GESS – Gravity energy storage systems

This blog is quickly evolving in an energy-related blog, to complement the stuff I write, mosty in Italian, on my Electric Mobility blog.

For no reason I could discern, my timeline showed today this story about Energy Vault, a Swiss-company which makes GESS, i.e. gravity-based energy storage systems. Being behind a paywall, the headline prompted me to check out Energy Vault, a company that popped on my radar last year. Lo and behold, I did find a couple of articles on PowerTechnology and Forbes which describe in some details EV’s business and technology.

gravity-based energy storage
Image courtesy of Energy Vault

The principle is very similar to Pumped Hydro: lift stuff to store energy as gravitational potential energy and lower it to release said energy; however what in PHS happens by pumping water up a reservoir and letting it fall down a chute to move turbines, EV accomplishes by lifting 35-ton concrete blocks with a multiple-necked 150mt crane and then lowering them.

The numbers look interesting (albeit, being the source mainly Energy Vault’s CEO, one is advised to use caution):

The systems are about three times more expensive to build than PHS, but about half as expensive as battery systems. They could therefore be slotted in between as far as application scenario go, with a sweet spot around 50MWh for $10M. However, once built, they cost very little to operate and their LCOS (Levelized Cost of Storage) is a fraction of that of any competing technologies, also due to their higher round-trip efficiency.

PHS is often criticized for its environmental impact (the main reason we’re not building it like crazy) but daresay that 150mt tall concrete towers are not my idea of landscape embellishments: I’m sure people who resist wind farms will welcome the addition of a couple hundreds of these towers to season-shift the energy one such farm produces.

Moreover, energy storage and delivery (unlike PHS) is not linear: the block you stack at the height of 1 meter stores 100 times less energy than the same block stacked at 100 meters, which means that when the tower is using 80% of its blocks, it is storing only 64% of its maximum energy capacity:

Another drawback might be the land requirement: if the system is capable of a full discharge, in that state all of its 5,000 blocks sit at ground level; assuming 2x2x4 m blocks, the footprint of a fully discharged single 35 MWh tower (assuming that Energy Vault’s algorithms can keep unused space at 5%) is about 19.000 square meters, i.e. 5,25 times more than a comparable capacity PHS.

Pay for the sewer

What is LCOE? The acronym stands for Levelized Cost of Energy, and is defined as the total cost including capital, maintenance, operations and decommissioning of a certain power generation facility divided by the total amount of electricity that will be generated by said facility.

A comprehensive guide to understanding LCOE can be found here.

As you can imagine, these are quite complex calculations which rely on assumptions; Wikipedia has a good overview of LCOE values for different generation technologies:

Source: Wikipedia

Which explains why coal and baseload natural gas are so popular, especially in developing countries: their cost are among the lowest, especially for fully amortized older plants.

This also explains why so many people (including yours truly) subscribe to Michael Liebreich’s view that existing nuclear facilities should be kept in operation for as long as it’s safe to do so, because they generate cheap and clean power.

However, there is one cost that is treated differently, biasing the comparison: while the cost of treating and disposing of nuclear waste is fully included in the LCOE figure for Nuclear, no such cost provision is made for fossil fuels for all the stuff that gets dumped irreversibly in the atmosphere.

Yet, the very reason we are discussing this is exactly the fact that for the past century the atmosphere has been treated like an unlimited, free-of-charge public sewer, and today we find that… it is not so!

So, many legislative proposals have been aired to create a tariff for the use of such sewer, according to the simple principle that the more you dump, the more you pay. As far as US legislation goes, a list of such proposals can be found here, and discussion is under way in the EU. For the purpose of this discussion, we can assume an average value of €30 per metric ton of CO2.

The effect of such tax would be different according to the current carbon intensity of electricity in a given country, and I have calculated it (using the carbon intensity data from OWID) for countries with low, medium and high carbon intensities:

As you can see, these offsets would be enough to make gas and coal much less competitive than they are now, especially if (as it is the case with nearly all proposals) the tax rate would be set to increase year after year.

Goodbye, Bellatrix

Today our lovely blonde bullmastiff had to be put to sleep. We knew the day would come when she was diagnosed bone cancer back in July, but it was a heart-breaking moment none the less.

Bellatrix (after the star, not the Harry Potter character) was the sweetest of dogs, despite her imposing size, always friendly even though a bit on the lazy side, if I may say.

She didn’t like chasing wild rabbits in our backyard and wasn’t a particularly creative escapist, although she didn’t mind following Sauron in his outings and, before we rebuilt the perimeter fence, she enjoyed her fair share of visits to the local dog impound.

Surely there will be a comfy sofa where you are now..

The benefits of a PV system


At end 2013 I installed on the roof of my house a state-of-the-art PV system: 15 kW peak power of monocristalline Sunpower panels and a PowerOne inverter, the best (and most expensive) then available.

Today I realized that the benefits of my system are twofold, and to describe them I will use this infographic.

It represents various unit costs of the kilowatt-hour (inclusive of all charges and taxes):

  • The blue bars represent the minimum and maximum value charged by the utility during each year.
  • The yellow dot is the weighted average of the bought kWh (total expense / number of kWh).
  • The red dot represents the unit cost of the consumed kWh: it differs from the above because I self-consume some of the energy I generate, but this quota varies each year, so the distance between red and yellow varies.
  • The blue dot represents the weighted average of the kWh cost net of the revenue from the sale to the grid of the non self-consumed quota of the energy I generate; also the distance between blue and red dots changes, because each year I sell a different amount of energy at a different rate.

To sum up, I have achieved two benefits from my investment:

  1. I cut my yearly electrical bill (from €3,500 to about 1,000); on top of this, I occasionally charge my electric car, but I have ignored this because of the time shift between energy generation (day) and charging (night).
  2. I greatly reduced the variability of cost of my electrical consumption: without the PV system, rates could vary by as much as 20 or even 30 cents, while this range is now less than 5 cents.

I benefici di un fotovoltaico


A fine 2013 ho installato sul tetto di casa mia un sistema fotovoltaico di 15 kilowatt di picco, con pannelli monocristallini Sunpower e un inverter PowerOne; si può dire che, per l’epoca, l’impianto era al top di gamma per qualità e prestazioni (e prezzo).

Oggi mi sono reso conto che i vantaggi di questo sistema sono in realtà più articolati di quanto può sembrare a prima vista, e per descriverli userò questa infografica.

In essa sono rappresentati vari valori di costo (comprensivo di spese fisse, oneri di sistema, accise ed IVA) relativi al kilowattora:

  • le barre blu rappresentano il valore minimo e massimo in ciascun anno del prezzo praticatomi dal fornitore
  • Il punto giallo rappresenta la media pesata del costo del kWh acquistato (totale spesa / totale kWh)
  • il punto rosso rappresenta la media pesata del costo del kWh consumato: è diverso dal precedente perché una parte dell’energia che genero la autoconsumo, ma siccome l’entità dell’autoconsumo varia (negli anni sono andato da un minimo del 21% ad un massimo del 40%, con una media del 32%) la distanza tra giallo e rosso cambia da un anno all’altro.
  • Il punto blu rappresenta la media pesata del costo del kWh consumato al netto dei ricavi dallo Scambio Sul Posto; anche la distanza tra punto rosso e punto blu varia negli anni perché variano sia la quantità di energia conferita in rete che la tariffa a cui questa energia mi viene pagata.

In conclusione perciò ho ottenuto due vantaggi:

  1. Ho ridotto la mia spesa annuale (da 3.500 euro a circa 1.000); a questo vantaggio negli ultimi due anni si è sommato il vantaggio di poter in parte ricaricare la mia auto elettrica, che però è minimo dato lo sfasamento tra momento di generazione (giorno) e momento di ricarica (notte).
  2. Ho ridotto la variabilità del prezzo totale di approvvigionamento; senza il fotovoltaico infatti, il mio prezzo di acquisto nell’anno poteva oscillare anche di 20 o 30 centesimi, mentre ora si contiene al di sotto dei 5 centesimi.

Se Kafka avesse avuto un’auto elettrica…

“Ciao Vittorio, domani sono a Torino da un cliente, ti va se ci vediamo a pranzo?”

“OK, vediamoci da Eataly, così tu carichi l’auto mentre mangiamo”

Il parcheggio di GreenPea, paradiso dell’elettromobilista?

Accanto a Eataly al Lingotto c’è GreenPea, il concept store di Stellantis tutto dedicato all’elettromobilità: il suo parcheggio conta ben 12 pole AC e 6 DC, tutte di Enel X.

Cerco di attivare una pole (resterò al ristorante un paio d’ore, un rabbocco mi è sufficiente) ma non ci riesco, e chiamo il call center che dopo breve indagine mi spiega che quelle stazioni sono private.

Inizialmente mi arrabbio per la mancata segnalazione ma poi mi accorgo che è colpa mia: lo stallo infatti NON È dipinto di verde e, anzi, c’è scritto “Riservato”, che distratto!

Poco male, mi sposto di qualche metro, per occupare lo stallo accanto ad una imperiale Porsche Taycan in carica.

Ma in effetti, non è tutto oro quello che luccica: delle 6 Fast, 4 sono fuori servizio.  Le ultime due però funzionano e visto che sono di un tipo che non ho mai visto prima, decido di provarle.

Nemmeno qui funziona la mia tessera e allora richiamo il Call Center con il quale ho una conversazione kafkiana: prima leggo all’addetta il numero di matricola della stazione e lei mi risponde che non esiste, poi mi dice che non le risultano stazioni Enel X in tutta la via dove mi trovo, per concludere con un poco lusinghiero: “Ma è sicuro che siano Enel X?” che ascolto, incredulo, mentre fisso con l’occhio sbarrato il loro logo.

Totale, rinuncio anche perché sono ormai in ritardo. Conclusi i miei impegni, prendo la via del ritorno chiedendo a PCC di far tappa al McDonald’s di Alessandria.

Quando ci arrivo, nonostante un bel segnalino verde su PCC, trovo la stazione fuori servizio.

Cerco in tutta fretta un’altra soluzione e decido di tentare la sorte alla Fast di via S.Giovanni Bosco che è a pochi kilometri: PCC me la segnala occupata (alla peggio aspetterò, mi dico) ma invece la trovo libera e funzionante.

Franz se la ride, ma i geni che hanno realizzato quel po’ po’ di parcheggio hanno poco da ridere…

The true reason for the birth of the Internal Combustion Engine

My current business life deals with the painful transition from the internal combustion engine to the electric powertrain.

Advocates of the statu quo cry buckets of tears over the lost jobs, the threatened competitivity of the western automotive industry, the diminishing prospects of cherished industrial skills, the industrial threat of China to mention but a few of the current, querulous lamentations.

Historically speaking, however, this is not the first time this industry underwent such a profound transformation – and for exactly the same reasons, as we will demonstrate.

At the end of the nineteenth century, London was the largest metropolis in the world, its population of over 4 million dwarfing New York and Beijing.

As it turns out, there were over 300,000 horse carriages in the city of London, needing therefore over 300,000 horses.

As the father (and longtime sponsor) of a youngster who spent 20 years competing in show jumping, I have a clear memory of what it takes to look after horses: feeding them, shoeing them but most of all … dealing with manure!

Horse Manure In The Grass Next To A Farm Stock Photo, Picture And Royalty  Free Image. Image 82607100.

A beautiful 400-kilo horse will gift its owner with about 25 kg of manure PER DAY! This means that the over 300,000-strong London equine population deposited about 7,500 tons of the product on its streets every day, making manure a 2,7 million tons-per-year problem!

I am sure the roads in Mayfair were spotless, but the rest of the city lived with walls of the stuff piling up to waist height. The situation had gotten so bad the well-off had started to leave London, until technology came to the rescue.

As we all know, the first “horseless carriages” were electric, but the immaturity of the electricity transport network and the immediacy of the gasoline proposition made sure mr. Benz’ invention (the internal combustion engine, or ICE, patented in 1887) prevailed instead, to the point in 1910 the number of “horseless” already equated “horsed” in New York.

The rest, as they say, it’s history.

So the first technology transition in automotive was driven by the need to resolve a rather mundane issue which made life miserable for everybody:

the incumbent techhorsesICE cars
drops too much refusemanureGHG gases
in a common resourcecity streetsthe atmosphere

Sounds familiar?


I social in questi giorni strabordano di gente che si lamenta del prezzo della benzina o del gas.

Lasciate perdere le cretinate pseudo-ambientaliste e guardate al vostro portafoglio: il costo dell’energia è una voce di spesa che anche nelle famiglie DOBBIAMO imparare a gestire.

Questo grafico rappresenta il mio costo dell’energia elettrica (100% rinnovabile):

  • linea blu = €/kWh tutto compreso tranne canone
  • linea rossa = €/kWh al netto del ricavo della vendita dell’eccesso di produzione del mio fotovoltaico.

Oltre al FV installato nel 2013 sto molto attento alle bollette e a fine 2020 ho stipulato un contratto a prezzo fisso che spero mi permetta di scavalcare l’attuale crisi.

In totale spendo circa €2,300 l’anno (ho consumi molto elevati) nei quali sono compresi circa 1,400 euro l’anno di consumi dell’auto che però prima mi costava 5.000 l’anno, solo di gasolio.

Tutto ciò per dire che, se uno ha voglia, è possibile fare qualcosa per “gestire” il proprio costo dell’energia (famiglia ma anche Paese), ma solo se si spostano i consumi verso l’elettrico: rimanendo ancorati al fossile si può solo… lamentarsi su Facebook!

Making simple things unnecessary complicated

Very happy about the performance of my newly-installed Starlink satellite Internet connection.

The dish was installed in less than an hour on a normal antenna pole on my roof (not by me, of course) with the cable running down through the roof to the room where the rest of the equipment is.

This placement is optimal, as there are no obstacles, and the dish can happily connect to the low orbit sat network with minimal interruptions.

I will be keeping the existing ADSL connection as a backup for a while, until I am sure everything works OK then, given the high cost of Starlink, cut off that wire and go totally untethered.

Unfortunately I will need to replace the powerline extender (config utility no longer supported on MacOS) needed to get a decent signal through our thick (in some places almost a metre!) walls, but that’s OK because I’m getting TP-Link extenders where the receiver supports up tp 7 remote extenders all on the same SSID.

Also I will need a switch (EDIT: someone suggested I get a buffer router instead), as the very basic Starlink router only has one network port, so all that is next week’s task, after I get the hardware.

Today’s task involved moving my wireless printers/scanners to the new network. Unfortunately the Starlink router doesn’t have the insecure but practical WPS button, so configuration must be made manually.


  • [on the printer control panel]
  • Setup
  • Wireless network
  • [from the list of available SSIDs] Select SSID
  • Enter password
  • OK

HP LaserJet M148DW

  • Connect USB cable
  • Launch HP Smart app
  • Select printer
  • Printer settings
  • Advanced settings
  • Networking
  • Select SSID
  • Enter password
  • The HP Smart utility apparently installs a new printer, as the driver has a slightly different name, so on each computer’s printer list, you’ll need to select the “new” one (and delete the “old” one to avoid confusion)

Took me 5′ to connect the Brother vs. over 2 hours for the H-P, including innumerable resets, reading of manual and perusing of support boards and an assortment of profanities.

Still unclear why the H-P printer control panel does not simply display a list if available SSIDs to associate, but it doesn’t.