Lesson 10: generating power

First I asked how power could be generated, which elicited a long list, including the methods below that I had prepared earlier.

The first electric power was probably generated by water, just as water mills were probably the first regular power sources to be harnessed, long before the discovery of electricity or the scientific understanding of energy and power. In 1868 a hydroelectric power station was built at Cragside, a country house in Northumberland, UK. The first modern power station was built at Niagara Falls, 1895, producing alternating current that was sent over power lines to a town several miles away. Coal was first used to generate power in 1882, in Pearl Street, Manhattan. The first electricity was generated from wind in 1887 in Glasgow. The first commercial wind farm was commissioned in 1980 in Crotched Mountain, New Hampshire. Geothermal power began on a small scale in 1904 in Lardello, Italy, and was commercialised in 1911. Oil and gas are also used to generated electricity, using similar steam turbines to coal power stations.

More recently,  nuclear power was first generated in 1954 in Obninsk USSR. Silicon solar cells were first made in the same year, and the first large-scale solar power station was built in the Mojave desert, California, in 1984. Other forms of generation include biomass, tide and wave.

Which of these is zero carbon?

None of them!

Why not?

In each case, fossil fuels are used, and carbon is emitted at some stage in the construction process. Once solar cells have been installed or hydroelectric dams have been built, electricity can be produced without carbon cost, but we need to take account of the whole lifecycle when estimating carbon footprint. Radioactive decay does not produce any carbon, but the mining, transportation and purification of nuclear fuel do, and these must be taken into consideration. 

The more pertinent questions are: which is lowest carbon? which is cheapest? and which is best? I gave this question a little bit more depth by asking which is the best way to make energy if you're an electricity company; if you're a government; if you're a city; if you're a business or if you're a home owner.

There are at least three factors to take into consideration when we're looking at cost analysis. First is $ per kWh. Second is kilograms of carbon per kWh. Third is energy return on energy invested (EROI, or EROEI), kWh out per kWh in. You can see some comparisons in the table below from two different studies.

	Murphy and Hall (2010)	Scientific American (2015)
Hydroelectric	100	40+
Wind	18	20
Coal	80	18
Natural gas	10	7
Solar	7	6
Nuclear	10	5
Oil 1970	35
Oil 2007	12

If you are a homeowner, you would not want to live under a coal power station or a nuclear reactor, and most locations would not suit hydroelectric turbines or windmills, but living under solar panels seems like a good idea in most places.

The current economics of solar power  see costs falling, year on year, and the cost of the competition rising. Fossil fuels are finite, and the situation can be likened to hiding ten thousand yen in hundred yen coins around the room. The first few coins will be really easy to find, but as more are found, the time and effort taken to find each one will increase. You can see in Murphy and Hall's data above that oil in 2007 takes almost three times more energy to extract than it did in 1970.

Grid parity is the point at which solar power costs the same as other electricity available on the grid. Of course this will be different at the point of production to the point of use. If you are an electricity company considering building a new power station, the cost of solar electricity will need to be cheaper than other options such as nuclear, coal or hydroelectric. If you are a homeowner, then you are comparing the generation cost with the market value of the electricity, which includes the transmission costs as well as other overheads and profits of the electricity companies. In many places grid parity has been reached at the point of use. This depends greatly on the local cost of electricity, and local sunlight conditions, as well as local cost of solar panels and fees for installation. Conditions are skewed by grants and feed-in tariffs.

The advantages of solar power generation include no fuel, no pollution, no noise and a long lifetime. Solar power is modular so an array can be any size from a few watts to a few megawatts, to meet supply or demand, while other forms of electricity generation need to be on a large scale. The disadvantages and challenges include the high cost and relatively large area. Orientation must be carefully considered. Solar power is unreliable and varying: nothing will be generated at night time and clouds and weather make a difference. Sunny days produce a predictably high level. Overcast days produce a predictably low level. The worst days are partly cloudy, when generation will go up and down with each passing shadow.

This is a particular challenge for the electricity companies, who have long been working on the balance between electricity supply and demand. Unlike other areas of supply and demand, electricity must be immediately available when people turn the switch on. Usually the various users in the grid will average out, but George Monbiot, in his book Heat, writes about the FA cup final. When this is on, most TVs in England are tuned to the game. This is not such a big problem, but when half time comes, somebody sitting in front of each of those TVs gets up, goes into the kitchen and puts on the kettle. This creates a surge in demand bigger than the largest power station in the country. To cope with fluctuations in demand, there are hydroelectric facilities which pump water up the hill when there is too much electricity on the grid, and send it down again when more is needed.

I have an image of guy somewhere in Wales in front of a portable TV, glued to the first half of the game and ready to flick a switch as soon as the ref reaches for his whistle.

Storage may be needed to cover the unreliability of solar, but the extra cost of the storage, especially in terms of energy, may make an already marginal source of power unsustainable.

Will solar panels save us? Are they good for the environment? Until now more energy has gone in to making solar panels than has been generated from them, but that changed around this year, and as production becomes cheaper, the return on energy invested will improve. They may save us in the future.

I didn't properly have time to cover the installation of solar panels, the best orientation, angle to the horizontal and other conditions such as the avoidance of obstacles.

Also I didn't have time to talk about solar thermal collectors, which can make a difference to the energy use of a building. There are flat plate collectors and vacuum tubes, circuits and drain back systems. Challenges include overheating, freezing, hygiene, and once again we face unreliability and the need for backup

I also didn't have time to talk about PV-T hybrid systems that combine electricity generation and collection. In the process of collecting heat, the photovoltaic elements are cooled, which makes generation more efficient, and overall these kinds of panels can reach efficiencies of something like 80%.

References
Murphy, D.J. & Hall, C.A.S. (2010). "Year in review EROI or energy return on (energy) invested". Annals of the New York Academy of Sciences 1185: 102–118.

http://www.mpoweruk.com/solar_power.htm

http://www.theguardian.com/environment/2008/oct/17/wind-power-renewable-energy

http://www.edfenergy.com/energyfuture/the-energy-gap-climate-change

Lesson 9. Windows 2.0

Back to the windows again.

We started with the same question: how could you improve the windows in the classroom? And got a fairly good range of answers, which I covered for the rest of the class. 

I gave them a short history of double glazing, from the probable invention in Victorian Scotland to commercialisation in 1930s US. Coal was cheap and windows expensive in the UK until the oil shock of the 1970s, which gave birth to the predatory double glazing salesman. I found an Everest TV advert to show them with Ted Molt on top of the Pennines. Nostalgia for me. Alien historical relic for them!

The double glazing wars continued and thicknesses began to increase. At first windows had a 6 mm gap. This went up to 8, bringing up to 50% improvement in window performance and giving the salesmen a number to show customers that their products were better than others. This went up to 12 mm, which showed a slight performance improvement and allowed people to say: "The neighbours have 8 mm double glazing, be we have 12!" They then wanted to go up to 16, but in fact this does not improve the windows, and as they get thicker, the performance starts to get worse. This is because of convection. Air can circulate within the window gap, letting heat from the inside surface rise, then drop down the cold surface on the other side. 

Capitalism and competition are not always a bad thing, and in the case of windows they have brought great improvements in performance, which have certainly improved comfort and probably reduced energy use. With extra thickness shut off as an avenue for improvement, the manufacturers had to look to other tricks, such as low-e coatings, triple panes and noble gas fillings.

After this history lesson, I wanted to give them an exercise in choosing windows, and I'd spent a long time trying to find realistic costs of windows and U values. I wondered whether something like Heisenberg's uncertainty principle was taking place, and it was impossible to know both the cost and U values of a window at the same time. 

I put "double glass" in Japanese into google shopping and it came up with some rather nice looking Bodum drinking glasses. It certainly looks like insulation is a bigger priority in Japan for beer drinking than house building. There is also a semantic element. Japanese has two words for glass: garasu and gurasu. Gurasu comes from English and refers to drinking glasses. Garasu comes from Dutch, and refers to the material. Even a search for garasu seemed to yeild more drinking glasses than windows.

I had previously spent ages trying to find a U value for the double glazed windows in the classroom, which are basically single-pane frames with two bits of glass forced in there. I started trying to find the worst double glazed windows in the world. Australian wers.com has a useful searchable database. Their worst double-glazed windows have a u-value of 6.4. That's the same as a poor single-glazed window. 

I had time in this lesson to properly introduce the surface resistance, which is an extra R value applied on each side of an insulation unit. If you imagine a thin piece of paper in the middle of a wall, it's going to have some effect keeping you warm, just because it's stopping the air from moving. The surface resistance on the outside is 0.04 m²K/W, and on the inside it's 0.13 m²K/W. The surface resistance on the outside is less than on the inside because it's more windy and the heat will be taken away more easily. 

I asked them to calculate the U value for a piece of paper by adding up the R values and ignoring the R value of the paper. This gives a U value of 5.9.

Somebody asked how the windows could have a lower U value than a piece of paper. 

I know, it's impressive isn't it. That's the power of aluminium!

They did quite a good job comparing the different kinds of windows, working out how much heat each one would lose over a year, translating that into heating costs and working out how many years it would take for the heating savings to pay for the windows. 

References

An interesting article here on homes.co.jp (in Japanese). Title roughly translates to "Japanese windows: More interested in convenience for manufacturers than benefits for consumers"

engineering toolbox's U value calculator

Eight ultra low energy passive buildings around the world

The internet is as replete with exotic buildings of exemplary design as the real world is filled with concrete contortions and architectural afterthoughts. 

Here's a list of eight ultra-low-energy passive buildings from around the world. It says they are passive houses, but they may not all be certified, or even meet the standard. They are all at least based on PH principles. 

One of them is particularly interesting as it's a dome. As far as I know there are no certified passive house domes, which is a bit surprising. I'd love to find out more about the halo dome in China, but searching for it on Google mostly arrived at a vape pipe. I wonder if they left any cookies.

Domes are very energy efficient shapes, with a lower surface area to volume than any other. The only way to get a better form factor is to start turning it into a sphere and bringing it out of the ground. You sometimes see water tanks of that design. Even then, you may be better off with a hemisphere since the ground tends to be warmer than the air in the winter, so less heat will be conducted than into the air. On the other hand, heat is often more convected than conducted to air, so the conduction to the ground may be higher. Also, there would be less radiation and less convection from the parts of a protruding sphere pointing downwards. I probably need to investigate this more.

Looking at the geometry of form factors, a single storey dome of any size has the same form factor as a completely square two storey standalone building. If the dome has many storeys inside, it will have a better form factor than anything. The only problem is building without straight lines and right angles. A trivial problem when you're sketching ideas on paper, but a huge problem when you're procuring building parts and giving instructions to builders.

Lesson 8: Standards

There are several reasons to build a low energy building. It may save you money through cheaper bills over the lifetime of the building. It may reduce your carbon footprint and reduce damage to the environment. It may be eligible for grants or tax breaks that could make building or financing cheaper. 

Another reason, in some places, is that there are building standards that require you to build a low energy building. The earliest of these was probably the Danish BR77 standard, introduced in 1977 and obligatory a couple of years later. The 1980 Swedish SBN-80 (Svensk Bygg Norm) also set demanding energy efficiency requirements early on. Around the same time the R-2000 standard came out in Canada, although that was voluntary.

At the risk of coming out with a lesson dryer than the one on humidity, I started off putting my students into a couple of groups, telling them to imagine they were governments and getting them to come up with some standards to reduce energy use in buildings.


First they were to brainstorm a list of ideas. Later they would be able to use judgement and discussion to choose the best. They had various ideas, from banning aluminium windows and setting limits on carbon emissions to setting up bodies to reduce energy use and prohibiting air conditioners.

There are basically three different kinds of standards: prescriptive, performance based and outcomes based.

Prescriptive standards tell builders and designers what they must do, for example that walls must have U values of 0.13 W/m²K. The advantage of prescriptive standards is that they are clear and definitive. The disadvantage is that they may may be too conservative, leading to buildings that are over-engineered, or they may not take into account how prescribed building elements are used, for example the orientation of the windows.

Performance-based standards require calculations to predict how much energy a building will use. For example heating energy of less than 15 kWh/m²a. This gives designers more freedom in how to use building elements in optimal ways, and to make sensible compromises with the over picture in mind. They do mean that designers have to make those calculations. Performance-based standards may also help in the introduction and use of non-traditional features and techniques.

Outcome-based codes mean that the actual performance of buildings is measured and reported, to ensure that standards have been met. If it turns out they don't, it's too late!

I gave a brief history of building standards around the world, starting in the 1970's. I briefly mentioned the US's flirtation with energy conservation in that short era of energy democracy, before the energy republic of Reagan took over.

The main story was in Denmark and Sweden, where standards in 1980 were only reached in the UK in 2006. Meanwhile over here in Japan, the standards today in Matsumoto are roughly equivalent to those in 1985 in the UK.

Of course it is very difficult to compare building standards in different countries, and normalising for weather is one issue. Another is how many buildings comply to the standards. Not only are Japan's standards something like thirty years behind the UK and fifty years behind Sweden, they are also applied to well under half of newly built small homes.

Here are some links if you want to read more:
Global energy efficiency measures could save €410 billion by 2030
Map of global standards

WPBG Energy Codes

Country report on Japan

PNL Report from April 2009 

EU report on Japan

15 quid a year Passive House in Wirral wins award

On the BBC here.

And more details from architects John McCall here.

It's similar to our house in many ways:

• Roof integrated solar panels, although I think we about have twice as many
• Atmospheric heat pump, so electricity is the only energy source
• Underfloor heating
• The same foundation structure
• Similar annual heating load where we are and the Wirral 

The construction is completely different. Ours is wood but theirs is concrete block. It looks to have better insulation and better windows, and is more airtight.

They say they use about six times less total energy than the Passive house standard. I'm not sure how they calculate this. We use around 15% less than the standard. From the copy of their electricity bill, it looks like their house uses a little over half the electricity of ours. They don't give the area of the house but judging by the total cost and cost per square metre it looks to be 180 square metres. When the energy usage is worked out per floor area, I would expect them to be 40% of the standard. I calculated our primary energy use to be 2.7 times the electricity we used, and I think the UK has a similar energy profile to Japan, so every unit of electricity consumed in the home has taken 2.7 units of primary energy to produce and get it there. Some of their electricity is coming from solar panels, so they may choose a different value, and perhaps I should too! If they take the electricity as primary energy they get to 6 times less than the passive house requirement.

Whether it's 40% of the Passive house requirement, or six times less, it's still very impressive. 

2015: Hottest year on record

Yes, 2015 is the hottest year on record. It's official! Admittedly my records only go back three years. But this year is definitely the hottest!

Usually we switch on the heating 1st December. This year it's already a week later and we haven't thought about switching it on yet. It doesn't feel like we need it, but maybe that's just us getting hardy? 

With sixteen thermometers built into the the house, recording data for the past four years, it's possible to actually check the data. Numbers don't have feelings!

I looked at just three temperatures: the centre of the slab, the south-west corner of the slab, and the north-west corner of the slab. The slab is something like seventy centimetres deep, so there is a big different in the fluctuation of temperature from top to bottom, and up to a couple of degrees difference in actual temperature. The temperature at the top of the slab can vary by up to half a degree in a day, while at the bottom it's more like half a degree a week. 

As of 8th December, the middle of the slab is warmest, currently around 23 degrees. The South West corner is a couple of degrees cooler, around 21 degrees, and the North West corner is a few degrees cooler still, around 17 degrees. This is near the front door, and that's another story. 

As the temperature outside rises and falls, the temperatures inside slowly follows, heat making it's unassailable journey from hotter to cooler. The North East corner of the house gets cooler quicker, less affected by the sun, and more affected by outside air. The centre of the house is slowest to cool, surrounded by all the thermal mass of the concrete. In the summer it is the slowest to warm up.

Looking back over data for the last three years, the house was at the same temperature on 16th November 2014, 13th November 2013, and 20th November 2012. That's around three weeks earlier. 

The threat of global warming threatens increased flooding, extreme weather conditions and climate disruption. A reduction in my already very small heating bill may offer a silver lining, admittedly a pathetically thin one that may not help people who have to cross their living room by dinghy. I may be able to buy a new paddle for my dinghy. 

Lesson 7: Ventilation

The first attempt at teaching a course is always a much bigger lesson for the teacher than the students. As in warfare, the first victim of a lesson is often the battle plan. 

Three times I've found that a single lesson has turned into two, and the course feels like it is being resized and re-dimensioned. I thought we were almost half way through the time, but only a quarter of the way through the plan, but checking back with the plan I now realise that the lesson I had prepared on insulation included thermal bridges, and the lesson on air and water included ventilation, which were four lessons on the original plan, and I'm more or less where I thought I would be. 

The ventilation lesson began at the realisation that houses must be both insulated and airtight to have low energy loss. If an insulated building is not airtight, three things will happen: you will get condensation within the walls, you'll lose heat with the leaking air, and you'll get fresh air in the house. The last one doesn't sound so bad, and in fact you need fresh air in a building. I asked the class why, and how much we need. 

The most obvious is to provide oxygen. Although the most obvious it is not the most serious. We need around one litre of air per second per person to avoid a build up of carbon dioxide. Relatively low levels of carbon dioxide can lead to lack of concentration. 

You need about three litres per second to remove nitrous oxides given off while cooking, and 3.5 litres per second do remove unpleasant odours from the house. Then you need about 6.5 litres per second to be safe from the volatile organic compounds that are used in paints, varnishes, glues and other chemicals in building and its furniture. The biggest need for ventilation is to stop a build up of moisture, for which we need about seven litres per second per person. The air we exhale is close to 100% relative humidity, since we are mostly water, and close to body temperature, since we are warm-blooded, so we're putting out a lot of moisture. 

This means a design ventilation of 8 litres per second, or 30 cubic metres per hour per person. Taking an average of 35 square metres per person this means about one complete air change every three hours, or 0.34 air changes per hour. 

Air can be changed by opening windows, using air vents, using extractor fans or mechanical ventilation systems. 

Natural ventilation, whether by windows or vents, is cheap and easy. It works either on pressure difference or temperature difference. Opening windows on the north and south of a building will create a through draft. Opening windows upstairs and downstairs causes air flow through the stack effect. This can be calculated, but not in my lesson! 

Natural ventilation will usually provide too much or too little ventilation. There is also a risk that someone will get in and steal your telly if you leave the windows open. And it may not be a good idea if it's raining outside. Extractor fans are relatively cheap and will provide a more steady rate of ventilation. Mechanical ventilation systems are more expensive to install but will provide steady ventilation, and also allow heat recovery. 

So how much heat will be lost by ventilation? Using a few assumption, on a winter's day when it's freezing outside and 20 degrees inside, we lose heat at a rate of almost 200 watts per person. At first this doesn't sound like so much. 

We looked at heating degree days. For example, the graph below shows in blue how hot it was outside and how many degrees each hour we have to heat up the air by. 

As far as heating energy is concerned, a temperature difference of one degree for ten hours is the same as a temperature difference of ten degrees for one hour. 

You can add these up over the year, and for Matsumoto it's a total of 80,000 kelvin hours per year, or 80 kilo kelvin hours per year. Incidentally this is about the same as for Manchester. So you can work out that ventilation for a year is going to lose 768 kWh. This is about a month's electricity bill, so it looks like quite a lot. 

Finally I explained mechanical ventilation with heat recovery (MVHR), which turns out to be a very cheap way to heat your house, as long as you have gone through the expense of making it airtight and well insulated.

Also in today's lesson I gave out some questionnaires, which the school hands out in the middle of the term. Everyone seemed happy with the course the way it is, except one person who wanted me to make the calculations easier! I'm doing my best.