Natural gas powered fuel cells are available from some gas companies.[2]
Problems seem to be:
* Runs at very high temperatures, around 1000C, which means materials problems. Also, high grade heat is nice, but not that useful for home applications. So actual sales of this technology are to businesses.
* There's been recent work on catalysts to bring the needed temperature down to 500C or so.[3] That's easily managed; auto engines run that hot. The catalyst needs ruthenium, which is expensive, although cheaper than platinum.
* Sulfur in natural gas messes up the process, although this can be overcome. General problem with fuel cells: they need clean input gases.
* Apparently you get a lot of heat and a little electricity. This limits the usefulness. The gas company in the US which sells this services Maine and Vermont.
A nice application for this would be a little unit to provide backup power for natural gas furnaces, so you could run the fans without external power.
> Also, high grade heat is nice, but not that useful for home applications. So actual sales of this technology are to businesses.
Haven't there been some recent improvements in TEGs that would allow you to harvest a bit more of the available work whilst reducing the output heat to something useful?
In addition, generating electricity in a large power plant is significantly more efficient than doing so on a small scale even after taking transmission loss into account.
It looks like the primary advantage of a device like this is that you can make use of heat that would otherwise be waste.
This is not necessarily true. A power plant is only like 40% efficient at turning gas into electricity, but fuel cells are 40-50% efficient. This isn’t like comparing a car to a power plant which has a relatively inefficient internal combustion engine.
In practical terms, a therm of gas has about 30kWH of heat energy and costs $2.27 in California, for example. That’s $0.075 per kWh. Fuel cells are something like 40-50% efficient at converting gas into electricity and can even recover the rest as heat..so say it costs you $0.15 per kWh. That’s almost 50% cheaper than PG&Es Tier2 for residential electricity, and gas does not have the same issues with brownouts and power cuts, and you get 50% of the power back as heat. Fuel cells are silent, portable, and unobtrusive, and can scale to demand with extreme efficiency (Unlike power plants). Personally, if they were available I would seriously consider one.
Wouldn't that only apply to fossil fuels? I would think the watts per square meter of any solar panel I buy is similar to that of one used in a solar farm.
There is no micro nuclear to compare against obviously.
Actually thinking about it the conversion scheme (DC -> AC) used by the utility scale operator might be a bit more efficient. They'd care a bit more about getting that last 0.5% or 0.1% of gains than a residential customer.
Splitting hairs, but a 23% efficient mono perc panel will edge out a 19% poly silicon panel even if utility conversion is a lot better. Although I think in that specific case the perc panels are cheaper now for utilities too.
If you're using it at 12V and/or you shelled out the extra money for multi junction in your caravan you're probably still ahead. There will also likely be 5 years or so after hybrid perovskites hit the market before anyone is keen to put down big money on the lifetime predictions.
It's called combined heat and power or CHP. Usually used in district heating on a larger scale.
For example Helsinki gets some of its heat from the waste heat of coal electricity plants. The electricity produced is also of course used. There are a few plants and the hot water is piped underground to the district heating grid that spans the urban areas. Further away with sparse housing it doesn't make sense.
Basically, a heat engine needs a high temperature difference to make electricity. After that, there is still a low temperature difference left (100 C). That's still ok for heating houses.
There's a lot of discussion how do you calculate the efficiency or climate effects. You can say the heat is waste and free and no climate effect. Or then that it's 100% fossil.
CHP is an alternative to heat pumps. If you use wind or solar, they don't produce waste heat so CHP is not usable. Nuclear on the other hand would be a great fit for CHP, and is used for that in Russia.
The temperature in the district heating grid is higher than what heat pumps would prefer but they are still used to create district heat to reduce fossil fuel use.
You could use this to power AND heat the cold side of a heat pump, possibly getting far more than the original heat output of the gas into a building in a cold climate that would normally be too cold for a heat pump.
A heat pump can use 1 watt of energy to pull in the same amount of heating from the outside as 2 or more watts of resistive heat.
If the "waste heat" allows the intake not to freeze up on a heat pump, it would raise the efficiency of the heat pump, and it's quite possible that 1 BTU worth of natural gas could do the work of more than 5 if burned through a high-efficiency furnace.
That's not how that works. A heat pump can be more efficient than normal heating in the absence of a heat gradient.
If the outside of the house is colder than the inside, there is obviously no heat gradient to take advantage of. Thus a heat pump is a good choice.
If you're using what ever this micro fuel cell thing the article tasks about which apparently produces incredibly high temperature heat, you just heat the house with that. It's already hotter than the ambient temperature of the house You can't just slap a heat pump into such a system and have it suddenly gain efficiency. Where would the energy be coming from?
I don’t know if it’s been done for home heating, but there is such thing as gas powered refrigeration (Fun fact: early air conditioners from the 1930s and 40s ran off of gas). Since an air conditioner is just a heat pump in reverse, in theory you could use all that heat energy to drive a mechanical (Not electrical) heat pump and achieve a COP greater than simply using the gas to heat a house directly, and really juice the efficiency out of this thing, maybe even with some kind of hybrid electrical/mechanical heat pump.
The thing is, gas is so dirt cheap that we burn the stuff in furnaces, so I wouldn’t be surprised that this hasn’t taken off. Even electric source heat pumps in homes are a fairly new thing from the last 5-10 years.
The point isyou get x units of heat and y units of electricity (probably around 2 and 1) from x + y + a tiny bit units of chemical potential.
You can't put x units of heat that is already hotter than the hot well into the cold well of an idealized heat pump and come out ahead of just putting it into the hot well.
You could run it through a heat engine (TEG or stirling engine or similar) and extract some work with your heat pump's 'hot well' as your 'cold well' then use the work to move other heat inside but this is extra complexity.
There might also be eg. some temperature of your cold well where your heat pump's efficiency diverges because viscosity changes or you're not in a situation where modelling it as a single phase change in your working fluid is good or something. Then it might help to waste some free enthalpy (but not discard the energy into the environment entirely) to warm it up slightly.
Presumably none of these things are worth the added hassle especially if x + y is already close to the heating energy needed and y is close to the electrical energy needed inside. The benefit of whatever convoluted scheme you come up with would only be COP * second_heat_engine_efficiency * x which is likely around the same size as x or a bit smaller. Maybe a 30-50% reduction in overall energy input for more than doubling the complexity.
I honestly have no idea what you are trying to describe.
Outside of the peltier junction, there is no such thing as an electrical heat pump. They're all mechanical systems, usually with a working gas of some kind. So "mechanical heat pump" is a redundant term.
All that's required is for the temperature of the waste heat to be higher for it to be a waste (assuming a close to carnot or reduced carnot efficiency).
Of course if your heat pump's efficiency doesn't scale with temperature ratio there might a way to use the heat to move it towards carnot efficiency.
If you aren't getting enough heat from whatever this fuel-cell thing is, you would just run another heat source. You could in fact just run a regular heat pump at that point, which would get you more heat for the house.
That's not how entropy works. The heat already goes inside and is hotter than the hot side so your heat pump would just waste work.
You /could/ use a heat engine to diffuse your high grade heat and use the work in your heat pump. But that would require more moving pieces (or a complicated heat engine in your heat pump that could extract work)
So it's basically a Generac? I know that those are mostly for backup, but my understanding that they are perfectly viable for longer term use. (though they would need occasional maintenance)
If you mean "is this a reciprocating piston engine with a generator that's plumbed for natural gas?" then no ... this is fuel-cell technology, not internal combustion.
So it’s just a what we call in Germany Blockheizkraftwerk (literally a block heating power station) for Kraft-Wärme-Koppelung (Power heat coupling). They are very often used for district heating and were seen as the way forward for reducing CO2-emissions before the advent of renewables. It’s still a useful concept for biogas plants and trash incineration power stations. It makes sense though to have them more centrally as that increases electrical efficiency.
I've always been surprised that nobody has done home cogeneration for heat and hot water. Seems like an absolute no-brainer way to get a lot more mileage out of gas.
I read about a Mitsubishi home gas cogeneration system many years ago (10 ish). I think they haven’t taken off because they are expensive, only suitable in certain climates, and significantly less efficient at producing electricity from gas than a recent model combined cycle gas power plant.
Even if it were pitifully inefficient at making electricity it would still be better than just burning gas for heat, which wastes all of its thermodynamic work potential. Waste heat is still heat.
In Iceland, they cogenerate hot water and power due to the abundance of geothermal. Not exactly a common case that's replicable everywhere, but mildly interesting.
Genuine, this-never-occurred-to-me question: are there lots of people out there with boilers that DON'T do this, or areas where it is not normal?
If so - this might explain something that's been mildly irritating me. When looking for alternatives to fuel-burning boilers it seems easy to find positive stories about space heating - and much less info on water heating, to the point where it's starting to look like maybe some of these options might not be great. Water heating is my largest home energy usage and space heating very little because it is grossly overrated; if you are not really unwell an indoor temperature around 10 c is quite pleasant, so I tore my (rubbish) radiators out in 2017 and never looked back. This is making it surprisingly hard to figure out what replaces the boiler. If the marketing is aimed at pure heating boiler replacers, this difficulty is at least easier understood if not easier solved.
I would personally not like to live in 10°C but I prefer hot climates. 15°C I could do. How do you keep the temperature above 10°C? Or is the outside temp rarely below 10°C?
Thanks! that looks technically similar to the heat pumps aimed at space heating but a bit better - perhaps there's an efficiency in it being meant to do just one job? It looks like it (or its ilk) might be a good fit for me.
Outside wobbles around -2 to 8 in winter here, inside rarely less than 6, which is nippy but not dangerous. A not very insulated house with solid walls (this one's from about 1890 and has only had the easy things done) doesn't really sink to outside temperature if you live in it, cook, have appliances etc. There are plenty of heat inputs, just they do another job first. Hence my interest in water heat, I think it would start to be grim without it. Stove for a small number of really cold evenings, plus visitors. It would be a really bad idea to use it all the time but it would be hard to fit a radiator-type system to the job of "one hot room occasionally".
> Genuine, this-never-occurred-to-me question: are there lots of people out there with boilers that DON'T do this, or areas where it is not normal?
I understand that american indoors heating is mostly done through HVAC. Since in that case the heater would be heating the air directly, you'd need a separate boiler. Heating water to heat the air makes sense when water is your transfer medium (e.g. hot water radiators), less so when the air is.
So I expect US homes usually have separate air furnace and boiler, whereas in e.g. europe where water central heating is common you'd usually have a combined furnace/boiler.
Draughts :-) It's an old place, it doesn't seal. That and sleeping in rooms with the window open just a crack as much as possible. Mould tends to hit when people obsessively seal everything up.
I still have a condensation problem in a few specific places I have to keep an eye on. It's not general.
I think he's asking about the common trap people seem to fall into where, trying to keep heat in, they shut down air changes too far. Human breath puts a surprising amount of moisture into the air, and cooking can too. If you let that build up and have a cold wall it can build up a film of damp very quickly and if it's left damp and cool it can encourage mould. That kind of bad air quality is far worse than a bit of a chill.
Interesting. It claims "95% combined heat and electrical efficiency". I'm assuming this number is comparing immediately after the electrical generation occurs (i.e. - this doesn't have any transmission losses, while the electrical grid does).
Does anyone have any comments on the comparison in overall gas -> electrical output efficiency between large grid-scale natural gas plants and small natural gas generators like this one?
Combining heat + electrical energy makes the stats really muddy.
Does 10% of the burned energy end up as electricity? Or is it more like 30%? Hard to tell.
The real question is, what do you do with that heat when you don't want it? What's the efficiency then?
I will say, it would be pretty neat if one day we could get a mutli-device heat pump system going. Wouldn't it be cool if the heat pulled from your home was dumped into the water heater before being extracted vented? Or if instead of your fridge having a heat pump, it simply tied into a home heat pump system?
This sort of thing would call for a centralized compressed lines. And, perhaps the reason that's not happened is because we don't want to worry about what happens when toxic gasses discharge into the home.
Still, would be pretty neat if we could have a centralized cold and hot compressed gas system for buildings.
Commercial and larger residential buildings often have water at various temperatures as a utility. There will be a machine room that has large water-to-water heat pumps, then a chiller tower on the roof that takes hot water, evaporates some and cools the rest, then returns it to the hot-side heat exchanger. The cold side will circulate water around the building, where it will be used in water-to-air heat exchangers on the room or unit level to cool the building. In most climates, larger buildings need more cooling than heat, but doing the same thing with a hot water system is quite common as well.
> This sort of thing would call for a centralized compressed lines
The exchanger doesn't need to be the working fluid. You could have Freezer | Fridge | Ground | 30 degree water | 70 degree water
With each | indicating water or another coolant in an insulated pipe. Insulate each reservoir and place it inside/outside depending on climate.
Insulation on longer runs of piping might need to be exotic and expensive (aerogel or double walled vacuum sections), but there wouldn't be much of it.
We already do something similarish for some AC systems
Wikipedia has some reasonable figures about Cogeneration fuel cells (Ene-Farm is one of those "MicroCHP" fuel cell systems for home usage[1]:
> Co-generation systems can reach 85% efficiency (40–60% electric and the remainder as thermal).[5] Phosphoric-acid fuel cells (PAFC) comprise the largest segment of existing CHP products worldwide and can provide combined efficiencies close to 90%
For the "95% […] efficiency", I guess they take the hydrogen heat input for calculation of efficiency. What I miss are the losses from conversion of natural gas to hydrogen. This has to be considered when comparing efficienies eg. with gas fired power plants.
So when it comes to large-scale Combined Heat and Power plants [2], it depends.
There are not only different types of power plants (coal fired, gas fired, etc.) but also the heating part varies (process steam, district heating, etc.). If you go thermodynamically strict, you would also have to consider the quality of heat (at which pressure & temperature level is the heat extracted). This is normally not considered in the standard efficiency formula.
Gas power plants on the grid are pretty inefficient. Like a modern furnace they are pretty efficent at getting the heat energy out of the gas. However the efficiency of turning the heat into electricity is low. They get something like an average of 40% overall efficiency. The best gas turbine plants on the market can get about 60% efficiency max.
If the power plants were able to provide the excess heat to nearby businesses and the like, they could be a lot more efficient overall, and there are some that have tried to do that, but transporting heat itself is not an easy thing to do efficiently, and many plants are things like peaker plants, which don't run consistently, making it even harder to sensibly use the "waste" heat in the nearby communities.
Then there is the grid losses. Grid transmission loses 5 to 6% of the power in the US, making the grid 94-95% efficent.
If energy were a little more expensive you could have jerry can sized packs of sodium acetate or similar. But noone really wants to fill up their boot with jerry cans and burn $3 worth of fuel for $2 worth of low grade heat.
I wonder if there is a better PCM or thermochemical battery that could be worth moving on a not-train somewhere? Something that beats ice but works at not-4-degrees. Lye is okay but still a bit shy.
I'm not smart enough to know what's going on here. This is using solar power to help make hydrogen which is then using the hydrogen to create electricity? And then because of the heat generated it can also be used to heat a structure (to some degree)?
Natural gas powered fuel cells are available from some gas companies.[2]
Problems seem to be:
* Runs at very high temperatures, around 1000C, which means materials problems. Also, high grade heat is nice, but not that useful for home applications. So actual sales of this technology are to businesses.
* There's been recent work on catalysts to bring the needed temperature down to 500C or so.[3] That's easily managed; auto engines run that hot. The catalyst needs ruthenium, which is expensive, although cheaper than platinum.
* Sulfur in natural gas messes up the process, although this can be overcome. General problem with fuel cells: they need clean input gases.
* Apparently you get a lot of heat and a little electricity. This limits the usefulness. The gas company in the US which sells this services Maine and Vermont.
A nice application for this would be a little unit to provide backup power for natural gas furnaces, so you could run the fans without external power.
[1] https://www.panasonic.com/uk/corporate/sustainability/produc...
[2] https://www.eversource.com/content/ct-c/business/services/co...
[3] https://www.sciencedaily.com/releases/2018/10/181029130939.h...