More power of Energy Efficiency

21 11 2012

Just when we thought we could not lower our electricity consumption, along comes the next “bill”…..

Honestly, I was blown away……  never in a million years did I ever think we could get under 2 kWh per day, without even trying.  The only thing that occurred during this billing period is that the old upright freezer in which we kept the goat meat was converted to run as a fridge at 10°C for the cheese……  but all the same, the graph on the back of the bill shows we were going downhill for an entire year.  And there was I telling people we “only” consumed 2.4 kWh/day.  I am baffled.  Yes, the little freezer could quite conceivably use half a kWh/day running at 20 below, but this doesn’t really make sense.

The new bills are a little more sophisticated than they used to be now.  That neat little graphic that compares your consumption with that of other households “in your area” is eye opening.  Two person households “in our area” consume 1,255 kWh a quarter, while we only used 166…….  I’m justly proud of that.

What was disappointing though is that we only exported 903 kWh of excess solar generation, which over 90 days is a neat 10 kWh/day.  From 3.5 kW of PVs, that’s less than 3 hours of peak power.

This is due to my ageing SunProfi inverter putting a lot of power into the backup batteries, and the new PVs running very inefficiently when the weather’s hot, rarely producing more than 1800W from their rated 2200W…….  it’s because of a little understood phenomenon called thermal de-rating.

Panels are rated at X kW @ 25°C.  Some manufacturers must be ashamed of their Temperature Effect figures, as they don’t tell you what they are.  But they normally range from 0.2% to 0.5% per degree C above 25°C.  A panel would have to just about be in Antarctica to run at 25°C in full sun!

So if it’s 35°C outside (and it often is here), your black panels on the roof could be running as hot as 70°C, a temperature difference of 70 – 25 (degrees) = 45 degrees.  If your de-rating number is 0.5% (worst case scenario), then your panels’ power output could be de-rated by 45 x 0.5 = 22.5%.  On 185W panels like ours, that means they actually only produce 145W, so 12 of them would only produce 1740W……  which is pretty close to the truth!

I could complain, but I’m waiting for my $460 cheque…….

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9 responses

21 11 2012
Don

My electricity supplier seems to have had a brain snap. In my last bill they told me I used -0.29 tonnes of CO2. I wondered If I was somehow sucking CO2 out of the atmosphere (joke). I have a 2kW system and over three years it has averaged 7.76 kWh/day. Unfortunately I haven’t been able to include a scan of the usage as supplied from the electricity supplier in this message.

21 11 2012
mikestasse

Hi Don… if you’re in credit, they may have deducted your solar generation from your grid buy in and come up with a negative CO2 emission number…

BTW, I didn’t scan my bill….. AGL now have a 100% online service where you get an email notification of your bill, and after logging in to their website you can download a pdf of it, and pay (or in my case be paid!) by direct debit. Cool paperless transactions.

26 11 2012
Yuralani

Up here in FNQ the electricity suppliers are randomly switching off peoples grid feed-in, saying that they cant cope with all the electricity coming into their system.

26 11 2012
mikestasse

Well they should’ve checked before approving the install. Down here in SEQLD, they are upgrading transformers all over the place….. but blaming solar is a bit naive. Or should I say stupid?

The way it works is like this. A transformer may be rated 100kW. It might have originally been put there to feed 100 houses an average 1kW steady feed (there’s really no such thing, we don’t all switch things on all at once, some houses may need 2kW right now, ours less than 100W..)

The trouble is, they rarely accounted for growth. In our town, I reckon there are easily 25% more houses here than when we first bought 10 years ago. On top of that, most of those houses now run aircons and those stupid low voltage downlights by the millions…

Along comes feed in solar…. and now we have maybe 125 houses attached to it… out of those 125 houses, 40 might have decided to install solar, and put up 3kW each, or loading the transformer to 120%. Houston, we have a problem. Transformers have been known to spectacularly blow up…… one reason why they lowered the allowable limit on your roof from 10kW to just 5kW a couple of years ago….

Here they now check the load on your transformer BEFORE they let you put in solar. I have known people to be knocked back. The trouble is now the lines have been privatised, any unplanned spending on the grid cuts into share holders’ returns, so we’re down to doing something not because it’s worth doing but because there’s money to be made……..

For years now, the electricity distributors spent nothing and treated the lines as cash cows. So now they have to spend money, they charge you a fee to be connected (like Telstra does with phone lines) AND raise the cost of each kWh.

There’s so much solar in now that some generators have been switched off. And THAT is now affecting the profitability of the generators as well. And you wonder why the likes of AGL want to reduce the RET target…..

8 03 2013
John P Morgan

Mike, we’ve just met on Climate Spectator.
I have been “off grid” for more than twenty years and for me that is important.
I have no need to economise because the 2.8kw array provides more than enough for the 5kwh load (in rural Victoria).
That load includes a dishwasher and all the usual ‘stuff’.
With the recent drop in panel prices, I’ll soon add more capacity.
But the house efficiency means that I have no heating costs, no cooling costs, and although gas (LPG) is available, it is not generally used.
Winter heating comes from the sun (collected mostly in summer).
I’m delighted to find this site.

8 03 2013
mikestasse

Welcome to Damnthematrix……..! Of course, lowering your consumption means your batteries will last a lot longer. When we move to Tasmania, we are going off grid too. Exactly how we do this will be determined by the land we buy, but I am absolutely determined to build a house that needs no heating, even at 42 degrees South…..

12 03 2013
John P Morgan

I admire your taste.
Tasmania is one of our favourite places.
I expect you have done your homework but our choice is around the Mole Creek area – in the shadow of Cradle Mountain and within reach of Launceston and Devonport.
My background is 40 odd years teaching Physics and then twenty years designing and installing renewable energy power plants across central Victoria – mostly PV but a few wind and hydro as well.
I am enjoying retirement!
Hope you are too!

1 04 2013
alternative energy

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23 08 2014
Another Silver Bullet Jams in the Breach……. | Damn the Matrix

[…] ridiculous the whole concept of running the world on solar is.  Like me, he also understands the Power of Energy Efficiency.  Even the power of a sticker…  The must see talk is here…..  it will blow you away, […]

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