Why is the electricity company paying us so much?

The arrival of bills is not usually the high point of joy, but in our house, each time an electric bill comes, there's a burst of excitement.

The electricity bill for August is 54,240 yen. That's what they are going to pay us. The only thing I wonder is, why so much?

This compares with 44,976 for July--about 10,000 yen more. We sold 1130 kWh, which is a record. July was 937, which is typical, so we sold about 200 kWh more than usual. Either we must have made a lot more, or used a lot less in the daytime. We used less than usual, or at least paid for less. We are being billed for just 5,205 yen compared to 5,935 yen for July, which gives us an idea of how much we used in the evening and at night. This was for the period 24th July to 23rd August, which corresponds pretty much exactly to the school holidays, so in fact I'd expect three people to use more electricity in the day time than just one.

As the meter is read by a human being, with daily generation up to 60 kWh, it could make a difference of a couple of thousand yen on the monthly bill whether the person comes to read in the morning or the evening. 

I'll have to wait until the end of the month and my ritual of copying numbers from one computer screen to another before finding out for sure, but I think there was a lot of generation in this period. Judging by the graph on the display panel, there was at least 25 kWh everyday. Usually there are a few days every month when it's cloudy or rainy all day and there is a single figure generation. 

Not complaining of course!

Recalculating the windows

Solar gain is a massive part of the passive house philosophy. It is probably no coincidence that the word "passive" is also used in "passive solar" design, whereby the natural radiation of the sun is used to the maximum benefit. Positioning, size and G-value of the windows makes a huge difference to the amount of direct solar gain, as do any obstacles outside.

So it was with some trepidation that I started adjusting the figures in the PHPP file to take account of the houses to the South and South West, and have a more careful look at the numbers in there.
For each window, you start with the dimensions, U Value of frame, U Value of glass, Psi value of frame and Psi value of installation. The U value is a simple, one-dimensional heat loss per unit area per degree of temperature difference between inside and outside. The Psi value is the thermal bridge effect, which is the extra heat loss per unit length along a boundary between two insulators, per degree of temperature difference. For example a square window, one metre on each side, has an area of 1, but there are 4 metres of boundary between the window and frame, and 4 metres of boundary between the window frame and the wall into which it is installed, so there are 8 metres of thermal bridge to take into account.

Those figures are enough to calculate the heat lost through the windows, over the year. As a rough guide, there are 70,000 heating degrees hours in the Matsumoto year, compared with 80,000 in central Europe. That's the total of the temperature differences for each hour over the year, so if it's freezing outside and 20 degrees inside for an hour, that's 20 heating degrees. Just as you can multiply a U value by the temperature difference to work out the instantaneous heat flow, you can multiply the U value by the heating degree hours to get the number of kWh of energy you need to replace the heat.

That's the heat being lost through the window. Window U values are based on the area of the frame and take into account the U value of the glass and the U value of the frame. Solar gain of course will only come through the glass, and not the frame. The heat being gained also depends upon the angle and orientation to the sun, depth of overhang on the top window sill, depth of sides to the left and right, and any obstacles in front. A south-facing window will get the most solar gain, and if the window is tilted from the vertical it will also increase the gain. All obstacles and overhangs will reduce the heat gained.

As far as the PHPP software is concerned, as well as the straightforward orientation and angle, which for most of our windows is due south and vertical, we need to put in the depth and distance of window reveal, depth and distance of overhang, and height and distance of shading object.

We started off with the house to the south as a shading object for all windows, 16 metres away and 5 metres above the ground floor windows, 3 metres above the upstairs windows. This makes a surprising difference even though the sun is never behind them. For the window reveal, which is to the left and right of the window, we put in a depth of 100 mm, and distance of 100 mm. The upstairs overhang we put in as 100 mm deep and 150 mm high, while the downstairs overhang is set as the balcony which is 600 mm deep and 600 mm high.

This gives us a total Passive house score of 12.3 kWh per square metre of house area per year, with a total solar gain of 5,392 kWh per year.

Actually the ground floor window panes are all at a depth of 140 mm. This change of 4 cm on the south facing windows wipes 0.3 off our score and loses us a total of 76 kWh per year. The middle concertina window panes are 120 mm from each side. The window to the West, a double tilt turn, dreh-kipp as they say in German, has panes 100 mm from each side.

Actually, they are not all at a depth of 140 mm. The west side of the kitchen window is fixed into the frame rather than into a leaf inside the frame, and is only 125 mm deep and 65 mm from the side.
It's actually not so simple, as there are wooden pillars supporting the balcony, right next to the reveal, so should we be looking at the reveal for the right side of the middle concertina as 140 deep, 120 mm away, or 300 mm deep, 150 mm away? Or in fact 800 mm deep as there is another pillar further out on the terrace supporting the balcony. I think putting in these details is going to give us a mean score as there is only one figure for reveal, which it presumably puts on both sides of the window pane. For the middle concertina pane, we can put the reveal a metre away, which should help our case.

For the furthest west window, the house next door should probably be treated as the reveal, which would be 10 m deep and 3.4 m away, were it a part of our house, which it most definitely is not, event though it is so close that it seems as if it wants to be. There are also a couple of balcony pillars there, 180 mm away and I suppose 800 mm deep, or 300 mm deep depending on which pillar you take. Perhaps these should be treated as the reveal. There is daylight between them, so it seems mean to treat it as 800 mm deep, but probably little radiation gets through that as there is a solid house beyond. The next house gives a figure 50 kWh per annum worse than the two pillars, which is another 80 kWh/a worse than one pillar.

I wonder whether it takes reflected radiation from the reveals into account. Also there's probably a considerable amount of heat reflected off the stone tiles on the terrace and into the house. It would be great to measure all of this with a solar radiation meter. I don't happen to have one though!
And the balcony is actually 800 mm above and 800 mm away from the top of the window panes, rather than 600 mm. This is the same angle, but the further away overhang leads to less solar gain, presumably because less indirect radiation from the sky above gets through. This is a difference of 47 kWh/a.

More accurately, the upstairs window reveal is 170 deep and 100 distant, taking into account the rails for the shutters, and the overhang is either 125 deep and 75 high, or 350 deep and 350 high depending on whether you take the plaster or the box for the shutters as the cutting edge of the light. That makes a difference of 97 kWh/a.

So having started with a total score of 12.3 kWh per square metre of house area per year, putting all these adjustments in, in the worst case of each scenario, we lose 541 kWh per annum solar gain, and get a score of 14.6, still within the Passive House limit of 15 kWh/m²a. There are plenty of places we can argue the toss, if necessary, especially with our double-leafed windows where the strict conditions have been applied to both sides of the window.

Science project - Electricity generation, temperature and sunlight hours in winter and summer

With a couple of days of summer holiday left, my oldest son, aged nine, began his project, or jiyu kenkyu--literally free research although if it were really free, then I'm sure he wouldn't have done it. His mum had been encouraging him to do something on flags of different countries, but in the end he decided to look at solar generation and the weather. This was partly inspired by his cousin, who was going to look at the amount of electricity and the amount of water they use. It wasn't my idea, although I was very happy to help him. It seems that these projects are more for the parents than the kids, and it felt like I was putting a lot more time and effort into this than I have done for my own research projects that have gone on to academic publications.
His first idea was that solar power generation depended on temperature, so he set about making a graph. One set of points was the the daily generation, which I've been copying into a googledoc spreadsheet from the display in the house, with his occasional help. Another data set was the temperature, courtesy of tenki.jp, who show nice monthly calendars with daily highs, lows and weather, with suns for sunshine, clouds for cloudy and so on. Because he wanted snow, he chose February first, then he decided to compare summer and winter, so he did another one for July later. He'd added the weather onto the February graph, which meant four lines running along the month, making it almost unintelligible with too much information.  The weather was very blunt, simply showing cloudy, sunny or snowy as of 3 pm. What we really wanted was the hours of sunshine.
It took a while to find data for sunlight hours online. Tenki.jp has the data but won't show it. Their live amedasu page has the last 12 hours for Matsumoto, but when you click for past data, it switches to Nagano city, which has different weather, on the other side of a mountain range, lower in altitude and closer to the influence of the Sea of Japan. We're in the mountains so even the next village has a different weather system.
JMA, Japan Meteorological Association, jma.go.jp, has extensive downloadable data, all the way back to 1872. Here they have nice monthly charts with the vital statistics for each day.
This allowed another two graphs of power generation (below in green) against hours of sunlight (in orange), which immediately appeared to be following each other, perhaps unsurprisingly.
His final report also showed graphs of power generation against temperature for July and February (daily highs in red, daily lows in blue). The power on the July graph seemed to be following the high temperatures, while the February graph power seemed inversely proportional to the low temperatures.

This makes sense as fine summer days are usually sunny, and cold winter nights are usually clear and followed by sunny days.
Next there was a table of the highest five days generating in February and the highest five days in July. The five best days in February were all over 50 kW hours, while the best five days in July were all under 50 kW hours, although the hours of sunlight were comparable. The averages were 52.1 kWh, 9.8 hours sunlight and 5.5 degrees maximum temperature in February, and 49.0 kWh, 10.2 hours sunlight and 32.5 degrees in July.
So it looks like, rather than higher temperatures meaning more generation, given the same hours of sunlight there will be more generation in Winter.
This is consistent with solar panels being more efficient at lower temperatures, which I think is because the resistance goes up with temperature. This was beyond the scope of this fourth-year elementary-school summer project, as we'd filled up the two pages which had already been a massive effort for all of us.

Confounded by car culture

We got a new car. It's a bit of a digression from house building, but relevant to the larger narrative of conservation at the mercy of consumerism.

Our old car was one of the most environment friendly in the city, but not because of high efficiency or low emmission technology. It was twenty years old and did 7 or 8 km to the litre, which car dealers call 10 km to the litre. I'm not sure what that is miles per gallon, and I'm not sure of the units of fuel efficiency in the UK where people buy litres and drive miles.

We took it to get a shaken, the two-yearly test the car must go through to be allowed on the road, much of which seems to function as a tax on old cars, and an incentive to get a new one and keep the wheels of the motor industry turning. I was expecting this would cost around one hundred thousand yen, but after taking it to the garage they said it would probably be two or three. They spent a day or two looking at what needed to be done on it, and found a dodgy brake cable and a leaking fuel pump, as well as the erratic speedometer that goes up to 60 when you turn on the engine. We then had to decide whether to get a new car, or fork out for the shaken.

After looking at the cost of a new car and the cost of shaken, as well as house-related costs over the next year, we decided to go for the shaken. This would have lasted another two years over which time we could look for a new car. Also this would give us time to build a car port to put it under.

As we arrived at the garage with our decision, the guy rushed out to tell us that the problematic part was not available. Toyota had stopped making that fuel pump and they couldn't source any. I suspect if we had gone through a smaller garage they would have been able to get some pump to work on it, but the place we went to was part of a chain and bound by insurance policies to only fit parts from the original manufacturers. But we didn't have the time and energy to go around looking for another place, and the car is being scrapped. Cut down in its prime at the age of 20, only around 90,000 km on the clock. Or perhaps sense will intervene and someone will fix the pump and drive it into a new future. Another dawn rather than a sunset.

Another option was to do without a car, using taxis or rentacars when we need one. This would probably work out cheaper long term, after considering the price of the car, insurance, tax and shaken. It would certainly have been the cheapest option short-term. The garage would have charged us for scrapping the car, but included it in the price if we got a new one. This influenced our decision to get a new car, even though the saving in the grand scheme of things was tiny. It's ironic that false economies like this are keeping the economy going.

The main reason for deciding against going car-free was that this would probably be very limiting on our freedom and convenience. It's certainly possible in theory to get taxis and rentacars, but probably not in practice. I'm not sure whether this would really be a bad thing as freedom is a fluid and flexible concept. We went for luxury and convenience anyway.

While we were talking about new cars I asked about hybrids, and told them that I'd hoped the next car I got would be electric. They seemed to think that these are way off, although I'm not so sure. Apparently there are EVs with a 300 km range, but if you're driving them in the winter the range drops to about 100 km if you use the heater. Electric motors are more efficient than combustion engines, so they put out much less heat. A hundred km is barely enough to get to a ski resort and back, which is one of the things we'd use our car for. In fact the main reasons we have a car - going camping in the summer and skiing in the winter - are the most challenging types of journey for electrical vehicles. If we wanted to ride around town and go shopping, they would be perfect.

When I say a new car it's not brand new, just new to us. Four years old actually. Belonged to an elderly couple. It looks new.

The worst thing was that we'd just put new tyres on the old car. It had only done a hundred km on them. I asked them to give me back the tyres when we scrapped the car, so I could try to sell them. It turns out that when you scrap a car, it needs to have wheels on, so I took in the winter tyres, and asked them to change them, then give me back the summer tyres. This seemed OK, but in the process of changing the tyres and the guy I was dealing with taking the day off, my tyres vanished somewhere. He told me he could give us a discount when we go to buy winter tyres off them. I suppose we need winter tyres. Actually I wonder whether we really need summer tyres or whether we could use our studless winter tyres all year round. That's a whole other issue.

The insurance man came since and the premium has gone up by 1500 yen a month, just to give another tug on those suspicions that we made the wrong decision, and make me feel that everything that is happening is primarily to get more money flowing out of my pocket.

The best thing is the number plate. I hadn't really looked at it until we got home and my wife asked me whether I'd chosen it specially. I thought perhaps it was one of our birthdays. I looked at the number and it seemed a little familiar. It's our wedding anniversary!