Home solar update

The 1.5 KW solar system on our roof has just passed a good round number in its total output – 12 000 kWh, or 12 MWh – and that’s a good enough excuse for another update.

We installed the system in May 2011 so it has produced an average of 6.26 kWh per day for five years. That’s a useful percentage of a household’s consumption: according to Ergon’s figures on the back of our power bill, the average consumption for a household like ours is about 20 kWh per day, so our panels are producing nearly a third as much as we use.

Of course, we use some of our solar power during the day and export the rest of it, and then use Ergon’s power all night, so our net benefit doesn’t quite reflect those numbers. I did the sums a year after the installation and came up with a figure of $700 p.a., with the expectation that that would increase if power prices increased. Using the same logic now for the five year period, we find:

  • Total produced = 12 000 kWh (6.26 kWh/day)
  • Total exported to grid ~ 5200 kWh, for ~ $2300 income
  • Total PV power used at home ~ 6800 kWh, for ~ $1700 savings
  • Total benefit ~ $4000

In 2011 I said:

All in all, making the best guesses I can for the unknowns, pay-back time for the whole project (PV system and switchboard) looks like being in the 5 – 8 year range. That’s perfectly acceptable … Of course, if the electricity tariff rises (hands up everyone who thinks it is going to fall? No, my hand didn’t go up either), pay-back time will drop accordingly.

The cost for the system was $3500. Even if my new figures on exports and savings are on the optimistic side, it looks like our system has paid for itself, just a few months ahead of the earliest date I anticipated.

That’s pleasing, of course. The thought that it will continue to  bring us that $800 p.a. benefit indefinitely is even more pleasing. So is the thought that we have done our little bit to reduce CO2 emissions, and that it has basically cost us nothing to do so.

Was there any downside?  Maintenance costs? Repair costs after the cyclone? None at all. It just sits there quietly on the roof, collecting photons and turning them into useable electricity, day after day.

For the record, the general tariff was 19.4 c/kWh when we installed the system five years ago, had risen to 30.8 c/kWh by July 2014 and has now (surprisingly) dropped back to 22.3 c/kWh. In May 2011 the “service fee” or “daily supply charge” was only $23 per quarter, whereas by May 2014 it had risen to 55 cents per day ($49 per quarter). It has continued to rise and is now $1.07 per day, closing in on $100 per quarter. The supplier is simply trying to maintain revenue in the face of flat or falling demand and the service fee is a favoured strategy – but that’s a topic for another day.

PV solar from toy-size to utility-scale

Tandy 'Science Fair' Solar Power Lab, c. 1978
Tandy ‘Science Fair’ Solar Power Lab, c. 1978

We came across a time capsule when we were clearing out a spare room a few months ago: a ‘Solar Power Lab’ given by one family member to another nearly forty years ago and passed down through the family ever since.

Project list
Project list

Photovoltaic cells were cutting-edge technology back then. The cells in the  kit – four of them, each about 5 x 1 cm, in a line along the back of the circuit board – were novel enough to be the selling point of an otherwise unremarkable electronics construction kit, and may well have accounted for half the cost of the kit.

The introduction to the manual, like the box, was all about the ‘space age’ technology used to power satellites – which were big news themselves in those days.

The ingenious recipient could construct any of twenty-odd projects, from logic gates (these were the days when home computers with 64KB of memory were considered powerful) to LED demonstration gadgets (LEDs were new, too) to transistor radios.

Construction manual
Construction manual

Moore’s Law was relatively new back then, too. I wonder how many people had any idea what its impact would be over the ensuing forty years? The purely quantitative differences have been so large that they have led to qualitative differences (from “big data” to the ubiquity of mobile phones.)

And solar power has grown almost beyond belief, too, on a similar path of dramatically falling costs and steadily improving efficiency. This ThinkProgress article presents a good overview of the current state of play, with one chart which sums it up beautifully:

Solar’s exponentially declining costs and exponentially rising installations (the y-axis is a logarithmic scale)
Solar’s exponentially declining costs and exponentially rising installations (the  vertical axis is a logarithmic scale)

Progress hasn’t been as rapid in solar power as in computing (Varun Sivaram explains why here, if you’re interested) but has been enough to overtake older technologies and to transform our future.

Once again, quantitative improvements have led to qualitative changes. Solar power is no longer a novelty and no longer a last resort for difficult situations such as satellites, but a realistic, cost-effective solution for all sorts of applications. Garden lights? Solar, of course – it saves wiring them in. Bore pumps? Solar, of course – no need to cart diesel down to the pump every few days. New suburbs? Solar with grid backup – not even vice versa. Parking meters? Lanterns for remote PNG villages? Traffic hazard warning signs? Domestic hot water systems? Solar, solar, solar.

Having kittens

It is an embarrassingly long time since my last post but a large part of the reason is that I was busy doing other good things, so I don’t feel quite so bad about the gap as I would otherwise have done. My major project was setting up the website for Kittens for the Reef, a cute video which I think everyone should watch:

Kittens for the Reef was launched on May 31 by one of its stars, Dr Charlie Veron (Fluffy couldn’t make it) at Townsville’s Eco-fiesta, an annual event which brings together all sorts of greenies. I attended and enjoyed it, as I have in previous years.

There is usually a new gadget or idea which catches my attention more than the others, and this year it was a cleverly designed and engineered portable solar power system from SolairForce. Continue reading “Having kittens”

Going solar – two updates

I have been connected with two domestic solar power projects which I described here on Green Path at the time, and today I have news on both of them.

bushland
Hervey’s Range in winter

The first item concerns our solar bore pump on Hervey’s Range: we pulled down the disused power line over the weekend and took it to a scrap metal merchant. Pulling it down made the property tidier and safer and was a good excuse for mucking around in the bush for a few hours on a beautiful sunny day, while the $150 we got for it was a belated cash-back bonus on our purchase of the solar pump system. 

The system itself, six months down the track from its installation, has performed well. Cloudy weather has not troubled it as much as we thought it might, and neither has the shorter span of daylight in winter.

Back in town, the 1.5 KW system we put on our roof has just passed a good round number in its total output: 7 000 kWh, or 7 MWh. We installed the system in May 2011 so it has produced an average of 6.2 kWh per day for three years. By power-station standards that’s nothing, of course, but it’s a useful percentage of a household’s consumption: Ergon says (on the back of our power bill) that the average daily consumption for a household like ours is about 20 kWh per day, so our panels are producing nearly a third as much as we use.

Of course, we use some of our solar power during the day and export the rest of it and then use Ergon’s power all night, so our net benefit doesn’t quite reflect those numbers. I did the sums a year after the installation and came up with a figure of $700 p.a., with the expectation that that would increase as power prices increased.

The general tariff has just gone up from 29.4 to 30.8 c/kWh, which doesn’t look like a big change until you note that the same tariff was only 19.4 c/kWh when we installed the system three years ago.

In May 2011 the “service fee” or “daily supply charge” was only $23 per quarter, whereas by May this year it had risen to 55 cents per day ($49 per quarter) and it has just increased to 92 c/day (about $83 per quarter). That will make it a major part of our power bill.

The huge increase in the supply charge is obviously Ergon’s attempt to make up for people like ourselves who still want the security of mains power but don’t actually use much of it because we generate a lot of our own. That’s fair enough, maybe, but it simultaneously encourages us (and people like us) to go completely off-grid. I will return to this scenario in another post; meanwhile, Australian households could go off-grid by 2018 is a thought-provoking introduction to it.