Tesla Power Wall (Solar Energy Storage) ☀️>🔋>💡 💻 ... 💰❓

[nelsonic]

One of our Key goals @home is to be 100% Carbon Neutral and Energy Independent¹. 🎉
We will partly achieve this goal by having an array of Solar Panels #20 on the roof. 🏡 ☀️
This is fine during the day (and great on sunny days!) but as we all (hopefully) know useless at night! 🌃

If you're unfamiliar with Powerwall, watch: Fully Charged Tesla Powerwall 2: youtu.be/nWLzlrGGuxQ
The product page is quite informative and they have their own videos: tesla.com/en_GB/powerwall
A relevant/unbiased article on battery storage and Powerwall economics:
https://www.energysage.com/solar/solar-energy-storage/tesla-powerwall-home-battery/

While living in rainy London, I read many articles (both "media" and academic papers) and watched all the videos I could on energy storage² and concluded that at present the best price per kWh stored and value-for-money system (including the good App/interface) is Tesla's system! According to many reviews online the system has an excellent battery management system (BMS) which means that capacity does not decline significantly with age, so the "useful life" of 15-years

I have estimated that we will need Two Powerwall units for a total of 24kWh overnight capacity.

We will be ordering the units from Tesla in Portugal: https://www.tesla.com/pt_PT/powerwall

(obvs we are not going to put our battery investment outside the building...)


Specs in Portuguese:

Investment Payback Period?

Assuming that at "full capacity" we will drain the 24kWh stored in the Powerwall each night,
and a kWh price of €0.1649: https://www.edp.pt/particulares/energia/tarifarios/

And 200h/month (average) sunshine hours. (200 hours x 12 months / 365 days =) 6.58h/day

https://weather-and-climate.com/average-monthly-hours-Sunshine,braga,Portugal

On average it rains on 157 days each year. (note: most of the time it's not continuous rain like in England! more like intermittent showers and then the sky clears! Winter is actually relatively sunny!!)
https://weather-and-climate.com/average-monthly-Rainy-days,braga,Portugal

Conservatively, we should be able to collect enough energy from our PV cells to power the house during the day and fully charge the batteries for 200 days of the year.

Note: the sun still shines when it's overcast and solar panels still collect quite a lot of energy.
But for simplicity's sake, let's assume 200 days per year.

The "back of the envelope" calculations are: 200 days x 24 kWh x €0.1649 = €791.52 per year.
If the Powerwalls cost us €15k to install, it will take (15000/791.52 =) 19 Years to "pay off"!! 😮
(this does not factor our "cost of capital" which is currently 2% interest)

This is the "worst case" where there is zero sun for 157 days per year.
Obviously that does not happen. So a more realistic calculation is using 300 days:
300 days x 24 kWh x €0.1649 = €1187.28 per year. or (15000/1187.28 =) 13 Years "pay back".

Obviously these numbers aren't great from a purely financial investment perspective.
Investing the same cash in a portfolio of tech stocks will deliver a significantly higher return!!
So we need to "make the case" for "being the change we want to see" ...
and decide when to make the investment. (see "Next Action" below)

---

If you want to understand this calculation in more detail, consider watching this video:
Payback period for Tesla PowerWall 2 and 5kW Solar Array: 10 Years (conservatively)

https://youtu.be/Sc1rPLhkLQc

Baring in mind that we will have considerably more people in the house than the "average family"
I feel that 3 x 4KW is the minimum we should go for in terms of Solar Panels.
Note: Electricity Cost in PT is more than double that of Australia (11 cents/KWh vs 23 cents/KWh!)
So the cost of using "Grid" Power in PT is much higher see:
https://www.statista.com/statistics/418111/electricity-prices-for-households-in-portugal

The cost of Electricity might come down in PT in the future
given that "Wholesale" prices have dropped last year (because of the "renewables glut"):
https://www.pv-magazine.com/2018/04/12/portugal-renewables-are-driving-down-electricity-prices

But I would not "count" on the prices coming down in PT because EDP basically has a Monopoly ...
Further reading: https://smartexpat.com/portugal/how-to-guides/home/services/electricity

Next Action

• Determine when the appropriate time to make this investment decision is ...
  • baring in mind that we don't need to have the batteries installed at "launch" because nobody will book a stay @home on the basis of us having solar power storage and €15k is quite a lot to pony up before we need 24kWh over night!
  • my suggestion is that we re-visit this in April 2019 after we reach "capacity" and have had chance to gauge our energy usage over the winter months.

Note: my strong preference would be to use a Redflow ZCell (Zinc Bromide Flow Batteries)
Watch: Fully Charged Redflow ZCell batteries: https://youtu.be/4OHstY_kKUY
Read: https://www.greentechmedia.com/articles/read/can-redflows-home-flow-battery-really-beat-lithium-ion
Product Page: https://redflow.com/products/redflow-zcell
Sadly, at the time of writing (a) ZCell does not ship to Portugal (and there are no distributors in the country!) and (b) ZCells are more expensive than Tesla's Powerwalls.
But in "Phase Two" I will be using "Flow" Batteries for sure because Lithium is (relative) scarce!

¹Our plan is to combine Solar Panels with Energy Storage (initially in the form of Tesla Powerwalls, hence this issue) to capture enough energy during the day to power everything in the house and store enough to power to use at night. Once the Power Walls are fully charged we will supply the surplus solar power back to the Grid so we may end up being a net exporter of power. (TBD!)
We are fully aware that sun does not shine all year, so we'll be supplementing our on-premises Solar with Grid power from EDP Renewables edpr.com/en €0.16/kWh which comes from Hydro and Wind. Our reasoning for not relying 100% on the grid for power is three-fold: (a) demand for electricity is going to sky-rocket in the next 5-10 years with the accelerated adoption of electric vehicles (thanks Elon, Nissan/Renault, Hyundai, etc!) so we want to do our part in not straining the grid. (b) we are very keen on Energy Independence both from a resilience and security perspective. Finally, (c) We plan to have an Electric Smart Car (or similar "budget" electric city runabout vehicle, e.g: Zoe or Leaf ...) for people living in the house to use for short trips. This is a totally separate issue/decision, but it's "on the horizon" and we're planning for it!

²@dwyl we pitched to work with/for an Renewal Energy company and in addition to my natural curiosity for renewables I did a "deep dive" into the sector while preparing our proposal and pitch "deck" ... dwyl/hq#417 at the time this could have been my "Mastermind Specialist Subject" https://en.wikipedia.org/wiki/Mastermind_(TV_series)#Specialist_subjects ...
I still retain much of the info in memory, so feel free to "quiz" me on it if you are curious! 😉

[nelsonic]

Asked the HN community for help: https://news.ycombinator.com/item?id=18567051

[nelsonic]

Cross posted the question to: https://sustainability.stackexchange.com/questions/6974/is-telsa-powerwall-a-good-investment

[iteles]

So, so excited about making the investment in being carbon neutral and showing that it can be done 👍 This doesn't feel like a sustainable investment yet.
Agreed with revisiting in April 2019 to see if this is the best way to accomplish this, but thanks for opening the issue so we can capture research.

[iteles]

In light of the amount of energy we will need to power home and the fact that the local energy company is dragging their feet on the higher energy provision, I have been reading up on Tesla Powerwalls in more detail as we may well need as many as we can charge ourselves (solar panels to be discussed separately).

To be added to calculations

EDP costs

Our new calculations will need to factor in the costs that the energy company is looking to charge us for the installation of extra equipment for grid electricity, which we are waiting for.

Powerwall installation costs

We will also need to factor in the additional installation costs, which have gone up considerably since your screenshot two weeks ago 🤦‍♀️ as well as anything EDP charges us to connect to the grid (if this is a thing, need to research this next).

O custo típico de instalação varia entre € 1.100,00 e € 3.400,00. Isto não inclui a instalação solar, upgrades elétricos (se necessário), impostos, taxas de permissão ou quaisquer taxas de distribuição/de conexão que sejam aplicáveis. Esta estimativa inclui um imposto sobre o valor acrescentado (IVA) de 23%.

Accounting for maximum output

Lastly, Powerwalls have a maximum continuous output of 5kW, so even with 3 powerwalls (which we likely won't have the roof space to make efficient), there will be times when even on a sunny day, with air conditioning, showers and a couple of machines/stoves running, we'll need grid electricity.

Feed-in tariffs

Feed-in tariffs could be considered but are honestly negligible in Portugal as they are no longer subsidised for solar (since 2015), meaning they are among the lowest in Europe.
Source and http://www.res-legal.eu/search-by-country/portugal/single/s/res-e/t/promotion/aid/feed-in-tariff-tarifas-feed-in/lastp/179/ and http://www.res-legal.eu/search-by-country/portugal/tools-list/c/portugal/s/res-e/t/promotion/sum/180/lpid/179/

3-phase grid

In the meantime however, there is one thing I've been researching which hasn't yet been mentioned: Using Powerwalls with a 3-phase grid.

home will necessitate a 3-phase grid connection. In Portugal, the EDP grid is 3-phase but most small homes only get monophasic or 2-phase connections into the home itself.

So far, the information I have found points to this meaning that the Powerwall 2 can only be connected to a single phase:
http://www.solarmagec.com/home/625-tesla-powerwall-2-.html

Other than having 3 powerwalls, is there a way to overcome the inefficiencies of having one powerwall connected to a single phase, meaning that it will only be able to be used for that single phase rather than all 3 phases?

It looks like there are a few options:

• 1. Use one single-phase hybrid inverter with three consumption current transformers
  • These 3 CTs export enough power during a single phase to then offset the cost from the grid across the other 2 phases once it gets to the 3-phase energy meter
  • Only some single-phase hybrid inverters allow you to do this: "Single-phase hybrid inverters controlled by a Reposit controller can do this." (Configuration RGB House #3) ⬅️ requires more research into what's available in Portugal
  • Note: hybrid inverters are both solar inverters and battery inverters in one - this is likely to be unfeasible with a Powerall because of their built-in inverters (see option 2 below)

• 2. Use a three-phase solar inverter, one battery inverter with three consumption current transformers
  • Same as the option above but splits the solar and battery inverters rather than having a hybrid
  • I believe this split in inverters is would be what we would have to go with for a Powerwall specifically as they have in-built (battery) inverters
  • We need to finalise calculations but likely won't have enough roof space to fill 3 Powerwalls every day with solar energy
• Having the 3 CTs would mean we could use the battery inverter that's already in the Powerwall with the 3-phase meter from EDP
  

• 3. Use a three-phase solar inverter, three batteries each with their own battery inverters with three consumption current transformers

  • By far the most expensive option as 3 batteries/powerwalls are involved
  • Each battery is hooked up to a single phase
  • This would only make sense if we have enough solar panels to fill all 3 batteries regularly
    

• 4. Use a micro-inverters on each solar panel, one battery inverter with three consumption current transformers

  • This is the same as option 2, but each solar panel has its own micro-inverter - a cursory search show this option to be quite a bit more expensive in Portugal and require more maintenance
  • There's only one read advantage in that if a single solar panel in a string is shaded, you don't lose the power from the others in that string
  • You also don't have the high DC voltage running through your house to the inverter so there is a bit more safety (though this shouldn't be an issue with good installations)
    

See here for more on micro-inverters:

Note: A 3-phase hybrid inverter is not an option for the Tesla Powerwall 2 because it is an AC coupled system.

[nelsonic]

⚠️ New Info: EDP Saga to Increase Power Supply! 😞

A big part of preparing the house to accommodate more people is increasing power supply from the "domestic" 30 Amp (6.6kVA) to a commercial 90 Amp (19.8kVA) power so that multiple people can cook simultaneously and/or use the Air-conditioning without the power cutting out ... ⚡️

Sadly, a task we were assured would be "straightforward" when we started this project is turning out to be anything but that! EDP, the company that basically owns a Monopoly on energy infrastructure, is now saying that they need to install a "PT" ("Posto de transformação" i.e. high tension transformer box) on our property that will occupy 5m (width) x 3m (length) x 2.5 (height) ...
these are the examples we've been given: postos-de-transformação

The "technician" from EDP claims that it's not a matter of giving us 3 x 30 Amp cables from the existing transformer to our property, that we must have this hideous eyesore on the property if we are to increase the electrical capacity of the house ...

How Much Power do We Need...?

We calculated that our PEAK power consumption could be well in excess of the 30A the house currently receives from EDP; in fact we could easily exceed 100 Amps just by having the Air Conditioning units on simultaneously and using the Oven and Hob to make food ...

Our Google doc spreadsheet for calculating PEAK power consumption is:
https://docs.google.com/spreadsheets/d/1_87JQzwjoNmvGEIQ9PJwo3jtNqoDnAvqQTfTchN3UuQ

Our baseline consumption will be around 6.725 kWh including all the essentials such as Lights, Water heating, Laptops, Fridges/Freezers and Security systems.
This is the "good news" ... i.e. we can open the house to a handful of people without increasing the power in the house. However if we switch on any other high-energy appliance
(e.g: a Kettle, Oven or Heater) it will overload the system and cause a blackout in the house.

We need to increase the power in order to be able to use the "nice things" e.g AirCon/Heating, Dish washers, tumble driers, heated pool, spa and sauna! 😮

30 Amp x 220 Volts = 6.6 kW

Using Ohm's law we have a simple formula for calculating Power and/or Current:
If the stated Amperage (I) of the house is 30A (which is perfectly acceptable for a single family dwelling),
And the voltage is 220V @ 50 Hz in Portugal.
We can multiply the I x V to get Watts ... 6.6 kW in our case.

https://www.rapidtables.com/calc/electric/Amp_to_Watt_Calculator.html

If your high school physics is a bit rusty, see: https://www.wikihow.com/Calculate-Wattage

How to increase electrical capacity?

The EDP website makes it look/sound like it's relatively easy to increase the electrical capacity:
https://www.edp.pt/particulares/apoio-cliente/perguntas-frequentes/novo-contrato/o-que-preciso-de-saber-para-contratar/o-que-e-a-potencia-contratada-e-qual-devo-escolher/faq-4676

Bi-horária ("Off-peak" Tariff) €0.0974 / kWh

https://www.edp.pt/particulares/apoio-cliente/perguntas-frequentes/tarifarios/o-que-preciso-de-saber-para-contratar/o-que-e-a-opcao-horaria-e-qual-a-melhor-para-mim/faq-4823

Probably the easiest/best way of viewing EPD's pricing table is not on the EDP website,
but rather on the "Light Shop" comparison website:
https://lojaluz.com/fornecedores/edp/tarifas/preco-kwh

€0.0731 / kWh Off-peak

Can we use Cheaper Off-peak Power to Charge the Powerwall? €0.0731/kWh

If you need a succinct video explaining this, see: Charging the Tesla PowerWall 2 from grid:

https://youtu.be/xCKQ1LQCyX0

---

The Future: Increasing Power Consumption

It's virtually guaranteed that (national/aggregate) power consumption is going to continue rising thanks to the adoption of electric vehicles for personal, public transport and commercial use.
There are electric-only parking spaces in most shopping malls in Portugal and a charging station 100m from the Braga house; mainstream adoption is coming.

Look no further than the most recent Geneva Motor Show where there were more Electric vehicles than "ICE" https://www.wired.co.uk/article/electric-cars-geneva-motor-show-2018
e.g: Jaguar i-Pace, Hyundai Ioniq & Kona/Kauai, VW E-Golf, Merceds EQC, Audi e-Tron, Porsche Mission-E, Mini Cooper Electric, Honda Clarity, Nissan Leaf 2, Mahindra KUV100, BYD e6, etc.
watch Fully Charged Geneva 2018 coverage: youtu.be/HfWOTMz5HUI

The increased national consumption will inevitably put pressure on supply
meaning that power failure is likely even if (regardless of whether) we increase our supply amperage.
Additional signs that power consumption trend will continue:

• https://en.wikipedia.org/wiki/Tesla_Gigafactory_Europe
• https://futurism.com/elon-musks-former-employee-is-building-a-european-rival-to-teslas-gigafactory

https://en.wikipedia.org/wiki/World_energy_consumption

---

Power Cuts?

Electrical power is something most people who live in "developed" countries take for grated ...
Many energy rich countries use ten times more power/electricity per person than in developing nations.
https://en.wikipedia.org/wiki/List_of_countries_by_electricity_consumption (sort by average kWh/capita)
Note: basically ignore the Nordic countries who have extremely cold winters
and use their abundant Geothermal energy to heat their homes ...

Notice how average energy consumption (per person) in the USA is 12 Million Watt Hours (12,071 kWh)
Whereas in the UK 4,795 kWh and Portugal 4,245 kWh per person per year respectively.
That's almost 3 times as much power use. This might be due to in part to norther US states skewing the numbers because, like the Nordic countries (which lead the power consumption table by a wide margin) heating homes in the freezing winter takes a lot of energy! But it also has a lot to do with the southern states using Air Conditioning 24/7 in the summer which uses obscene amounts of power! 💸

People in countries at the "bottom of the pyramid" essentially have almost no access to electricity,
in many cases they use diesel generators which are not counted as "grid" generated electricity.

The fact is that for most humans around the world power cuts are still a regular occurrence in 2018
https://www.worldatlas.com/articles/power-outages-in-places-of-business-around-the-world.html

Portugal has a reasonable reliably electrical supply (due mostly to the sustained investment in Hydro during the Salazar years and massive investment in Wind over the last decade)
Sadly, power supply is still not 100% guaranteed. see: http://portugalresident.com/edp-cuts-all-the-time
And in 2017: http://theportugalnews.com/news/lisbon-metro-in-the-dark-following-power-cut/42162

The average is 2 minutes per month of power cuts. Not an issue if all you're doing is watching TV,
but if your house has critical security systems that require power such as Doors and servers/NAS which will suffer if power is "yanked", we basically need to re-think the priority of Tesla Powerwall ... 💭

Use Powerwall as Backup Power Supply?

Watch this video: 5 Awesome (and Not-so-awesome) things about the Tesla PowerWall 2

https://youtu.be/5wFXCrfM140

Must remember to factor 30% degradation of battery efficiency into calculations. (see below).

Tesla Powerwall 2 Local Gateway API

The

According to this GitHub repo: https://github.com/vloschiavo/powerwall2
The Tesla Powerwall 2 runs a Linux server with a read-only web UI
that any web browser can connect to on the home/internal network:

This means that:
a) Anyone in the house can view the current energy consumption in the house without needing to download the Tesla App. Therefore everyone can be a "conscious consumer" and avoid wasting energy.
b) We can display the current energy consumption (via both the @home App and on strategically located e-ink displays) for each room in the house in real-time. Play a warning sound/alarm on each connected device when we are approaching the maximum power consumption for the house.
That way everyone can know when we are reaching our max load point and turn off that "extra" induction hob or AirCon unit!

Notes

• Solar panels still work 10-20% on cloudy days:
  https://cleantechnica.com/2018/02/08/solar-panels-work-cloudy-days-just-less-effectively/
• Electrical Load Management: http://large.stanford.edu/courses/2010/ph240/malone1
  read this to understand load shifting.
• Tesla installation process:
  https://www.tesla.com/support/energy/install/powerwall/powerwall-installations
• Powerwall JSON API:
  https://teslamotorsclub.com/tmc/threads/powerwall-2-gateway-api-documentation.112341/
• Induction hob power consumption:
  https://forums.moneysavingexpert.com/showthread.php?t=5652536

Micro Solar Generation Feed in Tariff (FIT) €0.095 / kWh

If we install 8kWh of Solar power and have fully charged Powerwall we can take advantage of the FIT to turn back our electricity meter. If we buy off-peak at €0.0731/kWh and use it during the peak time we could use the Powerwall for "load shifting".
We could even sell during peak time as "arbitrage", but this is unlikely to be profitable as it won't offset the cost of the Powerwall depreciation.

https://www.pv-magazine.com/2018/01/24/portugal-announces-fit-distributed-solar-generation-fit-of-e95-mwh-for-2018/

Next Action

• Calculate payback period for 2 or 3 Powerwall units.
  • Charging from the grid at night on cloudy/rainy days at €0.0731/kWh
  • Useful life of batteries 10 years.
    (even if they last longer, we should 100% depreciate by the end of the "useful life")
  • Factor in 30% battery efficiency degradation over 10 years.
  • Factor in "round trip efficiency" of 87% ... see:
    • https://en.wikipedia.org/wiki/Tesla_Powerwall#Technology
    • "real-world AC-AC round trip efficiency drops to 87%"
      http://www.catalyticengineering.com/top-ten-facts-about-teslas-350kwh-powerwall-battery/
• Contact Tesla Portugal and ask them for the following info:
  • Price and timelines for installing Two Powerwall units with grid charging/backup functionality.

[nelsonic]

Powerwall Long-term review: https://youtu.be/6s6kN9Ezws0 (18 December 2018)

[nelsonic]

https://www.tesla.com/findus/list/stores/Portugal

El Corte Inglés Av. António Augusto de Aguiar 31
1069-413 Lisbon

@iteles do we have time to go past Tesla on our way home today?

[iteles]

@nelsonic Only if we delay our fire safety meeting to tomorrow (perfectly doable) as otherwise by the time we get to Braga it will be dark (sunset at 17h30).

[nelsonic]

@iteles I feel that getting a "face-to-face" meeting at Tesla (even if it's just with a "sales rep")
is worth the effort. To be clear: El Corte Inglés is pretty much only a 30 mins "detour" from our path.
So we could still make it to Braga by 17:00 if we leave Lx no later than 13:30
https://goo.gl/maps/9TNwoBvQ6LU2

What time have you agreed with the fire safety people? (separate issue but related to today...)

[iteles]

@nelsonic Your lunch will finish at 13h00, so I feel it might be quite tight to make it to Lisbon before 13h30, let alone see the Tesla people first.

I agree with you it's important, so we should delay our fire safety meeting til the end of the morning tomorrow.

This also means we can finish the electrical plan tonight/tomorrow morning and then run through it in person with the electrician tomorrow too.

[nelsonic]

@iteles sounds good.

[nelsonic]

We visited the Tesla stand in Lisbon. 😍
The sales rep informed us that no Powerwall deliveries have been in made in Portugal yet. 😞
And that the waiting list was estimated at more than a year. 😢
I'm glad we went. At least we know we cannot rely on Tesla for our backup power. ✅

[iteles]

The proposal we have been given to include batteries

For 2 sections of the roof

24 x 315W panels and 9kW of storage via two 4.5kW batteries.

We have been quoted € 7 182,00 (plus VAT) for the setup without batteries and €11 944,80 (plus VAT) with batteries** (this includes a different inverter and the batteries themselves).

Battery setup = €4, 762.80 more expensive or €5,858.24 including VAT.

For 3 sections of roof (if this is even possible)

32 x 315W panels and 12.6kW of storage via two 6.3kW batteries.

We have been quoted € 10 176,00 (plus VAT) for the setup without batteries and €16 981,00 (plus VAT) with batteries** (this includes a different inverter and the batteries themselves).

Battery setup = €6,805 more expensive or €8,370.15 including VAT.

Spec for the proposed batteries

Triple-Power_cn-batteries-by-SolaX.pdf

[iteles]

@nelsonic I really want to invest in these batteries as an MVP to test out the ability of being energy-independent for a portion of the year.

According to the calculations you laid out in the original post here:
200 days x 12.6 kWh x €0.1649 = €415.548, which means it would take us 20.14 years to pay off the batteries (far longer than their warranty). 😞

From a purely financial perspective, this doesn't make sense.

However, I feel that if we want to make a true effort to be energy conscious and 'green', this is the time. If we want to extend this beyond 'home' in the future, having hard data from this place is the only way to convince anyone who may want to join us in the future that this is a worthwhile endeavour. Of course I am under no illusion that people outside of the two of us will appreciate the investment for now!

Secondly, the batteries provide us with a failsafe. Should there ever be a power outage, we can still run basic security systems from the batteries.

[iteles]

@nelsonic Given this is a big investment I wanted to check: Is this thumbs up an acknowledgement of my thoughts on this or an agreement we should give the go-ahead for the batteries?

[nelsonic]

@iteles we have already agreed that the Batteries are a security feature.
The EDP "box" with the main power cutoff is on the street outside the house.
Anyone with a 3D-printed plastic key can get into the EDP box and cut the power to the house.
by doing this they disable all our security systems and can access the house unimpeded.
I'm sorry I did not write a more conclusive reply when I checked my notifications on my phone this morning. But yes, as per our original budget, we are getting the batteries.

[nelsonic]

Sadly Tesla Power Wall is still unavailable in PT. 😞
Closing as we now have "Solax" batteries installed. ✅
Re-open or open a fresh issue if/when we buy our Tesla car ... 👍