DIY Offgrid Project – PV panels

I found 13 x 250 watt PV panels on Gumtree for $100 each. It turned out they came with mounting rails and most of the clamps. That’s about $500 of cost avoided! The panels all appear in perfect condition. That’s 3,250 watts of panels for 40 cents per watt. By the time I get them on the roof they will owe me nearly 60 cents per watt. That’s about 4 cents per kWh over ten years. Cheap power!

IMG_0833

The open circuit voltage of the panel, Voc is 37.6 so three in series is 113 volts which is less than 120.

There is an interesting loophole in the electrical safety rules. You don’t need to be a licensed electrician to install DC equipment that operates below 120 volts. Technically you don’t have to follow all the pesky safety rules around isolators, conduits, fuses and earthing. You know, all the SAFETY rules. I will be following those rules regardless. (You can find the rules online if your Google-foo is good. I don’t want to draw attention to them because hiding Standards behind paywalls is what we do in Australia: put up a fence and charge rent and if I link to the set I found they will probably be taken down.

More to come! Installing and wiring the panels is next.

DIY Offgrid Project – goals

The goals of my home brew off-grid solar storage system are:

  • make my house relatively black-out proof – keep the lights, fridge, hot water and internet running
  • run big daytime loads direct from solar – the pool, the air-con
  • reduce my effective electricity cost to $0.10 per kWh assuming a 10 year life of the system
  • cover the capital expense with two years of savings

I need to generate around 1 megawatthour of electricity each month to do this.

Based on the performance of my current system, in summer I need 5 kilowatts of solar panels, but in winter I need significantly more, around 10 kilowatts.

I have 3 kilowatts on a 2.8 kW grid-tie inverter already and I want that to export like crazy to maximise my return.

A key reason for building an off-grid solar system is to avoid losing my feed-in tariff. That’s going to take some dancing at some point after SAPN look at the NearMap photos and notice I have a bunch of new solar panels.

In the short term I need around 6 kilowatts of extra panels to generate all the electricity my household consumes.

Of course I will need to focus consumption into daylight hours as much as possible because that’s easier than storing it. My largest nighttime consumer is the pool but I can just change the timer. If I have a surplus and my car is home I will charge it. That will be a whole other project 🙂

 

DIY Offgrid Project – Batteries

A couple of years ago I bought a Tesla and put vanity plates on it that say OFFGRID.

Ever since then I have been trying to make the dollars make sense to install some batteries, an inverter and a bunch of solar panels in an attempt to charge my Tesla and keep my pool clean with free solar electricity.

About five readers are about to leave a comment that I don’t need a battery to achieve that and indeed I don’t but why have a simple life when I can add technology?

Recently some associates found a stash of 460 AmpHour Lithium Iron Phosphate storage cells being disposed of and I managed to get 16 which means I now have a 52 volt, 460 Ah, 23kwh battery. You can cycle these cells to 80% discharge thousands of times. If you keep them between 20% and 80% State of Charge (SoC) they should last much longer. 60% of 23kwh is still 14kwh which is more than my overnight electricity consumption.

It seemed appropriate to put the batteries in the boot of my Tesla.

LiFePo4 cells are great technology. They don’t need water and don’t produce hydrogen gas. If you over charge them or allow the terminal voltage to exceed 4.2 volts you will damage the battery and the classic failure mode is to catch fire. If you over discharge the cell, to below 2.8 volts you will damage the battery and the classic failure mode is to catch fire. I’m obviously going to need some sort of battery protection or management system.

Before the project is finished I’m also going to need solar panels, mounting frames, isolating switches, fuses, circuit breakers, an inverter and some sort of overall monitoring and control system.

I’m going to try to do as much of it myself as I can but there are some parts which will need an electrician.

Welcome to my solar storage adventure!

Correlation implies causation?

Let me start by warning that this isn’t investment advice.

I found an interesting graph at the end of a Finder.com.au article on mobile performance showing the falling cost per gigabyte of mobile data on what they described as flagship plans. I take that to mean approximately $50 per month which has been the popular Australian price point for Telstra SIM only mobile services.

The graph runs from October 2015 to October 2017 showing the $/GB every six months.

It reminded me of  how Telstra’s share price has fallen over the three years since Telstra launched 4G.

I wondered what the mobile retail price is at April 2018 so I looked at Telstra’s current pricing which has fallen to $2 per GB. Internode sold it’s flagship ADSL2+ service with a 40GB quota for $80 in 2006.

Now it’s May and Telstra have announced “Unlimited*” (* 40 gigabyte limit with 1.5 megabit speed limit thereafter) mobile data. They are trying raise revenue from $50 to $70 with it but it’s still well under $2 per GB, continuing the downward trend. Sadly for Telstra TPG have rained on their parade by offering $10 for 1 gigabyte per day which adds new line to the graph at around $0.33 per GB which must have caused a few folks at Telstra, Optus and Vodafone distinctly painful weekends.

TLS vs Mobile value

2016, 2017 and now 2018 show a remarkable correlation between Telstra’s share price (which can be a proxy for the investor view of Telstra’s future profits) and the “value” of Telstra’s flagship mobile product.

Why is there this correlation?

Telstra’s monthly average revenue per user (ARPU) for mobile and fixed line services remain largely unchanged in a decade so total revenue is directly a function of market share.

Really? Well yes, according to Telstra’s 2006 annual report their revenue from being a telco was $22,750 million and in 2017 the report stated $26,013 million which was largely unchanged from 2016 where it was $25,911 million.

So let’s come forward to May 14th when Income is forecast to be in the middle of the range $27.6 to $29.5 which is $28,550 million. It’s also stated NBN DA (“NBN Definitive Agreement” compensation) one off revenue is forecast to be in the “mid to upper” of the range $1.4 to $1.9 billion. Let’s assume it’s $1.9 billion.

That leaves Telstra’s telco revenue at $26,650 million which is only 2.4% more than last year and in line with inflation. If “middle” means slightly less than middle, revenue could be $26 billion for the third year in a row.

I think we have to accept that Telstra’s revenue is flat. It has been for the last three years and unless the entire industry plays the drinking game and just happens to decide to raise retail prices at the same time we aren’t going to see a shift upwards.

Is it capex? Telstra are forecasting capital expenditure of around $4.8 billion dollars for FY18. Last year they said they would spend $15 billion over three years which is all being depreciated. The FY17 depreciation figure was $4.4 billion so every $1 of revenue costs $0.17 of capital investment write down. But this is actually fairly flat so it’s not driving down Telstra’s profit.

So why is there this correlation? Good old fashioned “operating expenses”. It’s expensive to pay NBNCo, all those people, all that electricity and all that A grade rent. It’s an expense that rose 5.8% in FY17 and has probably risen faster than inflation in FY18 too. This drives a  margin crunch and at some point Telstra are going to need to find dramatically cheaper ways of delivering $26 billion of services.

Some of this will need to come from lower capital expenditure but that isn’t going to happen in a world where Chinese vendors are being banned on national security grounds. The rest will need to come from operations and that’s going to be very hard for an organisation that still sees itself commanding a premium price for premium service.

It’s going to be super hard when everyone pays NBNCo the same fixed price for the same services. It’s going to force Telstra off NBNCo for lower speed, lower volume users and the “unlimited” wireless products are an early shot over NBNCo’s bow.

Maintaining mobile revenue is also going to be super hard for Telstra now that TPG have announced $10 per month mobile data plans.

Ah, but Telstra just need to grow the $26 billion revenue, you say. Go read this article from 2016. It’s all the stuff Telstra CEO Andy Penn promised would grow revenue from $26 billion in FY16.

Tabulating the subsequent write-downs and write-offs is left as an exercise for the reader.

HW-655 ESP-01 Relay Board

HW-655 - 1

 

 

This is a HW-655 relay board designed to work with an ESP-01, the nifty tiny embedded WiFi device. It appears to be a clone of a China LC Technology ESP8266 5V WiFi relay module. I found some documentation here and some more details of a similar product from the same vendor here. I also found warnings that some clones did not have programmed STM8 micro controllers so they don’t work.

The missing element in trying to make this device work was the concept that you control the relay by transmitting serial characters from the ESP-01 rather than controlling an OUTPUT pin. There is a STM8 micro controller on the board. Why do this? I’m not sure but it does leave a couple of IO pins you can solder to. One theory is it ensures the relay doesn’t close without something quite deliberate happening in the ESP-01 which could prevent the ESP-01 crashing and leaving your controlled device powered.

The magic string is four bytes long.

A0 01 01 A2 causes the relay to CLOSE.

A0 01 00 A1 causes it to OPEN.

It’s probably a good idea to flush out any crud in the serial port before you send the string. I have noticed that A0 01 A0 01 01 A2 doesn’t cause the relay to CLOSE.

I wanted to test my relay module to see if it was programmed since it was obviously a clone. I couldn’t enter the four byte sequences in my terminal emulator so I wrote a bit of Perl on my Mac:

$| = 1;
printf("Close");
sleep 1;
printf(chr(0xa0) . chr(0x01) . chr(0x01) . chr(0xa2) ); # close
sleep 1;
printf("Open");
sleep 1;
printf(chr(0xa0) . chr(0x01) . chr(0x00) . chr(0xa1) ); # open
sleep 1;

And ran it like this:

perl < relay-close.pl > /dev/cu.usbserial-A703EA9U

While monitoring the serial being sent like this:

cat /dev/cu.usbserial-A703EA9U | hexdump
0000000 43 6c 6f 73 65 a0 01 01 a2 4f 70 65 6e a0 01 00
0000010 a1 43 6c 6f 73 65 a0 01 01 a2 4f 70 65 6e a0 01

And it worked! (Actually the codes I found online were Open: A0 01 01 A2 and Close: A0 01 00 A1 which are backwards!)

The ESP-01 has an ESP8266 system on chip and some flash. It is also Arduino compatible so you can write C++ code that will execute directly on the device. The next problem is 00 is NULL and strings are terminated with a NULL in C languages so you have apply a bit of effort like:

void setup() {
  Serial.begin(9600);
}

void loop() {
 Serial.write("\xa0\x01\x01\xa2"); // CLOSE RELAY
 delay(1000);
 Serial.write("\xa0\x01"); // OPEN RELAY
 Serial.write(0x00); // null terminates a string so it has to be sent on its own
 Serial.write(0xa1);
 delay(1000);
}

I compiled it for a board type of ESP8266 and uploaded it via my handy little ESP-01 programmer.

ESP-01 programmer - 1

Then plugged the ESP-01 into the HW-655, applied power and the relay will happily turn on and off every second forever.

ESP01 with relay

The ESP-01 is quite clever and can be loaded with some off the shelf firmware that does WiFi and can listen for a TCP connection so you could open a socket and send the four byte sequences from a machine on the same network. If you do some digging you will find some projects using some of Espressif’s IoT tools that let you control these devices from your mobile phone.

Note that there are two versions of the ESP-01. If you’re blowing $3 of your hard earned cash on one or five you should probably buy ESP-01S modules with 1MB of flash rather than the ESP-01 with only 512K of flash. You need the bigger memory for Version 1.5 of the AT “modem” firmware which can remember WiFi and TCP settings.

Other differences between ESP-01 and ESP-01S found online:

– blue PCB vs black
– 512kB flash vs 1MB
– Red power LED vs -No- power LED
– Blue LED on GPIO1 (TX) vs GPIO2 (and low = on)

The difference in LED may cause confusing when using BUILTIN_LED in the Ardunio IDE because the IDE expects the LED on GPIO1 (TX) and it’s inverted so OFF is lit and ON is dark.

 

What is the NBN for?

The NBN is primarily a machine for winning elections.

Conroy created it (I know the people who put the idea in his head but he did the political leg work) and used it to get Rudd elected.

Conroy then had to build it and he used it to get Julia elected.

It didn’t work a third time for Rudd because the slow progress of the NBN just confirmed the perception that the government were hopeless.

Abbott didn’t understand the NBN and told Turnbull to demolish it.

But Turnbull kept the NBN because he knew what it was really for and he eventually used it to help win his election.

Now Fifield has been given control of the machine with strict instructions to not touch anything.

I think Turnbull’s plan is to get millions of people migrated to the NBN then reduce the CVC charge in 2018 to ensure users are finally happy with the performance.

Late in 2018 he will announce a sale process and TLS shares will jump in value which will make a lot of Liberal voters happy.

Then he will have yet another go at riding the NBN machine to victory in 2019.

Or ScoMo or Dutton will.

Should NBNCo be scared of gigabit LTE?

I saw a media article today about Telstra demonstrating one gigabit LTE and claiming this was somehow superior to the NBN. I can’t let a claim like that go unchallenged.

First, some history. In the early days of analogue mobile phones (AMPS) operators broke their radio spectrum into 21 blocks of voice channels and designed their networks to services “cells” from three“base stations” connected to antennas with overlapping coverage on three towers or buildings.

Every cell could see one to three towers and this allowed for a “handoff” between towers. There was no data service. Every call required a channel and that channel would have little interfere from another call on the same frequency in a distant cell.

I found a picture that illustrates this:

celltowersatcorners

(Source: https://en.wikipedia.org/wiki/File:CellTowersAtCorners.gif )

The frequency reuse factor, k = 21 for this scheme. So you can use no more than 1/21 of the spectrum you bought in any one cell. By the end of AMPS carriers had dropped k to 7 at the expense of more interference but it improved the commercial yield on their spectrum investment by a factor of three. The CFO loved that. 

GSM, being digital, improved things such that nine or twelve sets of channels of digital data could form cells in a similar manner. Frequencies can be reused much more readily and the overlap doesn’t need to be so large. 114kbps data services can be delivered via this architecture from 200KHz data channels in 25MHz blocks. (You need 2 x 25MHz blocks, one for data UP and one for date DOWN.) You still need _relatively_ low interference so ironically this can work BETTER in a built up area where buildings block the interference. Combining two channels doubles the data rate and that is the service known as EDGE.

gsm-radio-frequency-planning

(Source: http://www.rfwireless-world.com/Tutorials/gsm-radio-frequency-planning.html)

The reuse factor, k = 12 for this scheme so you can use 1/12 of the spectrum you bought to service customers in any cell. In practice this meant you could service 124 channels / 12 = ~12 X 114kbps or a bit over a megabit from each sector of your base station. This is why mobile tower backhaul was only 2 megabits! 2 megabits for an entire tower with three cells but given the theoretical maximum data was 124 / 4 = 31 X 114 = 4.4Mbps it wasn’t a bad contention ratio. 

3G introduced “spreading codes” or code division multiple access aka CDMA which encode data on a radio carrier by multiplying it by a random digital number at a much higher bitrate than the data. To decode a specific data stream you multiply the received signal by the same random digital number and get the original data back. It’s like black math magic but it works!

reuse-pattern1

(Source: https://goengineer.wordpress.com/2009/10/08/frequency-planning-gsm)

With 3G you can drive the frequency reused down to k=4. You take the 2 x 25MHz spectrum you bought for GSM and turn it into 2 x 4 x 5MHz. (2 x so you have UP and DOWN links.)

Data is transmitted on the entire 5MHz channel in frames that are 10ms long with 15 slots that contain data and control information directed towards users.

The 3G UMTS standard delivers 15 x 384Kbps data slots to the users in each cell. That’s a total of 5.8Mbps which was quite a thing from 5MHz of spectrum at the time.

HSDPA increases that to 7.2Mbps per user largely by squeezing more out of the 5MHz of spectrum  and joining a bunch of data slots together. Over the life of UMTS the modulation rate has been increased to get THREE times more bits out of the spectrum and to use spectrum from TWO towers so the pinnacle of 3G is DC-HSPA (Dual Channel / Dual Carrier HSPA) which is 42Mbps (six times the basic 7 Mbps service). That 7, 14, 21 or 42Mbps is shared by every user within a cell.

LTE is the logical evolution and convergence of these technologies.

Cell towers traditionally use three antennas per sector. Originally the strongest received signal from each user was selected. Then some beam steering was added to concentrate the signal to and from each user. This is called Multiple In and Multiple Out (MIMO). In LTE this beam steering is done for every user UP and DOWN continuously. 

The available spectrum is broken into numerous 180KHz channels (called resource blocks) with the maximum allocation being 100 blocks over 20MHz. These resource blocks are in turn modulated on subcarriers using orthogonal frequency division multiplexing which is rather like vectoring on VDSL2. It’s high-tech and it can carry 1 megabit over 180KHz which was theoretically impossible when I went to school but yields 100Mbps over 20MHz.

Together with MIMO,  LTE’s modulation technique you can set k = 1 i.e. you can use the same block of frequencies everywhere.

That’s “LTE”, a hundred megabits more or less shared by all the users receiving their service from a given sector (or cell) on a given tower.

What if you had lots of money and could buy lots of spectrum? Well you would find 5 lots of 20MHz blocks of spectrum and send the data in parallel over 500 resource blocks at once. That’s known as “LTE Advanced Cat15” and it delivers a gigabit shared by all the users receiving their service from a given sector (or cell) on a given tower.

Is this enough to scare NBNCo?

No! Because even using fibre to the node NBNCo can deliver a separate 100 megabits to each and every house served by a sector on a tower, potentially hundreds of houses, which would be tens of gigabits.

LTE off mobile towers and roof tops isn’t going to put the NBNCo out of business just yet.

What if you could make your cells quite small? What if they were mounted on power poles or on top of NBN Nodes, if you happened to own them?

Well that’s something that should scare NBNCo and I think it’s one of the NBN defeating or eating endgame options Telstra have in their kit bag.

BUT, all those basestations serving all those cells need backhaul and that needs gobs of fibre. Physically small LTE basestations will emerge as a fibre to the node or distribution point technology but at the same time fibre will always be able to drop infinite bandwidth to individual end users. This suggests that fibre to the premises will inevitably return to favour as bandwidth demands keep spiralling up. 

In the mean time mobility is the killer app and the mobile operators can charge a premium for it. LTE is going to satisfy low volume users but the price will be prohibitive for hundreds of gigabytes per month. That said, they are the very users NBNCo is counting on to cross subsidise the roll out. 

We live in interesting times.