Tuesday, 25 August 2015

36V 11.6Ah Super Tube Battery Real Life Review

For lithium batteries, people always discuss how many charge-discharge cycles their battery last, but very few data regarding the electronics (i.e. the BMS, or Battery Management System).

My beloved 36V 11.6Ah tube battery (with original Panasonic cells) just died on the weekend :(. To my surprise, the cells themselves are still good. It's the electronics inside the battery system that is the culprit, i.e.:

  • the charging port is no longer be able to charge, and
  • the 4-pin output port also gives no output voltage (but can charge from this port).

This particular battery electronics have MOSFET driven switch for ON/OFF switch and the charging port ideal diode circuit (on top of the BMS).

I initially thought the PCB must have corroded since I always ride regardless weather (and it's been very wet lately). However, when I opened the BMS, it was dry-as, no sign of moisture what-so-ever (kudos for the battery design and build).

Since I have no time (yet) to further dissect the electronics, I already purchased the same battery for replacement. Again, to my surprise, the new battery did not perform any better compared to the old one. This, basically saying, the old battery has NOT lost ANY performance compared to new.

I get to work in 45 - 47 minutes (27km one way distance), which was same time compared to old one. When fresh, my cycle analyst shows peak power close to 800 Watts (old battery did the same). So, WOW! However, I haven't had the guts to test the capacity loss though. My guess the old battery probably have lost some of its capacity.

So, for documentation sake, my old battery has gone through (according to cycle analyst):

  • 497 cycles
  • 3701 Ah total

Based on the above, average 7.45Ah usage (65% Depth of Discharge) for its lifetime. And no noticable performance degradation. Impressive indeed.

Now, somehow I need to fix the electronics...

Tuesday, 21 April 2015

Cheapest Commuting Challenge

What is the cheapest form of commuting [7]?

With my electric bicycle, I commute 54km round trip with 460Wh of energy, or 8.5Wh/km [1]. This energy usage is equivalent to 0.052 litres of fuel, or 0.1 litre/100km [2].

Well, hangon, surely it is cheaper to pedal with your own muscle, right? That's what I thought as well. So, being a skeptic, I did my own calculation:

Assume the rider is from Tour de France (NOT me), which can 'easily' produces 300 Watt all the time in the commute duration (to achieve the same comparison with my electric bike commuting). Let say the rider manage to output 460Wh exerted at the same time duration (1 hour and 40 minutes round trip). The rider would need 400 Calories [3]! Quick googling tells me, this is equivalent to a bigmac [4].

For food cost, this translates to $5 for a round trip. Heck, that is the same cost (fuel only) if I use my Toyota Corolla! There you go. Human powered commuting is NOT cheap [5]! (Of course, I'm ignoring the health benefit here).

My electric bike fuel cost? ... Nothing! That's right, because mine is solar powered (one way). The other way, I charge at work for free :)

"Wait a minute, you have not included your capital cost!" I hear someone complaining. Well, since I'm a cheapskate, my total electric bicycle cost is around AUD1,600. This price includes: new electric bike kit, second hand bike, second hand solar panel, and my own custom MPTT charger [6]. To date, I've clocked 11,000km and 420 cycles of charging (quite deep too) and definitely still have my 80% capacity (I haven't had the guts to test the actual remaining capacity). I predict I'll be good for at least another 400 cycles (before I need to buy a new battery), so the life-cycle cost would be AUD1,600 / 800 trips = 2 bucks a trip (or 7.5 cents per km). Try to beat that!

[1] Exact value is highly dependent on wind. This figure is anywhere between 350 to 550Wh. The average speed for the whole ride is between 33 to 34km/h (not much affected by wind, almost none I say). Data source from installed Cycle Analyst on-board (http://www.ebikes.ca/product-info/cycle-analyst.html)
[2] A litre of fuel contains 8.9kWh of energy, using data from http://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf
[3] 460Wh = (460Watt)(3600seconds) = 1.656MJ = 396kcal (or 396 food Calorie, yes the Calorie unit IS confusing)
[4] Assuming 100% efficiency converting those bigmac calories to pedal energy.
[5] More reading if you don't trust me: http://www.fao.org/docrep/010/ah810e/AH810E08.htm
[6] http://epxhilon.blogspot.com.au/2014/06/bmppt-solar-charger-3.html
[7] For smart a$$ out there that says "cheapest commuting is no commuting at all, i.e. work at home!". To that, I can't top it off. Yes, I agree with you.

Thursday, 16 April 2015

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.

[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

Menghitung Untung Rugi Sistem Panel Surya On-Grid

Langkah menghitung untung-rugi pemasangan panel surya on-grid:
  1. Dapatkan ongkos pasang (total, termasuk inverter dan ongkos pasang);
  2. Hitung berapa banyak kWh yang dihasilkan oleh sistem di atas, per tahun;
  3. Hitung berapa Rupiah yang dihasilkan dalam setahun;
  4. Hitung Return on Investment, atau butuh berapa lama supaya modal kita balik.

Contoh hitungan:

1. Mendapatkan total ongkos pasang:

Masalahnya, melihat pangsa pasar di Indonesia sekarang, pemasangan sistem ‘on-grid’ di Indonesia belum marak. Alhasil, harganya tidak bersaing (alias mahal). Berhubung saya belum dapat menemukan data, mari kita berasumsi harga pemasangan di Indonesia sekitar USD2,5/Watt (atau sekitar Rp 25.000/Watt). Asumsi ini untuk menunjukkan contoh perhitungan. Prakteknya, kemungkinan besar lebih murah.

Menggunakan asumsi ini, kita akan membutuhkan modal sebesar 25 juta rupiah untuk sistem panel surya sebesar 1.000 Watt.

2. Berapa banyak kWh yang dihasilkan per tahun:

Ini tergantung banyak hal:
  • Tempat tinggal (Indonesia itu gede);
  • Apakah panel surya terhadang oleh bayang-bayang (dari pohon atau gedung lainnya) ketika matahari bersinar;
  • Iklim setempat.

 Untuk Indonesia, sepertinya produksi rata-rata 4kWh per hari (dari sistem sebesar 1kW) cukup akurat (melihat peta dari referensi [1] dan juga [2]). Dengan asumsi ini, kita mampu mendapatkan listrik sebanyak 1.460kWh dalam setahun.

3. Hitung penghasilan (Rupiah) per tahun:

Menggunakan tarif PLN terakhir (Rp 1.352 per kWh, untuk golongan R-1/TR [3]), dan dari hasil hitungan sebelumnya (1.460kWh per tahun), kita mampu menghasilkan (offset) sebesar 1.9 juta rupiah setahun.

4. Hitung berapa lama modal balik (Return on Investment):

Dari total ongkos 25 juta rupiah, dan penghasilan 1.9 juta rupiah setahun, kita baru balik modal setelah 13,2 tahun [4].

  • Setiap 1.000 Watt panel surya dipasang, kita menghasilkan (atau meng-offset biaya) 1.9 juta rupiah per tahun. Untuk sistem lain, lebih kecil atau besar, tinggal dibagi atau dikali dengan faktor per 1.000 Watt.
  • Pasang panel surya on-grid di Indonesia, dijamin untung! Walau beberapa pembaca akan bilang, balik modalnya lama amat yah (13 tahun)? Mudah-mudahan ini akan membaik. Jika total ongkos pasang hanya Rp15.000 / Watt (Rp 15 juta untuk 1.000 Watt), balik modal (ROI) hanya sekitar 8 tahun.
  • Untung-rugi tidak tergantung berapa banyak pemakaian, dengan syarat kita tidak menghasilkan lebih dari yang digunakan. Kalau menghasilkan lebih, ya nggak dibayar sama PLN [3].

Catatan dan Referensi:
[1] http://solargis.info/doc/free-solar-radiation-maps-GHI
[2] http://www.solarchoice.net.au/blog/wp-content/uploads/Solar-Choice-Clean-Energy-Council-Solar-PV-Consumer-guide.pdf
[3] http://www.containedenergy.com/residential/pln-net-metering-indonesia/

[4] Mayoritas panel surya memang memiliki jaminan 25 tahun. Tapi, inverter biasanya hanya 10 tahun. Yang murah atau jadul, paling cuman tahan 5 tahun. Jadi, hati-hati! Ongkos total bisa naik (karena kita harus menghitung ongkos selama 25 tahun untuk akurasi hitungan di atas).

Wednesday, 15 April 2015

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.

Thursday, 12 June 2014

BMPPT Solar Charger (3)

In pursuit improving my Boost MPPT charger, I have done the following:

  1. Update the software to use in-built PWM functionality of Arduino Uno. I've found out increasing frequency of the PWM is easy-as (simply add a line of code!!). The converter is now no longer making audible noise. Also, I get back most of the computing power of the Uno, instead of fully dedicated PWM routine. The negative of increasing PWM frequency is reduced efficiency. In my case, running 31kHz has reduced efficiency by 1%!
  2. Use MOSFET gate driver: this has increased efficiency by 2 - 3%, not bad! My inexperience made me choosing MOSFET gate driver without under-voltage lock-out, which caused the converter unstable during start-up. After much troubleshooting, I've found out the MOSFET gate driver locks the MOSFET to ON position during low voltage start-up, which cause the whole circuit short-circuited. This is now rectified by choosing another driver with under-voltage lock-out;
  3. Inductor: I've wound my own inductor using proper gapped core ETD34 core with much thicker copper wire. This has increased the current capacity and reduced EMI (so they said). However, no increased efficiency whatsoever compared to my old cowboy inductor.

I'm a bit disappointed that I haven't managed increased the efficiency significantly. I suspect my measurement method is inaccurate. As I simply read the watt reading from the el-cheapo watt-meter at the input. As the current is rippling, actual watt figure is probably different. So, next time I need to measure it properly using oscilloscope. None of the component is hot this time, so surely it's better than 90%.

New Schematic:

New software, click here. Note that the software includes my customised voltage selection during start-up. This is to accomodate my lead-acid 24V battery charging for the UPS. Yup, that's right, my shed is now off-grid too!

Thursday, 8 May 2014

Arduino Uno Shield Boost MPPT Cost

So, how much it cost exactly my home-made Arduino Uno shield for Boost MPPT charger? Have I reached my original goal to create the el-cheapo version of Genasun boost MPPT lithium charger?

If I didn't account for:

  • Hundreds of hours spending time in this project (I'm a slow learner),
  • Buying an awesome picoscope USB oscilloscope (to find out what was wrong with my boost converter due to my lack of knowledge),
  • PCB making infrastructure (solder, etching, etc etc).

Then the answer is absolutely yes! So far, components only cost me AUD65.80. If I were to get Genasun, that would cost me USD300!! Yes yes, it would financially much more beneficial if I were to buy the Genasun in the first place and not spending hundreds of hours and testing equipment... but... I learnt a lot from this project.

Breakdown of component cost as follow:

Total minimum purchase cost is shown above, as the minimum retail quantity was not one. I purchased them all from RS components.

There are components not shown in the cost table above (i.e. resistors and some diodes) because I've used my left-over components from my previous adventure. I ended up buying new Arduino Uno board, because I've blown up my original Uno freebie due to my own stupid mistake (literally, there was smoke coming out from the board after a 'POP'). So stupid, I won't share.

I can't share my board layout as it's riddled with problem, i.e. power jack is sitting on top of the USB connector, and the current sensing pad size is slightly wrong. I 'designed' the board using Microsoft Word, how silly is that?

Too bad, no one (that I can find in Google) has made buck/boost Arduino shield, nor boost only version that I can buy. So, until then, I'll be still using mine in the near future.