Five energy generations of tall buildings: an historical analysis of energy consumption in high-rise buildings

Here's an interesting look at energy consumption in high rise buildings by Philip Oldfield, in the Journal of Architecture: Vol 14, No 5.

A lot of sky scrapers today use less energy than the first ones built at the end of the 19th century, but it is difficult to say that there has been a trend towards less energy consumption over the years, and there is no evidence that it has been a prime concern of builders and designers.

A fundamental in the energy efficiency of a building is its form factor. This is the ratio of surface area to floor area. Buildings lose or gain heat through surface area, and are basically used by floor area, so other things being equal a lower form factor will mean less energy consumption, since the heat lost in winter needs heating to replace, and heat gained in summer needs cooling to remove. 

The form factor seems to have taken a couple of steps backwards. The first was in the zoning of buildings. As high rise buildings began to sprout up around New York, they grew not only upwards but also outwards, reaching for the sky and spreading out into whole blocks. This cast big shadows, stealing light and air from the surrounding neighbourhoods, leading to the 1916 Revised Zoning Regulations limiting the bulk of buildings at certain heights.

Although this inspired a lot of Art Deco, it increased the form factor since taller and pointier also has more surface area to less floor space.

The zoning represents the second generation of energy, and buildings of this period have higher form factor, higher U values and more energy use.

The next generations was heralded by the glazed curtain wall in 1951. These statements in steel and glass brought the form factor down, but the U values kept going up, and they were still heated by steam, so the energy use kept going up. Apparently buildings from the late 60s used more than twice the energy of buildings from the early 50s. Doubling in twenty years! 

The oil shock of 1973 stopped those energy bills from rising, bringing in the fourth generation. Form factors were down below the first generation, and those glass facades were doubled up and the U values also came down below the first generation of sky scrapers.

The fifth generation, since 1997, is marked by environmental consciousness. Interestingly the form factors of these buildings have gone up. The U values have gone down as they are using triple glazing, and energy generation is being incorporated, as well as natural ventilation techniques.

I can't help feeling that basic design considerations and simple thermodynamics are being overlooked in favour of adding green dressing and making bold statements. Building a windmill in the middle of your skyscraper looks cool, but couldn't you just clad it with solar panels?

Energy Thoughts and Surprises: How much electricty does the solar hot water panel pump use?

Here's someone else blogging about energy.

https://energy-surprises.blogspot.com/

I'm not the only sane person in the asylum after all!

Advice on dishwasher connection running hot and cold

When we were planning the kitchen, we were advised to plumb cold water into the dishwasher. I think the reason given was that if the dishwasher is in control of its own water heating, then it will be at the right temperature. Domestic hot water was going to start off cold until water from the boiler got through the pipes, and this would upset the wash.

Meanwhile, the Japanese manual we have for the dishwasher announces that you can save energy by connecting hot water rather than cold water, since the dishwasher uses electricity to heat water, and electricity is a very expensive way of producing heat.

At the one (and a half) year inspection last year, one of our questions was about the dishwasher plumbing, and the builder came out with the same story we'd heard at the beginning: that the domestic hot water may be cold when it is first turned on as it goes through the pipes.

Further discussion with the Japanese suppliers of the German-made dishwasher confirmed this. Also, rinsing with cold water first is apparently better for removing proteins, like egg, which can be baked on with hot water and become more difficult to remove. So plumbing cold water allows the dishwasher to use both hot and cold water, but if you plumb in hot water, it can only use hot water.

There is a range of forum discussions online discussing whether to plumb dishwashers with hot or cold water, which seem to veer towards the side of cold water and leaving the dishwasher to deal with the heating, unless you're getting your hot water from a solar thermal system, in which case the hot water is effectively free.

But our hot water is not solar thermal, and even though the domestic hot water would save some electricity, and some cost since it's using night time rates rather than evening rates, so it doesn't represent free heat. The water is still using some electricity, probably more efficiently, but by the time it's lost heat waiting in the boiler to be used, lost heat in the pipes on the way to the dishwasher, been used when the dishwasher would rather have been using cold water, and possibly been further heated, then the saving is really marginal.

So once again, we're counting the number of angels that can dance on a pin head. 

Carbon accountancy

In Energy cost, energy use and carbon I wrote that the new house emits about half the carbon of our old house. At first sight this doesn't seem so impressive, but it's important to note that the whole of the new house stays warm throughout the winter and relatively cool through the summer, while the old house was literally freezing in many places for some of the winter, and although cooler than a lot of other modern buildings, was not coping with the record temperatures of the decade we lived there.

Having noted this, I should still re-emphasise that we were only using twice the energy in the old house, so while the efficiency of our new house may be many times better, the actual carbon emissions have only halved. This is an example of the Jevons paradox, and the old adage: a little energy efficiency is a dangerous thing. We would probably emit a lot less carbon if we lived in a tent, but I'm not sure whether I'd still have a job and a family. 

Also I should note that the calculation of our carbon emissions did not consider the electricity we produce, which may substantially change the equation.

The electricity we use from the grid was probably turned from burnt fossil fuel, with all the inefficiency involved in the burning process and the turning of turbines and generators. Then it's been stepped up, sent hundreds of kilometres and stepped down again, wasting little energy on the way, but more in the stepping processes, and then some more in the wires on the way to your house. So by the time you get one kWh to your electrical appliances, you've used something like 2.7 kWh of fossil fuel. Each kilowatt hour of domesticated electricity is going to release around half a kg of carbon dioxide, and its equivalents, into the atmosphere. 

But what about the electricity from our solar panels. That's green isn't it? Not completely green, but perhaps a lighter shade of grey. 

It's relatively straightforward to get a figure for the electricity we buy over the grid, making assumptions about the overall energy picture in Japan. Of course the exact carbon cost of electricity varies around the country, from region to region and even from house to house depending on whether you're next door to the stepping-down station, or up a valley at the end of a few kilometres of cable. Nagano prefecture has a lot of hydroelectric power, but most is owned by Tokyo Electric rather than Chubu Electric, which supplies our electricity.

The performance of each region's power company can be found here and here here at the department of environment's site. Chubu electric (which supplies power to Nagano) produced 518 grammes per kWh sold in 2011, and 473 g/kWh in 2009, when the nuclear power stations were running. Tokyo electric, with the help of the hydroelectric power stations they run in Nagano, produced 464 g/kWh in 2011 and 375 in 2009. They  had more nuclear power stations to switch off, as you may have heard. There improved carbon performance is possibly due to more urban consumers living within shorter cable lengths.

We also have to estimate the carbon emitted from the electricity we use from our own solar panels, which amounts to something like 10% of what we generate and 30% of what we use.

Our solar panels were made in China. They may be leading the green revolution on many fronts, most of which are invisible to a western media usually not even trying to understand what's happening behind the Great Wall, but they still use a fair bit of coal, so most of the electricity used to make the panels is from dirty fossil fuels. They make shoes for everyone, but walk barefoot.

The estimate here at EDF Energy, based on a 25-year life time of the panels, is that each kWh of solar electricity produces 72 grammes of carbon. This is around one seventh of the grid electricity, so as the site says, it's low carbon, not zero carbon. Nuclear power is similarly encumbered with carbon costs in the extraction, purification and transportation of radioactive materials, and windmills also need to be made out of something other than air. There's no such thing as a carbon free lunch.

Of course the estimate of kg carbon per kilowatt hour of solar power depends very much on the insolation, in other words how much sunshine you get. We perhaps get twice the sunlight to somewhere like Glasgow, so our 25 years are going to produce twice the electricity for the same embedded carbon costs, and our carbon per kWh would be half of theirs. We're also closer to China, so transportation costs are a little less, but they're still using those dirty coal power stations. Conservative estimate: 50 grammes of carbon per kWh.

So our consumption of electricity, both from the grid and from our own panels emits something like 2.7 tonnes of carbon per year.

Next, how do we account for the electricity we supply to the grid in calculating our carbon emissions?

In the simplest terms, we sell a little under 12,000 kWh to the grid per year. So instead of 12,000 kWh of fossil fuels being generated, at 500 g CO2/kWh, we're generating solar electricity at 50 g CO2/kWh. This is a saving of about 5.4 tonnes of CO2 per year. So we're in carbon credit.

This is simple, but almost certainly wrong. This assumes that the moment the electricity hits our meter it's going to be used by hungry consumers. In fact there is over ten metres of cable before it even gets to the next house, and the chances are that they'll be away at work while we're generously generating their power. Ten metres may not sound far, but my ballpark estimate inside the house was that we lose 1% of electricity every 5 metres.

In the worst-case estimate, the electricity from our panels is not going to make any difference at all. Chubu electric employees are not going to be sitting at the controls of their gas-fired power stations, looking at the weather forecast and turning down the volume because my house is putting out a couple of extra kilowatts.

We can perhaps split the difference and say that half of our solar electricity is going to be of use to someone, so the amount of dirty power is reduced by 6,000 kWh per annum, and we're saving 2.7 tonnes. This balances out the 2.7 tonnes we produce, so we're carbon neutral.

If you're interested in carbon, Sunearthtools.com's may be useful.

Energy cost, energy use and carbon emissions

While looking through the Nedo data, I decided to look at energy use for our old house. We used electricity, gas and paraffin. The electricity came from the mains. The gas was in tanks out the back, which would be replaced every month or two, usually before they ran out. Our house was not connected to town gas, and in fact it may be more sensible in an earthquake-prone country to deliver tanks to houses rather than pipe inflammable gas around. I used to fill 18 litre tanks of paraffin at petrol stations or hardware shops, and drive or sometimes cycle them home, remembering the Russian proverb: chop your own wood and it will warm you twice.

The paraffin heated the bath water year round, and was used in fan heaters in the winter. The gas heated the shower, the stove and the geyser that supplied hot water to the kitchen sink. We also used electricity for a kotatsu table heater and an electric carpet. And we had a futon heater that blew hot air between the sheets, which we have to consider part of our heating cost.  

This is what the energy costs were. I think we were away for part of February.

By comparison, this is the energy use, converting the gas and paraffin to kilowatt hours. Although the winter use of gas, electricity and paraffin were roughly the same cost, the paraffin was packing a lot more energy. 

Here's the kg of carbon released. An 18 litre tank of paraffin will release 53 kg of CO2. This seems to be defying the conservation of mass, but what is happening is that the paraffin provides the C, while the two Os come out of the air. It's difficult to understand whether that is a lot, but over the year, as a family we emitted something like thirty times our own weight, 4.6 tonnes. It seems a lot. On a very rough and conservative estimate we're emitting about half as much carbon in the new house, which is obviously better, but still fifteen times our own body weights.

The calculation of kWh per cubic meter of gas and per litre of paraffin came from rekauk.com.

The kilogrammes of carbon is fairly straightforward for the fossil fuels as it's chemistry, although you need to add a little bit to the amount of carbon dioxide released in burning to account for how much was used in its production and delivery. For electricity it gets a bit more complicated as you have to work out where the electricity came from. A whole new post of carbon accountancy is needed to go into this. For now I used data from carbonindependent.org, which I hope gives a roughly accurate answer. 

Energy: Horses for courses

Energy is everywhere. In fact if we follow on from Einstein and the notion of modern physics that there is no wave-particle duality and everything is simply waves, then there is only energy. It takes on different forms, and we measure it in different ways. In very large amounts it is the mass of the matter, so perhaps we shouldn't be worrying about an energy problem at all. Getting the energy out of the matter has had mixed reviews though.

The energy in our food is usually measured in calories, which actually are kilo calories.

Electricity is bought and sold in kilowatt hours, kWh.

Oil, petrol and paraffin, the latter also known as gasoline and kerosene, come in litres or gallons.

Gas is measured in cubic metres or British thermal units, BTUs.

It's almost as if someone were trying to make it difficult to compare them.

The average calorie intake in the world takes a few searches to find. At first almost every hit is on a website about healthy eating and dieting, telling you what your calorie intake should be, or how to get it under a certain level. I guess people who are starving to death don't use the internet! There's a list on wikipedia by country. No points for guessing which country comes top of the list at almost 3,800 kilocalories per person per day. The European average is a little less with the UK weighing in at 3,400. The Japan average is significantly lower at 2,800. Converting to Joules, the standard SI way of measuring energy, US consumption corresponds to 5.8 gigajoules per capita per annum; Japan 4.2 gJ/a; UK 5.3 gJ/a.

The Food and Agriculture Organisation of the UN recommends a daily minimum of 1,800, which is a little under half the US and European consumption. The actual figures are probably a little exaggerated, as they refer to market consumption, and don't account for food wasted between production and table, or table and mouth.

Here is another angle on energy consumption and energy waste.

In energy consumption, the US comes in 11th with 300 gigajoules per capita per annum, beaten by several gulf oil states, Trinidad and Tobago and its northern neighbour Canada. Iceland comes top of the list with over twice the consumption. Japan around half, at 160 gigajoules pa. UK less still at 140 gJ/a.

So, comparing food and other human energy use, we use something like twenty times more energy than we eat. My first reaction to this was one of pity, that we need so much more energy for our tools and toys than for our bodies.

One consequence of this is that biofuels could be devastating. If we tried to produce 1% of our energy needs by biofuels, this would mean 20% less land is available for food. This would likely be the 20% that the poorest 80% of the world live off. Advice on keeping calorie intake down would probably still ride to the top of the internet hit list.

Is proper tea theft?

The other day I went into the teachers room and pressed the reboil button on the pot to make a cup of proper tea. There are a couple of two-litre insulated electric kettles there, of a kind very common in Japan, but not that I've ever seen in the UK. I think this goes down to point number 6 of George Orwell's eleven essential points to making a good cup of tea.

George and I agree on ten of them. I have to confess to being a mif, no doubt having been handed down the practice of putting milk in first from some of my proletarian forebears, who had to use milk to protect their inferior quality porcelain or earthenware from cracking upon impact of hot tea. I completely agree on the absolute necessity of the water being on a rolling boil as it is poured into the teapot, or at least soon before. 

This is the part that sets thermo-economic alarm bells going, knowing that electrical heating is expensive, and that converting water to steam requires the input of a lot of latent energy. According to this blog by Ro Randall, which PJ sent me along with the George Orwell essay, 4% of UK domestic carbon emissions come from the kettle.  This is an astounding figure, so I traced Ro's link to Chris Sherwin's blog on Green Alliance, which in turn gives you a link to Chris Goodall's book How to Live a Low-Carbon Life: The Individual's Guide to Stopping Climate Change on Amazon. I presume this is a reference not an advert. I know from George Monbiot's Heat that when it's half-time on the FA cup final, and half the country get up to put the kettle on, the extra demand on the system is more than the capacity of any one conventional power station, and, since mains electricity is instantaneous and cannot be stored, the load must be made up by a hydro-electric station in Wales that spend the rest of the time skimming excess supply from the grid to pump water uphill for such emergencies.

I like Japanese tea, but there was some milk in the fridge in the teachers' room, and there is nothing like a cup of proper tea. When I say proper tea, I mean English tea of course. The kind that's grown in India. Not the kinds you can actually identify leaves in. Not the fresh green tea they have in Japan or the naturally-fermented Chinese kind, but tea fermented by yeast. It's called koucha (crimson tea) in Japanese, and getting badly made cups of proper tea in Japan is very common. The main reason, I think, is that Japanese tea brews at a lower temperature. In fact to make a good cup of Japanese tea, you should pour water from the kettle into a cup, then from the cup into the teapot, onto the leaves which it will meet at around 70 degrees C, then straight from the teapot back into the cup to drink. Also, they have the dreadful non-British habit of putting cream in, or, perhaps worse, heating up the milk before adding it, but this gets back to Orwell's essay rather than the main point. It also gets onto milk which is a whole different area of ecogeddon.

The point is that making a cup of tea uses a lot of energy, but it is part of a ritual, as Ro Randall points out. Boiling the kettle and then waiting for the tea to mash gives you a valuable break from work, and the process takes you through a routine that is comforting in its familiarity. Technology can perhaps give us some answers, but I'm not sure whether it will stop people from over-filling kettles, or drinking tea in the first place. One of the most compelling reasons to drink tea in the first place, at least from the point of survival, was that boiling the water kills the germs in it. In many ways, with our current infrastructure, cold tap water is about the best thing you can drink, except of course its absence of psycho-active drugs like caffeine.

So we should always remember what Marx said about proper tea being theft. Actually it wasn't Marx, it was Proudhon who said that all proper tea is theft. And it wasn't proper tea either.

Using more electricity

Another record electricity bill came through. 9,000 yen. Almost 2,000 yen higher than any bill since last February. Deja vu. And we haven't put the heating on yet. Once again, this inspires me to look through the numbers and work out exactly what they are charging us for. The electricity bill doesn't say what the rate per kWh is, which I eventually found on the electricity company's website. 

Day time: 31.43 yen/kWh

At-home time: 21.23 yen/kWh

Night time: 9.33 yen/kWh

Then there is a fuel surcharge. This started the year at 1.3 yen/kWh and crept up to 1.8 in August, then dropped a little. It's going to be 1.64 in December. How careless of the electricity company to forget about the cost of fuel when deciding their tariff. I blame the airline companies for this practice, and I'm worried how far it will go. Perhaps the next time I go to the cinema they will charge extra for the film, or the next time I buy a carton of milk they will charge me extra for the milk.

Even so, this only makes at most  700 yen of the bill, and the difference between the higher rate and the lower rate is a less than 200 yen. 

Then there is a solar surcharge, which lets the electricity companies pass on the burden of paying people like me with solar panels for our electricity. This is only a tenth of a yen. 

Since August, they've added a renewable energy generation surcharge. Not sure why they need to do this as well as the solar surcharge. I thought solar was renewable, at least in the long-range future, if not aeonic future. This similarly makes a difference of tens of yen. Writing this paragraph probably cost me considerably more.

So we're no nearer explaining the 2,000 yen hike and it must be down to consumption. I can't compare with the previous year yet, but compared with the previous few months, the at-home consumption went up about 150 watts, night time 300 watts. That's a 40% an 45% increase.

Part of the reason is probably the humidifier, which I'll go into more later. We got a cheap humidifier at a second hand shop in preparation for the dry winter. If that accounts for the 150 watts at-home time, and some of the night time increase, then it was an expensive bargain!

I don't know if we're using more hot water, but heat pumps are less efficient at lower temperatures, so the drop in night time temperatures may account for the higher usage of night time electricity. 

An extra 2,000 yen

Talking electricity again: this time the bill we have to pay. After the delight of earning ten thousand yen more than expected in July-August, it was a surprise to see the amount we pay go up by a couple of thousand yen in August-September.

There is only one wire going in and out of our house, and two meters outside measuring what goes in and what goes out, so if we use electricity during the day time while the panels are generating, we will use our own power and sell less. 

The electricity bill gives a breakdown by time, and we usually buy the most electricity at night time, about 50% more than we buy in "at home time"  which is in the morning, 7am to 9am, each evening, 5pm to 11pm, and all day Saturday and Sunday 7am to 11pm. We buy very little during the day as we are usually generating far more than we need. Night time is 11pm to 7am, which is 8 hours per day everyday. Considering weekends, at-home time averages a little over 10 hours per day, and day time a little under six. Although we use much more electricity at night, we pay much less for it, and at-home time is the most significant part of the bill we pay.

From the solar panel monitor we can also see how much we consume and how much we generate. At the moment this has to be copied manually, and detailed information is lost after a month, but I hope one day to be able to download the data onto a computer. That's another story.

So why did we use so much more? I don't think we did a lot of cooking or washing, which are two of the main power users. We'd need to charge a few hundred phones to make that difference, and leave the TV on all the time. If we had been using a lot more hot water, the night time usage would have gone up but not the at-home usage, as the boiler heats water at night time. 

Another thing that appears from the bill is that this was a 33 day period, containing two weekends, so there were several more hours of at-home time than usual. Perhaps this is part of the answer. Also, while it was a couple of thousand yen higher than the August bill, that was almost a thousand yen cheaper than the bills for the past three months,

I wondered whether it was the extra load on the ventilation system because we hadn't changed the filters. A closer look at the numbers shows that the main difference was in the at-home time, where we were using around 140 watts more than the last few months. In fact at night time we were using less, if anything, so it doesn't look like a constant electricity user. The ventilation system is on all the time, so we would expect to see both night time and at-home time consumption increase. Day time consumption, as far as the electricity bill is concerned, would be lost in the fluctuations of generation. 

The only thing I can think of that we had changed was switching off the monitor from the solar panels. Before, it had been set to switch on whenever we were generating, and part of the display was encouraging us to save more electricity, or praising us if we were meeting a target. I've switched it back on again, and perhaps that will encourage us to use less electricity.

This echoes something David MacKay said in his fantastic book of energy exposition and explanation,   Without Hot Air, available in full online: "Since I started paying attention to my meter readings, my total electricity consumption has halved" (p. 156)

I had only switched off the monitor to save electricity!

A watt metre

How much is that fridge costing? Apparently as fridges get older they become much less efficient. In a more rational world, we might have MOT-type tests to check whether the fridge is still environment-worthy, and fridge maintenance teams to fix it if not. Perhaps they would come and top up the refrigerant or change the seal around the door. 

At the moment if we want to do something about it, the only choice we have is to get a new one, and when we do, this is up to chance, how long we've had it and what's growing inside or whether it matches the wallpaper.   

And maybe the argument that new fridges are much more efficient than old ones is just propganda from the manufacturers to get us to buy more fridges, and in fact the energy and resources used to make a new one are equivalent to several decades of running costs keeping the old one off a scrap heap.

Anyway, here's something that should be cheaply and widely available. A watt metre that you can plug any appliance into, that will keep track of how much electricity it is using. 

http://store.shopping.yahoo.co.jp/dejima/44135.html 

At 3,150 yen, I'm not sure how long it would take to pay for itself though.

More than just a pretty name

Having established that the Eco Cute is not particularly cute, and is only 'eco' if you're talking about economics, and macro-economics rather than anything on the micro level of the household or consumer, we have to admit that it is an intelligent device.

I somewhat maligned the eco cute in how much electricity it was using while we were away. Here's a graph of the daily usage. You can see that it's using more for the first week (average 6.6 kWh/day), then very little for several of the remaining days (average 3.9 kWh/day). The least the house used in a day was 2.1 kWh, ie running at a little under 100 watts. Looking at the hourly usage for that day, there was a flat graph whereas there are usually some bumps in the nighttime up to a few kWhours each hour while the Eco Cute is doing its thing. Taking this 2.1 kWh/day as the house base usage, for the first week the Eco Cute was using 4.5 kWh per day, then for the rest of the time 1.8 kWh per day. At 9 yen per kilowatt hour, this is hardly going to break the bank!
From the perspective of heat, this heat is going to be leaking into the house, so it gives us an idea of the extra heating bonus in the winter, and also the extra over-heating burden in the summer.
As far as working out what goes on inside the Eco Cute's brain, it appears that it calculates how much hot water is needed based on the usage over the past week, so for the first few days while we were away, it was labouring under the misconception that we were about to run baths of water. Doing this led to a tank full of hot water, leaking 4 and a half kWh of heat into the house each day. After a week, it realised that we weren't using any water, so it started producing more modest amounts, or in fact none for a couple of days.

Not so Eco and not so cute

The electricity bill for the month of March just came through, and the good news is that we only used 147 kWh. The bad news is that we were away for all of the covered period--23rd February to 25th March--so most of this energy was being used while we were out of the house. Maybe not a big deal in the grand scheme of things. This only added about 1800 yen to our electricity bill, which is little compared to the repayments on the loan, or on the amount they are paying us for our solar electricity generation, which was 45,000 yen for the same period. 

It seems a lot compared to last month when we were in and used 573 kWh. 25% in fact. 29 kWh were used in at-home time, and 117 night time. Only one kWh was used during day time, but this is not surprising as the panels will have been producing electricity for most of this time.

At-home time is 7 am to 9 am and 5 pm to 11 pm; 8 hours per day. For the 32 days, that's a power consumption of around 110 Watts. Night time is 11 pm to 7 am, also 8 hours, and you'd expect the same consumption, but it averaged 460 Watts. The only difference is the eco cute, programmed to come on at night.  Taking 110 Watts as the background consumption of the house, mainly the ventilation system and the fridge, which we left running, but also the circuitry and leds on display panels, and maybe some phantom consumption on the light bulb sensors, that means the eco cute used 88 kWh over the month. That's almost 3kWh per day, and we didn't use any hot water, and the underfloor heating was switched off. The energy it was using was just making up for the heat it was leaking into the house.

I'd set the tank to low temperature while we were away, but when we came back the display said it had one bath and 50 minutes of shower. I suppose this is less than one bath and 90 minutes of shower that it usually has, but this still seems to be a lot of heat. The exact meanings of the high, medium and low temperature settings are far from clear or explicit, and it seems like it's impossible to set them to actual temperatures, for example having the water in the tank at 50 degrees. Also, having thought that I could vary the amount of hot water in the boiler, it suddenly clicked that the setting of full tank, 50 litres or 100 litres is just for the amount of hot water it will add to the tank when you press the re-heat button. It doesn't make any difference to the amount of heat in there.

Without knowing the COP of the heat pump, it's difficult to know exactly how much heat this represents. I can maybe get some ideas by looking back over the temperature each night, and the electricity consumption data, and work out the relationship between the two, assuming that it's losing the same amount of heat each day from the constant set temperature of the tank (whatever that is) to the more or less constant temperature in the boiler room. Heat loss is proportional to temperature difference.

In a way this is the worst possible conditions for heat loss, as the tank was left full. But it was set to the lowest setting, and the boiler is inside. Imagine the usual situation where the boiler is outside, and it is left set to high. 

Microeconomics of solar power

As we look at our power consumption and think about ways of shifting it from daytime, when we lose the opportunity to sell our solar power, to night time, when they are trying to give it away, three basic approaches spring to mind: Design, technology and habits.

We also need to think about comparative power consumption. Lighting began as the major user of domestic electricity, and indeed the Japanese word for electricity, denki, is synonymous with the word for light. But today it represents a tiny fraction of our power use. Our electricity display panel shows our consumption down to the nearest 0.1 kW, or 100 watts, and switching lights on or off has never made any difference to this. Leaving every light in the house on would use perhaps 200 Watts, and require a great deal of running around, inside and outside, as several of the lights come on automatically. We seem to be using very roughly 20kWh per day, over four times this hypothetical maximum use. Of course we don't use any of the lights all the time; neither during the day time, when we're out nor when we're asleep.

The sensors on the lights seem like a good idea as they can't be left on. Someone was complaining that they stayed on a long time after being activated, about a minute, and it would be good to be able to regulate this. These lights use about 6 Watts, so if they're on for a minute, that's 0.1 Watt hours, or 0.0001 kWh. Boiling the kettle uses around 2kW, two thousand watts. Leaving the kettle on for an extra second is equivalent to leaving one of the lights on for five minutes. Watching the pot boil, and not  putting too much water in it makes much more sense than worrying about putting lights on. In fact, in terms of energy usage, I'm not sure that the decision to use sensors was sensible. It certainly makes sense in terms of light switches, or their absence, but that is another story.

In rough orders of magnitude, heating appliances use a hundred times more electricity than lighting appliances.

A lot of technology exists that can shift power consumption into the night time. For example our washing machine has a timer so we can set it to finish the cycle by 7am, and use the night-time electricity. The washing machine is using hot water from the boiler, and electric motors use less power than heat, but more than light. The washing machine has a heat pump to help with the drying cycle, which uses more power than the motor, but not as much as a heater. I'll come back to that in a moment.

The dishwasher, on the other hand, has no timer, so it relies on us remembering to set it off after 11 at night, or first thing in the morning when our electricity is cheaper. Also, the dishwasher heats cold water, rather than using hot water from our boiler. We were advised that this was wise, although that was before we realised that the adviser did not know about pipe insulation, and in fact the manual for the dishwasher advises using domestic hot water to save energy.  

The rice cooker has a timer, and we have been routinely washing rice at night and setting it to be ready for breakfast, so we are using electricity at the cheap rates.

The boiler, AKA Eco Cute, has a heat pump, which uses the power of a compressor to bring heat from the atmosphere. This uses a lot less energy than it would to directly heat the water with a heating element. The ratio of heat out to energy in is known as the COP or coefficient of performance. If the heat pump has a COP of 5, then it will get 5 units of heat energy out for each 1 unit of electrical energy. I need to look into what exactly the COP is, and how it varies with temperature, but if we were to take it as 5, and compare the dishwasher using hot water made in the Eco Cute at night time with hot water made from cold water in the middle of the day, then the former would use five times more electricity at five times the rate, and so would be twenty-five times more expensive.

If the design is right, and we use appropriate technology, we don't need to worry so much about changing our habits.

If we make breakfast before 7am, this will save us money. Easy on a weekday. Can be tough on weekends. Putting the oven and kettle on, and cooking with frying pans uses a few kilowatt hours. In fact before the breaker was boosted from 60 amps to 50 amps, the breaker would trip if the kettle and oven were both on while the eco cute was was still boiling water, and the washing machine or dishwasher were on. So we were using perhaps 5 kW to make breakfast. We weren't using all those kilowatts for an hour, but over a week, that adds up.

Another thing that would make a small difference is an electric thermos flask, with a timer to boil water before 7am, rather than a kettle using live electricity.

I'm sure, in an ideal word, the fridge would do it's cooling when the electricity is cheap and abundant, whereas now it comes on when it feels like a chill. This is more likely to happen in the middle of the day when it's hotter inside rather than the middle of the night. The fridge seems to use a couple of hundred watts for its heat pump.

It would be nice to have a power logger on each appliance so that we can see when it's using electricity. I've started tracking the hourly electrical consumption and production, so we should be able to infer some of the major users.

Apparently Eco Cutes, which have been sold largely to utilise night time electricity, have been so successfully sold in Hokkaido, the northenmost, coldest island of Japan, that night demand is now stretching the generating capacity and they're considering building more power stations.

An end to fossil fuels?

I went to buy some more kerosene yesterday. Hopefully for the last time, although I thought I was buying kerosene for the last time last year. It's now May, but it's still cold in the morning, and the heater goes on. Hopefully the new house will only need heat for January and February, and it should stay warm on its own from March. I got three cans of 18 litres, so all five cans are now full. I suppose we could have got a tank by the house and had it delivered, but that would have been more expensive and I couldn't thoil to pay. In the middle of winter I can get one tank in the front panier and one in the back panier of the bicycle and ride to the nearest petrol station, on the lines of the Russian proverb, "chop your own wood, then it will warm you twice". 

Most of the heaters we use are fan-heaters which blow out up to 3 or 4 kilowatts of heat. We also have some older heaters that will work with no electricity, and on which you can put a kettle or a pan of food. A friend in Sendai  used some old ones after the earthquake when it was bitterly cold and there was no electricity. In situations like this, movable heaters make sense, as they need no infrastructure, and there are no gas pipes to leak. We have nine rooms in the house and four electric fan-heaters, so we can be flexible about which room we heat. Usually it's just the ones we're in. If we heat more of the house, we'll get through an 18 litre can every day. 

To put that into carbon dioxide and into perspective, 18 litres of kerosene will release about 54 kg of CO2. It may seem strange that it can release more than its own weight in gas, but it just releases the carbon, which is the main constituent, somewhere between 6 and 16 atoms per molecule. Each carbon atom takes two oxygen atoms hostage from the atmosphere to make one carbon dioxide molecule.  The lowest twenty CO2-producing countries emit less than 100 kg per capita per year, so in a couple of cold days with a couple of cans, we're well over our average, and that's before we've switched on the TV, done any cooking, or got into a car, bus or train. Average emissions in Japan are a hundred times this, at around 10 tonnes per person per year, very close to Germany, and about half the US.

It makes more sense to me to have a high level of insulation and keep the house warm the whole time. In spite of poor insulation levels, Japanese houses use very little fuel for heating. I think this is down to an idea "gaman" which translates fairly neatly into "keeping a stiff upper lip". People quite happily put up with cold, because it's good for them. This is a great thing in times of crisis, although I can't help feeling there are times when people need to stop putting up with hardship and make life better.

There seems to be a kind of wisdom in the philosophy of Japanese architecture that there's something wrong with a house if it doesn't reflect the outside temperature.  If it's cold outside, it should be a little colder than normal inside, so that people are in touch with the seasons.This is ironic in a culture with such a strong sense of "inside" and "outside". Luckily there is no such sentiment regarding rain, as the same philosophy would mean that you should get slightly wet when it rains. Actually, I have heard many stories of newly-built houses leaking, but I'm sure that's not deliberate. There does seem to be a resistance to my quaint idea that houses should maintain a difference between the temperature inside and outside and it is not just a case of inability or incompetence. This is not just a matter of comfort; there are health consequences.  Levels of stroke are much higher in Nagano Prefecture than in Hokkaido. Hokkaido is colder, but insulation is standard, and the temperature inside is much higher. Nagano is still one of the coldest parts of Japan, but only 18% of new houses meet the "next generation" energy standards, which correspond to European energy standards a couple of generations ago...