When I read my Economy 7 electricity meter on 3 October and registered the reading in the spreadsheet that I use to monitor my electricity usage, I noticed that the day time usage had increased from 2.8kwh to 3.3kwh during September. It’s been around 2.8 for a long time so I was a bit puzzled.
I wondered if perhaps I had left my kitchen spotlights on too long because there are 3 of them rated at 20 watts. All my other lights are low power ones using 6 watts or less but the spotlights are very small and have special fitting for which I haven’t been able to find a low power bulb!
If I left the spotlights on for an extra 8 hours instead of turning them off when not required they would use an extra 0.48kw which might explain the increased daily power usage. I removed two of the spotlights and resolved to turn the other one off when not required. After a few days that made no difference so it wasn’t that.
Then I suddenly remembered that I had changed the TV Picture Setting from Normal to Dynamic which made for a much brighter and more lively picture. I looked it up on the Internet and discovered this article: OLED and LED TV Power Consumption and Electricity Cost which included the following graph:
which makes it clear that if you double the brightness you increase the power consumption by 50%. In the case of my 40inch LCD TV the rated power consumption is 90 watts so, by using a picture setting of Dynamic, I had increased the hourly power consumption by 30 watts – ie it was 60w and became 90w after the change.
NB: When I purchased a power monitor and checked out the TV it became clear the backlight increase from Normal to Dynamic had increased the power usage by 48w from 40w to 88w making a total of 768wh a day which increased the total daily usage from 2.8kwh to 3.6kwh.
Now as a retired gentleman of leisure I keep my TV on all day. If I’m watching it I choose BBC News in the morning, Documentaries in the afternoon and Detective, Spy or Action Thrillers in the evening. Sometimes I turn it to the music channels or the radio for background music. Sometimes I search YouTube for interesting videos on my phone and cast them to my TV Screen – pole dancing and belly dancing being my favourites. Sometimes I use my TV as an extended screen for my laptop when I want to view something at the same time as producing another document or when I want to play a video that I want to watch on TV – for example a salsa video for me to practice salsa on my own or with my bubble partner.
That means the TV is on 16 hours a day and the 30 watts extra for a Dynamic picture must have used up an extra 0.48kwh which would explain the increased daily power usage. I changed my picture setting back to Normal which halves the backlight brightness and also turned on the Adaptive Brightness which reduces the backlight in dark areas of the picture. I tried the Ambient Brightness setting which is supposed to take into account the lighting conditions and reduce the brightness accordingly but this seemed to make the picture too dark so I turned it off again.
I will monitor the situation for a few days to see if my daily power usage goes back down to 2.8kwh but the picture is better anyway as the Dynamic setting did make it a bit too bright – particularly in the dark areas during night scenes for example.
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METER READINGS FOR DAYTIME ELECTRICITY (at 09:00 each day)
| DATE 2020 | METER READING | KW USED | KW PER DAY | COMMENT |
|---|---|---|---|---|
| 3Aug | 2892 | |||
| 3Sep | 2979 | 87 | 2.8 | 2.8kw per day as usual in August |
| 3Oct | 3078 | 99 | 3.3 | 3.3kw per day in September! Usually 2.8 so why so high? Removed 2 of 3 spotlights in the kitchen which were 20kw each. |
| 5Oct | 3085 | 7 | 3.5 | Made no difference |
| 6Oct | 3089 | 4 | 4 | ditto |
| 7Oct | 3092 | 3 | 3 | ditto |
| 8Oct | 3096 | 4 | 3.1? | ditto – so changed TV picture setting from Dynamic to Normal |
| 9Oct | 3098 | 2 | 2.5? | Must be 2.9 or less so it’s working – will have to measure over several days to get an accurate estimate of the new daily usage! 🙂 |
| 10Oct | 3102 | 4 | 2.5? + 1.5? | My girl friend had a shower before 01:45 when the night rate comes on! Optimistically guessed the power usage. The shower uses 10kw per hour so even a 6 minutes shower is 1kw. Will need some more readings to discover if the normal daily usage is down to 2.8 or better! |
| 11Oct | 3104 | 2 | 2.5? | Wow! I had to re-guess the last 3 days to make the readings possible! Looks like I’ve reduced the usage form 3.3 to 2.5. If 0.5 is attributed to the TV that leaves 0.3 for the spotlights which is possible if they were on for 8 hours saving 8 x 40w! Maximum usage in 3 days is 8.9 (3104.9 – 3096.0) – a minimum of 1 for shower leaving 7.9 / 3 = 2.63kw for everything else. Minimum usage is 7.1 (3104.0- 3096.9) – a maximum of 1.5 for shower leaving 5.6 / 3 = 1.87 for everything else. Therefore likely usage is the average of these which is 2.25 which is even better! But is it likely that 1.05 could be saved every day? I think the maximum is 0.64 per day for TV ((0.090-0.050) x 16) and 0.3 for spotlights which is 0.94 which means the likely usage is between 2.63 and 2.36 which brings us back to 2.5! |
MONITORING FROM 8 OCTOBER | ||||
| DATE | METER READING | KW USED | KW PER DAY | COMMENT |
| 8Oct | 3096 | Changed TV picture setting from Dynamic to Normal | ||
| 12Oct | 3106 | 10 – 1 for that shower = 9 for 4 days | 2.25 | Looks like we’re down to 2.25kwh per day which means that the reduced brightness on the TV must have reduced the 90kw per hour to 53kw or better rather than the 60kw I estimated! That means the increased brightness from Normal to Dynamic increased the power usage by 70% This reduces my monthly expenditure on electricity from £44.03 to £38.67 which is a yearly saving of £64.24 and means my current direct debit of £42 need not be changed in spite of the recent increase of prices at Bulb and may be reduceable to £40 at the end of winter if my estimates prove to be correct! |
| 13Oct | 3109 | 13 – 1 for that shower = 12 for 5 days | 2.4 | I’ve just discovered that the spotlights are 3.7w each not 20w (the writing on the stem is very small) which means the observed reduction of 900w per day is totally down to the TV which comes to around 60w per hour which is amazing as the maximum power usage of the TV is supposed to be 90w. So that means the increased brightness from Normal to Dynamic was from 30 to 90 an increase of 200%! I don’t believe this so I think the power usage on Dynamic must have been at least 120w which then reduced to around 60w! This means the rated power usage quoted on the back of the TV of 90w is incorrect! I have now reinstalled the other 2 spotlights to get my bright kitchen back again . . . I turned on all 3 spotlights for 8 hours in the eventing just to prove that they really are low power LEDs using only 11w per hour (3 x 3.7)! |
| 14Oct | 3112 | 16 – 1 = 15 for 6 days | 2.5 | Will have to wait until tomorrow for the reading which should be 3114 if the current usage really is 2.5kwh per day! |
| 15Oct | 3114 | 18 – 1 = 17 for 7 days | 2.42 | Looks like the daily usage really is around 2.5kwh per day! |
| 16Oct | 3117 | 21 -1 = 20 for 8 days | 2.5 | One more reading tomorrow to confirm 2.5 and then I’ll record once a month on 3rd as usual. |
| 17Oct | 3119 | 23 -1 = 22 for 8 days | 2.5 | Final daily reading for the monitoring exercise – 2.5kwh is the daily usage now not 3.3 as last month! |
| 3Nov | Usual monthly reading to confirm actual average daily usage for the last 16 days! |
12Oct: I have just purchased 3 GU10 3W Spotlight Bulbs on eBay for £7.99 so that I can use all three spotlight using only 9w of power rather than one using 20 watts for a brighter but cheaper to run kitchen! They should arrive by Thursday! They only save £6 a year but my kitchen will be brighter with all three spots instead of only one! Compared with 3 x 20w spots the 3 x 3w spots save £28 a year!
13Oct: I can’t believe that I forgot I had already replaced those spotlights with low energy versions – see Spotlight Happiness! – maybe I really am getting old – but it will be useful to have spares and the new ones are 3w instead of 3.7 so I might as well use them if they produce the same brightness as the current ones!
15Oct: The new spotlights arrived. During the day they looked like they were going to be brighter than the old ones but when it got dark it became clear they were not. The light was just whiter, colder and more focused but not brighter so it looks like I’ve wasted my money there but maybe they will be useful one day. On the other hand I recently received a voucher for £10 for tasting some Doritos and bought a Digital Power Meter with it from Amazon. You just plug a device into it and it tells you how many watts it uses currently (eg a TV while it on) and how many kw hours over a measured period of time (eg for a fridge which has a thermostat which turns it on and off to keep the temperature constant).
20Oct: The power meter arrived so I’m testing each device in turn:
TV: Varies between 29w & 49w depending on how bright the current picture is so I’ll take that is around 40w average until I test it for a measured time period. For 16 hours that’s 0.640kwh per day – all at day rate.
Sound bar: Varies between 3.3w & 3.8w so I’ll take that as 3.5w average for 16 hours = 0.056kwh per day – all at day rate.
Laptop: Varies between 20w & 12w while charging after being unplugged for 10 minutes and then settles down to around 8 to 12w when fully charged going up to 18w occasionally when processing power is used so I’ll take that as 12w average during the day and 10w average at night = 0.274kwh per day – 0.204kwh at day rate
Microwave: Strangely the 800w setting uses 1400w which is used for about 33 minutes a day which comes to 0.770kwh a day – all at day rate. I discovered there’s a big difference between the input power required and the microwave power produced. For my microwave the 800w setting uses 1400w continuously while the 100w setting for example turns on the full power for only 1/8 of the time set which for my microwave means that it goes on every 30 seconds for 3.75 seconds. See this article for more information.
Lights: All lights are low energy – 5.7w for living room (8 hours), 11.1w (3.7 x 3) for Kitchen spotlights (3 hours), 5.7w for reading lamp (4 hours), 5.7w for bathroom (half an hour) , 5.7 for outside light (12 hours) – estimate a total of 0.180kwh per day – 0.120kwh at day rate.
Fridge: 56w when thermostat switches it on going down to 51w after a few minutes and 48w after half an hour. After 24 hours of monitoring at 17:00 on 21Oct the fridge used 410kw which means it was on 35.6% of the time. So that’s 6.05 hours per day during day rate and 2.49 hours per day during night rate. That comes to 0.290kwh at day rate.
Virgin Tivo box: Around 10w while starting up and then 12w while running the TV. 24 hours a day comes to 0.288kwh per day – 0.204kwh at day rate.
Virgin Broadband: Around 7w while starting up increasing to 10 or 11w then 12 or 13w then 13 or 13.5w when connected to the Internet. At 24 hours a day comes to 0.318kwh per day – 0.225kwh at day rate.
22Oct: I discovered that boiling the water with tea bags in it to make my tea in the microwave for 3m@800 + 2m@100 was a bad idea because the microwave is only 65% efficient compared with a kettle which is 100% efficient. Using my 1400w microwave delivered only 800w of heating power and used 75wh for a cup of tea, whereas my 3000w kettle delivered 3000w of power and used only 50wh to do the same job. For the average of 4 cups of tea a day that comes to using 200wh instead of 300wh. Similarly with my porridge, instead of heating the porridge in the microwave for 4.5m@800 using 105wh, I boiled the water in the 3000w kettle first using 50wh and then heated the porridge mixture in the microwave for 30s@800 + 4m@100 and used 24wh making the total used 74wh instead of 105. To make this possible you need a kettle like mine with a flat metal bottom over the heating element so that you can only heat the amount of water you need! Actually if you watch the kettle carefully you can boil 300ml (a mug full) of water in only 40secs rather than a full minute which uses 33wh for a cup of tea thus saving 42wh for each one – ie for 4 cups of tea with the kettle uses 133wh instead of 300wh with the microwave which is a better than a 50% saving! Similarly with the porridge the use of the kettle reduces the 105kh to 57wh which is nearly a 50% saving!
I monitored the microwave for the day using the kettle to boil water instead of the microwave and it used 510wh instead of the 770 previously estimated (22 minutes on full instead of 33). I used the kettle 4 times and that used 200wh making a total of 710wh instead of 770 so it didn’t make a lot of difference to my estimate but on the other hand the tea is faster to make and tastes better and I am saving 2.3p a day which comes to £8.35 a year!
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23Oct: I put the TV on 16 hour monitor at 08:50 today just after the electricity switched over to day time rate. It’s supposed to do that at 07:30GMT which is 08:30BST but the timer must be set wrong because it’s always 15 minutes late. I noticed that the meter mostly showed around 30w but when I watched BBC News with lots of white background with black writing on it the power usage went up to around 40w. I switched the TV picture to Dynamic and the usage went up to 88w. It went down to 40w on Normal and then back to 30w on the Custom settings I set up for optimum power usage. So in fact reducing the backlight brightness on the TV did save around 50w for 16 hours a day which comes to 0.800kwh which totally explains why the daily usage went up by around that amount when I switched the TV picture to Dynamic half way through September! When I’ve finished today’s monitoring of the TV at 00:50, which is likely to show a decrease of power usage from 640wh to 480wh, I’ll update the Summary of kwh a day used at day rate electricity & Total cost of running the TV per day
At 00:50 the reading was 0.510kwh used over the 16 hours monitoring period which gives an average of 31.9w. Please see the updated summary of kw used at day rate below.
As a matter of interest I noticed the following:
- When I opened the curtains to a bright day the power usage went up from 34w to 44w and then back down again when I closed the curtains thus proving that the Ambient sensor was working!
- When I set the TV Picture to Normal the usage went up to 44w but if I turned Adaptive Backlight on it went back to 34w thus proving that the Adaptive Backlight setting saves on power.
- The Brightness & Contrast controls didn’t seem to make much difference. Neither did the Vivid Colour, Sharpness, Colour Temperature, Tint or Colour Saturation so all of these may be set without worrying about power usage.
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Bathroom Ceiling Extractor Fan
I totally forgot about the bathroom ceiling extractor fan. My bathroom is around 60 square feet so I’m guessing the fan is rated for 130 cfm (100 + 0.5 x Area in square feet) which is probably rated at 30w as they typically use 1w per 3 to 5 cfm. (cfm = Cubic Feet per Minute)
I assumed it turned on with the bathroom light and probably turned off 10 minutes after the light is turned off. If I use the toilet 10 times a day that’s 10 x 30w x (2m + 10m) / 60 = 60wh per day which is 0.060kwh which at 17.6p per kwh costs me around 1p a day, 30p a month or £3.65 per year so I’m not going to bother to add it into the summary of kw used at day rate.
The following day I discovered that the extractor fan only turns on when you pull the cord dangling near the toilet. It turns itself off 15 minutes after you pull the cord again. This is presumable for use when there’s a smell after using the toilet as well as for reducing humidity after a shower. With my Natural Low Density Eating regime I don’t produce smells when using the toilet so I only need to use it when I have a shower which reduces the power usage to when I have a shower which is covered below.
Showers
My electric shower is rated at 10kw which means even a 3 minute shower uses 0.5kwh at 9.2p per kwh because I always shower between 00:30 & 07:30 GMT for night rate electricity. That costs me 4.6p a day while the fan will use 30w x (10m+15m) / 60 = 12wh (0.012kwh) which costs 0.1p a day. One shower a day would therefore cost me around 4.7p a day, £1.41 a month or £17.19 a year. If I forgot to shower at night rate it would cost me 9p a day, £2.70 a month or £32.89 a year so I guess it doesn’t matter that much! As I do in fact only use night time electricity for showers, I don’t need to include this in my summary of kw used at day rate. On 8 June 2021 my electricity supplier provided me with a SMART meter which meant I could use the mobile monitor to find out how much power it uses. It turns out that on full power it uses 8.25kw and on half power 5kw.
Washing
There is also the washing machine & tumble dryer which I use once a week. I time the washing machine to switch on every Monday at 5am on economy which means it only uses electricity for the motor which I assume is 300w until I can find the correct value. The economy wash lasts for 90 minutes and therefore uses 0.45kwh. I transfer the clothes to the tumble dryer at 6:30am and run it for 90 minutes on full power which I think is 2.3kw which uses 3.45kwh. That’s a total of 3.9kwh at 9.2p per kw which comes to 36p. Actually it’s 3p less than that because the last 10 minutes of the tumble dryer is on cold air to cool down the clothes to save them creasing when the drum comes to rest. As my washing only uses night time electricity, I don’t need to include this in my summary of kw used at day rate.
Using a tumble dryer specification to calculate the power of the motor!
I have discovered that the specified tumble dryer power usage for Synthetics Full Load is 1.460kwh. The specified time for that is 75 minutes which includes 10 minutes without heat which means just one of the heating elements is on for the first 65 minutes. If we assume each of the two elements are 1kw then:
65 * (1 + m) / 60 + 10*m/60 = 1.46
65 + 65*m + 10*m = 1.46 * 60 = 87.6
75*m = 87.6 – 65 = 22.6
m = 22.6 / 75 = 0.301
where m is the power usage of the motor.
which means the motor runs at 301w which sounds reasonable! In fact a search on Google revealed that many tumble dryers and washing machines use a 300w motor.
Therefore, using it for 90 minutes on full power takes:
(80 * 2.300 + 10 * 0.300) / 60 = (184 + 3) / 60 = 3.117kwh
which cost 9.2p * 3.117 = 29p
while the washing machine costs 9.2p * 0.45 = 4p
making the total for washing clothes per week only 33p which is a lot cheaper than taking it to a launderette which is likely to cost between £3 & £6 for an average load of washing.
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3Oct: Monitored Washing Machine and Tumble Dryer
Washing Machine turned on at 5am and finished at 6:25 having used 210wh at a cost of 9.2p x 0.210 = 1.9p. I noticed that it used 260w for the pump out and 410w for the fast spin at the end.
Transferred clothes to the tumble dryer and started it at 6:31 on full heat for 80 minutes. At 7:35 I noticed it had 20 minutes to go so I moved the dial on 10 minutes to the cold section so that it would finish at 7:45 when the day electricity kicks in. It used 2.27kwh for 64m full heat + 10m on cold. I noticed the tumble dryer ran at 2364w at the beginning and 215w at the end and should therefore have used (2.364 * 64 / 60) + 0.215 * 10 /60 = 2.56kwh so it must have spent some time using less perhaps when the drum changed direction. The cost was 2.56 x 9.2p = 20.9p which means the total for washing and drying was 22.8p even cheaper than the 33p previously calculated. Had I left the tumble dryer run for the full 80 minutes it would have use an extra 2.364 x 6 / 60 = 0.236 making a total of 2.8kwh costing 2.8 x 9.2p = 25.8p.
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Other high power devices not monitored yet
Toaster: 1036w
Kettle: 2860w
Vacuum Cleaner: 1320w
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TV, Sound bar, Tivo Box, Virgin Modem, Laptop
TV on: 1.310kwh / 17.75hrs = 74w
TV off: 0.220kwh / 6.5hrs = 34w
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Summary of kwh a day used at day rate electricity (07:30 to 00:30 GMT):
- 0.512 TV (32w for 16 hours)
- 0.204 Virgin Tivo box (12w for 17 hours)
- 0.225 Virgin broadband (13.25w for 17 hours)
- 0.056 Sound bar (3.5w for 16 hours)
- 0.204 Laptop (12w for 17 hours)
- 0.600 Microwave (1200w for 30 minutes) changed to 700w microwave in Jan2022
- 0.095 Kettle (2860w for 2 minutes)
- 0.290 Fridge (48w for 6.05 hours on thermostat)
- 0.120 Lights (all bulbs are low power: 5.7w or 3.7w for kitchen spotlights)
- 0.000 Toaster (1.023kw but not used any more)
- 0.000 Vacuum cleaner (Cordless – so it gets charged weekly)
- 2.306 Total kwh per day at day rate (see red note below)
The first 3 plus 7w for the microwave represent the background watts of 64w that I observe each day with the fridge kicking in every now and then to make it 1240w. The microwave is more complicated than I first thought but I know it uses an average of 600w per day because I monitored it for 8 days recently. (Last updated 14Jul2021)
This is very close to the average of 2.500kwh of electricity I use during the day so, the estimates are quite good. This was confirmed on 3Nov when the power usage since 17Oct came to 2.470kwh per day. I always take the readings of night and day electricity on 3rd of each month and register them on the Bulb website so that they can use this to generate my bill on 5th on the month when my monthly DD goes through. I sent them the reading on 17Oct too because the cost per kwh changed on that date from
16.627p (day) 8.148p (night) 20.642p (standing charge)
to
17.599p (day) 9.211p (night) 21.158p (standing charge)
all prices inclusive of vat at 5%.
I saved more by monitoring my power usage and making changes than the rate increases would have cost to the extent that I predict that I will be able to reduce my monthly DD from £42 to £38 in a few months time when I’m sure my estimates are correct!
I changed the microwave to a 700w one without a turntable in Jan2022 so I updated the total kwh per day down to 2.3. The actual amount recorded has been higher during the winter months of 2021-22 because after the Smart Meter was installed on 8 July 2021 the electricity started to switch over from the correct time of 00:30 GMT but the Smart Meter rate wasn’t changed from day to night until 00:38 which meant that around 333w got incorrectly charged at the day rate because the storage heater was running at 2.5kw during those 8 minutes. The supplier E.on Next finally corrected this on 12 March 2022 after 15 weeks of email exchanges. I have not updated the costs in this page to reflect the tariff I’ve been on since they took over from Bulb on 13June2021.
- Supplier: E.on Next
- Tariff: Next Exclusive v8
- Fixed term ends 18/06/2022
- Day rate 22.31 p/kWh
- Night rate 11.44 p/kWh
- Standing charge 7.35 p/day
- (All rates inc. VAT)
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Total cost of running the TV per day:
- 9p = 0.512kwh x 17.6p TV (40w for 16 hours at day rate)
- 4p = 0.204kwh x 17.6p Virgin Tivo box (12w for 17 hours at day rate)
- 4p = 0.225kwh x 17.6p Virgin broadband (13.25w for 17 hours at day rate)
- 1p = 0.056kwh x 17.6p Sound bar (3.5w for 16 hours at day rate)
- 0.8p = 0.084kwh x 9.2p Virgin Tivo box (12w for 7 hours at night rate)
- 0.9p = 0.093kwh x 9.2p Virgin broadband (13.25w for 7 hours at night rate)
That’s a total of 19.7p per day x 365 = £72 a year or £6 a month which isn’t bad compared with the £68.50 a month it costs me for Virgin services! In other words I’m paying around £74.50 a month to keep myself connected, informed and entertained. My laptop only costs me a further £1.50 a month to keep me connected, informed and entertained on the Internet too and to keep my blog site up to date. My mobile phone cost me a further £14 month to complete my connection, information and entertainment services. That’s a total of £90 a month or £21 a week to nourish my brain which is about the half of what I spend on keeping myself well fed with nourishing food!
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FURTHER INFORMATION
You might find this article useful for working out the best power usage to which you could calibrate your TV: Compare TV energy consumption
Here’s an interesting article about the level of lighting needed in your rooms and the relationship between lumens, standard wattage and LED wattage: How Many Lumens Do I Need?
NB: By the way, you may have heard that leaving a TV in standby mode still uses a substantial amount of power. My TV uses 0.5w when in this mode which comes to less than 0.2kw per year which costs a maximum of 4p anywhere in the world so whenever you hear that please blow a raspberry in the appropriate direction! 😉