Comment by homerowilson | Hacker News Reader

Comment by homerowilson | Hacker News Reader

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My partner and I have been living "off grid" using PV + battery for electricity for the last 5 years in the Appalachian mountains. We track energy use meticulously. We try to use mostly wood heat in winter, but also have a buried propane tank for supplemental heat and hot water in winter. So that is arguably not fully off grid? We have a 2,400-sq. ft. A-frame house with R-52 insulation in most walls (closed-cell + batt) and low-e glass windows (but, alas, lots of windows). We mostly cook with electric or the woodstove in winter. Our woodstove is a massive, pretty efficient soapstone masonry stove central in the house by design. South-facing windows are backed by local stone floors that capture and radiate heat in winter. The house is angled to allow sun to enter windows in winter and block sun in summer for passive heating/cooling.

The two of us use just under 5kWh / day average electricity. Our big energy use is heat in winter though! Here is the breakdown:

5kWh/day electric * 365 days = 1825 kWh/year electrons

2.5 cords wood (mostly oak) = 17584 kWh/year wood heat

300 gal. liquid propane = 8400 kWh/year propane heat

That's a total of ~27800 kWh/year for the two of us including heat. That's about 76 kWh/day or 38 kWh/day per person on average. *This includes charging my e-bike for my work commute--but we also have a gas car so not nearly all transportation energy costs.[edited to add this]

I can't see any way to go much lower than that without freezing in the winter. 2 kWh/day seems crazy low to me.

The easiest way to go lower is to live in a smaller house. Two people don't need 2,400 square feet.

a smaller house, and fewer exterior walls. common walls instead of all exterior walls drastically reduce heating requirements.

i understand that probably doesn't fit OP's lifestyle, and i'm not suggesting they move to an apartment. but i think it's important to acknowledge that dense urban living can have significant environmental benefits over the sort of self-sufficient, off-grid, rural lifestyle that's typically regarded as being more environmentally friendly. cities, and specifically apartments, are very efficient.

Cities have never been and will never be sustainable. You can cram 100 people into an apartment building, but you’re never going to be able to grow all of their food in a rooftop garden.

Although high density can be more energy efficient, it’s not the only metric to consider. Apartment dwellers are completely dependent on importing resources, while rural people at least have a chance at breaking the dependency.

You're saying that cities don't have enough surface area to collect the energy for their residents, but that's irrelevant since the energy doesn't have to be collected within the city. There's nothing unsustainable about a dense city core surrounded by fields.

At best, you've proved that a planet composed entirely of cities is unsustainable. I hope nobody wants that, but sadly some people do.

It's relevant where the resources come from. If a city depends on importing from nearby or distant fields (as well as distant mines and factories), what happens if the people who live in those places do not want their land exploited for the benefit of city dwellers? That is why civilization is based on violence: https://derrickjensen.org/endgame/premises/

Higher density living reduces heating costs... but it also increases summer cooling costs.

I don’t see how 2 people living in a 500 square foot house in the mountains would have significant cooling needs.

If you’re talking about high density in a concrete city, then cooling is a problem.

That's almost three times the size of my family's home.

> low-e glass windows > South-facing windows are backed by local stone floors that capture and radiate heat in winter.

Have you done any analysis or testing on low-e vs normal glass windows in the wintertime? In summer, obviously you want the low-e glass to block the radiant energy. But in the winter, you'd want to allow that radiant energy through, which the low-e glass is not doing.

It seems like low-e glass is only good for summer, and not winter. Have you put any thought into this? Maybe I am missing something crucial about the situation though.

> But in the winter, you'd want to allow that radiant energy through, which the low-e glass is not doing.

Low-E glass reduces inside heat radiating to the outside, too. You can find many articles online discussing the advantages during winter/heating season if you look.

I tested a couple years with/without a tinting film on my west-facing windows (under mini-blinds) and noticed a very, very small increase in winter heating costs, with a big decrease in summer cooling costs, and more consistent temperatures throughout the day in both seasons, which is a benefit in itself (you can use a lower-capacity HVAC system). I suspect a proper upgrade to low-E windows (or at least tinting ALL my windows) would have done much better.

The article suggests aiming for 2 kWh per hour (why don't they just say 2 kW?), not 2 kWh per day. So you're already there: 38 kWh/person/day = 1.6 kW/person

I'm not entirely sure if the article intends to measure embodied energy, though, which your calculations don't capture.

If you aimed to reduce your heat requirements further you can either improve the insulation or reduce your living space (or add a person to improve efficiency :P).

For comparison, we're currently working on our home (bought last year around this time). The new insulation will be U=0.1455 for walls & roof (R-68?) and U=0.29 to the basement. I don't recall the values for windows & the front door. We'll also replace oil with a heat pump and add a ventilation system with heat exchanger. And we only have 1500sqft for two (no additions planned). That will probably be still miles away from those 2kWh/d/person, but much better than the status quo (~2.5kW of heat alone, per person).

Obviously you're already in a good ball park, but GPs value of 2kWh/d/person is just really amazing.

> Obviously you're already in a good ball park, but GPs value of 2kWh/d/person is just really amazing.

It's 2kW/person, or 2kWh/h/person, or 48kWh/d/person

You are of course right, 48kWh/d/person is what the article is all about (& I'm perfectly aware of that).

But as GP[0] replied to GGP

> 2 kWh/day seems crazy low

I was under the impression that he was actually pondering a much better personal energy consumption of 83W/person. And yeah, I'm inclined to say that (with our current level of technology) achieving this number without lowering standard of living might be nearly impossible in many climate zones.

The rest of my comment is more generic.

[0] GP: https://news.ycombinator.com/item?id=32911031

The article mentions "no more than 2,000 watts (i.e. 2 kWh per hour or 48 kWh per day) by the year 2050, without lowering their standard of living" so it is not 2kWh/day but 2kWh/hour. You are already below it in your household.

There are still a lot of omitted factors in the above accounting. The car's petrol use was mentioned but not added, then you have all the embodied energy in the food and other consumed items that were never included. Finally all the energy in the construction and maintenance of infrastructure used, such as roads and internet.

48kWh/day is not hard to achieve at all. That’s just about what my solar array produces and that’s more or less energy neutral for our household. We are far from energy misers as well.

Some of it depends on the local climate and other factors that you don’t have a lot of control over though.

That 48kWh/day is supposed to include the energy used to make all of the objects you own and use though, not just your household energy usage. It takes a lot of energy to produce a house or car just to name two examples.

note that the example in the article of a swiss person's 5.1KW usage includes only 0.6KW of electical power draw, with the rest coming from other sources.

> I can't see any way to go much lower than that without freezing in the winter. 2 kWh/day seems crazy low to me.

Apart from insulation energy required for heating changes massively with local climate and scales directly with living space. So directly comparing those numbers without additional information is quite meaningless.

Here in Germany, which seems to have a roughly similar climate, ~120kwh/m2 and year is the average for a detached home. Modern buildings are usually a lot less though, 30-50 kWh/m2year seems standard. With specialised construction ('passive house') and heatpumps 10 kWh/m2year is well feasible.

Could district heating (https://en.wikipedia.org/wiki/District_heating) help? I'm from the US so I'm not familiar with the idea in practice.

> I can't see any way to go much lower than that without freezing in the winter.

Since your house is very large for just two people, you could occupy only a fraction of it, and heat only that part. Or, just move to a smaller house.

as others pointed out i misread the article, which says 2kwh per hour. indeed that is easily do-able.

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