Mostly for myself, trying to organize thinking about what comes next: What are the paths and roadblocks to zero-carbon residences?

Homes and Energy

How can humans live in a manner that doesn’t harm the planet, doesn’t use up non-renewable resources, doesn’t take all the land, doesn’t warm the place up?

What are the boundaries our homes and their energy footprints need to fit inside?

Apologies that this is a bit all over the place, like I said this is mainly for myself organizing my thoughts.

Land use

“Built up area” is, when seen next to grazing for beef and cropland, actually kinda small. 83 million hectares for towns, industries and cities, vs 3.2 billion for cattle grazing.

If we can stay within our current footprint for housing, approximately, call it 100 million hectares split across a future 10 billion people. That makes 0.1 HA per person, 0.3 HA for a family of 3. Roads apparently take up about 20% of land area (though I’ve seen numbers as high as 50%), and residential lots take up about 75% of what remains in urban areas, according to this.

So, 0.3HA for family of three, 20% for roads etc, then 25% for non-residential stuff, leaves 0.18HA or 1800m^2 for a single-family dwelling, if you abide significant hand waving.

In short, the space used for homes today is maybe alright? The land use problems seem squarely with the cows, which we need to stop eating. But note to self I should validate this with someone that knows, maybe 0.3HA per person is still way too much?

Materials

The difficulty for materials is - thankfully - not that there aren’t options, but that those options are not necessarily the lowest cost choice. You can build a house today without concrete - foundation out of foamglass or pressure treated lumber, stick or timber framed etc. If you stretch you can remove a significant amount of plastic, though I’d be surprised if you get it to zero - think things like waterproofing layers in bathrooms, electrical wire insulation etc. Steel you’ll struggle to do without, but there’s no fundamental carbon emissions in steel production.

When our grandchildren step out on their porches and balconies, they will hopefully have a mostly cellulose-and-mineral based home behind them, with modest amount of steel in a few key places.

It would be interesting to compare costs here - how much more expensive is a foamglass foundation than a concrete pad? Can pressure treated foundations be a real alternative? We built a house on a pressure treated foundation back in 2018 and so far she’s still standing tall.. but I remain nervous and the termites in the area remain excited.

This would be a really interesting space to explore, though many of course are already!

Energy

This is where the trouble starts. You need to keep these homes heated and cooled.

Insulation

Lets start with insulation, your homes blanket to keep it warm and cool.

In theory insulation also kind of a solved provblem - passive houses, super-insulated houses, and so on: Just buy an insane amount of insulation, do some clever placement of windows and shades, bada bing bada bom. Two things create diminishing returns here.

First, the amount of insulation you need grows exponentially. If you add 1cm of insulation to a home with 1cm of insulation you cut your heat loss in half. But add the same 1cm to a home with 100cm of insulation and you’ll barely notice a change in your utility bill. For these super-insulated homes, you’ll find you need very thick layers of insulation to counteract the diminishing returns. That feeds into problem number two.

Second, insulation is surprisingly expensive. If you’ve ever bought some rockwool or EPS foam for a wall, you know what I mean. How can it cost so much?!

Expononential growth in materials need for a very expensive materials means most homes built today are not super-insulated passive homes.

Part of this maybe can be fixed with cheaper insulation products? But much of it is, frustratingly, just the physics of heat flux.

Solar

Solar is incredible. It’s a fusion reactor in the sky with wireless energy transfer via elecromagnetic waves to earth. All you need is a receiver - a solar panel - to get zero-marginal-cost energy.

The volumes are also insane. If you average all the energy humanity produces it’s about 18TW continous power globally. Most of it, 16TW or so if memory serves, from oil, gas and coal. Meanwhile the solar radiation reaching earth continuously is 173,000TW. Add up all the oil, coal, gas, nuclear, hydro, wind, geothermal and solar we’re producing today and you’ll get a number that’s four orders of magnitude smaller than the sunlight reaching our atmosphere every second of every day.

You don’t pay for the fuel, production can be colocated with consumption so you need much less expensive transmission and distrubtion infrastructure, and the receivers are essentially made out of sand! We take sand and forge it literal quantum power crystals, it’s like straight out of a 70s sci-fi.

For buildings close-ish to the equator, this makes solar a no-brainer winner for residential and commercial building load. This is why it was so easy to build off grid for us in Missouri - a small solar system generates nice power for our house there year around.

Up north the math is different. For our house in Sweden, generation in winter is something like 10% of what it is in summer - right when peak energy need for heating the home arrives, a terrible mismatch.

In summary, solar dwarfs all other sources of energy on a global scale by something like four orders of magnitude in power. If you’re in a place like southern USA, Pakistan, India etc, you can take advantage of this year around. If you live closer to the poles though, you can’t, creating a problem.

Side track: Solar and Battery costs

Because prices are changing rapidly, it’s useful to have a picture in our heads of how these prices might develop.

Everyone knows at this point the prices of PV and batteries keep dropping like rocks, continuously making forecasters look like fools. But for how long, there must be some sort of floor?

The raw materials of a solar panel - mostly refined sand in the form of glass and silicon wafers - costs something like $204/kW when I’m writing this. Panels sell wholesale today around $260/kW - a very small markup over the raw materials cost! I’m not going to rule out innovations reducing the need for materials, but it seems reasonable to say: one path here is that the price for a solar module may not be able to get below the cost of an equivalently sized sheet of glass.

Batteries are a different story. They currently sell around $77/kWh for LFP, but the raw materials for that chemistry is, currently, around $20/kWh. Seems reasonble that prices can keep dropping there for years to come as they improve production scale and efficiency.

So: Using wild hand-waving I’d expect PV to maybe level off soon, barring innovation that cuts material, and I’d expect LFP to keep falling in price.

Heating in the Nordics

For detached homes, ballpark 50% of homes use electric heating, 30% use wood pellets or similar, 20% use district heating.

Nordic district heating is absurdly polluting, because we burn plastic trash and Canadian forests for heat. Last time I did the numbers on this the district heating we had in our apartment in Malmö was significantly worse than the old leaky gas furnace we had in our old house in Missouri. The district heating can be fixed though! If you retrofit the heating source to use something like large heat pumps instead they have huge efficiencies.

The wood pellets I’d expect have disturbing land use and emissions profiles, though I haven’t done the math here. A normal detached home consumes something like 4,000kg of pellets a year. If you make the pellets from the worlds fastest growing cellulose source, bamboo, you’re looking at 2.5kg of dry matter per m2 using super intensive cropping methods, and not considering how you’re procuring the nitrogen fertilizer. That would then be about a 0.5HA of land per detached home for growing pellets.. Of course that’s not what we’re doing, the pellets come from Swedish forest industry which uses drained peat bogs for growing industrial pine. Those forests grown on drained peat bogs, in turn, account for more emissions than cars in Sweden, about 20% of total national emissions.

But it’d be interesting to do the math on the bamboo. It’s effectively a seasonal solar battery - store solar energy in the summer season as cellulose, release it in winter.

Still, we said 0.3HA max per family at the outset of this stream-of-consciousness post. If we wanted to heat homes with pellets we’d need to get them efficient enough that the pellets can be grown on something like 0.1HA.. that might be possible to do though?

TL;DR: If you want to focus on the Nordics you’ve got at least three interesting paths here. Biomass heating land use, comparing something like bamboo to solar plus storage; district heating heat pumps and sourcing energy for electric heating.

Summary

What have we discovered here, then?

  • Land for residences is likely not a huge problem(?)
  • Materials exist to allow carbon-neutral homes, but traditional methods involving concrete are cheaper
  • Insulation is great but has exponentially diminishing returns and high cost
  • Solar is an outlier energy source
  • Solar panels may struggle to keep getting cheaper, but batteries won’t
  • Solar isn’t good enough in the Nordics
  • Solar is good enough closer to the equator

Which leaves several avenues I’d like to explore:

  • Focusing on the Nordics (because that’s where I live):
    • What happens when you add wind to the model?
    • How does growing bamboo compare to solar+storage?
    • What about the peat bogs and the forest industry, maybe that’s where those of us in the Nordics could have a bigger impact?
  • Looking broader:
    • What is driving global energy growth, I recall A/C in warm places being a significant source?
    • Where specifically are solar residences viable, any places close to where I am? Germany? France? Spain?