Friday, 3 September 2021

Hydrogen. Really?

Green hydrogen may be the solution to a cleaner carbon-free future, or it may just be another bit of greenwashing from the fossil fuel industry that will make no real difference but let them carry on as normal. My initial hunch is that it's not a solution. Rough calculations and careful research also suggest that it's only a good idea if you want to keep selling gas and pumping oil out of the ground. Who on earth would want to do that? 

In theory it sounds great. Hydrogen is literally floating around in the ocean and all we need to do is snip off those oxygen atoms. Then we can burn the hydrogen and it will just give off clean water.

Getting hydrogen out of water is simple: you just need to pass electricity through it. The molecules will break up, oxygen will bubble up from the anode and hydrogen will bubble up from the cathode. I tried that when I was a school kid, after hearing the squeaky pop in a science classroom. In practice it's not as easy as just taking the Os off the H2 atoms. Not everything that is simple is easy. To get electricity to pass through the water you have to add a bit of salt, otherwise it doesn't really conduct. This means you have sodium and chlorine in the mix and start getting some build up of chemicals and noxious gases coming off the electrodes. This was Ok for a little after-school science experiment but to do this on a larger scale there are more complications. 
Picture from Walt Disney,
I mean Penn State University

Actually it probably wasn't that good an idea for a child to do since you're also going to get some chlorine gas coming off the anode, which is deadly poisonous. The sodium ends up as sodium hydroxide which is highly corrosive, or can act as an insulating coating on the electrode. In fact electrolysis does not split the H2O into H2 and O; it actually splits it into H and OH, but I don't want to get into too much chemistry. My own experiment stopped working after a while, and I had to replace the electrodes. A large-scale application needs an electrolyte that will let the electrodes keep working without regular replacement or cleaning. 

The most critical difference with the real world is that I wasn't worried about how much electricity I was using in my experiments. This was only a small fraction of our household use and my parents were paying the bill anyway—it would be at least ten years before I took an electricity bill seriously. And only a small fraction of that electrical energy was going into the splitting of those chemical bonds with most of it probably just warming up the water. I was really only interested in the squeaky pop when I burnt a small collection of hydrogen and not the amount of energy it would release when burning.

Energy is the biggest consideration if we're talking about Hydrogen for energy use in a real-world application. Chemical energy is all in the electrons and the energy required or released when a chemical reaction happens. So energy is required to split two hydrogen atoms from the oxygen atom. You get energy back when the two hydrogen atoms combine with an oxygen atom, but you will never get back all the energy you put in. Are you keeping track of all these inefficiencies?

Also, you need to collect and store the hydrogen, then transport it. It would be lovely to put the hydrogen into bags and send them floating to where they are needed. There was some experience with floating bags of hydrogen up to the 1930s which I will come back to later. More likely you'll need a compressor, which will use more energy but will make it easier to store in terms of space and perhaps easier to transport in gas bottles.

Quick reality check: the energy in the hydrogen is just in the electrons, and if you're thinking of transporting that hydrogen it may be a lot less efficient than just using electricity, which sends the electrons only. It's the difference between sending an email and printing out the email and sending it as a letter. When people say that hydrogen is the future of energy, you have to wonder whether letters are the future of communication.

Until now commercial hydrogen has not been made from electrolysis, it is produced by steam cracking fossil fuel gas, which is some combination of carbon and hydrogen atoms, and then throwing the carbon away, usually in the form of CO2. This is called "Grey Hydrogen" and produces more global warming gases than just burning the fossil fuel gas.

"Blue Hydrogen" is split from fossil fuels, but the carbon is captured, which in theory means there is no carbon. However, some of the carbon escapes rather than being captured, and since carbon-capture also uses energy, this still ends up being worse than just burning the fossil fuels in the first place. It's not as bad as grey carbon, but it's still worse than burning coal.

Some companies are also making electrolysers so renewable energy can be turned into "Green Hydrogen". This is probably going to produce less carbon than Blue Hydrogen, but it depends on the electricity being low carbon to start with, and I'm really not sure if it's better than sending the electricity over the existing grid, or putting it into batteries.

We haven't even talked about using the hydrogen yet. To be honest I can already see enough problems above to write off hydrogen as an energy source because it's going to use so much energy to make.

Hydrogen is a gas. Natural gas is a gas. So we can just use it the same way. Right?

Again there are a few problems to work out. Hydrogen has much smaller molecules than natural gas, so it has more chance of leaking. Also it's much more reactive, and will react with most kinds of steel so you need to make sure the pipes and cookers or boilers are free of steel.

Of course hydrogen does not produce Carbon oxides when burnt, which is great, but it can produce six times more nitrous oxides as it burns more of the nitrogen in the air. At a local level NOx are already much more dangerous pollutants than Carbon dioxide.

What about vehicles?

Using hydrogen in an internal combustion engine is also not impossible, as long as you first get over those issues of leakage, reaction and pollution. Since internal combustion engines are not very efficient it turns out to be much better to use a fuel cell to turn hydrogen and oxygen back into water and release electricity, then use an electric motor. If you have an electric motor, please remind me why we're not just using a battery? We have battery technology, and there is already a grid to get it around wherever people go, and connect it to sources of renewable energy. And you would probably want a small battery at least in your vehicle to handle some energy recovery braking with the electric motors.

To summarise, conventional "grey" hydrogen is a carbon disaster. "Blue Hydrogen" produces more carbon than just burning the fossil fuels. "Green" hydrogen may be possible from renewable energy but is not likely to be very efficient. Different infrastructure and units will be needed to use hydrogen domestically or commercially instead of natural gas. For transport it will make most sense with fuel cells and electric motors. So why not just use batteries?

As for transporting hydrogen around the world, bags of hydrogen were floating around in the 1920s and 1930s. Airships may seem like a ridiculous way to travel, but the first round-the-world flight was in an airship, as was the first aircraft to clock up a million miles and the first scheduled transatlantic air crossings, which knocked days off the alternative ocean liners. Until the 1940s travelling a long distance by fixed wing plane would have seemed as realistic as travelling by space shuttle did in the 1990s.

A few high-profile airship accidents helped bring down the airship as the future of long-distance transport, but in the end it was probably the second world war that brought their era to an end. Switching from hydrogen to helium would have made the airships much safer, but the airship technology was mostly in Germany and trade became difficult with the United States which had all the helium. More critically, the war came and a fight between a fixed-wing plane and an airship is something like a fight between Mike Tyson and a piece of damp tissue paper, so technical development went into aircraft of increasing speed and size. The passenger jets that arrived after the war resulted from developments that were driven by the need to fight and flee more quickly and to carry more and larger bombs.

Back in the 1920s when the R100 was being designed, they considered using an engine that could switch between diesel and hydrogen. Airships usually got their lift from hydrogen and their thrust from diesel engines. As a journey went on the diesel would burn away and the airship would get lighter. In order to descend they would need to release some hydrogen. Rather than throwing it away, it would make more sense to burn the hydrogen in one of the engines.

They did not develop hydrogen engines even when they were literally carrying around bags of hydrogen that they were going to throw away. There is some evidence that we are much cleverer now and could easily come up with hydrogen engines, but I don't think the evidence is very strong.


Hydrogen: Get-out-of-Jail-free card for the building industry?

"the greenhouse gas footprint of blue hydrogen is more than 20 percent greater than burning natural gas or coal for heat and some 60 percent greater than burning diesel oil for heat,"

"Two European studies have found that burning hydrogen-enriched natural gas in an industrial setting can lead to NOx emissions up to six times that of methane"

ITM power is set to leave blue hydrogen in the dust by producing electrolyers as cheap as £500,000 per Mega Watt. (This compares to the cost of solar panels at around £700,000-£1.3 million per Mega Watt

Tuesday, 15 June 2021

Thinking of Getting a Wood Burning Stove?

There is something magical about wood fires, and people are often tempted to put them into their houses. In writing on low energy building, I haven't really talked about wood burning stoves. People sometimes ask how you can fit a wood burning stove in a low energy building, but the question you first need to answer is: why do you want a wood burning stove?

Before you get one for your house, and especially before you plan to build a new house around a wood burner, you should check that you meet at least four or five of these seven criteria. You don't have to meet all the criteria, and in fact some of them may contradict each other. But you should meet most of them.

1. You have a sustainable source of wood.

Perhaps you live in a forest, or a relative has an orchard, or you live next to a timber yard, or you just inherited a derelict warehouse with a large collection of broken pallets. If you don't know where your wood is going to come from, then you will need to buy it. You may have thought that wood grows on trees. In fact wood does grow on trees, but those trees grow on land, and that land usually belongs to someone. The trees also play a major role in creating habitat for wildlife, and are acting as a sink of atmospheric carbon and a source of oxygen. 

Well-managed forest can provide better habitat for wildlife and can provide more effective carbon sinks, but burning wood will send some of the carbon that has been stored over the last decades or centuries straight back into the atmosphere. Even if the forests are well managed, burning the wood that grows there may not be the best use of it. If left on the forest floor, wood can provide excellent nutrition for the forest and habitat for some of the diverse life there. 
Not really firewood!

So wood may not be the best fuel for your house in terms of economics or ecology.
Or it may be the best thing in terms of economics and ecology. 

I don't know the answer, but if you're thinking of using wood, please find out!

2. You like chopping and storing wood, making fires and cleaning stoves and chimneys.

Having a wood burning stove is a lifestyle choice. That's another way of saying that it will take more time, cost more money and may be worse than the alternatives in various other ways. Wood needs to be chopped and stored where it will stay long enough to dry out, but not too long in the same place where it will attract insects and other undesirables. If you only occasionally want to burn stuff, it may be better to go camping. There are some great campsites that allow you to have a fire!

3. You have no neighbours.

You may be planning to go off-grid, which is a great idea if you live away from civilisation, and this may go hand-in-hand with the first criteria. If you are in a residential area, your neighbours may not appreciate smoke getting into their washing. This article in the Huffington Post suggested that the most efficient wood-burning stove will put out the same levels of pollution as 18 diesel cars. Would you like a fleet of cars driving around your neighbourhood?

4. You are going to get the most efficient model available, with a properly installed chimney.

Benjamin Franklin did make significant improvements to stove design back in the 1700s, but even in the 1800s wood burning stoves were only 30% efficient. They sent out particles at levels that would be illegal today, and allowed creosote to build up in chimneys, creating a fire hazard.

Things have got better since the 1800s but even the most efficient wood burning stove will only burn wood at around 80% efficiency. 

5. Your wood burning stove can run on pellets.

Part of the problem is the wood itself. It seems that wood was not designed with burning efficiency as the first priority. Wood pellets provide a more even fuel and allow higher efficiency. Many wood pellets are currently made from sawdust or waste wood products. There are also pellets made from grass cuttings. If demand increases, wood will be cut directly to make pellets, which may remove some of the supply-end energy efficiency, but they will still burn cleaner. 

More efficiency means more of the wood is turned into water and carbon dioxide, rather than other more polluting substances or unburnt particles or residues. So more efficiency means less pollution and less cleaning. Air quality is an issue in many places, and burning wood certainly does not improve it.

You may consider a dedicated pellet burner, which will be easier to clean, and easier to use since it feeds the pellets via a hopper and may be controlled by a thermostat and a timer. It will probably be cheaper to install since the unit usually has a heat exchanger so a simpler chimney can be used. If you're still wondering about the answer to question 1, wood pellets could be your answer. 

6. You are only going to light your stove a few times a year, and are mostly getting the stove because it will look nice in your living room.

If you're thinking of adding a wood-burning stove to a ready-built house, you may not need to worry about this question. But if you're building new, I recommend your first priority to be insulation rather than burning wood.

Depending on your climate, if you have a well-insulated house, most wood burning stoves will make your house overheat, except on the coldest few days of the year. Your well-insulated house should also be airtight, and this may not be sensible if you are burning wood.

7. You know that if burning wood was the best way to stay warm, everyone would still be using it.

Most of us no longer send telegrams, spin yarn on spinning wheels, or nip down to the local smithy to get a horse shoe fixed. We stopped doing these things because of new technology that is cheaper and more time-effective. Burning wood will likely be more expensive and more time consuming than the options. Wood was our first fuel source; if wood produced more energy than fossil fuel reserves, we would never have deforested vast areas of the planet to mine coal or pipe oil and gas. 

There is an old saying: if God had not intended us to burn wood, he would never have invented matches. Actually that's not an old saying at all, I just made it up. But there is something natural and wholesome about a wood fire. 

Burning wood is better for the carbon cycle than burning fossil fuels. However, it may be better to burn nothing. If you want to avoid or reduce fossil fuel use, the first thing you need to do is improve your insulation. Then it may be better to electrify your heating, which allows you to use renewable energy. 

If you see yourself as an eco-warrior and see fire as one of your weapons against the machine, then be aware of the possibility that with fire you are fighting against ecology rather than fighting for it! I know in the situation we are in, the choice between wood burning or electrified heating may be something like choosing between a bicycle and a skateboard as you prepare to go over a waterfall. 

I don't have all the answers, but I do have the questions! 

So how did you score? If you answered yes to most of them, you're good to go. If not, I recommend looking into heat pumps, either in self-contained air conditioning units, or producing hot water for radiators or underfloor piping.

Remember, taken in moderation, wood burning stoves can form part of a calorie-controlled energy diet for your planet!


If you want to get a stove, go to Michael's Stove Shop.

For recent developments, analysis of factors that effect efficiency and a call to get below 1g of particulate per kg of wood, see "Performance history and further improvement potential for wood stove" by Øyvind Skreiberg & Morten Seljeskog (2019) in Chemical Engineering Transactions, 65. pp. 199-204.)

More details from the US Office of Energy Efficiency and Renewable Energy: Choosing and Installing Wood- and Pellet-Burning Appliances

Chapter on Energy Return on Investment (EROI) of Different Wood Products by Zdravko Pandur, Marijan Šušnjar, Marko Zorić, Hrvoje Nevečerel and Dubravko Horvat (2015)

Friday, 26 February 2021

What to do now the 21st century is not even a teenager any more

Here is the third part of the Building Culture presentation, and the final video recording of the course.

Being the last video it should probably include a short summary of the main points, but it probably just ends rather abruptly, with more questions asked than answers, and many things left unsaid. A bit like this post.

Tuesday, 23 February 2021

Humidity and Traditional Buildings

When I talked about humidity the last time, I realised there was a lot more to say. It's not enough just to understand what humidity is, how temperature affects relative humidity, and how important it is to keep your walls airtight.

Keeping walls airtight is still very important, but we also need to understand how moisture moves through materials, and how important that is if moisture does get into your building materials, which is an undesirable, but unfortunately not unavoidable situation.

In this video I also look at traditional buildings, how they overcome humidity, and how traditional building culture can be influenced by events as well by the local climate and available building materials. 

Friday, 19 February 2021

Building Culture: Differences between Japan and the UK

Different countries have different building cultures, and the differences between Japan and the UK are immediately visible. Just like the buildings themselves, some of these differences are superficial and others are structural, some are easily visible and others are buried and hidden deep underground but have profound influences.

In Japan people like new houses but in the UK people like old houses. I think this comes from the fundamental difference that in the UK houses represent capital wealth, while in Japan the value is in the land, and houses are consumables. Before we decided to build, we spent a few years looking at buying a house, and visited many that were unsatisfactory, in one way or another. A few times we noticed houses for sale moving into the list plots of land for sale, as the building was knocked down. In these cases, the price usually went up, suggesting that an old building on a piece of land is a liability and the land becomes more valuable when it is removed.

In the UK, if people want a different house, they will sell up, buy a new one and move. In Japan they will knock the house down and rebuild. Redecoration and renovation are carried out on a regular basis on UK houses, while in Japan they are more of a recent trend.

Click here to read more of the original post.