Let me first of all commend the writer for actually getting most of the units and arithmetic right on the energy/power side. This is no small feat for some reason!

Your hot shower guilt, though, should vary with two factors: 1) time of day you shower and 2) the power market you live in. (Because power cannot be stored or transported easily) The writer is using as her baseline example an electric water heater that uses 5 kWhs of electricity to heat one shower (17000 Btus / heat rate of 3.4). This will cost you about 50 cents, btw.

But not all kWhs are created equally! The number you need to focus on is the heat rate—the rate at which heat (btu) is converted to electricity (kWh). The writer cites a heat rate of 3.4, which is a pretty good around the clock average number. This is important because carbon emissions come from that heat to electricity transfer (not to mention your own energy costs if you have a smart meter).

If you shower early in the morning, before peak school and work hours start and before the daytime temperatures require all the ACs in town to be turned on, you can shower without guilt, because the only generators required to handle your load are the really efficient ones (wind, nuclear, must-run cogeneration gas). You can especially rest easy if you live in a power market like ERCOT (Texas) or CAISO (California), where there is little or no coal generation and the ambient temperature doesn't freeze the water.

However, if you live in the northeast, and it’s summertime, and you’re showering at 4pm, they’re gunning the dirtiest, least-efficient, fifty year old coal unit to heat your shower. And if it's winter, you've got to heat the water from a much lower starting point. So don't live there!

If you live in west Texas you can keep that sucker running all day since there is so much constrained wind power out there that power is virtually free (and almost completely clean). And you'll need that hot shower after being hit by tumbleweeds and dust all day.

The exact time period that they take their shower is not relevant... it's the time that their tank re-heats the water that is at issue.

I have a tankless, and I live in SC... so I know that my morning shower uses mostly nuclear power. That's not really an excuse to take an endless hot shower, since that nuclear energy could be used to power something else or stored in the excessive pumped hydrostorage available in my state... but there it is all the same.

However, for most people, if they took an early shower, then their water heater would gradually re-heat the water throughout the day, and store it hot throughout the night. If they instead installed a timer to their water heater, they would use the water whenever, but the heater would only heat during the night, when nuclear and wind comprise a large portion of the energy content... but only in areas like the midwest - where there is no pumped hydrostorage - is this a significant excuse for a guilt-free extremely long and hot shower.

:)

Good point about the heater timing...I actually have one of those flash heaters, but I'm betting most people don't.

Pumped storage! You lucky basterds. I don't live in one of those states.

I live in Chicago, so I'm pretty much using coal. Long showers and baths in our old claw foot tub are my only real environmental "sin" and I doubt I'll give that up.

On the plus side, I found an interesting review of the economics of getting to 350 ppm C02. The article is here but I found the embedded hyperlinks hard to notice. The main report seems to be this review (PDF warning).

Chicago uses nuclear.

I know you didn't write the report, so I'm not saying this to spite you, specifically... but in order to accomplish this we are going to have to agressively plant over a million km2 of trees, which we would then have to lumber but not burn.... I'm not saying it's impossible, but it is certainly not something that we could even concieve of how to afford.

Furthermore, the idea of eliminating or sequestering all coal power emissions by 2030 seems like a complete economic fantasy.

In both of these cases - sequestration and non-burnable lumbering - you are adding a pure burden to society that carries an uncertain benefit. It's not going to be an easy sell, and shifting 7 billion tons of coal burning to sequestration facilities (or eliminating it entirely) while the world is seeing rapid growth and development in poor countries... it just isn't going to happen.

I want to mitigate emissions as best I can, and I'm even working on new technology to help the world both provide needed energy and mitigate global warming emissions... but we are going to have to spend some money on accomodation, and we are going to see some things lost or destroyed. This problem is simply too big for us to target that quickly.

If so, you might be VERY interested in the work that we're doing, since your power company is undoubtably going through hell trying to accomodate the ever-growing wind penetration: www.WindFuels.com

Tell me what you think. (we're at the early development stage and looking for venture investment right now... I'm not trying to sell you something).

They're pretty much all natural gas. I'm guessing that someone's going to tell us what the difference is in terms of energy use, or I hope so anyway.

:)

I'm not sure I understand the question. Nuclear energy is not carbon-neutral, but it's pretty close. Natural gas is fairly efficient (40-50%), and averages ~1 ton of CO2 for every 2 MWhs.

Coal is less efficient (31%), and has a lower energy density per ton C than natural gas... Coal electricity produces ~1 ton CO2 for every 1 MWh.

I don't know Chicago's energy profile, but I would be surprised if a significant portion of Chicago was natural gas...

The Midwest ISO governs the electricity trade for most of the regions around the Chicago area (though not the Chicago area itself), and MISO generally gets ~80% of its electricit from coal, ~15% of its electricity from nuclear, 2.3% of its electricity from wind, and 1.8% of its electricity from gas... That's not to say individual regions cannot have much higher and/or lower concentrations - for instance, Minnesota and Iowa get 7-8% of their electricity from wind, and North Dakota gets 6%... but it's hard to imagine a region where only 1.8% of the total energy is derived from gas to surround a city that has a large percentage of its power derived from gas.

Not impossible... and I'll admit that I don't know. But according to the DOE, ~48% of Illinois' electricity was generated by nuclear, and 48% was generated by coal, with only 4% generated by gas and 1% generated by other (wind) in 2007... Since then, the wind energy has doubled... and the nuclear generation would have remained the same.

I think Messy was referring specifically, and accurately, to the water heaters in Chicago homes. So its not a matter of how efficiently natural gas tanks can heat the water rather than efficiency of power plants.

If MISO excludes Chicago and has much higher rates of coal usage than Illinois does that mean Spud is right to say Chicago is all, or mostly, nuclear? I was thinking of the Illinois general numbers assuming that is more relevant.

In general natural gas water heaters are responsible for ~25% of the emissions from electric water heaters using coal power... so every minute under the shower with a low-flow showerhead each morning increases your CO2 footprint by ~25 kg/day.

As for the relevence of the electric utility numbers, of course you are right...

I happen to know the MISO numbers without looking anything up... so that was just spitballling. MISO does not include much of the greater Chicago area... it merely encircles the area (all of Minnesota, Wisconsin, Iowa, half of Illinois, most of Indiana and Michigan, and much more...)

I then quickly looked up the DOE information on Illinois at large, which I posted.

It's impossible for all of Chicago to be nuclear. They have to be able to dump the excess energy at night. I'm actually shocked that they achieved 48%, though I remember joking about a lot of the wasted energy I saw in the city during the night - saying that they had to do something with their nuclear power... Chicago is working on some underground pumped hydro... and they're using a ton of waste energy at night... But there's no way that they could support 100% nuclear energy. I'd guess they are getting away with 48% because they are selling a large portion off to non-nuclear heavy neighbors. A quick check showed that Indiana and Kentucky have no nukes, and Iowa and Missouri only produce 10% of their power through nuclear plants.

Nuclear power is "always on"... which can be a real beast of a problem if you don't have sufficient demand for that energy in the middle of the night... because if you can't sell it then it will burn out your grid. When too much energy is produced during the middle of the night, power companies start paying their neighbors to take the energy... Prices have dropped as low as negative $250/MWh, though prices that low are extremely rare... Negative pricing has occured ~5-6% of the time throughout the midwest this year (no decent pumped hydrostorage on the plains plus rapidly expanding wind power is giving them hell).

Tundrayeti,

Regardless of the type of hot water heater that is in use, the time of the shower is the time of the power usage. Whether tankless of tanked, insulated or not, old or new, if it's still working, it's replenishing the hot water as it's being used and even the oldest, most lame water heater reheats 30 to 40 gallons from ambient ground water temperature in 30 minutes or less. So about 30 minutes after you begin your shower, the water heater is done using "catchup" energy -- essentially at the same time as the shower.

Tankless water heaters are great but, unless you'rfe doing it yourself (which I have) the cost to retrofit the vast majority of homes and apartments in this country which have 100 AMP service will never be recovered (not even close) so there is no energy savings incentive. Even with rebates for the hardware the total cost savings over the expected life of the heater are not enough to overcome the remodeling costs associated with upgrading to 200 AMP service and installing a second panel and oversize breaker for a tankless heater (or two) with enough capacity for multi-point use for a typical family.

If you're building a new home the whole equation changes quite a bit from the contracted services side but you're still left with the hardware cost, at retail, which is usually double or more (often 500% more) than sufficient traditional gas tanked heaters. Even that difference is hard to overcome during the expected lifetime of the heaters. If you switch to tankless there's only one legitimate reason (until they finally come down to where they belong -- below traditional heaters. The inherent cost to build a tankelss and ship it is far below that of traditional. Novelty, lack of competition, and lack of globally large market have allowed prices to stay artificially high. The cost TO the wholesaler of an average sized tankless "Off Brand" is less than $150 but it retails for over $700.) you're donating some of your hard-earned geld to help the environment.

My tankless system uses natural gas, like my old tank system did. It also has an electric "starter" that plugs into a regular socket that only lights the gas to heat the water on demand. The installation cost me no more than a conventional water tank installation, and I got a rebate from my gas company for that, plus I'll get an additional federal income tax credit.

So instead of a pilot burning 24/7, and a tank that kicks its burners on to keep 40 gallons of water continually hot, whether the hot water is in use or not, AND turns really cold when the stored, heated water runs out, I have a system that supplies me with unlimited hot water on demand at a fraction of the natural gas usage.

With the rebate, the tax credit, and the continued savings every month on my gas bill, plus the fact that tankless systems require far less maintenance and last far longer, tankless makes all kinds of sense.

very smart