EV sales have doubled. Is a ‘tidal wave’ coming?

[HaulingAss]

I interpret that as; two EVs in one household, household electricity consumption doubles. And if heating comes from electricity too (probably heat pump) for a house, then three times the electricity consumption per household. ;-)

That was specifically for household consumption, not commercial or industrial. That doesn't mean they won't double or triple too.

Theres heaps of embodied energy in products and services.

I'm happy that this statement confirms my initial comments regarding how much electricity consumption will increase. And with it an overall network capacity increase IF it doesn't come with embedded storage or V2X that without could result in shortages (like UK fuel atm).

We still need to heaps of RE just to replace fossil atm, let alone increase to follow EV uptake.

Another thing I thought was funny was that EM was also sitting in the dark at his friends house in the Texas blizzard. I mean even I've been offgrid for various houses and businesses for at least 15 years now. Didn't his mate get the memo?

But seriously though I doubt a solar roof and even a string of powerwalls and a heat pump would have got him too far in those conditions. Better off getting out a good ole woodgas CHP.

With a well insulated, non-drafty house of a normal size, I think you would be surprised just how much heat 4 or 5 Powerwalls could provide using an efficient heat pump, especially if only the occupied rooms were fully heated. Suitably sized solar would only extend the length of total power outage that could be handled. At this point in time that would be quite an expense for an emergency that may or may not happen but the price will be a lot cheaper as 4680 cells ramp into high volumes.

 

[Cybr on]

I don’t think it’s a tidal wave, it’s more like a tsunami?

 

[ajdelange]

With a well insulated, non-drafty house of a normal size, I think you would be surprised just how much heat 4 or 5 Powerwalls could provide using an efficient heat pump, especially if only the occupied rooms were fully heated. Suitably sized solar would only extend the length of total power outage that could be handled. At this point in time that would be quite an expense for an emergency that may or may not happen but the price will be a lot cheaper as 4680 cells ramp into high volumes.

No need to be surprised as the calculation is pretty simple. Say you are in Zone 3. You will need about 40 BTU/h/ft^2 so for a normal size house (2000 ft^2 ?) that's 80,000 BTU/h which is 23.4 kW. An "efficient" heat pump is 4.1 COP (as required by new regulations) meaning input will be 5.7 kW. Assume that the duty cycle is nominally 50% so your heating requirement is, on average, 2.85 kW (higher on colder days when the duty cycle goes up and lower on warmer days when it goes down). A Powerwall's capacity is 13.5 kWh so 5 of them hold 67.5 kWh not all of which is available but assuming it to be so 67.5 kWh would be consumed in 23.7 hours.

The heating load is 2.85*24 = 68.4 kWh which can be collected from a 22.8 kW solar system given 3 hours FSE per day (last week I got 1.7h/d on average but I have also gotten 6 in summer).

Now I would say this is dissappointing perhaps but it's not really surprising. Solar systems are not really practical in temperate zones if the building is heated electrically. The reasons for this are
A)It takes a lot of electricity to heat even a small space
B)The most heat is needed when the sunshine is least (night in winter)
C)The electricity must be stored and storage is hideously expensive

 

[HaulingAss]

No need to be surprised as the calculation is pretty simple. Say you are in Zone 3. You will need about 40 BTU/h/ft^2 so for a normal size house (2000 ft^2 ?) that's 80,000 BTU/h which is 23.4 kW.

You can use whatever kind of unfavorable assumptions you want to make it sound sketchy but 40 BTU/h/sq. ft. would not be considered "well insulated and non-drafty" on a typical heating day.

Your error is not fully understanding how the recommended number of BTU's per sq. ft. relates to actual consumption (the recommendations have to do with how long it takes to re-heat a cold house on the coldest day of the year) not how much heat energy the house consumes to maintain a temperature on a typical heating day. So, if you want a worse case scenario with a house that is not particularly well insulated on the coldest day one could reasonably expect, then you have an answer for that scenario.

But my point was a well-insulated home. American homes have been built based on the assumption of cheap energy and tend to be very wasteful. A super-insulated home can be warmed with a small fraction of that. On many days owners report they stay comfortable with waste heat from family or friends combined with the heat given off by a few lights, refrigerator and electronics. So we are talking about two different things and it's apparent you don't even understand the meaning of "well-insulated" or what the primary metric all your energy consumption figures are derived from was based on.

 

[Crissa]

I don’t think it’s a tidal wave, it’s more like a tsunami?

Synonyms?

-Crissa

 

[ajdelange]

Your error is not fully understanding how the recommended number of BTU's per sq. ft. relates to actual consumption (the recommendations have to do with how long it takes to re-heat a cold house on the coldest day of the year) not how much heat energy the house consumes to maintain a temperature on a typical heating day.

Afraid the error is yours. Those ratings are, of course, nominal and represent what is required to maintain the house at some nominal temperature (usually 70°F) at the design temperature which depends on zone (or, when an actual calculation is done on the actual location). What happens in a typical case depends on a whole lot of factors (one of which isn't how long it takes to heat the house up from cold - common sense should tell you that would be a pretty useless way of specifying the demand). Things like the direction in which the house is facing, wind shielding, the R factors of all the windows and doors and which side of the house they are on, room volumes, infiltration (intentional or unintentional), heat recovery systems etc. all go into it. My error is in assuming that you understood enough about HVAC to be able to understand that the 50% duty cycle I used was to allow for the fact that you aren't always at the design temperature (it is to be hoped you never are). Look up "Manual J" to gain some familiarity with how these calculations are made and what they mean.

 

[HaulingAss]

Afraid the error is yours. Those ratings are, of course, nominal and represent what is required to maintain the house at some nominal temperature (usually 70°F) at the design temperature which depends on zone (or, when an actual calculation is done on the actual location). What happens in a typical case depends on a whole lot of factors (one of which isn't how long it takes to heat the house up from cold - common sense should tell you that would be a pretty useless way of specifying the demand). Things like the direction in which the house is facing, wind shielding, the R factors of all the windows and doors and which side of the house they are on, room volumes, infiltration (intentional or unintentional), heat recovery systems etc. all go into it. My error is in assuming that you understood enough about HVAC to be able to understand that the 50% duty cycle I used was to allow for the fact that you aren't always at the design temperature (it is to be hoped you never are). Look up "Manual J" to gain some familiarity with how these calculations are made and what they mean.

Wrong. The heating values you supplied are the same figures used to determine the required furnace capacity per sq. ft. in Zone 3. When sizing a furnace, the coldest expected weather is assumed and it's over-specified about 10 percent to ensure the furnace doesn't struggle to bring a cold house to temperature on a cold day. But your biggest misunderstanding is revealed by your assumption that a house would use 50% (on average) of it's total heating capacity on the average day. That's not how thermodynamics work. People would be more than shocked how high their heating bills would be if the average home used 50% of it's total heating capacity 24/7. That's not what happens in reality.

I don't mind people who have "engineer syndrome" if they are a good engineer but that's the problem - many engineers, especially the most vocal, live in a text book and have trouble applying their book knowledge to real world problems in a meaningful way. This is the real problem illustrated here.

 

[Cybr on]

Synonyms?

-Crissa

?‍ ?
Honestly, I thought they were 2 very different things.

 

[Crissa]

?‍ ?
Honestly, I thought they were 2 very different things.

Were you thinking a tidal bore? ^-^

The brain, it makes connections. Not always the ones you needed!

We tend to use the word 'tsunami' now since it is less confusing and more specific. And the English language has no shame in borrowing words! ^-^

-Crissa

 

[Cybr on]

Were you thinking a tidal bore? ^-^

The brain, it makes connections. Not always the ones you needed!

We tend to use the word 'tsunami' now since it is less confusing and more specific. And the English language has no shame in borrowing words! ^-^

-Crissa

??

 

[ajdelange]

I'll explain briefly how the wise man sizes his heating system and then relate that to how long a properly sized heating system can be run on 5 Powerwalls. As an example I'll use the project I am doing now which is a 2000 ft^2 garage/storage/workshop building with about 3/4 of that heated space. We start with a Manual J calculation which shows the building leaks 0.477 BTUh per square foot per degree rise. This quickly leads to a diagram like this one which shows heating load against inside and outside air temperatures:

Obviously one should size for the coldest parts of the year during which time, in my area temperatures tend to hover around freezing during the day and dip below that at night. 0 is seldom reached but 10 °F is not that uncommon (5 days a year at night) nor is 15 °F (10 da/yr) so it's clear that a 45 kBtuh system is a good choice. During the daytime when the temperatures are around 30 °F it would run at about 50% duty cycle (of course the modern ones don't do "duty cycle" as such - they adjust motor speed to move more or less refrigerant per hour). Now one can, of course, spend a lot more time on thinking about say a 40 kBTU system with E-heat etc but that gets into additional analysis which probably isn't necessary. I chose 47 kBTU total split pack heat pumps (with propane backup).

The electric load required to supply the heat is easily calculated:

The only comments I'll make on this are that the curves are steeper at the left side of the plot than on the right because COP falls off as the outside temperature drops. The other comment is on the 24 kWh/da dotted curve. I stuck that in there because that is the power I am estimating that I will have available in December (the building has no grid connection). I am using this as a garage and so 50 °F for the indoor setting is fine and I'll be able to maintain that as long as the outdoor temperature is above 30 and when it isn't I can shut off heating to some of the areas (storage) and/or heat them with the E-heat system. Looking forward to collecting some data on this system this winter!

Final step gets to the question which I think is at the heart of this particular diversion to the main thread: how long could 5 Powerwalls run this heating system in the event of an extended outage. That's easily calculated knowing how much energy a Powerwall stores which is 13.5 kWh.

This chart is clearly bad news for those who fancy that they can run even a small house in Zone 3, 4 or 5 for days on a couple of Powerwalls. But for me it is really good news. I can set all the thermostats for 50 °F and as long as the temperature stays above freezing run forever on solar even if the sun goes in for 3 days. But of course I wouldn't do that if I knew a cold snap was on the way. I'd set some of the rooms to 45 or even 40 and pick up a day right there.

Now of course the same strategies apply to someone in a residence of this size. They would have 1.25 days coverage if they set the themostats to 65 °F rather than 70° F at 30 °F outside. Some may live in warmer climates and it may be possible to get load coefficients down to less than 0.477. Clearly if that can be halved, the times would double.

If there is an overall message here it's DO THE ENGINEERING. Modern HVAC systems, especially when integrated with solar and battery, are very complicated systems and if you skip the systems engineering you will likely get a result that is not as effective as it could be. The last four times I've had systems put in they would have been very disappointing had I accepted what the contractors proposed.

I hope at least a couple of people have found this interesting. To the others I apologize.

 

[JBee]

Once you do the battery heat pump costs you realise just how good hydronic thermal mass storage is in price comparison.

But either way, regardless of storage type, the argument originally was around network and generation capacity rise because of EV uptake and the reduction in use of fossils because of the RE uptake on the grid.

"No fossils" makes it fairly hard still in temperate climates with plenty of sunshine because of peak production of solar in relation to spinning reserve and cloud events and TOU so you need heaps of storage still. SC's to boot.

Then if you move to colder climates and add house heating you end up with even more energy requirements on the grid because now you have both low solar input and high heat energy demands at the same time.

Essentially you could instead say its easier to cool with solar power than it is to heat. Which is sort of an oxymoron, until you realise that high ambient temperatures are the result of lots of solar energy gain, and cold temperatures are because of less solar energy gain. The more solar power the more power you can COP up to cool with a heat pump, typically without much need for battery storage too.

Regardless of this however, I feel vindicated by EM statements regarding expected household energy consumption increases because of EV and house heating coming from the electricity grid instead of direct from fossils, and as such that a significant increase in network capacity will need to result unless some V2G or huge and expensive emebbed storage comes along.

 

[HaulingAss]

I'll explain briefly how the wise man sizes his heating system and then relate that to how long a properly sized heating system can be run on 5 Powerwalls. As an example I'll use the project I am doing now which is a 2000 ft^2 garage/storage/workshop building with about 3/4 of that heated space. We start with a Manual J calculation which shows the building leaks 0.477 BTUh per square foot per degree rise. This quickly leads to a diagram like this one which shows heating load against inside and outside air temperatures:

Obviously one should size for the coldest parts of the year during which time, in my area temperatures tend to hover around freezing during the day and dip below that at night. 0 is seldom reached but 10 °F is not that uncommon (5 days a year at night) nor is 15 °F (10 da/yr) so it's clear that a 45 kBtuh system is a good choice. During the daytime when the temperatures are around 30 °F it would run at about 50% duty cycle (of course the modern ones don't do "duty cycle" as such - they adjust motor speed to move more or less refrigerant per hour). Now one can, of course, spend a lot more time on thinking about say a 40 kBTU system with E-heat etc but that gets into additional analysis which probably isn't necessary. I chose 47 kBTU total split pack heat pumps (with propane backup).

The electric load required to supply the heat is easily calculated:

The only comments I'll make on this are that the curves are steeper at the left side of the plot than on the right because COP falls off as the outside temperature drops. The other comment is on the 24 kWh/da dotted curve. I stuck that in there because that is the power I am estimating that I will have available in December (the building has no grid connection). I am using this as a garage and so 50 °F for the indoor setting is fine and I'll be able to maintain that as long as the outdoor temperature is above 30 and when it isn't I can shut off heating to some of the areas (storage) and/or heat them with the E-heat system. Looking forward to collecting some data on this system this winter!

Final step gets to the question which I think is at the heart of this particular diversion to the main thread: how long could 5 Powerwalls run this heating system in the event of an extended outage. That's easily calculated knowing how much energy a Powerwall stores which is 13.5 kWh.

This chart is clearly bad news for those who fancy that they can run even a small house in Zone 3, 4 or 5 for days on a couple of Powerwalls. But for me it is really good news. I can set all the thermostats for 50 °F and as long as the temperature stays above freezing run forever on solar even if the sun goes in for 3 days. But of course I wouldn't do that if I knew a cold snap was on the way. I'd set some of the rooms to 45 or even 40 and pick up a day right there.

Now of course the same strategies apply to someone in a residence of this size. They would have 1.25 days coverage if they set the themostats to 65 °F rather than 70° F at 30 °F outside. Some may live in warmer climates and it may be possible to get load coefficients down to less than 0.477. Clearly if that can be halved, the times would double.

If there is an overall message here it's DO THE ENGINEERING. Modern HVAC systems, especially when integrated with solar and battery, are very complicated systems and if you skip the systems engineering you will likely get a result that is not as effective as it could be. The last four times I've had systems put in they would have been very disappointing had I accepted what the contractors proposed.

I hope at least a couple of people have found this interesting. To the others I apologize.

What we learned is that the garage/storage/workshop building that you are using as an example is not particularly well insulated and you have done the calculations for weather that that is far from average for zone 3. Remember, my comment was not about heating a home through the middle of winter using only Powerwalls, it was that you might be surprised how long it could last during a random power outage (in a well-insulated home).

It looks like you are not familiar with well-insulated structures that are designed to be heated with minimum losses. People are building homes that don't require much more than the normal waste heat of equipment, electronics and habitants. Please note, I didn't say they don't require ANY additional heat, I said they don't require MUCH more. Your calculations show how things were done in a world of cheap and easy fossil fuel. Well-insulated houses can reduce heat loss by 500% or more.

 

[ajdelange]

Essentially you could instead say its easier to cool with solar power than it is to heat. Which is sort of an oxymoron, until you realise that high ambient temperatures are the result of lots of solar energy gain, and cold temperatures are because of less solar energy gain. The more solar power the more power you can COP up to cool with a heat pump,

It's much easier to shade the sun than it is to "shade" a cold wind. In summer there is much more sun and, most important, there is, in temperate climates at least, much less ∆T to deal with. For example where I live, near Washington, DC, ACCA uses 52 °F rise for determining heating load but only 16 °F for determining cooling load. Offsetting this is the solar load on the roof. For example the garage I just built should lose 31 kBTUh to the cold air of winter but only gain 19.6 kBTUh from the hot air of summer plus the sun - actually even less than that because a large part of the roof will be covered with solar panels. A secondary effect of smaller ∆T is better COP in the heat pumps. In the summer I get about 5 hrs/da FSE. In the winter it is more like 1.7.

..typically without much need for battery storage too.

Ummm. People just don't seem to realize that batteries are not very inefficient practical storage media for energy. You really have to push some numbers relevant to your particular situation before coming to conclusions about batteries. I'm doing a 2000 ft^2 solar garage with 5 Powerwalls. This is a tight building (spray insulation in all exterior walls, under the roof, insulation on slab, low e doors and windows, tight construction....) for a very good heating U = .269 BTUH/ft^2/°. I'm using Mitsubishi high COP split packs, COP(45°F) = 4.14; COP(17°F) = 2.53, and expect to see this sort of performance:

ACCA uses a design temperature of 16 °F for my region (and room temperature of 68 °F). Were this a residence that I wanted to keep at 70 °F clearly 5 Powerwalls wouldn't carry me long in a run of cloudy days at the design temperature. But in January, the coldest month in my area, the average temperature is 34 °F and I'd be good for 2 days with no sun. But of course one doesn't design for the average temperature. He designs for the design temperature because he wants to be prepared for that (a point that our correspondent doesn't seem to be able to grasp). So clearly 5 Powerwalls isn't sufficient capacity for a residence in my area unless he as backup, is willing to go to a hotel etc.

But this isn't a residence. It's a garage and I'd like to keep it at about 50 °F. As long as the temperature stays at and above average I'll make it on sun alone even in January but, of course, it doesn't. For example, in the last 11 years, the average daily temperature in January has stayed at or below 25°F for 3 or more days in a row 17 times. Obviously I'd be in trouble if any of those cold snaps coincided with a span of low sun! But, of course, I have other strategies (such as backup heat).

Is it better in the summer? U is larger (solar load) at 0.55167 but the rise is only 16 °F (design temp 91 °F, assumed load temp 75 °F) so the design load is only 19560 BTUh. The Mitsubishi's have an EER of over 13 so that means 1.5 kW A/C load which is 36.1 kWh/day. Thus the 5 Powerwalls would only carry me for 1.87 days of no sun were the temperature steady at the design temperature which is better than the 0.8 days they'd carry me in winter but still not very impressive. Clearly there are considerations related to the statistics of the local weather in the summer months which effect the conclusions one draws. But there is another ameliorating aspect to the A/C load as illustrated in this picture:

These curves clearly show that the A/C load is strongly correlated with the sunshine. If the day's sunshine is weak or non existent the A/C load is reduced. Hence a day of little sun means reduced demand on the Powerwalls. And, of course, the fact that the heavy A/C load presents when the sun does means less shuffling of lithium than is the case with the winter load (which does not show this pattern).

In any case I really don't feel at this point that the summer situation will be very much better than the winter one with respect to the adequacy of 5 Powerwalls. The goal is to have the backup generator run as little as possible. I am now most curious to see how the system will perform in summer (and winter too of course)!

 

[ajdelange]

What we learned is that the garage/storage/workshop building that you are using as an example is not particularly well insulated

Actually it is quite well insulated (U = .257)

...and you have done the calculations for weather that that is far from average for zone 3.

Anyone who knows anything at all about how to size an HVAC system understands that this is exactly what one is supposed to do.

It looks like you are not familiar with well-insulated structures that are designed to be heated with minimum losses.

Familiar enough to know how to run a Manual J and direct a contractor as to where to beef up the insulation to get me the U value I need and to direct the HVAC people as to what equipment to install.

Your calculations show how things were done in a world of cheap and easy fossil fuel.

Wrong there too. My calculations are done per ACCA recommendations using current ACCA databases for my region. Though I must say that this discourse has caused me to look into this in much greater depth than I had at the outset.

Well-insulated houses can reduce heat loss by 500% or more.

Relative to what? What range of U (BTUh/ft^2/°) are you claiming?

Seems that what we have learned is that you haven't learned a thing from this discourse and that your understanding of HVAC is very limited.

But I have learned a great deal and so I am grateful for the dialogue. I have gone back and looked at the drawings for the garage project much more closely than I had previously and analyzed IAD weather data to a much greater extent than I ever have before. I am now quite confident that my neighbors will not be hearing my backup generator as much as I had previously feared.