Sunday, May 31, 2015

Bikes for transport, electrified xtracycles

I've written about bikes before. I first introduced my xtracycle here, the ebike and associated thinking here, and talked about cycling with two kids here.

As I introduced last post, if we want to lessen the destruction we cause to the biosphere, it can be hard to identify where to best focus. Here is the priority list (as I see it):
  1. drive less or (preferably) not at all
  2. eat less industrially-produced meat, fish and dairy
  3. use less energy and buy GreenPower
  4. buy less stuff
In terms of reducing environmental damage, I think these are the Big Four. It's also great to buy organic, go to farmers' markets, do gardening, and play acoustic guitar (we try and do all these) but if you drive across town to pick up your organic veg in your Pajero, it's of questionable benefit (in my opinion). To my mind, this is similar to the (well-intentioned) person with a drawer full of washable nappies, and a disposable nappy on their child.
This is the reason I haven't written much about the garden. We put a fair bit of effort in, but it seems to me in many ways the less important part of what we are striving for -- though that could be seen as my prejudice as an engineer! I'd love to hear people's thoughts/criticisms of this idea. I do plan to write about it though.

We have a car (a small SUV in fact!), and are exploring how little we can drive it (it has been about a fortnight since we drove). I'm keen to see whether we can share a car with some like-minded people nearby but we're yet to organise that. A difficulty is that my youngest child is under 3, and so we have many years of car seats ahead of us.

In terms of thinking about efficiency, 1 L of petrol is equivalent to about 10 kWh. That is extraordinary, and shows just how much energy a car is using (and just how energy-dense petrol is). This is a big reason I love bicycles.

I recently made some changes to our bikes. The xtracycle was on a bike that was really too big for my wife and I hoped that putting it on a smaller bike would let her use it more effectively. Also, we sometimes took the kids places quite far away (or up a decent hill) that was hard to pull the trailer. I hoped that combining the xtracycle with the ebike would solve all these problems.

The xtracycle, now with electric assist front wheel and disc brakes.
I also took the opportunity to alter the platform on the back (using some found material) and bring the child seat forward. This greatly helps the dynamics of riding it, as the kids' weight is now in front of the rear axle. I've also mounted the battery for the ebike beneath the rear tray. I'm yet to finish installing a front rack on the bike.


The bike rides well. It carries a rider and two passengers (front passenger sits on platform and holds rear-facing handlebars, rear child sits in the plastic seat). It has a huge luggage capacity. It is fast, and can easily be ridden at 25 - 30 km/h on the flat when fully loaded. Handling is greatly improved with the children's weight further forward. Because the rear wheel is now 26" instead of 27", the weight is also marginally lower, which also improves handling. At some point, I might consider replacing the rear wheel with a strong 20" or 24" wheel.
In its previous  configuration (here) I carried a child and about 100 kg of luggage on it. It's quite amazing how much weight it can bear!

The problem is that it is still relatively hard to ride with a child in the rear seat, and my wife is still uncomfortable. It requires a lot of upper-body strength to balance -- particularly when the rider is getting on/off with two kids on the back. I do think a smaller rear wheel would help this, but we may consider a bakfiets (or similar dutch bike) instead. Not sure at this point. Also, our oldest child is nearly at the point where he could ride a tag-along (he can ride his own bike 5 kms, so could probably do 15 km on a tag-along).


We use this bike a lot. It's good for two kids, and great for cargo. Also, there have been many times that the ebike has allowed us to leave the car at home. I believe that, if electric vehicles are the future, it will be electric assisted bikes for most people -- electric cars will remain too expensive for most.

Monday, May 25, 2015


The problem that we are facing, as a species, can be summarised in one word: overconsumption.

Simply, we are using more than the Earth can sustainably provide and so are degrading its natural capital. It's like the young man who inherits $1million, only to be broke a few years later because he overspent -- he didn't spend only the return on his investment, he spent his capital. That is what we are doing.

The problem is that we are individually so disconnected from the fact that our goods and services are ultimately dependent on natural goods and services that we often don't know what we actually need to do to cause less damage.

Here is an example to clarify what I mean. I know people who want to do the right thing by the environment, so they have bought washable nappies for their baby. They were excited about this, and felt good about doing it (as they should). Here's the catch though: washable nappies are only good for the environment if their use displaces disposable nappies that would otherwise have been used.

Put this way, it is obvious, but this pattern runs deep and there are other, less obvious, examples. It is also made more confusing because marketing is a $500 Billion per year industry, and marketers have identified the environment as being a useful method to sell products.

Solar PV

In Australia, most people who buy solar PV panels for their house sell STCs (formerly RECs) [1]. Essentially, they are selling the "green" part of the energy that those panels will produce over their lifetime. Companies buy these credits, so that products can be packaged for sale.
You may say but I've still got the panels so my power is Green, right?, well, no. Consider the person who pays extra to buy GreenPower from the retailer. The retailer can call the power GreenPower, because they have bought sufficient STCs -- many of which have come from new PV installations.


There is a widespread idea, encouraged by advertising, the dishwashers are Green because they use less water than hand-washing. Here's the catch: this assumes a perfectly full load in the dishwasher. Also, it doesn't include the energy-and-water that was used in the dishwashers manufacture, packaging, distribution, installation and disposal. The depth of the problem is well summarised here, although I don't agree with that article's conclusion. But, again, this is presented by advertisers as a settled debate: buy a dishwasher -- it's green!


Hopefully these examples help you identify this pattern in your own life, and be more resilient against the Evil Forces of Marketing. As a general rule, the best outcome for the biosphere (and for our collective future) is not to consume and not to buy.

[1] for the record, I sold my STCs when I installed my system. I regret it now, and may buy them back at some point.

Monday, May 18, 2015

Winter warmth

I have got the rooftop solar space heater working. It's quite simple. This is what it looks like from the roof:
My north facing roof. From left, the mini-kitchen-solar-HWS, the solar space heater collector, the solar PV, the main solar HWS
It's not easy to see in this photo, but on the top right of the solar space heater collector, there is a 6" galvanised steel duct connected, which goes through the tile. I picked up the ducting cheaply from a car yard for $10 (I saw it from the train and made an offer). In the roof, I connected insulated, flexible ducting to the galv ducting and ran it to a pump (the pump draws about 55 W -- not much). From there, it is ducted to a 3-way splitter, and then to three outlets that I installed in the ceilings. They look like this:

Installing them was quite simple, although sawing through my ceiling was a bit intimidating! I used a cheap thermostat from ebay so that the pump only turns on when the air in the solar collector is warm enough. It is available here (It works fine, but I can't recommend it yet as I don't know how it will last). The thermostat is designed to keep a space at a certain temperature, which is the opposite of how I'm using it. I've put the thermometer in the rooftop solar collector, and anytime that collector rises above a certain temperature (23 C at the moment), it activates the pump [1].

The controller seems to work fine. Note that I also installed a 1-way flow valve (like this), so that warm air can't flow out the house through the solar heat collector at night time)

Performance and improvements

It's early days to judge yet, but I think it has raised the inside temperature of the house from about 15 C to about 17.5 C, which I'm pretty happy about. The weather hasn't changed much from before it was running, and we've had a mixture of gloomy and sunny days.
  1. Insulate the back of the collector. The collector loses a lot of radiant heat from the back. I need to insulate this, which will make the pumped air warmer.
  2. Experiment with collector air flow. I may try to make the air flow a two pass thing, either by double-glazing and running the air intake between the glazings or running the air behind the corrogated iron, to preheat it and make the insulation less important. 
  3. Pump speed. I think the pump has a higher speed setting, and I'll try that
  4. Insulate. I've still got more work to do insulating and draft-proofing the house. That will help
When winter sun is shining in Adelaide, it is about 1000 W per square meter. My collector is about 3 square meters, and I think I'm achieving at least 33% efficiency,  which makes my heater at least 1 kW when the sun is shining (it costs about 50 W to run). This gives a coefficient of performance of at least 20, making it at least 4 times more efficient than the best-performing reverse-cycle heater (and also a lot cheaper to install).


I think that, when finished, this will show it is possible in Adelaide to do a cheap retrofit (I will itemise this sometime) on a 1950s house with relatively poor thermal performance and keep internal winter temperatures above about 18 C.


I have also just put a "lid" on the shower using some of the left over plastic sheet from the solar heat collector. I built a simple wooden frame, and attached the plastic sheeting with some screws, and have just sat it on top of the shower screen. It makes the shower much warmer by trapping the warm air. The shower is more like a sauna, and so it feels warmer (because heat loss by evaporation from the skin occurs less in a warm humid shower). It also has the benefit that not so much steam goes into the bathroom -- we don't even need to run the exhaust fan now. This is really easy to do (about 30 mins work, with children helping), and is really worthwhile.

[1] To work in this way, the thermostat is run in its cooling setting (where it switches on above a certain temperature). In summer, I will switch it to its heating setting, so that it only switches on below a certain temperature. Then I can tell it to pump air into the house, when it is below (for example) 24 degrees. This sounds confusing and backwards, but it works.

This article was written by Angus Wallace, and first appeared at

Tuesday, May 12, 2015

What is the best tilt for solar PV?

We have a 2 kW solar PV system, and solar hot water. Our house is a net exporter of electricity (we don't use gas). This is by quite a margin: our average consumption is about 3 kWh/day and our average export is about 6.5 kWh/day.

Thus, we export more than double the power that we import from the grid.

However, at this time of year our import/export is about equal. We are using slightly more power than during the shoulder season (though we're yet to boost our solar hot water), but the production of our solar PV system has markedly decreased. There are two reasons for this:
  1. The angle of the sun is much lower at this time of year, resulting in lower irradiance to the panels
  2. Cloud cover
Clearly, there's nothing that can be done about cloud cover. But it is the sun's angle I want to talk about here.

PV tilt

There has been much discussion of the optimal tilt for PV panels. Back when there was a well-paying feed-in-tariff (FiT), people advocated installing the panels nearly flat. At Southern Australian latitudes, the annual production of clean panels is maximised when they are flat (note the word clean -- below ~10 degrees tilt, panels must be manually cleaned).

Now that there is no FiT, the equation has changed. For me, the FiT is less of a consideration -- my goal is to to live within my solar budget throughout the year. But why?

EDIT: It is worth mentioning that choosing the "best" tilt is important for all solar collectors: solar thermal, solar hot water, and solar PV. If anything, it is more important for solar thermal than solar PV, since solar PV collects diffuse light energy from the sky and not just the sun.

Your solar budget

Growing up in an age of cheap fossil fuels, we have been conditioned to the idea that gratification follows expectation. Want to heat your house to 35 C in the middle of winter? Sure. Want an outside spa in the snow? sure. This simply will not happen in the age of renewables. For a society powered on solar and wind, there will be times (sustained cloudy and calm periods) where power is significantly more expensive. By "significant", I imagine 10 times dearer or more.

This can be mitigated by installing battery storage, however batteries are expensive. To install sufficient storage to provide during prolonged periods of low production will be out of reach for many. I think in Australia a 3 kWh (usable) battery system would (currently) be affordable by the majority, and might cost $3000 including installation. Note that such a system would really only provide power for one day, and then only for the frugal.

This is a side issue, about which I will elaborate in another post, let's get back to the PV tilt.

It's all about winter production

If you want to live within your means, it is the winter production that is crucial. There is a solar bounty in summer, so there's no problem there. Therefore, we need to increase the tilt of the panels to increase winter PV production. Here comes some maths:

Let's imagine we have a solar panel that is directly facing the sun. We would say that its surface is normal or perpendicular to the sun. This maximises the production because it catches as much sun as is possible.
Now, let's imagine that we tilt the panel so that it is not directly facing the sun. Now it catches less sunlight (its shadow is smaller) and so it will produce less energy. If we keep turning it, eventually it will cast no shadow (it's sideways to the sun) and receive no direct sunlight [1] and produce little.

So, as we turn the panel from directly facing the sun, to being side-on to the sun, let's imagine a scaling factor that describes the production of the panel. This factor will be decreasing as we increase the angle away form the sun form 0 degrees (facing) to 90 degrees (side on). The curve that describes this is called the cosine curve.
The cosine curve, showing how production decreases as the PV panel is tilted away from direct sunlight. Remember, that this does not consider energy production from diffuse light (in practice a panel will still produce energy if oriented away form the sun, it will just produce a lot less). Note that for low angles (less than, say, 20 degrees) there is little effect on production, but by 40 degrees it is falling sharply. That is the characteristic of the cosine function.

Looking at the amount of power exported from my house since September 2014, this pattern is clearly visible as we approach winter.
These data start on December 20 2014 (summer solstice) and the decrease in production through Autumn 2015 is clear.

My panels are oriented at about 23 degrees, which means that at the winter solstice, my panels are oriented about 40 degrees from ideal, significantly effecting production.

Given that we have lots of available PV power in summer, I would happily sacrifice a little to gain extra winter production and I would do this by increasing the tilt of my panels. I think the optimum would be to increase their tilt to about 45 degrees, which would reduce the winter sun's angle to about 20 degrees and increase winter production (at the cost of some summer production).


Orienting PV panels to ensure optimal winter production is a strategy that will help maximise your self-consumption. This helps you get the most from your PV system during all seasons.

[1] PV panels also produce energy from diffuse light form the sky, but it is a lot less than direct sunlight. Here, we consider only the direct sunlight.

Monday, May 4, 2015

bits that fall through cracks

As I've described in how much do we use and renewable energy as investment, we have made an effort to reduce our power consumption, without going to absurd lengths. We regularly export about 8 kWh/day to the grid from our 2 kW solar PV system, and draw about 2 - 4 kWh/day from the grid. This is changing as we approach winter (read on).

As I said quite bluntly in Solar PV: opinions, merits, challenges, I am a believer in using the grid where it exists, because a battery storage system must be greatly oversized when off-grid to cope with the worst possible conditions -- conditions that are encountered only rarely [1]. Despite this, Australian utilities seem determined to cause grid defection: the process where people decide that they're economically better-off without the grid and leave it. I believe this will be a bad thing for Australia, because a lot of investment has already gone into the grid, and this will be wasted if people defect from it [2].

However, I'm also unhappy about our patterns of power use as they are. We don't have any fancy monitoring installed at our meter, I just take regular meter readings. I usually take a meter reading just before going to bed at about 10pm. Sometimes I check the meter again in the morning, just to see what has been used overnight. Without any intervention, we used about 1 kWh overnight.

Overnight power use

What's using all this power? Here's what I estimate/measure:
Consumption (W)
microwave0 (5)
mini oven0 (5)
fridge (continuous equiv)33
clock radio5
master bedroom cd player5
kids' bed cd5
old laptop5

Our Electrolux ETM4200SB fridge is one of the most efficient consumer fridges (we bought it second-hand for $500), and uses about 800 Wh daily, when the fridge's environment is about 24 C.  800 Wh/day is the same as 33 W (continuous equivalent) [3]. All the other values in the table are standby power consumption that I measured myself with a plug in Watt-meter. If you add all these values up, and multiply by 12 (hours), you get about 1 kWh used overnight. Note that I've counted the microwave and mini oven as having a standby power (also known as a phantom load) of zero -- that's because I switch off the microwave at the wall.

Clearly, if we want to draw less power from the grid, this is what needs to be reduced. Particularly at night when solar PV isn't producing. On windless nights, those electrons are supporting coal power, even though we buy GreenPower [4].

The fridge is the big one, and it would be good to get a fridge like the ozefridge, that can "store coldness" for use overnight (so that it doesn't use electricity at night time), but it's too expensive to justify right now -- if we were considering going off-grid it would be a no-brainer though (because storing energy in batteries is less efficient, with greater maintenance, than storing the energy as coldness in the fridge). 
I will install proper switches on the supply cables to the two CD players, and I want to put a timer on the office computers and router (so that they're properly off at night time). EDIT: I have found that the timers consume a significant amount of power and are unreliable, so I have just been switching things off or unplugging them.

Doing this reduces our overnight power consumption to about 0.5 kWh overnight (10pm to 7am).


(Note that the resolution of these measurements is 0.1 kWh, so they are a bit approximate)
  • I turned off the router and the two CD players overnight. Instead of using 1 kWh overnight, we used 0.7 kWh.
  • Then I turned off the study computers and washing machine too, which reduced our consumption to 0.6 kWh overnight (I bought cheap powerboards for the study PCs (~$10 each) that have a switch on them that turns off the whole board)
  •  If I turn off the router overnight our consumption is about 0.5 kWh overnight.
  • We've unfortunately needed to run a night-light for the kids, which is using almost 0.1 kWh overnight
In looking to save power, this is a significant saving for us (about 20% of our total grid draw), for very minimal effort and no sacrifice.

Solar -- Winter

This is a sun path diagram. It slows the path of the sun through the sky in Adelaide across the year. The upper green line (top of the yellow area) is the path taken at the Winter solstice. The lower blue line (bottom of the yellow area) is the path taken at the Summer solstice. The red line is the path taken on May 5th (today) -- you can see it is not far from the Winter solstice path, even though the Winter solstice is nearly two months away (this is because the path the sun takes is a sinusoidal curve, and the time of greatest rate-of-change is behind us (that occurs at the Autumn/Spring equinoxes) -- the rate of change occurring near the Solstices is small (for example, if you pay attention to the time of sunrise and sunset, you'll notice it changes most rapidly at the equinox, and most slowly at the solstice).
Sun path diagram. The original is here

Below are meter reading data that I have collected. In these data, look at the date and the pattern of solar PV production and electricity consumption is clearly variable as the seasons progress. In particular, the decrease in solar PV production (green line) during Winter is marked.
Also obvious is the large change in grid-draw (red line) that occurred on September 1st, 2014. That was when we switched off our electric storage hot water heater and went to solar hot water.
There is also a further reduction that occurs in early February 2015 -- this is the reduction that resulted from my targeting of phantom loads! It is subtle on this graph, but is clearer on the next graph which shows the cumulative data. The switch to solar hot water is also apparent in this graph, as an inflexion point at September 1st 2014, and a second inflexion point is visible at early February 2015. This shows that the savings from our reduction in phantom loads are significant.


Once the main areas of energy reduction are targeted,  it is very worthwhile to reduce phantom loads, particularly overnight. For essentially no effort, we're saving money every day, and reducing our support for coal and gas fired electricity.

[1] Another alternative is that off-gridders accept that sometimes they run out of power, and use candles for light, fire for cooking, and nothing else. This is fairly widely accepted by rural off-gridders, but something tells me that city folk will be less inclined to accept this.
[2] Note the idea of a proposal being "economical" -- I don't believe that economics adequately captures many of the most important elements in a decision, and that this is due to economic externalities (economic costs being imposed on non-players). Let's take an example. It is widely considered that cheaper to install a larger solar PV system and use the excess electricity to heat water. It costs less money. This is because solar panels are artificially cheap (their cost to society is much higher than the price paid for them -- I won't substantiate this claim here, it's an article to itself, but there are many such articles written already). In comparison, the monetary cost to install a solar hot water system (that uses sunlight to heat water directly, without converting it to electricity) is higher but the cost to society much lower.
This shows that "economic considerations" are not necessarily indicative of overall merit.

[3] I have considered playing with the fridge's thermostat. My idea was to run the fridge much colder during the day, then raise the thermostat so it didn't work as hard at night time. This would make a dent in our night-time consumption. I haven't done anything with this idea yet (there are clearly food-hygiene considerations here!)

[4] This is probably a somewhat contreversial statement. We buy 100% Greenpower, so in theory our power is all sourced from renewables. However, if there is a windless night, then any power consumption increases the electricity spot price, which aids coal/gas fired power stations (currently there is almost no storage of renewable energy in the grid).

This article was written by Angus Wallace, and first appeared at

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