Net-zero houses going mainstream

Some news from Proud Green Home about net-zero homes going mainstream. 

I think the key development to make this possible has been the reduction in cost of solar panels. Of course it would be very difficult without all the low-energy building technology, but without a way to generate electricity all bets are off.

The definition of net zero is also a little suspect. If a building is off-grid and not drawing any power from the outside, then it can certainly be said to be net zero. If it is connected to the grid, taking power from the grid and sending power back, then there should be a certain amount of daylight between the generation and the consumption. This is necessary to account for line losses and grid inefficiency.

The electricity that a house draws from the grid is a lot less than the power fed into the grid from thermal or nuclear power stations, because energy is lost in the wires carrying it and in the step-up and step-down transformers that convert the voltage to travel over the long distances we like to keep between out houses and those forms of dirty power. This is called the primary energy factor and varies from country to country. We used the number 2.7 to evaluate our house.

Even if a house uses fossil fuels directly, for example with a gas cooker or oil-fired boiler, you have to take into account the energy used getting the fossil fuels out of the ground, so you can't simply look at the energy use as the amount of energy going in to the house, but you have to add the amount of energy used to get that energy out. This is something like 10% of the energy you get out of them.

Similarly, when we supply our electricity to the grid, a certain amount of it is going to be lost, inadvertently heating up the wires between our house and wherever the electricity is used.

Also we have to address the issue of embodied carbon. In other words, how much energy was used in building the house, and how much carbon did that release? With a net-zero house, the question is: How many years will it take to pay back the carbon released during construction? 

Anyway, there tends to be a trajectory of good ideas from pipe-dream to realm-of-nutters to community-hobby-horse to common practice. Net-zero houses now seem to be breaking through from realm-of-nutters to community-hobby-horse. 

Building a house

(Reposted from September, 2009, with pictures added. )

We're now heading fairly surely towards actually building a house. People keep asking me what kind of house it's going to be, and I'm not really sure how to answer. I wonder if they want me to say that I'm building an igloo, or a fourteenth century Venetian palace or a brick Victorian end terrace. Certainly they want some short answer and not a long description of what colour each wall will be and what the doorknobs will be made of.

It certainly seems like I should have a short answer for this question. As building is much more of a philosophical journey than a technical one I'm just going to set out what I want to do and what that means.

I want to build a house that has an energy consumption of less than zero.

An explanation of why I'd like to build a house that produces energy should not be necessary, and in my opinion in a developed country you should not be allowed to build to consume when you can build to conserve.

Following from this basic condition for building are four topics: Energy efficiency, thermal inertia, generation of electricity and collection of heat. They are of course interconnected, but I'll try to explain each one.

When it's going to be ten below zero outside, a big part of energy efficiency is thermal efficiency. First of all, this depends on the size and shape of the building. The bigger it is, the more heat it will need. The bigger the surface area, the more heat it will lose in the winter, also, the more heat it will gain in the summer when it's over thirty outside. As well as the design and layout of the house and the rooms, the materials used are important. It must be well insulated. A lot of the heat is lost through windows, so these are very important.

Thermal inertia will keep the building at a constant temperature. The more heat the building can contain, the better. This can be both active and passive. The air in rooms contains a certain amount of heat, and it will make a difference how this air moves by convection and how it is forced and fanned where it might not otherwise go, and whether heat can be recuperated from air as it leaves the building. Water, or other liquids, can also store heat and can be moved around the house to where heat is needed. In addition, building materials can store heat. While wood is a good insulator, stone can store a lot more heat. Another possibility is phase change materials: for example floor panels containing a liquid that freezes at 19 degrees. Because of the latent heat of freezing, this can absorb a lot of heat as it is melted, and release a lot of heat as if freezes, all at the ideal temperature of 19 degrees.

Photovoltaic solar cells are pretty much the only practical way of generating electricity in a small plot in the middle of an urban area. The amount of solar energy that falls on the earth in one hour is the same as the amount used by the human race in a year, so some kind of harnessing of this power is very feasible. In fact most kinds of energy production come indirectly from the sun, whether you're burning wood, using fossilised wood in the form of coal or prehistoric microbes in the form of oil, or even using wind and waves that have been generated ultimately by temperature changes and the evaporation of the oceans. Only nuclear power and tidal generation are not originally solar. The sun is, of a course, a large nuclear reactor so I suppose you could say that all energy is ultimately nuclear. Solar cells are not highly efficient, perhaps only converting 10 to 20% of the sun's energy that hit them into electricity, but that's worth a whole new blog.

The collection of heat is most simply achieved by facing windows to the south. As the winter sun is low and the summer sun high, eaves can easily be extended to allow heat in in the winter and keep it out in the summer. This, on its own, is not going to be enough to heat the whole house and of course the more windows there are, the more heat is lost. Solar walls, developed to dry grain in Canadian barns, can absorb heat from the winter sun and convert it to hot air inside the house. Roof mounted solar thermal panels can be used to heat air or water. Combined with photovoltaics these can greatly increase efficiency, also worthy of a whole new blog. Heat pumps are another way of getting heat. They use a small amount of power to defy the second law of thermodynamics and get heat from a colder body.

I'll come onto the colour of the walls and the doorknobs later, but these will probably be influenced by the points above.

original post: http://minuszeroeco.blogspot.jp/2009/09/building-house.html

Out of the fire and into the frying pan - but what about standing in the sun?

There seems to be a bit of a panic at the moment about radiation,
nobody's calling for more coal-fired nuclear power stations and
everyone is wondering what to do. Renewable energy seems like a great
idea, but what can we do to support it?

It's a bit obvious but buying solar panels is one option. Especially
in Japan, photovoltaics (panels that produce electricity) already have
a payback of less than ten years, with national and local government
subsidies and contracts with electric companies to buy electricity off
you at a premium rate for 10 years, so if you've got spare cash it
makes more sense than putting it in a bank. Especially a Japanese bank
where interest rates are a fraction of a percent. As well as directly
producing electricity, increased demand will mean higher production of
panels, which will mean more efficient and cheaper panels, so they
will be more affordable for more people.

Japan subsidised solar panels for around ten years from 1994, during
which time prices fell to well under a half. Grants began at 900,000
yen per kW of generation, more than you would pay now, but a little
under half the cost at the time. Installations increased from 539 in
1994 and peaked at 72,825 in 2005 when the grant had dropped to 20,000
yen/kW and was to fall to nothing. The number of installations started
falling after the government grants stopped, but picked up again in
2008 when grants were re-introduced.

For each kilo watt (kW) of panel, you get very roughly 100 kilo watt
hours (kWh) of electricity per month. If the orientation of the panel
veers from due south you get less, although it drops less than you'd
think. Even at 90 degrees it's worth installing, although east-facing
roofs are better than west-facing as they heat up less and efficiency
drops as panel temperature rises. Vertically, a bit over 30 degrees
from the horizontal is optimum, but again a few degrees doesn't make a
huge difference. If you have obstacles to the south, you'll get less
sun, but most radiation is around noon, and even at midwinter the sun
is 45 degrees above the horizon, so unless you're in a deep valley, a
forest or north of a skyscraper you should get most of it.

Each kW of panel costs around 600,000 yen. The price on the
electricity bill is around 24 yen per kWh. (That's 200 months - 17
years payback.) Until the end of March 2011, the national government
was offering a grant of 70,000 yen per kW installed, and you could get
a 10-year contract with the electric company to pay you 48 yen per
kWh. If you can use cheap off-peak electricity and sell all your
daytime electricity, that's a pay back of 90 months - 7.5 years. From
April 1st, the government grant went down to 60,000, and the electric
companies will pay 42 yen. Not as good, but still a pay back of 100
months - 8.7 years.

Wind power is a bit more tricky for individuals as you need a good
site, on the top of a hill, or offshore. You can't really just stick
one on your roof; if it was going to produce significant power it
would probably tear the roof off. There are some people in the UK who
have been building wind farms and helping others to:
http://www.baywind.co.uk/ are part of http://www.energy4all.co.uk/
supporting community wind farms. Nobody ever heard of a community run
nuclear power station!

Comparing wind and solar, I suspect wind is more compatible with the
Westinghouse model for power generation--big plants and long
distances--and solar more to the Edison small scale model. Edison's
idea lost out to Westinghouse in the battle of the currents at the end
of the nineteenth century, along with several animals that Edison
electrocuted in a pyrrhic attempt to show how dangerous AC was. In the
worst irony, there are still US states that can use the electric
chairs his employees invented, for killing people. It looks like the
electric chair is on its way out, and also I'm optimistic that we're
going to see a move from the big scale model to the small scale model,
and smart grids with micro-generation, electrical storage and
intelligent devices, but that's probably more to do with my politics
than the technical and economic factors that are usually in control!

I think there is increasing momentum to move away from fossil fuels,
but just looking at CO2, nuclear seems like a good option, even to
some environmentalists (at least oustide Germany). In the 1990s
Britain had the NFFO (non-fossil fuel obligation) but this was set up
and almost exclusively used for funding nuclear power. I think going
from fossil fuels to nuclear is going from the fire into the frying
pan, rather than the frying pan into the fire, but it still seems a
bit hot!

Building a house

We're now heading fairly surely towards actually building a house. People keep asking me what kind of house it's going to be, and I'm not really sure how to answer. I wonder if they want me to say that I'm building an igloo, or a fourteenth century Venetian palace or a brick Victorian end terrace. Certainly they want some short answer and not a long description of what colour each wall will be and what the doorknobs will be made of.

It certainly seems like I should have a short answer for this question. As building is much more of a philosophical journey than a technical one I'm just going to set out what I want to do and what that means.

I want to build a house that has an energy consumption of less than zero.

An explanation of why I'd like to build a house that produces energy should not be necessary, and in my opinion in a developed country there should be no option to build to consume when you can build to conserve, but perhaps I can go into that on another day.

Following from this basic condition for building are four topics: Energy efficiency, thermal inertia, generation of electricity and collection of heat. They are of course interconnected, but I'll try to explain each one.

When it's going to be ten below zero outside, a big part of energy efficiency is thermal efficiency. First of all, this depends on the size and shape of the building. The bigger it is, the more heat it will need. The bigger the surface area, the more heat it will lose in the winter, also, the more heat it will gain in the summer when it's in the thirties. As well as the design and layout of the house and the rooms, the materials used are important, so it is well insulated. A lot of the heat is lost through windows, so these are very important.

Thermal inertia will keep the building at a constant temperature. The more heat the building can contain, the better. This can be both active and passive. The air that circulates in rooms contains a certain amount of heat, and it will make a difference how this air moves by convection and how it is forced and fanned where it might not otherwise go, and whether heat can be recuperated from air as it leaves the building. Water, or other liquids, can also store heat and can be moved around the house to where heat is needed. In addition, building materials can store heat. While wood is a good insulator, stone can store a lot more heat. You can get floor panels containing a liquid that freezes at 19 degrees. Because of the latent heat of freezing, this can absorb a lot of heat as it is melted, and release a lot of heat as if freezes, all at the ideal temperature of 19 degrees.

Photo voltaic solar cells are pretty much the only practical way of generating electricity in a small plot in the middle of an urban area. The amount of energy that falls on the earth in one hour is the same as the amount used by the human race in a year, so some kind of harnessing of this power is very feasible. In fact most kinds of energy production come indirectly from the sun, whether you're burning wood, using fossilised wood in the form of coal or prehistoric microbes in the form of oil, or even using wind and waves that have been generated ultimately by the evaporation of the oceans. Only nuclear power and tidal generation are not originally solar. The sun is, of a course, a large nuclear reactor so I suppose you could say that all energy is ultimately nuclear. Solar cells are not highly efficient, perhaps only converting 10 to 20% of the sun's energy that hit them into electricity, but that's worth a whole new blog.

The collection of heat is most simply achieved by facing windows to the south. As the winter sun is low and the summer sun high, eaves can easily be extended to allow heat in in the winter and keep it out in the summer. This, on its own, is not going to be enough to heat the whole house and of course the more windows there are, the more heat is lost. Solar walls, developed by all accounts to dry grain in Canadian barns, can absorb heat from the winter sun and convert it to hot air inside the house. Roof mounted solar panels can be used to heat air or water. Combined with photo voltaics these can increase efficiency by a few hundred percent, also worthy of a whole new blog. Heat pumps are another way of getting heat. They use a small amount of power to defy the second law of thermodynamics and get heat from a colder body.

I'll come onto the colour of the walls and the doorknobs later, but these will probably be influenced by the points above.