Sometimes, things really are too good to be true

Recently, while staying with my parents in the US, I was persuaded to purchase a 64 gb micro SDHC card from eBay.

The price seemed too good to be true (around $20), but the seller had a good rating, and maybe the card was legitimately this size, so we ordered it, and it arrived quickly.

Then the problems began.  I tried to format it to NTFS, and Windows reported the card could not be formatted, but formatting back to exFat yielded a 64 gb card!

A little digging turned up a small utility named H2testw v1.4, which is a burn in test program for SD cards.  Here’s the result on this “bargain” card:

The media is likely to be defective.
1.9 GByte OK (4091392 sectors)
60.5 GByte DATA LOST (126972416 sectors)
Details:0 KByte overwritten (0 sectors)
0 KByte slightly changed (< 8 bit/sector, 0 sectors)
60.5 GByte corrupted (126972416 sectors)
0 KByte aliased memory (0 sectors)
First error at offset: 0x000000007abc0000
Expected: 0x000000007abc0000
Found: 0x0000000000000000
H2testw version 1.3
Writing speed: 8.48 MByte/s
Reading speed: 5.67 MByte/s
H2testw v1.4

A little more digging turned up an article on counterfeit sd cards:

http://www.chinaelectronicsinsider.com/technical/how-counterfeit-usb-drives

Naturally we returned the item, and the seller refunded, but they also attacked other buyers who reported the fakes. 

So, my advice:  Stick to a reputable seller, like Amazon, and do make sure you check the actual seller.

Winter 2013 Heating

This winter seemed to be longer and colder than previous winters.

My normal mechanism defines the heating season as being when we use more than 50 kWh of gas on average a day.  This year, the winter by that definition was  175 days long, running from 22 October to 15 April.

Using our MetStats program to analyze our weather data gives us a reading of 2090 degree days, which means it was pretty much the same as every winter except for last year (see last years calculations).

Our baseline gas usage appears to be about 12 kWh/ day, and our electricity usage about 8 kWh for high rate, and 4 kWh for low rate.

Below is the table with units of kWh per degree day, once the base line is removed for the 175 days in the heating season.

	Low Rate Electricity	High Rate Electricity	Gas	Total
10-11	0.307	1.024	4.772	6.104
11-12	0.193	0.958	4.983	6.134
12-13	0.176	0.973	5.111	6.261

So a 2% degradation over the previous years, this despite getting our hands on a thermal imaging camera and putting a curtain over a single glazed door which is at the top of the stairs by a radiator.

In addition, we pretty much stopped heating the very back room of the house this winter.  However, the temperature differences were greater this winter, so that possibly contributed to more losses.

Solar generation was also down this winter, generating only 0.245 kWh of high rate electricity per degree day.  In addition, there would obviously be less passive heating available.

Fingers crossed for the results next year, when there will be two fewer members of the household for at least part of the winter, as the children both head off to university.

Energy prices-here we go again

Well, my fixed deal with Scottish Power is coming to an end, and the price hikes I described last year seem still to be with us, with the increase on the total bill at 18%, a 15% hike on daytime electricity, a 16% hike on night electricity, and a 19.7% hike on gas.

And then they’ve also cut the discounts offered, and hiked the price on the first units.

So, this is fixed until August 2014.  They do have a cheaper tariff, but there’s an exit penalty.  This special offer has to be chosen by the end of June, and may be withdrawn at any time.

So, my reasoning is that it’s best to lock into this price, and then see if any cheaper deals appear as we approach the winter, as we don’t actually use much energy during the summer anyway.  Fingers crossed for some price drops.

 

Electricity prices Your current prices* Your new prices1 from 1st July 2013* Your alternative Offer prices2 from 1st July 2013* Online Fixed Price Energy July 2013 Offer Standard monthly Direct Debit Online Fixed Price August 2014 Offer Daily Service Charge   27.39p   First 225kWh used each quarter 20.785p   23.906p All/Day remaining kWh 10.926p   13.436p All/Day Units kWh   14.256p   Night Units per kWh 5.448p 6.742p 6.354p

Gas prices	Your current prices*	Your new prices1 from 1st July 2013*	Your alternative Offer prices2 from 1st July 2013*
	Online Fixed Price Energy July 2013 Offer	Standard monthly Direct Debit	Online Fixed Price Energy August 2014 Offer
Daily Service Charge		27.39p
First 670kWh used each quarter	7.099p		7.294p
All/Day remaining kWh	3.156p		3.778p
All/Day Units kWh		4.009p

Updating to Windows 8

Updating ought to have been easy, but I found it incredibly frustrating.

First, I went to the upgrade site, but after getting all the way through the purchase process, it stated that the upgrade wasn’t for commercial use.

OK.  Off to Curry’s to reserve a DVD which also prevents me having to download the whole thing: Get Windows 8 upgrade on DVD from Currys at £49.99 and apparently doesn’t have the commercial restriction, a premium of £25.00.

When I got there I started looking at a new laptop as well, but that’s another story.

So, I’m now installing from the DVD I purchased.

The first thing I need to do is uninstall the incompatible apps (some Dell stuff, an Intel USB3 driver?, and Security Essentials!?) followed by a reboot.

I chose to keep my existing, files, programs and settings.

After quite a long delay, my machine installed devices, then spent quite awhile longer preparing. 

Another reboot, and “Moving your settings” was the next task.

Following that, a personalize choice, followed by connecting to the network via wireless (I’ll do that later).  I then chose express settings, and entered my previous admin password, and chose sign in without a Microsoft account.  After “Finalising your settings” a disconcerting black screen before “Hi” Finally appeared along with the W8 intro stuff.

It eventually booted into W8, so after the initial confusion about licensing, not too bad.

Be careful when buying new tyres for your car

I was advised at my last service that I needed new tyres on the car, and was given 3 different prices.

I asked about fuel economy, and was pointed toward the most expensive offer, with the statement that they’re what you have at the moment.

So, I called around a few places and got quotes, and eventually the dealer matched the quote, so I had the tyres fitted this morning.

However, when I got back to the car, I noticed that the new front tyres weren’t Michelin Energy like the rear tyres, and so my hunt for the difference began.

Bridgestone has a good document that describes the efficiency.

 

What I cant determine is if the increase in consumption is per tyre or per set of 4.   Let’s assume it’s per tyre (as that’s the worst case).

My new tyre is rated E, and the tyre available elsewhere is rated B, so that’s a difference between them of 0.04 l /100 km.

On this set of tyres, I drove 43,000 km (or 26,500 miles) so that looks like it will cost me 43,000 km * 0.04  l / 100 km = 17.2 l which at the current price of fuel for diesel at £1.42/l = £24.42.

That’s £100 if the rating is for each tyre, which is quite a difference for just fitting a different tyre to the car.

So, look for the label and choose wisely!  Clearly if the price per tyre is more than the savings a lower rating may be a better choice, though at the same price, it’s a no brainer.

Solar PV a year on and some illuminating thoughts

At the beginning of September, our 2100 kWp Solar PV array had been installed for an entire year.  The output was 15% over what had been predicted by the installer, generating  just under 2000 kWh in the year, and the investment is still looking to pay off in just over 7 years.

I also noticed that for the price I paid, you can now get a system that’s twice as big, so even though the FIT rate has halved, you can still get your investment back in 7 years, while generating twice as much as I am.

However, in the Northern Hemisphere, the days are getting shorter (watch it change on your PC’s desktop with Terminator for Windows Desktop) and it’s got me thinking about how we can shave bit more off of our consumption.

Ikea have an offer on in the UK for the next few days, giving you £3 off each LED bulb you buy.  This website also looks promising: http://www.directleduk.co.uk/

Should I replace all my CFL bulbs?

For example, this 60W replacement (at £11.95) replacing an 11W CFL bulb to a 5W bulb will pay for itself after 100 kWh at 11p/kWh, or about 20000 hours.  Assuming the light is on for an average of 3 hours a day, that will take 18 years to pay for itself—maybe not worth it just yet, as you can currently get CFL bulbs for about 10p each in the UK (heavily subsidised).

What about CFL downlighters?

We do however also have 8 CFL downlights that are probably reaching the end of their life (they’re on many hours a day in the kitchen), and the best price I can find at the moment for them is Pack of 3 - Megaman BR0711i Ingenium GU10 Spot Bulb 11W Warm Whitefor £14.99.  Where these apparently direct replacement GU10 LED 4.5 W  lamps are £9.95.  If the lights are on 4 hours a day, I save 10p every five days, saving £7.30 per year.  Replacing all 8 bulbs (£40 difference in price) will take just over 5 years to repay the investment, so this probably is worth doing.

How about Fluorescent Tubes?

We also have some fluorescent tubes in our bathroom placed beside a large mirror.  Three of these at 30W uses quite a lot of electricity, and I actually don’t like them very much anyway.  Also, the seem to light up a lot of the box they’re in and not so much of the mirror.  But, these IP68 LED Tape Lamps look like they might be exactly what I need.  5 meters of tape should be enough for the job at 24W and output 1800 Lumens, and again will cost just under £40, and I’ll also need a driver for the LEDs that costs about £20.  Every 15 hours these are on, I’ll save 1Kw of electricity, so they’re paid for in 9000 hours, which at an hour a day for a bathroom will take around 24 years to pay back.

That’s not a great return, but I might do it anyway.  I can probably build it in such a way that if they don’t work there, I can repurpose the strip of lights for use somewhere else.

More energy price hikes

I just got notice that my current tariff for electricity is set to end.

Lo and behold!  Prices are now going to go up 12% for electricity, and 6% for gas for me if I switch to their cheapest deal.

Or I can opt for a fix until July 1, 2013, at about the same levels as I’m currently paying.

Does anyone think prices might actually drop over the winter period before then, as that’s the period where we use the bulk of the electricity?  If so, let me know.  At this moment, I’m tempted to go for the fixed rate based on the cynical winter price rises we’ve seen for the past few years.

By the way, for anyone interested in the existing rates from Scottish power.

Your energy details at a glance
Electricity prices	Your current prices	Your new prices from 1st May 20121	Your alternative Offer2
	Online Energy Saver 13*	Standard monthly Direct Debit*	Online Energy Saver 18*
First 225kWh used each quarter	21.006p	22.267p	20.975p
All/Day remaining kWh	9.777p	11.706p	11.027p
Night Units per kWh	5.174p	5.837p	5.498p
Gas prices	Your current prices	Your new prices from 1st May 20121	Your alternative Offer2
	Online Energy Saver 13*	Standard monthly Direct Debit*	Online Energy Saver 18*
First 670kWh used each quarter	6.730p	7.606p	7.164p
All/Day remaining kWh	2.992p	3.382p	3.185p

Energy consumption down, but efficiency is too

It’s been a warmer than average winter, only 75% as cold as last year according to an independent source, and my calculations bear that out too.

Season	Degree Days @17.5C	Average Per Day
2008-2009	2134	10.51
2009-2010	2121	10.45
2010-2011	2072	10.21
2011-2012	1567	7.71

This smaller temperature difference  complicates things, as we now have a much bigger effect from our baseline usage, which had been ignored in previous calculations.

	Low Rate Electricity	High Rate Electricity	Gas	Average Total	Per Degree Day
08-09	7.20	16.30	71.90	95.40	9.08
09-10	7.09	16.18	62.52	85.79	8.21
10-11	7.14	18.46	60.73	86.33	8.46
11-12	5.49	15.38	50.42	71.29	9.24

As you can see, our total energy use per degree day has actually increased, despite the changes made with better lighting and timed radiator valves.  In addition, we reduced the heating to only 7.5 degrees in a 3m x 4m room at the back of the house with 3 outside walls which uses electrical heating.  I have to admit, I’m disappointed.

Maybe if we look at the numbers differently.  Our baseline gas usage appears to be about 12 kWh/ day, and our electricity usage about 8 kWh for high rate, and 4 kWh for low rate.

Below is the table with units of kWh per degree day.

	Low Rate Electricity	High Rate Electricity	Gas	Total
10-11	0.307	1.024	4.772	6.104
11-12	0.193	0.958	4.983	6.134

While this is better, you can see that the overall usage is still the same, with no measurable effect from the changes, though High Rate electricity is actually down 7 per cent, and low rate is down 38 per cent, but gas usage is actually up 4 per cent, overall though we used 0.5% more energy per degree day than last year.

I’ll have to put this down the the fact that we have the gas fire on in the lounge in the evenings, and it is really toasty in there.

The other good news though is that we did manage to generate .45 kWh of high rate electricity per degree day over the period, which is included in the consumption figures above.

So in terms of fossil fuels, our consumption has dropped by 7% over the period.

In terms of absolute cost, we used 18%  less energy we did in the previous heating season, but that was unfortunately offset by an 18% rise in prices over the same period, so costs were similar to the previous year.

LED Lighting photos

Yesterday, my sister complained there weren’t any pictures.  Well, here they are:

First, the light fixture the LED’s were replaced into in the bathroom.  The one on the right is the LED, as is the one you can’t see on the left.  I had to leave one halogen, so left it in the middle pointing to the mirror.  This fixture used to be 60W, it’s now 26, and the light appears to be the same warm color from both the LEDs and the halogen.  Output is 285 Lumens, but they are not dimmable.

The photo on the right is of the lamp directly above the mirror.

This is a 240V 50W halogen equivalent led drawing 6W with a GU10 fitting.  Again, the light is a very warm color.  You can see in the reflection on the tiles, the 3 individual LEDs.

This was done before, and isn’t counted in the costs below.

 

Finally, the rebuilt desk lamp that had failed.  The old plastic head is on the desk for comparison, with its 20W capsule halogen, compared to the new 3W LED.

You can see that the clamps cause the arms to splay out slightly, but it doesn’t appear to be putting any excessive strain on the fitting.

The lamp is quite a bit larger than the one that was originally in this fitting, but I don’t think it looks too bad from the angle I see it from most of the time.

The total cost of this project was £17.94, and given I replaced a desk lamp that was broken, I think was very good value.  And £10 of the total was an Amazon gift voucher for using their credit card!

Payback time on the project on energy costs alone looks like this:

Old wattage: 60+20 = 80 W
New wattage: 3 + 20 + 3 + 3 = 29 W
Difference = 51 W

Cost savings per hour at 51W = £0.0055

so £17.94 / £0.0055 per hour = 3261 hours

At two hours a day that’s 5 years, and a CO2 saving of 1400 kg to boot.  Lifetime of the lamps is forecast to be 50000 hours, so I should never have to replace them.  We’ll see how they cope in the moist environment of the shower room.

More LED Lamps

Yesterday, I ordered some new 3W LED 12V bulbs to replace the 3 20W lamps currently in the kids bathroom.  I had been warned that I might need a new transformer, and that they might not work without changing it.

My brother-in-law is an electrician in France, and I asked him about the likelihood that they wouldn’t work, and he thought it would probably be worth a shot, but he had said that electronic transformers might not like such a low current draw.

Well, I plugged all three in, and it appeared to work, however after a short time, I noticed a distinctive hum.

The solution of course is to plug in one of the original 20W halogens, taking the load of the light from 60W to 26W with the new bulbs.  Still a big improvement!

As for the third bulb, I happened to have a failure simultaneously of my halogen desk lamp, which has a transformer, and two antennae which carry the 12V AC.  And from our redecoration of the kitchen several years back, I had kept an old halogen light fitting that clamped onto two rails.

So, a quick unscrew of the old fitting, and a clamp on of the new and I have a new desk lamp that also draws only 3W!

Result!

Financing University Study in England for £150 a month!

My son is going to study Engineering here in the UK.  It’s a 4 year course, and we have to find some way to finance it.

The cost of tuition is £9000 a year, and the living expenses are about £1000 for each of 3 terms.

Where will we get the money?

Anyone can apply for a loan of £9000 for tuition, and for living expenses up to £5500 a year if you live away from home outside London.  The living expenses is means tested, but anyone can apply for 65%, so there’s 3575 available.

That brings the annual loan funds available to £12,575, or over the entire course, £50,300.  After you add the 3%, you get a total of £51,809 in todays money at the end of the course owed.

For reference, here’s a link to the direct.gov page on loans

How does interest accrue?

The loan costs RPI + 3% while studying.
After you leave, if  you earn £21,000 or less, RPI
£21,000-£41,000 RPI + rate between 0-3%
£41,000+ RPI+3%

Source: direct.gov

As a side note, it is not apparent whether the RPI changes year on year or not.

How is the loan Paid Back

The loan is for a fixed period of 25 years from the date you finish. 

You repay 9% of the amount you earn over a threshold (£21,000 a year), and if after 25 years, it’s not repaid, the debt is wiped out, or if it’s not repaid by the age of 50, or if you die or are unfit to work!

How much do you need to earn to pay this back?

51,809 / .09 = £575655.  Divide this by 25 years, and you get an average annual salary of £23,000 over the threshold required to pay this back, giving an average  monthly cost in today’s money of £172.50, but the reality is slightly different.

Assume you earn the worst possible situation for accruing interest, that is income of £41000 a year, so you get hit with the full 3% + RPI.

After 25 years, you’ll end up having repaid 46,800 of the £50,300 originally borrowed.  That’s a savings of  £3500!

If you average £50,000 a year, your loan still is not paid back, in full, leaving a balance of £13,000, but the effective interest rate you borrowed the money at is 1.2%  + RPI

Try getting that rate from a bank for a mortgage!

If you average £60,000 a year, you finally pay back your obligation:  After 20 years!  The effective rate is 1.9% + RPI in that case.

Finally, let’s say you get really lucky and earn £100,000 a year.  Then payback happens after 9 years, at an interest rate of 3.9% + RPI.

Am I better off with a smaller loan? Probably Not!

Lets assume you have some money put aside, and you use that to fund the maintenance expenses entirely.

Your total borrowing drops to £36,000, Initial loan starts at £37,080.

£100,000 salary pays back after ~5 years at about %4.2 + RPI
£60,000 salary pays back after ~12 years at 2.0% + RPI
£50,000 salary pays back after ~18 years at 1.8% + RPI
£41,000 salary leaves a balance of £12,010, but you’ve repaid an extra £10,800 at a cost of 1.05% + RPI.

All of these outcomes are worse!

CurrentCost meter updates

Recently, I’ve been leaving my main PC on 24 hours a day to collect the readings streamed out of my CurrentCost meter.

This obviously wastes 100 watts, which is about 25p/day.  Clearly that’s a waste.

So, I’ve decided to take the plunge and build my first ever hardware project, based on an ARM mbed processor that my son who’s doing electronics had sitting around gathering dust.  I’m a software guy, and I hate hardware.

I’m powering the circuit from a DC adapter I had in the loft, generating 6V DC, 600mA, so it shouldn’t cost me more than about 3.6w when I’m finished.

Here’s a bad picture of the breadboard and the device.

The idea is simple, keep the output format of my device similar to the original, but add buffering.

The mbed code captures data from the serial port (Pin 8 on the RJ45 from the current cost meter, and pin 4 ground if I remember correctly) which I crimped together into an RJ45.

I then spool the data into an SD card (writing raw blocks).  The current SD card is 16MB (I had it from an old Canon Camera), but I’m planning to put in a 256 MB card which will give me about 2 weeks of buffering with my existing setup that includes 4 sensors in addition to the main sensor, though there’s no reason a 1GB or larger card couldn’t be inserted instead.

The PC will then poll for data in the mbed by sending a carriage return, and in response the mbed will send out the next LF delimited xml message it has stored, which will be transmitted back to the PC at 921600 baud, and processed by my software.

One pitfall with the current cost data is that there isn’t any way of finding out what date the data was logged on.  To deal with that, I’ve reserved the first 4 bytes of each block in the 512 byte SD card sectors to store the real time clock of the mbed, and the PC can then query what date/time the message was actually collected on.

Electric Cars? I’ll stick with my bike.

My son may soon need a car for commuting to work, and the question is, is electric viable?

I recently looked up the Nissan Leaf’s statistics, and see that it’s rated at the equivalent of over 99mpg by the epa.  Of course the real question is how many miles per kWh?

The answer appears to be around 3.4 miles / kWh.

My bicycle is 62.5 miles per kWh.

http://www.inference.phy.cam.ac.uk/withouthotair/c20/page_119.shtml

Programmable Thermostatic Radiator Valves

Just programming up the new valves before installation next week, and thought I’d do the calculations.  The valves shown on the right aren’t the same, but the price is about the same, and the calculations still apply.

I managed to get two valves with bodies for £53.44, and our gas prices at the moment are £0.03182/kWh, so I need to make savings of 1700 kWh to reach break even point.

The plan is to put them in the lounge on the radiators there, which are 600mmx1400mm (1500 W), and 600mm x 1000mm (1000 W).

Currently the radiators have no thermostat whatsoever, and our heating is on from 6:00 until 8:00 every morning and from 15:00 until 22:00 every evening for the 180 heating days of the year.

That equates to (1.5+ 1.0 kW) * (2 + 7 hours) * 180 or 4050 kWh/year to heat that single room, but our total usage doesn’t seem to be anything near that high when scaled up.

Last year our annual usage was 15200 kWh of gas, of which we averaged 15 kWh/ day for heating water and cooking (or 5500 kWh/year), leaving 9700 for heating.

I’d guess that based on the sizes of the other radiators in the house that the heat used in the lounge is about 1/5 of the total, or 1940 kWh a year.

I propose to limit heating in that room to be only between the hours of 17:00 and 21:30, representing a reduction of 50% on the amount of time heated, generating a maximum savings of  970 kWh/year.

Being very pessimistic (by assuming we get only half that savings), it looks like the devices should pay back in under 4 years.

For comparison, last year our gas consumption in the heating season was 60.73 kWh/degree day. Our target this year for kWh of gas per degree day is now: 55.55 representing a 9.5% reduction in consumption if we are to achieve payback in two years.

Energy Saving Halogen Replacements

When we first moved into our house 15 years ago, we installed halogen lighting in our hall.  Back then, electricity wasn’t quite so expensive, and we didn’t use the room that much anyway, and there weren’t that many options for recessed lighting.

We opted for a mains voltage system that could go on the existing dimmer switch, and therefore didn’t require expensive transformers for each light of the eight downlights.

Yesterday, I changed two of the lights over the table for the new Philips MASTER LEDspot PAR 20 MV dimmable LED lights.  I have to admit, I was ready to be disappointed, however the lights are very good.  Nearly as warm as the old lights, dimmable like the old lights, and fit in the sockets neatly as well.

I bought them from http://www.camelecws.co.uk/ in Cambridge.  I did get a quote from someone else for a discount of about £1.60 per lamp online, but I’d have had to buy 6 to get the discount.

Also on Amazon

 

The new lights have a slightly wider angle (40 degrees) but that was intentional, as the lighting was a bit too focused before anyway.

The downside?  These are really expensive (£26.34 each including VAT).

So, the break even calculations are:

£26.34 / £0.09 kWh = 293 kWh (amount of energy to break even at current prices)

293kWh / (50W – 7W) = 6813 hours (amount of time lights must be switched on to break even)

The old lamp has a life of 2500 hours, and they currently cost about £5.00 each, so it looks like we’d be replacing two of them during the payback period, so we put that back into the calculation:

(£26.34 - £10.00) / £0.09 kWh = 181 kWh

181 kWh / (50W – 7W) = 3693 hours

Now, we would like to leave these lights on in the evening from about 5pm until 10pm in the winter time, which probably averages out at 2 hours per night over the year.

3693 hours / 2  hours/day / 365 days/year  = 5 years.

That’s the payback for two of  the lights, but the 0ther 6 are more difficult, as they won’t be on nearly as often, probably averaging 20 minutes a day at best.  That makes it a 30 year payback, using the current levels of  lighting.

So the plan at the moment is to use up the stock of existing bulbs as they blow in the existing fixtures, and keep our fingers crossed that the prices come down over the next few years.

Please don’t raise the speed limit to 80mph!

There’s talk in the press today of raising the speed limit here in the UK.  While admittedly most people seem to drive at 80 anyway, increasing the limit will definitely affect most people’s pocketbooks.  I also feel it will increase pressure on other people to drive faster.  If the limit is raised, perhaps it should become an absolute limit, removing any margin of doubt.

This summer, we drove to Spain fully loaded with a roof box on top of the car with my wife and two children.  A 2500 mile marathon!

On the journey down through France, we drove at just under the speed limit of 130 kph (~ 80 mph).

We don’t do a lot of driving long distance in the UK, but specifically bought our Kia diesel for long trips like this one, and carting my daughter’s sailboat around the country to various events, and we use the cruise control a lot.

The car is fairly efficient, having averaged 46 mpg with a boat on top.  On the journey to Spain, we averaged only 44 mpg, with some legs in France getting as low as  38 mpg.  Once in Spain at 120 kph and the mountains of the Pyrenees, the economy rose, bringing the average up.

You’d think that would be the end of the story, but on the way home we made another change.  We bought wine; a lot of wine!  About 60 litres in Spain, and then added another 30 in Calais.

When we stopped for dinner, I realized my tyres were looking a bit low, so I dug out the manual while crossing in the tunnel, and decided that they were probably pretty underinflated.

Don’t forget to keep your tyres inflated properly

I decided that despite the very late return home, we had better get some air, so stopped at the exit of the tunnel, and inflated them to the recommended level for the load.

What a difference.  On the journey back through Spain and France, we managed to average only 39.5 mpg.  That’s 11% down on the journey down, just because I didn’t inflate my tyres properly.

To complete the exercise, we drove home in the car in the same state, but this time stayed at 60 mph, as it was very late at night, and we were tired, and the car was very loaded.

Having filled up in Calais, I had a new baseline, and this time with the same full load and roof box, we managed 49 mpg.

You can trade time for money

It looks like driving 20 mph faster decreases fuel economy by 11% as well.  And driving additionally with underinflated tyres decreases by a total of 20%!  I’m lucky the fuel averaged only £1.10 a litre on the continent instead of the £1.40 pretty much balancing out the extra unnecessary expense.

Further mileage tests

I also had the occasion to do two other long trips recently.  To London in the C1, where driving at 60-65 on the motorway increased mileage from the 47 mpg my wife got to my 55 mpg, again a 15% decrease for a 10 mph change.

Finally, I drove to Southampton with 4 people in the car and no roof box.  We had a good journey from Cambridge, and again, drove at between 65 and 70 mph.  This time, we managed to achieve 58 mpg, a record for the car, showing that adding weight and a roof box appears to decrease fuel economy by around 11%.

It’s Indian Summer here in the UK, 30°C/86°F here today!

The last two days (September 28, 29) we’ve had cloudless skies, so sun all day long.  We also had a very good day on September 23, but the temperatures were much cooler (around 17°C), and there was a bit more cloud.

What better way to find out how temperature affects solar PV output!

Though the total on each of the days was around 9kWh, with the peak both yesterday and today at 1.5 kW, but on the 23rd, we had our record output for a 5 minute period of 1.8 kW!  So it looks like a warm sunny day will reduce output by about 17%. 

The system is 2.1 kWp, and given the sun is pretty much over the equator on the 23rd, we can calculate that at noon on that date, the sun is at 38° (90° – 52°) elevation, and the roof is at 30° elevation, making an angle of incidence of 58°.

Sin(68°) * 2.1 = 1.94, so the panels seemed to be within spec on the 23rd.

Today, the sun was already down to 35° at noon,  therefore
Sin(65) * 2.1 = 1.90, so the difference in solar radiation was 2.1%.

Ouch—15% degredation with temperature!  I wonder if there’s any way to cool the panels more effectively?

Current Cost EnviR shortcomings regarding Power Factor

We recently installed a Current Cost meter

The system allows you to clamp a sensor around your mains cable which broadcasts readings of current to the display.  It also allows connection of up to 9 appliances.  The display aggregates the data into two hourly, daily, and monthly bins.  It also transmits the data on an RS-232 to any listening PC. The main sensor clamps onto the live output to the main fuse box in the house, which measures all current being consumed by the house.

Our challenge was to try to use this data to monitor where our energy consumption was going, as well as collect information on our solar PV installation.

In order to monitor additional systems in the house I bought a pack of three of the sensors on the left.  One clamps around the live feed from the Solar PV system, measuring Generation. I clamped another around the live leaving the fuse box going to the underfloor heating system. The final sensor was intended to be clamped around the mains cable to the cooker.

Current clamps work with a single core only

Unfortunately, my strategy of clamping around a cable in the loft to measure the current does not work.  You must clamp it around only the live cable, or the current on the neutral cancels out the live and you get no reading.

Because I had an extra transmitter, I made a special extension cable where the live passes through the sensor, so I can plug in any set of appliances into this cable.

What’s using all that “power”

When my system eventually was up and running after the initial set backs, and some opening of my fuse box to get the clamps on the circuits, I noticed that my under-floor heating was reporting 35 watts when it was not actually heating.  This struck me as too much.  I wouldn’t leave a light bulb on all the time.  While the thermostats were warm, they weren’t that warm.

So I powered down the entire house, switched on the under-floor circuit only, and found that they were not using any measurable amount of power.

Power Factor strikes!  This happens in several circumstances.  Large magnetic loads (refrigerators, and pretty much anything with motors) only use a portion of the power, returning some of it back out of phase.  The link above tells you more about it.

Now, it’s really hard to monitor “power”

Unfortunately, this makes life difficult as the sensors are describing power that is not actually being billed to you (though it does cause inefficiencies for the power companies, and the amperage actually does flow through the circuits in the house, increasing load).

What else suffers from this? My PC for one appears to show a power factor of 0.7, which means that I have to multiply the reading on my meter by this factor to get real power.

Oh, and the Inverter for the Solar PV as well.  It shows 80 watts at night, supposedly consuming this amount, though in fact it only consumes less than 1W.

There is a solution for individual appliances.   These measure the real power on the device.  Unfortunately they don’t also let you know the power factor, so as a result, you cannot subtract the “phantom” consumption from the total. They do though let you measure real cost for the individual appliance.

Note that in the UK, consumers are not billed for Power Factor.

Dimmer switches have no effect?

I also tried measuring what happened when I used the dimmer switches on eight 50W halogen lamps.  Apparently nothing, they use almost exactly the same power. 

Of course, that can’t be right, as the dimmer switch isn’t acting like a 500W heater when the lights are dimmed.

While researching the new LED lights I talked about yesterday I was warned by my electrical supplier that they’d had some problems dimming them.

Philips have a document that describes the way these things actually work.  Again, you can see what’s going on with the power factor, as it’s only consuming a portion of the load.

Too many Sensors?

So, now I’ve populated my system with a main meter, 3 additional clamps an an appliance monitor.  The system is supposed to be able to handle 10 inputs with up to 3 readings on each.

Unfortunately, it drops packets as they are colliding, and not being received by the main unit.  There is no protocol to avoid collision.  So we now have lumpy sampling to deal with as well.

Buyer Beware

I hope this has been a useful overview of the shortcomings of the Current Cost system, which while flexible isn’t really good enough for highly accurate measurements, due to the power factor issues, and lost packets.

We’re doing our best to produce some software that alleviates some of these issues, so stay tuned.

New energy saving gadgets ordered

Following on from today’s earlier post, I’m still searching for ways to make the house more efficient.

Lighting

We currently have some 240V, 50W halogen lighting in the hall, which generate 1000 candelas of light.  Now, there are 8 of these, so that’s 400W when they’re all switched on.

Today I ordered two Philips Master LEDlamps (these things aren’t cheap—over £25 each including VAT), but they do only draw 7W.  They’re also dimmable, and should fit in to the existing sockets.  If they don’t work out, I can still return them and get my money back.

Heating

In addition, I also ordered two electronic radiator control valves, that allow me to programmatically set the temperature a room should be at various times.  The target is the living room with the gas fire.  While the balanced flue fire appears to be around 90% efficient, it’s still easier to heat the lounge with the main central heating.

The plan is to not heat the room at all until 3PM, and then heat it to a base temperature until 8:30pm-ish, when the heating will switch off.  Normally, if we’re in the room, we’ll put on the fire to make it extra cosy, so if no-one’s in for any evening, it won’t keep heating.  When the fire’s on, it will warm the room sufficiently for the boiler to stop supplying heat to that room, and heat the rest of the house instead.

These devices aren’t cheap either (£25 each), and I need to drain the central heating system to add them, but as the current valves are leaking, I need to get a plumber in anyway.

Fingers crossed.  I can’t wait to see what effect these things have.

Solar PV, 3 weeks in

Our solar panels have now been in for exactly 3 weeks, and in that time we’ve generated 140 kWh of electricity.

It’s been a fairly sunny three weeks, but the panels are generating to specification.  If you want to know more, please contact me.

In order to see what is going on, I also purchased an energy monitor, which I’m developing some software for. The monitor measures the current every 6 seconds; measuring what the house is consuming, what the solar PV is generating, and aggregates the data. You can see our usage since I bought the monitor above. I’ve also got sensors on several appliances around the house as well as the under-floor heating, so more measurements should be coming as we enter the heating season in October.

The green dots at the top are the total kWh used by the house each day, and the yellow dots at the bottom are what was generated by the solar panels.   The bar graph is the consumption for two hour periods each day, the the sample immediately after the date line being from 1-3 AM.  The values above 0 are consumption, and the values below are generation from the solar panels.

The monitored values are currently inaccurate, as you’ll notice the generation in the middle of the night.  This is because the current measurement does not correct for power factor, but that is alas another blog post.

The good news though?  Over the last 3 weeks we’ve used almost no net power during daylight hours, averaging just 1.5 kWh.