Powerwall 2 Time Base Control Algorithm

Since PW2 (Tesla Powerwall 2) introduced the new TBC (Time Base Control) algorithm, I had a great difficulty in trying to understand the actual algorithm, especially during shoulder period. Consulting forum (such as here and here) only confuses me further, especially when the forum started to discuss incentives and local regulations (US centric). This, however, makes me appreciate the herculean task for PW2 engineers. You simply can't make everyone happy.

The ever evolving nature of PW2 algorithm (typical Tesla my guess), makes any 'User Manual' writing attempt a futile exercise. Reverse engineering the algorithm also requires different permutation, such as state of charge, how much PV production during the day, etc that can affect the PW2 behaviour.

Still, little documentation is better than nothing. Since I don't have the stamina to try all permutations, I deliberately write down as much details below (trying to be as neutral as possible, i.e. no incentive and regulation jargon):

Off-Peak Cost Saving Mode:
In this mode, PW2 does try to aim a certain State of Charge prior entering shoulder and peak period (by charging from the grid if necessary). Based on the limited 2 days experiment (see screenshot below), this State of Charge (SoC) is not a fixed value. How does PW2 decides this SoC level? Me no idea.

Also, some charge from PW2 is used during off-peak period (see bubble number 1 in the screenshot). I don't know how PW2 decides when to use the battery. One thing for sure: it mostly uses the grid to conserve the SoC for peak period.

I haven't tested what happens when you have solar production during off-peak period.

Shoulder Cost Saving Mode:
Now this gets interesting. In day 1 of the test (see bubble number 2), my PW2 behaved as I wanted it, that is: no grid activity (i.e. to behave exactly like peak). Too bad I didn't record the SoC, but I remembered it was roughly 40-ish percent at this stage.

In day 2 (see bubble number 3), my PW2 started to be less agressive (despite higher SoC compared to the previous day), i.e. grid activity is allowed by importing and exporting. Uh oh, for me, who has a power provider that value exported PV close to zero (yup, zilch, nada), this is bad news. Also, why PW2 allows a significant grid import when the battery SoC is relatively high (roughly 60-ish percent at bubble number 3). Is this because PW2 hasn't learnt that I don't usually use lots during peak period? My guess at this stage, this is due to the PW2 algorithm is based on US-centric market, where they have incentive to export PV to the grid (such as net metering). Pure guess though.

At this stage, my panic mode was on, and I switched it back to 'Self-powered' mode (as commented by the red line), which explains why the screenshot is no longer showing peak/off-peak on the 14-th May, and also 100-ish watt grid consumption during solar production after the switch (see my previous post).

After 14th of May, I changed PW2 to 'TBC Balanced' mode and extended the peak period to also cover shoulder (i.e. only peak and off-peak, no shoulder). This has worked perfectly for me, but...

In the last 2 days, I haven't had enough PV production to cover my shoulder and peak. This has caused me grief since now I need to import from the grid during peak period (see bubble number 4). So, I changed it to TBC 'Cost Saving' mode, thinking that PW2 would've charged from the grid during off-peak to cover my PV production shortfalls. To my surprise, it didn't (although the SoC was just a tad below under reserve).

So, here I am, finding another quirk in PW2 algorithm. If you don't set the shoulder period,  PW2 will not charge from the grid (despite the PW2 SoC at the reserve level). What the??

In the screenshot below (see bubble number 5), you can see that as soon as I bring back the shoulder period, PW2 behaves as I expected again by start charging from off-peak grid (I've found this by coincidence).

In short, for those who want exporting to the grid at the very lowest priority, I recommend to use 'TBC Cost Saving' mode with a wee bit of shoulder period (just enough to activate 'charge from off-peak grid mode').

PS: Peak period behaviour is consistent as expected, i.e. no import from the grid.

My Observation of Tesla PowerWall2

My Tesla Powerwal 2 (PW2) summary, freshly installed just 3 days ago:
[UPDATED 7 May 2018: see point 6 below]

1. PW2 can be installed in multiphase (mine is 3-phase). PW2 monitors each phase current using Current Transformer (installed by the installer of course).
2. PW2 basically absorbs all your solar power instead of injecting them back to the grid. What is worth to be noted, although you have load on different phases, the PW2 will compensate this so that your electricity meter reads export as 'zero' (since Australian domestic electricity meters don't care on which phase you're consuming). So, in my example, I was using an induction stove top at 1000 Watts on the 'white' phase, and the PW2 injecting back to the grid at 1000 Watts at 'red' phase, resulting net zero export. To mention the obvious, PW2 inverter maxed out at 5kW power.
3. Non-noticeable transfer time when the grid has failed. I've tested this 2 times: at first attempt, the solar panel inverter anti-islanding has to reset (causing the solar power to cut for about a minute). In the second attempt, the solar inverter didn't trip at all (as if nothing happen). I'm definitely impressed on this one. To mention the obvious, only 'red' phase of my home is backed up by PW2. Other phases are not. Now I can officially welcome mad max scenario!
4. During daytime (when the solar panel is active), I've noticed PW2 constantly draws around 100 Watts from the grid, but not at night time. I can't find any info in the internet on the why, yet. My guess, PW2 requires power for its own functionality and ineffeciencies in converting AC to DC and somehow only compensates during daytime? 
5. It is also worth to be noted, unlike the Tesla cars, users can't set the maximum charge level on PW2. My guess, Tesla is now extremely confident that this is no longer required. Maybe combination of newer chemistry and internal software to limit when required during hot days?
6. My particular one consistently under report kWh used and exported to the grid by roughly 15 - 20% (compared to my grid provided meter). However, the solar energy kWh is spot on (compared to my soalr inverter kWh measurement). No idea the why. Anyone experiencing the same issue?

What it doesn't do and I wish Tesla will update this functionality sometimes in the future:

• Change the timing on the 100-Watt constant draw from the grid. I wish this is user configurable. For example, to draw this at night time, or to use solar panel instead. For me who on Time of Use plan, this total of 1kWh on daytime is something I'm not willing to pay the grid for. Call me stingy.
• Ability to charge PW2 from the grid during off-peak via the app. At the moment PW2 only absorbs power from solar panel. Since my solar panel is not enough for my usage, I'd love to have the ability to get cheaper electricity at night to be used by my household during peak time. Quicker ROI anyone?

Now, to how I use the Tesla app:

• Once the installer enter account holder details via the installer page, your PW2 will be immediately visible on the Tesla app (you'll need wi-fi router for PW2 to connect to Internet). I haven't accessed the PW2 directly via the ethernet router (no reply). Will try again next time.
• The visualisation of the app is indeed very useful. For a data hoarder like me, the visualisation has altered my energy usage. For example, now I know my inverter reverse cycle Air Conditioner doesn't have linear energy consumption (I thought it does). It has step changes, i.e. 2.4kW at full power, then 1.5kW, then 900 Watts at lowest power (in cooling mode). When the PW2 is low in charge, I deliberately turn off my air-con to minimise grid usage and happy with slightly higher room temperature (but still comfortable). My guess, sometime in the future, all home appliance will talk to each other (via ethernet router, just like the PW2 at the moment) and have AI (Artificial Intellegence) based on user preference on how and when to consume energy (whether to save energy, or maximum comfort).

So here is my data, just 1 day after it's being installed (grid data not shown for clarity):

The data above is definitely not my average day. I had to travel 120-ish km on that day, so most consumption gone to EV (I'm guessing around 18kWh).

Now my debt has increased significantly again (thanks to PW2 as an expensive toy), so the family now have to be content living from boiled water and salt. At least we have a good-lookin' dead weight on the wall now (wheel added in MS Paint to make me feel less guilty by the dead weight):

[UPDATE 12 Oct 2020 for 2018 annual figure]:

Secondary Battery System for Camping Trip

So, I've done a few research into 4WD battery system (dual battery system) since I had few colleagues asking me what secondary battery system is best for their 4WD camping-bush-trip. The more I look into this (in Australian market), the more I am impressed of how expensive these battery systems are. By simply looking into REDARC website, one should wonder, why on earth battery management system can cost in the order of thousand of Australian dollars (excluding batteries). There is nothing 'smart' with lead acid batteries! Boy oh boy!!

It is true that you need some charging management system so that your car is protected from over-loading in charging deep-cycle batteries. But, do you really need to spend thousand dollars computerised battery charging system?

"People don't buy for logical reasons. They buy for emotional reasons" rings so true in this 4WD market. Just looking around the car park at my work, people spent literally tens thousands of dollars to upgrade their 4WD (or cars, generally). Nothing wrong with that of course, here is me being hypocritical, willing to spend hundreds of bucks accumulating second-hand batteries to satisfy my emotional needs! Luckily I can't afford those yet.

Anyhoo, for those who want to go camping trip, and simply need pure battery function (no emotion involved), then I got a surprise for you! Please don't buy those off-the-shelf power pack (the like of ArkPak) with batteries from camping shop, they are a RIP-OFF!! If you can tinker a bit, then you can save literally hundreds of dollars!!! (yup, that's right, 3 exclamation marks)

Here is my proposal (no need to tinker your car wiring either):

Component list:

1. Cigarette Lighter 12V plug from Altronics (click here)
2. DC – DC converter (to be set to 13.8 Volt and 5 Amp). Get it here.
3. 12V 100Ah lithium battery
4. Low voltage protection switch
5. 12V cigarette lighter socket

Technical note:

• The setup above is charging the lithium battery one way only, i.e. no current back flow from lithium to your car system.
• Since you plug it to your car's cigarette lighter socket, it ONLY charges when you turn the engine on. Do keep it connected all the time to ensure the battery charged, always.

The whole lot above can give you up to 1000Wh of electricity and cost less than AUD1000. Forget those expensive ArkPak or the like that can cost you more than double of what I proposed above. Well, yes, you do need to tinker a bit, but hey, I'm talking to those who are adventerous right? The electric is so simple: red to positive, black to negative. Come on, it's not rocket surgery (or brain science)!

If you feeling even more adventerous, you can replace the supply (item 1 and 2) with solar panel (minimum 60 Watt) with MPPT module. For the MPPT, I can recommend Genasun. Please, please, please, simply skip crap 'charge controllers' and save yourself troubles.

Happy camping!

Proposal Elektrifikasi Pedalaman Indonesia

Pedalaman Indonesia masih banyak yang belum terjangkau oleh listrik karena infrastruktur yang masih minimal. Memasang jaringan kabel listrik ke daerah pedalaman masih sulit dan mahal.

Biasanya, daerah pedalaman menggunakan genset (generator set). Nah, menggunakan BBM untuk listrik sangat boros dan mahal. Contoh, hanya untuk penerangan dan mengisi ulang baterai, penduduk ini [2] menghabiskan Rp50,000 per malam . Boros bukan?

Belum lagi masalah logistik bahan bakar minyak ke daerah pedalaman. Semakin terpencil, semakin sulit untuk mendapatkan bahan bakar. Contoh, di daerah Timur Indonesia, bahan bakar saja sampai dikorupsi [3]. Waduh, sudah jatuh, tertimpa tangga pula!

Nah, kebanyakan dari kita (yang bisa akses internet dan baca) sudah tahu, bahwa panel surya jauh lebih cocok untuk elektrifikasi daerah pedalaman. Dengan tidak perlunya bahan bakar (kecuali sinar matahari), semua masalah di atas, ya teratasi!

Tapi, kenapa kita (Indonesia) masih sulit menerapkan sistem panel surya ke daerah pedalaman? Instansi pemerintah sudah banyak yang mencobanya [4], dan juga organisasi non-profit [5], dan banyak lainnya. Tapi, tetap saja masih banyak desa dan daerah pedalaman yang belum terjangkau listrik. Tanya kenapa?

Menurut saya, masalahnya bisa dikategorikan sebagai berikut:

1. Keterjangkauan Harga
Panel surya dan baterai memerlukan harga beli yang tinggi, walaupun ongkos operasional selama penggunaan hampir nol. Masalahnya, para pengguna hanya sanggup membeli dengan harga beli yang rendah, dengan harga operasional yang 'terjangkau'.

Masyarakat pada umumnya lebih memilih untuk membeli gen-set kecil seharga satu juta dengan membeli BBM seumur hidup (ongkos operasional), dibanding membeli perangkat panel surya dan baterai seharga 3 - 4 juta rupiah (walaupun tanpa biaya operasional sepeser pun).

2. Standardisasi
Melihat contoh-contoh sukses dari lapangan (seperti [4] dan [5]), masih belum ada standardisasi seperti: tegangan, baterai, dan colokan apa yang dipakai. Semuanya terserah donatur.

Dengan adanya standardisasi, harga sistem secara keseluruhan bisa menjadi lebih murah. Para supplier tidak perlu memproduksi berbagai macam colokan, satu saja cukup. Contoh: bagi yang tinggal di kota, selama punya 'colokan' listrik, tinggak 'nyolok' bukan? Nggak usah pusing-pusing mikir colokannya nggak cocok, atau tegangannya ngaco?

Semakin banyak kompetisi untuk hal yang sama, harga akan menjadi lebih murah, gampang kan?

3. Skalabilitas
Lanjut dari masalah sebelumnya, berhubung tidak adanya standardisasi, sistem panel surya yang dibagikan ke rakyat sejauh ini tidak bisa di-'upgrade'. Kalau ada pengguna yang mau menggunakan listrik lebih kuat (kulkas, mesin, dll), bagaimana sistem yang sudah ada mengatasinya?

Sejauh ini, berhubung tidak ada standardisasi, kalau mau 'upgrade', ya mesti beli sistem yang lebih besar. Sistem sebelumnya jadi sama sekali tidak bisa digunakan. Ini sebuah pemborosan dan mahal.


Proposal:
Nah, berhubung saya nggak punya duit, proposal saya hanya untuk mengatasi standardisasi, alias 'the low hanging fruit'. Yang gampang-gampang dulu aja, yaitu standardisasi.

Berhubung produk di pasaran sudah banyak yang menggunakan 12 Volt, kenapa kita tidak mulai dari standardisasi 12V? Ya, tentu saja menggunakan AC 220V lebih ideal. Tapi, siapa yang mampu memasang dan merawat peralatan 220V AC? Kita harus realistis. Berhubung belum banyak teknisi listrik di pedalaman, yang kita butuhkan adalah peralatan pembangkit listrik yang bisa langsung digunakan oleh rakyat pedalaman, dan untuk dirawat oleh mereka sendiri.

Semua colokan juga di-standardisasi, jadi kalo salah 'colok', tidak mengakibatkan konsekuensi yang drastis.

Contoh proposal:

Ilustrasi sebagian diambil dari [6].

Dengan standardisasi 'colokan' dan tegangan, pengguna di pedalaman bisa menikmati keuntungan seperti penduduk di kota. Tinggal colok! Kalo mau 'upgrade', tinggal colok panel surya dengan hubungan paralel, dan juga batre, tidak perlu beli sistem baru dari 'nol'. Proposal sistem di atas juga dirancang untuk digunakan oleh pengguna yang kurang melek listrik-listrikan. Gampang kan?

Standardisasi juga menyederhanakan sistem logistik dan penerapan di lapangan. Donatur atau supplier manapun tinggal pasang-colok (plug and play) dengan sistem yang lain. Nggak perlu pusing panel surya buatan apa, dan runcian teknis lain-lainnya.

Kunci utama standardisasi adalah '12VDC bus' [8]. Selama ini diterapkan, semuanya menjadi jauh lebih mudah. Bagi pembaca yang melek panel surya, mungkin bertanya, "Itu penerapan 'kotak elektronik' dari panel surya ke '12VDC bus' gimana?"

Naaah, ini bisa diterapkan oleh:
1. Beli produk yang sudah ada di pasaran (alias '12V charge controller')
2. Bikin sendiri (produk dalam negri). Kalo saya sendiri aja udah bisa rancang dan bikin sendiri [7], kenapa situ nggak bisa?

Dari hitungan saya, harga beli sekitar 3 juta rupiah per unit. Ini untuk panel surya 50Watt-peak (dengan elektronik), dan baterai lithium 12V 20Ah, lengkap dengan colokan. Ini cukup untuk penerangan dan isi ulang batre handphone. Berhubung memakai batre lithium, sistem ini akan tahan selama 10 tahun, alias Rp 25,000 per bulan (kredit tanpa bunga selama 10 tahun)! Murah mana, dibanding Rp 50,000 per hari untuk pemakaian BBM?

Walaupun sistem ini masih belum bisa bersaing dengan harga PLN (harga sistem ini masih sekitar Rp 5,500 per kWh selama 10 tahun, dibanding harga PLN sekitar Rp 1,500-an per kWh), kita harus realistis. Sistem ini masih jauh lebih murah (daripada genset) untuk daerah pedalaman yang belum terjangkau listrik. Lagipula, harga PLN akan terus naik selama 10 tahun ke depan.

Bagi yang kebanyakan duit, silahkan hubungi saya! Duitnya akan saya pakai untuk elektrifikasi pedalaman Indonesia. Dijamin tokcer! [1]


Referensi dan catatan:
[1] Duit nggak bisa minta balik!
[2]  http://health.kompas.com/read/2012/09/29/03513482/listrik.untuk.kaum.pedalaman
[3] http://wildlifenews.co.uk/2014/05/indonesian-cop-is-jailed-for-eight-years-for-major-timber-smuggling-racket/
[4] http://regional.kompas.com/read/2013/04/25/09085871/Pemkab.Barito.Utara.Alokasikan.300.Unit.PLTS
[5] http://id.kopernik.ngo/update/menjangkau-desa-pedalaman-bersama-mama-mia
[6] http://www.solar-electric.com/how-to-use-mc4-connectors-cables.html/
[7] http://epxhilon.blogspot.com.au/2014/06/bmppt-solar-charger-3.html
[8] 12V dipilih karena lebih banyak pilihan untuk produk konsumen yang sudah ada di pasaran, dibanding sistem 48 volt misalnya (digunakan oleh: http://news.mit.edu/2015/microgrids-rural-villages-india-0601)

Perbandingan On-Grid dengan Off-Grid

“Listrik saya mahal banget! Pake panel surya bisa jadi lebih murah nggak yah?”, keluh pelanggan PLN, yang memakai banyak listrik gara-gara pake AC seharian.

“Bisa lah!”, jawab saya.

“Pasangin donk!”, jawab situ.

“Sini, kasih gue 25-juta”, jawab saya lagi.

“Gila luh, mending gue nggak pasang”, jawab situ.

Masalahnya, walau panel surya bisa mengurangi biaya listrik, harga pasangnya memang sangat mahal. Pertanyaannya, “ada nggak sih, perhitungan untung-rugi pasang panel surya?”.

Nah, tulisan kali ini bertujuan menjawab pertanyaan ini. “Kapan gue untung kalo pake pasang panel surya?”

Mari, kita semua berpegangan tangan dan cipiki (cium pipi kiri) dan cipika (cium pipi kanan) sesama. Karena, PLN sudah memberlakukan ‘net-metering’ melalui peraturan PLN nomor 0733.K/DIR/2013 [1].

Dengan adanya peraturan PLN ini, motivasi untuk memasang panel surya ‘supaya untung’, dapat terealisasi.

Contoh masalah:

Seorang pelanggan PLN menggunakan listrik sebanyak 300kWh sebulan (atau 10kWh) sehari, gara-gara pasang AC seharian. Menurut tarif PLN terakhir [2], si pelanggan harus membayar 400-ribu rupiah sebulan (Rp 1.352 / kWh, untuk golongan R-1/TR).

Dari contoh penggunaan di atas, bagaimana menghitung kalau pemasangan panel surya itu untung atau rugi? Berapa besar panel surya yang harus dipasang supaya untung? Ngitungnya gimana nih?

Tunggu dulu, perhitungannya memang tidak segampang ‘1 + 1’, tapi nggak rumit juga. Sebelum nyebur lebih dalam, harus diingat, tujuan akhir dari hitungan adalah mengetahui kapan modal kita bisa balik (inggrisnya ROI, Return on Investment).

Dari perhitungan saya [3], di Indonesia, pasang panel surya on-grid bisa modal balik dalam waktu 13 tahun (alias Return on Investment sekitar 7.7%). Jangan lupa, jangka hidup panel surya itu dijamin selama 25 tahun. Jadi setelah modal balik (13 tahun), selebihnya untung…tung…tung.

Terus, off-grid itu apa?

Waduh, ini topik tersendiri dan lumayan rumit. Intinya:

• On-grid: terhubung dengan 'grid'. 'Grid' di Indonesia adalah PLN.
• Off-grid: tidak terhubung dengan 'grid'. Jadi nggak ada hubungannya sama PLN.

Jadi, pedalaman Indonesia yang memakai gen-set itu 'Off-grid', karena tidak terhubung oleh PLN.

Referensi:

[1] http://www.containedenergy.com/residential/pln-net-metering-indonesia/

[2] http://www.pln.co.id/blog/tarif-tenaga-listrik/

[3] http://epxhilon.blogspot.com.au/2015/04/menghitung-untung-rugi-sistem-panel.html

Menuju Rumah Mandiri Energi: Pendahuluan

“Saya memakai beberapa lampu dan kipas angin, butuh berapa panel surya supaya rumah saya tidak perlu PLN lagi?”

“Saya sudah muak PLN byar-byar-pret melulu. Panel surya bisa mengatasi masalah ini nggak?”

“Kalau gubuk aja udah pake panel surya, kenapa kita tidak bisa?”

Sepertinya komentar-komentar seperti ini sudah tidak asing lagi belakangan ini. Nah, tujuan artikel ini adalah untuk menjelaskan secara terinci, apa yang dibutuhkan untuk mandiri dalam hal kelistrikan, alias, tidak perlu PLN (Off-Grid). Sebelum terjun ke ‘Off-Grid’, perlu diketahui ada juga yang namanya ‘On-Grid’. Untuk perbandingan on-grid dengan off-grid, ini merupakan topik tersendiri: klik disini.

Andai saja jawabannya sederhana, “Beli aja UPS (uninterruptible Power Supply), terus colok listrik rumah ke situ. Gampang toh?”. Kalo rumah situ gubuk, ya ini jawaban yang benar. Tapi, kalau rumah situ lebih besar dari gubuk, untuk mengandalkan seluruh rumah berdasarkan tenaga surya, ini lebih rumit.

Sebelum menjelaskan lebih lanjut, saya akan jelaskan ‘melistriki’ rumah, dengan analogi ‘mengairi’ rumah:

Dalam ‘mengairi’ rumah modern, air disalurkan ke seluruh rumah melalui pipa-pipa. Nah, biasanya, tekanan air dari PAM (Perusahaan Air Minum) sangat rendah, sehingga tidak bisa langsung digunakan.

Solusinya, air dari PAM ditampung di bak besar, lalu dipompa ke seluruh rumah. Alternatifnya, air dari PAM ditampung di bak yang berada di ketinggian, lalu disalurkan ke seluruh rumah melalui gravitasi. Ilustrasi sebagai berikut:

Nah, melalui ilustrasi di atas, kita bisa tahu beberapa hal berikut:

• Berapa banyak air yang dibutuhkan oleh semua penghuni rumah? Dalam sehari? Seminggu?
• Berapa banyak air yang harus di-supply oleh PAM?
• Berapa besar bak air yang harus digunakan?

Dari analogi di atas, pertanyaan ‘berapa banyak panel surya dan baterai yang saya perlukan?’ bisa dijawab dengan menggunakan analogi bak air di atas:

• Berapa banyak listrik yang saya konsumsi? Sehari? Seminggu?
• Berapa banyak listrik yang butuh di-supply? (Alias, berapa banyak panel surya yang saya butuhkan)
• Berapa banyak baterai yang saya butuhkan?

Nah, dalam tulisan selanjutnya, akan saya bahas lebih lanjut.