What is the point of having it power charging stations instead of just having it power the trains themselves? The regenerative braking energy is by definition less than the energy needed to...
What is the point of having it power charging stations instead of just having it power the trains themselves? The regenerative braking energy is by definition less than the energy needed to accelerate the trains. That’s just how thermodynamics works. It seems to me like this system just adds unnecessary complexity on top of normal regenerative breaking.
Per the article, it does: As for why it isn't used to fully power the trains: Considering the typical price of electricity in Spain, they make more money by selling the electricity than they save...
What is the point of having it power charging stations instead of just having it power the trains themselves?
Per the article, it does:
One-third of that powers the trains; the rest provides juice to station amenities and a growing network of EV chargers.
The transit agency has installed three inverters so far; 13 more are in progress. Once they’re all in place by the end of September, it expects regenerative braking to provide 41 percent of the energy needed to power the trains [...]
As for why it isn't used to fully power the trains:
MetroCHARGE has cost about $8.6 million (7.8 million euros), TMB expects to recoup that in four to five years through energy savings and revenue from the charging stations, where drivers pay about 33 cents per kilowatt-hour that flows into their cars.
Considering the typical price of electricity in Spain, they make more money by selling the electricity than they save by just using it to power the trains, so a faster return on investment.
Regenerative braking has been around in subway trains since at least the 1980s, typically used to return the power to the third rail to power other trains. Better systems and inverters are allowing it to be put to more uses now.
This is what I still don’t understand. They are effectively buying the energy at market rates, processing it through train brakes, and selling it to consumers. They can skip the middleman and just...
The they make more money by selling the electricity than they save by just using it to power the trains, so a faster return on investment.
This is what I still don’t understand. They are effectively buying the energy at market rates, processing it through train brakes, and selling it to consumers. They can skip the middleman and just buy it from the utility and sell it to consumers.
Let’s break it down. You get X energy back from the train brakes. X is strictly less than the total energy input of the trains because of thermodynamics. You can spend X in whatever way you want. According to your quote of the article, they spend one third each on trains, station amenities, and car charging. I will ignore station amenities because it doesn’t change my reasoning.
There are three separate but related infrastructure costs. First, the cost to outfit the trains with regenerative brakes. Second, the cost to build public car charging infrastructure. Third, the inverters and whatnot to connect the regenerated power to those car chargers. My issue is with that third infrastructure cost. Let’s take as a given that the agency has already decided to spend the cost for regenerative brakes and car charging infrastructure. They are simply deciding if they should connect the two systems.
If the company takes all of X power and spends it on car charging infrastructure, they now have to buy that same quantity X power from the utility to accelerate their trains. Remember, X is ALWAYS less than the power needed to accelerate their trains. So their total energy input from the utility is existing costs plus total car charging power.
If they feed X back into the train system, they reduce their utility costs by X. They then have to buy the power for car charging from the utility. The total power they need to buy from the utility is exactly the same as the previous scenario. There is no excess energy.
For both scenarios, the infrastructure cost to collect the brakes to the car chargers doesn’t change energy usage at all. It doesn’t change ongoing costs at all. It is just a waste of infrastructure investment.
The entire point of an electrical grid is it doesn’t matter where the energy comes from or where it goes to, as long as it is balanced. All the train company needs to do is dump the energy back into the third rail like metros have been doing for a long time. Adding car chargers is great, but connecting those chargers directly to regenerative brakes is a waste of time, cost, complexity, and possibly energy if there are inefficiencies.
That got pretty long winded, but I hope it is easy to follow. I am all for car chargers, but connecting them to a specific source of power instead of the grid seems like a waste. They will literally never recoup the investment cost because that part of the investment doesn’t change their expenses or income at all.
My personal suspicion is that there is somehow government money involved. Something like this ticks two boxes on some green energy grant application. Plus if you're not the one paying for (part...
My personal suspicion is that there is somehow government money involved. Something like this ticks two boxes on some green energy grant application. Plus if you're not the one paying for (part of) the costs, that might change the maths to the point where this is the most logical.
What is the point of having it power charging stations instead of just having it power the trains themselves? The regenerative braking energy is by definition less than the energy needed to accelerate the trains. That’s just how thermodynamics works. It seems to me like this system just adds unnecessary complexity on top of normal regenerative breaking.
Per the article, it does:
As for why it isn't used to fully power the trains:
Considering the typical price of electricity in Spain, they make more money by selling the electricity than they save by just using it to power the trains, so a faster return on investment.
Regenerative braking has been around in subway trains since at least the 1980s, typically used to return the power to the third rail to power other trains. Better systems and inverters are allowing it to be put to more uses now.
This is what I still don’t understand. They are effectively buying the energy at market rates, processing it through train brakes, and selling it to consumers. They can skip the middleman and just buy it from the utility and sell it to consumers.
Let’s break it down. You get X energy back from the train brakes. X is strictly less than the total energy input of the trains because of thermodynamics. You can spend X in whatever way you want. According to your quote of the article, they spend one third each on trains, station amenities, and car charging. I will ignore station amenities because it doesn’t change my reasoning.
There are three separate but related infrastructure costs. First, the cost to outfit the trains with regenerative brakes. Second, the cost to build public car charging infrastructure. Third, the inverters and whatnot to connect the regenerated power to those car chargers. My issue is with that third infrastructure cost. Let’s take as a given that the agency has already decided to spend the cost for regenerative brakes and car charging infrastructure. They are simply deciding if they should connect the two systems.
If the company takes all of X power and spends it on car charging infrastructure, they now have to buy that same quantity X power from the utility to accelerate their trains. Remember, X is ALWAYS less than the power needed to accelerate their trains. So their total energy input from the utility is existing costs plus total car charging power.
If they feed X back into the train system, they reduce their utility costs by X. They then have to buy the power for car charging from the utility. The total power they need to buy from the utility is exactly the same as the previous scenario. There is no excess energy.
For both scenarios, the infrastructure cost to collect the brakes to the car chargers doesn’t change energy usage at all. It doesn’t change ongoing costs at all. It is just a waste of infrastructure investment.
The entire point of an electrical grid is it doesn’t matter where the energy comes from or where it goes to, as long as it is balanced. All the train company needs to do is dump the energy back into the third rail like metros have been doing for a long time. Adding car chargers is great, but connecting those chargers directly to regenerative brakes is a waste of time, cost, complexity, and possibly energy if there are inefficiencies.
That got pretty long winded, but I hope it is easy to follow. I am all for car chargers, but connecting them to a specific source of power instead of the grid seems like a waste. They will literally never recoup the investment cost because that part of the investment doesn’t change their expenses or income at all.
My personal suspicion is that there is somehow government money involved. Something like this ticks two boxes on some green energy grant application. Plus if you're not the one paying for (part of) the costs, that might change the maths to the point where this is the most logical.