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).

Conclusion

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.

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[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.

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)
microwave	0 (5)
mini oven	0 (5)
fridge (continuous equiv)	33
clock radio	5
master bedroom cd player	5
kids' bed cd	5
computers-office	10
macbook	8
old laptop	5
router	10

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).

Data:

(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.

Conclusion

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.

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[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 guesstimatedapproximations.blogspot.com.au

Kitchen hot water

A while ago, I wrote about my reasons for wanting a dedicated hot water system for the kitchen. Today, the system is finally operational. It's a big day!

I decided I wanted to do all the plumbing myself, which has made things take a bit longer (I have no previous experience brazing or bending copper pipe), but it has gone reasonably smoothly (albeit slowly), and in the end I'm reasonably happy with the standard of work. I left the most visible parts until last, when I'd had most practice and they look reasonably professional.

Here is a picture of the little hot water system on the roof (with the unfinished space heater next to it). It holds 30L of water, and has 8 x 50cm evacuated tubes. It is a low pressure system, so I can't just connect it to mains pressure with a tap in the kitchen (as is the norm). This system cost me $300 on ebay. It came with the aluminium racking immediately underneath it, but all the rest of the aluminium on the roof I installed myself.

Because the unit can't run at mains pressure, I needed a system whereby the tap to it controls its supply (before that supply reaches the tank). Then the tank is just sitting there at atmospheric pressure. To do this, I used an electric solenoid valve, which cost about $20 on ebay, with a 12 V transformer that I installed in the roof. We had an existing powerpoint in the roof that is controlled by a switch in the kitchen. That switch now energises the solonoid valve, switching it from normally-closed to open and allowing more water to flow into the tank of the hot water system.

Because the tank is always basically full, this causes it to overflow. The overflowing water exits the tank via the (hard-to-see) pipe at the top-left in the first image, and that pipe leads straight down to a (tapless) faucet in the kitchen below. Here is the last bit of pipework that directs that overflow through the kitchen window and out the spout in the kitchen.

How to use it

In the kitchen, flick the power switch, and wait. That switch activates the solonoid valve, opening it. Water enters the tank and causes it to overflow, and come out of the kitchen faucet (separate to the existing tapware). A bit before we have enough water, flick the switch back off -- the rest of the water will drain from the pipe into the sink before it stops.

 Quirks

Yes, this is quite an unusual system.

The main quirk is that, because the "overflow" pipe is basically empty of water most of the time, there is quite a latency between flicking the switch and getting water out of the tap. There is also quite a latency between un-flicking the switch and the water stopping. There's more testing to go here, but I think it's about 20 seconds.

Also, because the faucet is open to the tank, it is possible that the tank will boil in summer and lead to dripping in the kitchen. This remains to be seen.

Reflection on goals

The goal was to have "instant solar hot water" available at the flick of a switch. I now think this was a bit naive, but I still think it will be handy for two main reasons:

1. Because it is a shorter run of hot water (it is basically hot immediately with no wastage), it decreases the load on the main solar HWS during winter. 
2.  For the same reason, less water is wasted in summer (when we really need it!) -- we've been catching that water in jugs and drinking it later, but it is a bit of a pain, and still results in some wastage (from the main HWS, there is just over 2 L wastage to get hot water in the kitchen)

If I was doing this again, I'd consider installing an additional full-size solar HWS down that end of the house and just run the kitchen from that. One day, I may do that (depending how we go for hot water in winter).

Winter approaching, roof work, more solar

I have been busy preparing my house for winter. Last winter (the first in this house) we did little apart from install curtains, and the interior of the house regularly dropped to 13 C on cold winter mornings. To be honest, this is quite bearable, especially with the electric blanket we use on the couch when reading or using the computer. But, it would be nice if the house was a bit warmer in winter.

Heat retention

Before working on heating, it is vital to minimise heat loss, otherwise any heat just rushes out of the house again. This has two main parts:

• drafts -- do this first. Drafts are a killer
• insulation -- stop heat conducting out

Our house is very drafty. Here's what I'm doing (work in progress):

• go around the entire house with a caulking gun and seal up all the skirting-board to floorboard interface with gap filler
• go around the ceilings, and fill all the gaps where the light supply cable penetrates the ceiling
• put door skirts on all external doors
• put rubber seats around all external doors so that they seal
• Install a DraftStoppa on the bathroom exhaust fan
• replace the kitchen exhaust fan with a proper (closing) duct that goes outside the roof

If I get time, I will also

• remove all light switches and power points in cavity walls and seal the cable penetration
• work on the windows to improve their seal

though, I suspect this might take until next year.

In parallel to this, I have also put a heap of insulation (rockwool) in the ceiling. There was insulation already, but it is old, dirty, compressed and thin and I just laid the new on top of the old, hoping that was adequate. I really didn't want to disturb 40 years of rat urine in the existing insulation! This job is only 1/2 done -- it's very easy to procrastinate going into the roof...
I have also started planning to retrofit double-glazing to some of the windows. For some windows, this will be easy. For some, hard. I'll leave the details of this to another article in the future.

Heating

Once the house is better at retaining heat, it will benefit from having more heat injected into it. To do this, I have started building a solar space heater from some salvaged material I had. Here's what I've used:

• some corrogated iron, from the carport I pulled down
• some light meranti timber from the pergola I repaired
• Some other salvaged timber of unknown heritage

I snapped a few photos as things progressed:

Materials I am using, mostly reused except for the roll of plastic sheeting top-left

Beginning of the framing. I decided to make the frame to fit the plastic sheeting rather than the iron. This means that the frame is wider than the iron, which was a bit awkward to fill without cutting a long thin bit of iron (which I didn't want to do for waste). I had a couple of pieces of flashing lying around, which I was able to rivit to the iron and seal.

The unit on the roof. I decided to use an existing TV antenna to support it. As we don't have a TV, it's good to see the antenna is finally good for something!

Another shot of it installed on the roof. A rear brace is visible. It's important that it is anchored well, as it's a bit like a giant sail on the roof. Note the aluminium rails on the roof. I used some solar PV brackets that slide under the tiles and anchor to the roof purlens. I hope it's strong enough!

A closer shot of the side. I also used tin to help anchor the struts to the frame (stop the nails pulling out). I've angled it quite steeply (over 70 degrees), so that summer sun won't make it too hot (this is because the sun is higher in the sky in summer)

A view behind. Here you can clearly see the flashing, as well as the two struts and the anchoring to the TV antenna. I plan to put in a third strut. Behind it, you can see a 30 L solar hot water system that will supply only the kitchen. More about this in a future post.

 Next step

I will buy some ducting, and a through-tile to let me get the ducting into the roof. I'll need to work out an air blower and switching. I need to insulate the back of the collector (to reduce heat loss). Note too that the unit needs to be quite well sealed, otherwise cold air will reduce its efficacy.
EDIT: I forgot to mention that I also need to paint the inside of the box matt black, and cover the front with the roll of plastic shown in the photo. I'll also put some small vents along the bottom of the box for fresh air to enter (although another option is for the box to accept air from the house, heat it and return it through a second duct -- I'd rather have fresh air I think).

Expectation

The collecting area is 3.1 m by 1 m. Assuming I can get it working fairly efficiently, I think it should be equivalent to at least a 1 kW bar heater in the lounge room when it's sunny. It might even be as good as a 2 kW heater. Time will tell...

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This post was written by Angus Wallace and first appeared at guesstimatedapproximations.blogspot.com.au

Power consumption at my house

Summary

We have a normal house, and have not invested greatly in energy efficiency, but we are very careful with our power use. We have spent about $2500 installing a solar hot water heater, and have bought some energy saving LED light bulbs, and are very aware when we use power. All of our appliances are at least reasonable when it comes to power use, and we have installed a small (2 kW) solar PV system (we paid $5000 for a good one, but similar systems are available for $2000). We are now in a situation where we are exporting (selling) about 3x the power we are importing (using), and I expect to have negative power bills (ie. the utility pays us). I have estimated our ROI for this investment to be about 17.5%. We do not have a generous tariff on our solar PV (we get 24 c/kWh when we sell, and are charged 35 c/kWh for what we buy). We buy 100% GreenPower. I think this makes the case that high electricity bills aren't a necessity, and that you have the power to do something about it.

Our power consumption

This is a short post which shows graphs of the power consumption at my house. There is nothing fancy about it -- I just take regular meter readings myself so that I can monitor the system's performance. These graphs should stay up-to-date as I add new data. I show these data so that you can see what is possible in a very normal Australian house. We don't have fancy passive-house design or lots of expensive modifications. We just don't use a lot of power because we're careful. Our house was built in 1955 and is unassuming. We do not use gas at all (well, we have a gas bottle on the BBQ which we use a handful of times each year).



We have a standard grid-tied solar PV system. This means that any power it produces, that we are not using then-and-there, is exported to the grid. The amount of power exported is measured. If we are using power (eg. electricity in the house) while the system is producing, then only the excess power is exported (ie. the difference between what's generated at the panels and what we consume). If our consumption exceeds what we're generating, then we're importing power.



The first graph shows daily consumption (get power from grid, red) and solar PV export (send power to grid, green). I don't take a meter reading every day, so where I don't take a reading the graph shows an average since the previous meter reading. Notice the sharp change at the beginning of September where the electric storage hot water system was switched off. This reduced our daily power consumption by about two thirds (from to 3 kWh/day). Note that I live in Australia -- winter is from June to August!




The second graph shows our cumulative consumption and solar PV export. Seasonal variation in exported solar PV production is very evident (green line, from May to August). The production decrease in winter looks worse than it actually is because this shows not the generated power, but the exported power (which has our instantaneous use subtracted from it, which is higher in winter). Also note that the angle of power consumption changes at the beginning of September, when the electric storage hot water system was switched off. Our 2 kW solar PV system is mounted flat on a tiled roof. I don't know the exact angle, but it would be less than about 30 degrees, which is sub-optimal for winter production (because of the angle of the sun in winter, they would produce more power if they were at a steeper angle -- 60 degrees in Adelaide). They do and are unshaded all day.













This article was written by Angus Wallace and first appeared on guesstimatedapproximations.blogspot.com.au

Imagine 100% renewables -- what happens when there's no sun or wind?

Imagine an Australia running on 100% renewable energy:

1. Each house has 2 - 5 kW of solar PV
2. Each house has 1 - 2 days' energy stored (eg. in batteries, or similar)
3. Ditto for commercial and industrial buildings
4. There are also scattered wind farms and singleton wind turbines where feasible
5. There is scattered storage that is owned by the utility

What is the issue? Intermittency.

Intermittency

This is the problem that is always raised when renewable power is promoted: renewable power is intermittent:

• solar PV only produces electricity when the sun is shining
• wind turbines only produce electricity when the wind is blowing

Neither of these conditions are met all the time, so does that imply rolling blackouts?

Problem

Imagine an interval between sunny, windy periods in NSW during which the local renewable generation produces very little, if any power. Imagine that there is somewhere else in Australia that at that time is producing plenty of power. Let's say it is in SA. From where will people in NSW get electricity?

Solution

Luckily, our scenario includes some distributed electricity storage. There is not very much (a typical off-grid house would have 5 days' electricity storage or more), so it is much cheaper. It does mean, however, that after a few days of cloud and no wind people's batteries would be running down.

The solution is to use the existing grid. While Australia's current grid cannot send enough power around in real-time (ie. if it's sunny in SA and cloudy in NSW, SA can't in real-time supply Sydney's power demands), what is rarely considered is that this is unnecessary. Remember that the existing grid is vastly underutilised -- it is built with peak demand in mind (which occurs a couple of times per year). Most of the time, the grid is running well below capacity.

In this scenario, power can be sent from SA to NSW overnight, when demand is low, to keep batteries in NSW topped up. It does not need to power customers in real-time -- all it needs to do is stop the batteries going flat.

To restate it another way -- the transfer of power from SA to NSW would not need to match the maximum instantaneous rate of consumption in NSW -- it would only need to match the average rate over the period covered by the batteries. In fact, even this is not required since the batteries can be assumed to begin this period relatively full and end it relatively empty.

By doing this, we would obtain maximum benefit from the existing grid infrastructure, and also be able to install a much smaller storage system, while retaining the benefits of distributed generation.

In other words, I question whether the oft-repeated statement that high renewable penetration requires a much more extensive grid is true. We can use electricity storage to greatly mitigate this (though by exactly how much, I am not sure. Some time, I will try to get the data together and run the numbers).

The post "Imagine 100% renewables -- what happens when there's no sun or wind?" was written by Angus Wallace and first appeared at guesstimatedapproximations.blogspot.com.au

Reducing electricity consumption to affect political change

Many people are concerned about the negative effects that humans are having on the Earth's ecosystems, and with good reason: those systems support us, and without them we would not survive. It is estimated that for every dollar of GDP produced, the natural world contributes .75c -- these are services that nature provides for free and, without which, our quality of life would drop by 75%.

A big cause of human destruction of natural systems is in the provision and delivery of energy. The main culprits are fossil fuels which are starting to alter the world's climate -- a change that, if unchecked, will wreak great destruction on both the natural and human systems that support us. There are now technologies (solar PV and wind turbines) that can produce energy with much  less damage to the environment, and it is imperative that we transition to these as soon as possible. Unfortunately, there are entrenched interests that are heavily committed to fossil fuels and use their influence to slow the adoption of newer, less harmful, methods of energy production.
What is clear is that majority political support for serious action on climate change is currently lacking.

There are huge forces at work here. In the absence of a government with the ability and disposition for serious action, what can an individual do to help this process?

Number one: Use Less

When it comes to reducing one's impact on the systems that support us, there is simply no substitute for using less. Even "green" energy sources have impacts (albeit much more minor). Using less frees money and resources that can be better deployed by helping other, less fortunate, people adapt.

Number two: Avoid electricity or fuel where possible

Electricity is hard to produce, and there are always wastes and damage to the environment -- even when using solar PV or wind turbines. This is because the manufacture, installation and maintenance of these generally result in carbon emissions and other forms of pollution.
Therefore, if a task can be performed without using electricity at all, it is preferable to do so. A great example of this is hot water, which can be heated directly from the sun without need for electricity at all. By doing this, your electricity consumption will be much lower.
Similarly, a solar cooker can cook food without fuel or electricity, using only heat directly from the sun. These are simple and cheap to build.

Number three: buy carbon-emission-free ("green") power, and/or install solar panels

Here is where your large reductions in consumption will help -- because you're now using a lot less power, you will not need many solar panels to offset your electricity consumption (cheaper!).
At my house, we have reduced our power consumption to about 3 kWh/day for a family of four without significant lifestyle sacrifices. I think it can go lower still. We have a 2 kW solar PV system, which produces an average of about 6 - 8 kWh/day (averaged over the year) -- more power than we consume. We do draw power from the grid though, as we do use power at night (when the PV panels aren't producing), which is why we also buy carbon-emission-free power. By doing this, we ensure that we're not directly supporting the use of coal for electricity generation and because our power consumption is so low, the additional cost is very small. This also supports the businesses that are producing renewable carbon-free energy in Australia.

Dirty companies only have as much money as we give them

Using less means less revenue for the large energy generation, distribution and retail companies that, generally, are slowing the adoption of renewable energy technologies, and affecting public policy in negative ways. Make no mistake -- the combined actions of individuals is very powerful. The uptake of domestic solar PV has already had a huge effect on the energy generators and retailers in Australia.
This is because solar PV is usually producing power at precisely the times that energy is most expensive (energy retailers pay a fluctuating ("spot-") price for electricity,  and the times when the spot price is highest are the most profitable for the generators. Domestic solar PV is taking the edge from this demand, which is having a significant affect on the profitability of some of the big dirty producers. These kinds of commercial disincentives work to the advantage of renewable energy technologies.

If Australians continue to reduce their consumption and simultaneously install distributed generation (like solar panels, solar hot water, etc) and buy carbon-emission-free power, this will help to encourage the necessary changes. This will have a concrete effect on Australia's carbon emissions and reduce the likelihood of catastrophic climate change.

Remember, a carbon tax only has benefits because it causes people to use less -- we as concerned citizens can use less all by ourselves.

This post was written by Angus Wallace and first appeared at guesstimatedapproximations.blogspot.com.au