch River reactor was the wrong vehicle.  As of some years ago the USA was sitting on enough depleted uranium to run the whole country for several centuries, and has no doubt accumulated more since then.

The Carter administration scotched the idea

Your timeline is wrong.  US advanced reactor research continued until 1994 when John Kerry was the key vote in favor of cancelling all advanced nuclear reactor research in the USA.  Carter had been gone for 13 years at that point.  Clinton was president.

because it is cheap to enrich fuel grade plutonium to weapons grade plutonium

Your physics is wrong.  "Enrichment" of plutonium is grossly impractical given that the bomb-grade isotope, Pu-239, is in the middle of heat-producing Pu-238 and extremely high spontaneous fission isotope Pu-240.  Isotopic separation by weight will give you one of the extremes, not the middle.  On top of this, the plutonium is fairly radioactive and the enrichment system will have to be decontaminated for maintenance.

studies even then identified terrorists getting their hands on fuel as the most significant risk to broadly-deployed nuclear power.

Used (not "spent") nuclear fuel has so much gamma radiation from Cs-137 and Sr-90 that it is effectively impossible to steal; anyone making off with it without many tons of shielding would die from radiation exposure before they could get far.  To do that at all, they would have to remove spent fuel from cooling pools or welded dry casks.  Given that both are well-guarded, this is effectively impossible in the west.  Anyone trying this would be captured or killed before they could do squat.

Terrorists are not stupid enough to have failed to figure this out.  This is why not one terrorist action in the WORLD has gone after nuclear fuel, but "environmentalists" harp on it day in and day out (their mission is to enstupidate the public and continue the use of fossil fuels indefinitely).

didn't they use much up in their depleted uranium spray in middle east aid?

"As of June 2000, the United States depleted uranium stocks (including USEC tails) contain about 480 000 tU." (source)  There's another 70,000 tons or so of used LWR fuel, the bulk of which is slightly-enriched uranium (~1% U-235) and 0.8% or so is transuranics including plutonium.

I'm surprised they are even talking breeder reactors

A number of people are.  They're called "realists".

Germany has a target of reaching 65 per cent renewable energy for its electricity network by 2040, but it is already capable of reaching such levels for shorter periods of time, as illustrated last week.

For “week 10” of 2019, the week finishing on March 10 (Sunday), Germany sourced 64.8 per cent of its electricity generation from renewables.

65% falls far short of what is required to halt CO2 concentrations from increasing; we need at least 80% across ALL sectors.  Aiming for 65% in the electric sector alone is planning to fail.

While the Green fanatics in Germany are planning to fail, France already proved that nuclear can provide 80+% decarbonization of a formerly-fossil dominant grid without actually aiming for that as a goal; it was an unplanned byproduct of replacing imported petroleum.  What Germany will never be able to do with "renewables", France accomplished by accident.

As for "why even talk breeder reactors", several reasons:

1. It takes about 0.8 tons of uranium to make 1 GW-yr of electricity, and about 0.32 tons to make 1 GW-yr of heat.  480,000 tons of DU fed to breeders would make 600,000 GW-yr of electricity, enough to power the entire US electric grid for about 1300 years, or enough overall energy to run the country for several hundred years.
2. We have plenty of lessons learned from the EBR-2 and IFR programs which are incorporated in new designs like the S-PRISM.
3. S-PRISM scales well.  It can achieve a breeding ratio of 1.22, with fissiles increasing at about 2.8% per year in the reference core (69.91 kg annual gain on 2458.8 inventory at beginning of cycle).  That's a doubling time of about 25 years.
4. It's a very good way to dispose of the inconvenient inventory of used LWR fuel and make it useful.
5. Last, talking about breeder reactors is planning to succeed.

REs are gaining ground at a very fast rate, as cleaner energy sources and will continue to do so, at least until new types of more efficient lower cost NPPs can be built and operated, sometime between 2060 and 2100?

Hydro plants, with very large water reservoirs (as big as the 5 Great Lakes) can be and will be used to store surplus Wind and Solar energy for extended periods. Wind/Solar will become the main energy sources to charge your electrified vehicles and feed your HVACs. Hydro will be used (as a back up e-energy source) during peak demand periods only, much the same as you would use batteries and/or stored H2.

Hydro and Wind energies potentials are often colocated and can be mated easily to produce clean lowwer cost energy 24/7 and 365 days/year.