Watts up!

Jamie Hall

Very brief (unlike me!). Looking over the various discussions which crop up from time to time on heat pumps or electric boilers or solar panels... and so on.

It seems to me that one of the problems -- a very big problem, actually, that many people have is that they are very fuzzy about the distinction between power and energy. Now it would be hopelessly pedantic of me to insist that people started using the term "alternative power" -- which would be correct -- instead of "alternative energy", but it would help.

Energy can be regarded, very briefly, as stored power. If it is converted in some way for use, the rate at which it is converted is power. Energy can be stored. Power cannot.

A few examples for illustration. A gallon of fuel oil contains energy (chemical). A gallon of water in a reservoir upstream contains energy (gravitational, relative to the lower river). A charged battery contains energy (again, chemical). But -- water flowing through a turbine has power -- releasing a certain amount of gravitational energy per unit time). A flame in a boiler has power (releasing a certain amount of chemical energy with time). A current flowing out of a battery has power (again, a certain amount of chemical energy with time). You can use power in ways to store energy (you can pump the water back up hill, for instance, or charge a battery) although the conversion often is not direct (that pump, for instance).

Now to the specific point: sunlight is a form of power (so is wind). Importantly, it is NOT energy and cannot be stored -- you have to convert it into something else and store that (sunlight, for instance, can be converted into electricity and the electricity used to charge a battery, storing the power as chemical energy; or it can be allowed to shine on an object and warm it up, storing the power as thermal energy).

And this, to focus, is where people trip up -- particularly the photovoltaics people. Unless you have a way to store that lovely sunlight, you must use the power at that specific moment in time. Any that you can't use in some way right now is gone forever. If you need power at some other time, it's simply not available.

Use it or lose it...

We don't help ourselves much with the units we use... BTU is a measure of energy. BTUh (more properly, BTU per hour) is power. KW is power. KWh (more properly KW-hours) is energy. You can't convert a BTU into a KW -- it has to be a KWh. You can convert KW to BTUh -- but not BTU. And so on. Be careful of the units!

You buy stored energy in the form of transmitted power from the grid or send it back (so and so many KWh) at a certain rate (KW). You buy stored energy from the oil company (so and so many BTU per stored gallon) and burn it in your boiler at a certain rate (BTUh). And so on.

DanHolohan

@Jamie Hall, I'm told that knowledge is power, but how do you force that through a wire?

ratio

I can explain it to you, but I can't understand it for you.

JakeCK

Now I feel I need to go back and review all my posts to make sure I didn't make a mistake anywhere. O.o I think I've been using the units correct. 

JakeCK

One thing I would like to add to your post is that while you are technically correct, the power returned to the grid in abstract isn't really lost. If for example you have a bunch of houses that can produce enough solar to power the rest of the houses that do not when it is sunny, and there is a NG power plant that makes up the difference when it isn't sunny, the energy that didn't need to be burned and converted to power is the battery. That is the beautiful thing about electricity, it is fungible.

Remember, a penny saved, is a penny earned. 

Dave Carpentier

So in Jake's solar-town, the panelled people are receiving power from the sun. As long as there is a load (demand), then what is flowing out into the neighbourhood should be energy I think ?
Ive always thought of voltage as power and current as energy (because it does the labour and gets consumed).

Jamie Hall

Dave Carpentier said:

So in Jake's solar-town, the panelled people are receiving power from the sun. As long as there is a load (demand), then what is flowing out into the neighbourhood should be energy I think ?
Ive always thought of voltage as power and current as energy (because it does the labour and gets consumed).

Still power. Now if there's a battery getting charged out there somewhere -- maybe even someone's Tesla! -- the stored power in the battery is energy, and can be converted back to power when needed.

Power is measured by volts times amps (current). Energy is measured by volts times amps times time.

To @JakeCK 's comment -- you are absolutely correct. The power isn't lost; it's being used somewhere else. And it does displace, so long as it is there, power that would otherwise have to be created from energy in some other manner. No argument there, either. What is often forgotten is your next sentence (I'm not surprised you kept it in mind!): when the nice solar power source quits, you need some other power source available.

Now from the engineering standpoint, that standby source doesn't have to be generating power when the sun is shining or the wind is blowing. If it's a battery, in fact, it can just be sitting there. Batteries can go from no output to full output virtually instantaneously. If it's a thermal power plant, though, or even hydroelectric, it does have to spinning (and warmed up, if it's thermal). Even a gas turbine or a hydroelectric turbine takes a few seconds to go from no load to full load, and the power is maintained by the spinning mass (flywheel effect -- which is stored energy). Other types of thermal plant take longer to ramp up. Nuclear is the quickest; it it's kept warm you can get there in a matter of seconds. Fuel fired plants can take anywhere from minutes to hours. This is an interesting complication in managing grids with sizable unreliable power sources, like solar or wind. It's also an interesting complication in evaluating energy storage approaches.

PC7060

DanHolohan said:

@Jamie Hall, I'm told that knowledge is power, but how do you force that through a wire?

heatinghelp.com works pretty well!!!  Wired or wireless.

Hot_water_fan

Now from the engineering standpoint, that standby source doesn't have to be generating power when the sun is shining or the wind is blowing. If it's a battery, in fact, it can just be sitting there. Batteries can go from no output to full output virtually instantaneously. If it's a thermal power plant, though, or even hydroelectric, it does have to spinning (and warmed up, if it's thermal). Even a gas turbine or a hydroelectric turbine takes a few seconds to go from no load to full load, and the power is maintained by the spinning mass (flywheel effect -- which is stored energy). Other types of thermal plant take longer to ramp up. Nuclear is the quickest; it it's kept warm you can get there in a matter of seconds. Fuel fired plants can take anywhere from minutes to hours. This is an interesting complication in managing grids with sizable unreliable power sources, like solar or wind. It's also an interesting complication in evaluating energy storage approaches.

It's interesting! If you look at the ERCOT data, they seem to manage it well. Some days, 58% of their GWh come from wind + solar! Looks like one hour was 65%.

ChrisJ

@Jamie Hall what about a flywheel?  Where does that fall into this?

mattmia2

It is basically power unless it is something like a flywheel ups system. Once it reaches a steady state the power entering equals the power leaving, it just stores very small amounts of energy to average out the input power

Jamie Hall

mattmia2 said:

It is basically power unless it is something like a flywheel ups system. Once it reaches a steady state the power entering equals the power leaving, it just stores very small amounts of power to average out the input power

That's about it. It's a very useful but short term energy storage device -- but a big one can store a lot of energy. To extract the energy in some useful form, however, the flywheel has to slow down. One application, though, is spinning reserve at a power station. The generators are really big, and really heavy, and so are the turbines to which they are coupled. So if you have them spinning -- even if they aren't generating power -- and you have to throw the unit on line, they will keep going for several seconds to tens of seconds, albeit at drooping frequency, until the turbine has a chance to start generating power.

ChrisJ

Jamie Hall said:

It is basically power unless it is something like a flywheel ups system. Once it reaches a steady state the power entering equals the power leaving, it just stores very small amounts of power to average out the input power

That's about it. It's a very useful but short term energy storage device -- but a big one can store a lot of energy. To extract the energy in some useful form, however, the flywheel has to slow down. One application, though, is spinning reserve at a power station. The generators are really big, and really heavy, and so are the turbines to which they are coupled. So if you have them spinning -- even if they aren't generating power -- and you have to throw the unit on line, they will keep going for several seconds to tens of seconds, albeit at drooping frequency, until the turbine has a chance to start generating power.

I've thought about adding a heavy flywheel to my home built generator to help with the AC starting.   The alternator is good for 12kw but the engine can only do 8-9kw on natural gas.   The flywheel would help deal with the short but large spike in current.  It gets by.. But I think the flywheel could help it do it with ease if it's big enough.

yesimon

Speaking of rooftop solar PV vs batteries, America is moving towards less favorable net metering laws and strongly incentivizing solar owners to also install batteries for self-consumption instead of grid-export during peak hours. While this is a great pairing for off-grid or those with unreliable electricity using batteries for backup, this is highly suboptimal for grid-scale energy policy.

Utilities and industrial operators are much better suited for large-scale battery installations to correct the "duck curve" and even out renewable fluctuations. They are exposed to wholesale minute-by-minute dynamic pricing and fine tune how much energy (and power) to sell in real time. Despite Tesla's "virtual power plant", residential customers are largely on predictable pricing plans and cannot respond in the same way (apart from a few unlucky customers during the big freeze). Not to mention that individual owners will be hesitant to fully draw down their batteries lest they lose their home backup capability - the primary selling point in the first place. Centralized batteries should also have huge economies of scale and risk containment. We've all seen the nasty lithium EV fires.

Rooftop solar makes sense because the primary cost of solar is land. Acquiring land is costly for a utility but essentially 0 for a homeowner in marginal terms. Batteries don't require nearly as much land.

Given how battery-constrained the world is right now, it's very unfortunate to see people showing off 2-4 powerwalls for "power outage backup".

Jamie Hall

ChrisJ said:

Jamie Hall said:

mattmia2 said:

It is basically power unless it is something like a flywheel ups system. Once it reaches a steady state the power entering equals the power leaving, it just stores very small amounts of power to average out the input power

That's about it. It's a very useful but short term energy storage device -- but a big one can store a lot of energy. To extract the energy in some useful form, however, the flywheel has to slow down. One application, though, is spinning reserve at a power station. The generators are really big, and really heavy, and so are the turbines to which they are coupled. So if you have them spinning -- even if they aren't generating power -- and you have to throw the unit on line, they will keep going for several seconds to tens of seconds, albeit at drooping frequency, until the turbine has a chance to start generating power.

I've thought about adding a heavy flywheel to my home built generator to help with the AC starting.   The alternator is good for 12kw but the engine can only do 8-9kw on natural gas.   The flywheel would help deal with the short but large spike in current.  It gets by.. But I think the flywheel could help it do it with ease if it's big enough.







Couldn't hurt.

Hot_water_fan

Rooftop solar makes sense because the primary cost of solar is land. Acquiring land is costly for a utility but essentially 0 for a homeowner in marginal terms. Batteries don't require nearly as much land.

Take a look at SEIA’s annual report - land is not a significant cost for utility scale. The panel, followed by margin/overhead, make up the majority. 

Jamie Hall

Well now. I really hadn't meant this to get into a discussion of solar power. Rather, I'd hoped that it would help people -- particularly lay people -- distinguish between energy and power. However...

A sort of side note, since we've wandered off into questions of utility scale vs. smaller commercial vs. residential grid tied solar. A very hot topic in electrical engineering just now is how to integrate small, distributed sources -- such as a residential rooftop or even a fairly good sized solar array -- a few acres of panels, perhaps -- with the grid itself. To date, almost all the inverters designed to do this make a fundamental assumption, or rather two: First, that the voltage sensed on the grid is highly stable, and second that it is at a locked frequency -- 50 hz in most of the world, except 60 hz in North America. The inverter senses that fixed frequency voltage and, though some rather sophisticated computations and high power fast switching devices, adjusts the local output of the inverter to that it adds power to the grid connection at exactly the same frequency and phase.

Problem. This works only if the grid voltage is, in fact, highly stable in magnitude, frequency, and phase. Which basically means that somewhere there is a very "stiff" source of power which is considerably bigger than any of -- or the sum of -- the various distributed power sources which are feeding it. In the present state of the art, that highly stiff source (or sources) is in the form of large -- very large, relatively speaking -- rotating machinery. This machinery resists changes in frequency and phase through its flywheel action, allowing time for its own controls to reduce or increase the power delivered to the generator as required to maintain the target frequency and phase.

In principle an all electronic inverter package can be built to do much the same thing -- but only if it contains, as part of the system, an energy storage device (that is, a battery or a very very large ultracapacitor) capable of absorbing power from the grid, in the event that the inverter output lags, or adding large amounts of power, in the event it leads, both without damage, and its internal output frequency must be very tightly stabilized and, in the event of lead or lag errors, it must be able to adjust its own phase angle to match the external, grid phase angle.

Note that all the same problems apply to wind turbine generation.

Also note that the grid tied inverters used in applications without storage are designed only to feed power, and only in amounts up to the power output of the panels or turbines; they track the grid parameters to do this, and shut down immediately if the grid signal is lost or degraded.

This is no mean feat, but doable. However, as the distributed generation capacity begins to approach the total power on the grid it becomes increasingly difficult (particularly if there are differing inverters and power capacities feeding). and, so far as I know to date this problem has not been solved Some thought has been given to using an external synchronizing time signal -- the GPS satellite system has been suggested -- but there are concerns, which I think are quite valid, that such an approach is subject to interference if not outright failure, with almost complete and instantaneous breakdown of the grid and wide spread equipment damage or destruction.

Stay tuned...

hot_rod

yesimon said:

Speaking of rooftop solar PV vs batteries, America is moving towards less favorable net metering laws and strongly incentivizing solar owners to also install batteries for self-consumption instead of grid-export during peak hours. While this is a great pairing for off-grid or those with unreliable electricity using batteries for backup, this is highly suboptimal for grid-scale energy policy.

Utilities and industrial operators are much better suited for large-scale battery installations to correct the "duck curve" and even out renewable fluctuations. They are exposed to wholesale minute-by-minute dynamic pricing and fine tune how much energy (and power) to sell in real time. Despite Tesla's "virtual power plant", residential customers are largely on predictable pricing plans and cannot respond in the same way (apart from a few unlucky customers during the big freeze). Not to mention that individual owners will be hesitant to fully draw down their batteries lest they lose their home backup capability - the primary selling point in the first place. Centralized batteries should also have huge economies of scale and risk containment. We've all seen the nasty lithium EV fires.

Rooftop solar makes sense because the primary cost of solar is land. Acquiring land is costly for a utility but essentially 0 for a homeowner in marginal terms. Batteries don't require nearly as much land.

Given how battery-constrained the world is right now, it's very unfortunate to see people showing off 2-4 powerwalls for "power outage backup".

The deal around here is that the power company pays for a battery bank, but they have access to pull from it whenever the need. I think it was a 3 or 5 year access. So thousands of these mini storage systems scattered around the valley for the power company to use.

Plenty of commercial roofs out there that could be collector mounts. Must be a 100 or more storage facilities here in the Salt Lake area, al sorts of carports at apartment and condo buildings,as in most high influx cities.

fentonc

I think modern power electronics are up to the task of providing virtual inertia and grid forming services to the grid, but all of the standards bodies in power generation aren’t used to moving at this speed. That being said, I applaud @Jamie Hall ‘s noble attempt to get people to stop confusing kw and kWh

hot_rod

fentonc said:

I think modern power electronics are up to the task of providing virtual inertia and grid forming services to the grid, but all of the standards bodies in power generation aren’t used to moving at this speed. That being said, I applaud @Jamie Hall ‘s noble attempt to get people to stop confusing kw and kWh

Same with Btu and Btu/ hr
No such thing as head pressure either

ChrisJ

hot_rod said:

fentonc said:

I think modern power electronics are up to the task of providing virtual inertia and grid forming services to the grid, but all of the standards bodies in power generation aren’t used to moving at this speed. That being said, I applaud @Jamie Hall ‘s noble attempt to get people to stop confusing kw and kWh

Same with Btu and Btu/ hr
No such thing as head pressure either

Since when is there no such thing as "head pressure" ?

JDHW

@ChrisJ

What kind of alternator do you have on your generator? Hard starting a motor (AC) can take 5-10 times more current than the running current. If you have an self-excited alternator that just has a parallel capacitor then this does not cope so well with high starting currents. AVR (automatic voltage regulator) alternators are much better in this situation. If you generator is being used for full house backup I would not trust anything other than and AVR or an inverter generator to powering electronic equipment.

John

ChrisJ

JDHW said:

@ChrisJ What kind of alternator do you have on your generator? Hard starting a motor (AC) can take 5-10 times more current than the running current. If you have an self-excited alternator that just has a parallel capacitor then this does not cope so well with high starting currents. AVR (automatic voltage regulator) alternators are much better in this situation. If you generator is being used for full house backup I would not trust anything other than and AVR or an inverter generator to powering electronic equipment. John

I have a brushless self regulating alternator and it seems to cope just fine.   A large part of why I went that route was simplicity and reliability.    They do make a regulator for it but again, simplicity and I feel it does more than good enough as is.  

I trust it just fine.


I'll take a good brushless alternator over many inverters any day.  

hot_rod

ChrisJ said:

hot_rod said:

fentonc said:

I think modern power electronics are up to the task of providing virtual inertia and grid forming services to the grid, but all of the standards bodies in power generation aren’t used to moving at this speed. That being said, I applaud @Jamie Hall ‘s noble attempt to get people to stop confusing kw and kWh

Same with Btu and Btu/ hr
No such thing as head pressure either

Since when is there no such thing as "head pressure" ?




It goes back to my early years with a man named Dan. No not that Dan, but Dan Bernoulli, 1738...

https://www.pmmag.com/articles/101174-siegenthaler-theres-no-such-thing-as-head-pressure

I'm guilty of using the term head pressure, I have hears pump manufacturers trainers wax poetically about head pressure also