On-grid domestic battery storage

Reed_Richards · 18 September 2019 at 8:50PM

I think there may be differences between what is done in a "farm" full of wind turbines and what is done with a single "domestic" wind turbine. I have read that all modern wind farm turbines operate Wild AC to DC to Grid AC as the most efficient/cost effective means of matching their output to the grid. But I don't know how close to the turbine each conversion takes place. By the way, older systems don't operate this way and you can recognise them because all the turbines rotate at the same rate.

Martyn has established that the Wild AC to DC conversion in a domestic turbine is integrated so what comes down the wires from the turbine is DC. The Wild AC to DC conversion has to take place somewhere and it is generally held that DC is safer than AC so on that basis it make sense to send DC down the wires..

Solarchaser · 18 September 2019 at 10:59PM

I guess maybe the container size box that sits right beside wind turbines would be the box of tricks to take turbine power to grid power.

It strikes me that this would be the perfect place to have a Mwh of batts attached to each turbine box, storing the energy when not needed, supplying it when required, I cant imagine it would add much to the cost of a wind turbine, as I'd expect they are a *little* more expensive than a ford fiesta anyway

Reed_Richards · 18 September 2019 at 11:18PM

Solarchaser wrote: »

It strikes me that this would be the perfect place to have a Mwh of batts attached to each turbine box, storing the energy when not needed, supplying it when required, I cant imagine it would add much to the cost of a wind turbine, as I'd expect they are a *little* more expensive than a ford fiesta anyway

But the most popular Tesla Model S has a 75 kWh battery so for 1 MWh you would need 13 of these instead of your Ford Fiesta.

Martyn1981 · 19 September 2019 at 8:28AM

Reed_Richards wrote: »

Martyn has established that the Wild AC to DC conversion in a domestic turbine is integrated so what comes down the wires from the turbine is DC. The Wild AC to DC conversion has to take place somewhere and it is generally held that DC is safer than AC so on that basis it make sense to send DC down the wires..

Just to be clear, I've no idea how it works, it was you that said this when I thought you'd gotten your AC and DC the wrong way round in this post:

Reed_Richards wrote: »

The electricity you will generate will be AC, at some frequency. You will probably want to connect that to your existing inverter so the inverter sees the electricity as more solar panels. I say this because you need to match your power output to mains frequency and phase and are not allowed to feed power to the grid in the event of a grid power failure; your inverter performs both these functions. So you would need some sort of AC to DC inverter to convert the output from your hydro power generator to DC but if you do it that way I imagine the new inverter could be relatively dumb and unsophisticated.

Up to that point, I'd never heard of small wind or hydro turbines outputting AC (still can't find any that do), I'd only ever heard of DC output, from DC generators (dynamo's) that then charge batts via charge controllers or go to a DC to AC inverter.

TBH my head started to hurt, but as we agreed that output was DC, that resolved the issue of the inverter that was needed. So sorted.

Reed_Richards · 19 September 2019 at 9:51AM

Martyn1981 wrote: »

I'd only ever heard of DC output, from DC generators (dynamo's)

Good article here on how a dynamo works: https://edisontechcenter.org/generators.html . There is a rotary switch called a commutator that takes the fundamental AC output of the turbine/bicycle wheel/whatever but switches it off when the current is flowing in the wrong direction so you get "half wave AC" which is usually then smoothed electronically to a more constant (direct) current. But obviously this isn't very efficient because you throw away half your generated electricity. So you would use other electronics, not a dynamo, in an energy-efficiency sensitive application like a turbine.

There used to be dynamo-powered bicycle lights but the lights went out when you stopped pedalling so I imagine they're not allowed any more.

joefizz · 19 September 2019 at 10:27AM

Reed_Richards wrote: »

Good article here on how a dynamo works: https://edisontechcenter.org/generators.html . There is a rotary switch called a commutator that takes the fundamental AC output of the turbine/bicycle wheel/whatever but switches it off when the current is flowing in the wrong direction so you get "half wave AC" which is usually then smoothed electronically to a more constant (direct) current. But obviously this isn't very efficient because you throw away half your generated electricity. So you would use other electronics, not a dynamo, in an energy-efficiency sensitive application like a turbine.

There used to be dynamo-powered bicycle lights but the lights went out when you stopped pedalling so I imagine they're not allowed any more.

Are you sure you arent confusing the operation of a commutator with a half wave rectifier? Might just be my reading of the above.

Commutator changes a sine wave output from positive and negative peaks to just positive only. Half way round, it reverses the direction of the current going to the load, it doesnt switch off for half the circuit. Thats of course a description of just a 2 section commutator.

Half wave rectifier only uses one side of the AC (as opposed to full wave rectifier - a commutator is like a physical rectifier).

Again slightly pedantic but technical point the wee generators on bikes were magnetos not dynamos. Dynamos use coils for the magnetic field magnetos used magnets (if you ever broke one open you would see the curved magnets). You can still get them, IIRC they are mostly built into bike hubs now.

mmmmikey · 19 September 2019 at 10:57AM

Reed_Richards wrote: »

Good article here on how a dynamo works: https://edisontechcenter.org/generators.html . There is a rotary switch called a commutator that takes the fundamental AC output of the turbine/bicycle wheel/whatever but switches it off when the current is flowing in the wrong direction so you get "half wave AC" which is usually then smoothed electronically to a more constant (direct) current. But obviously this isn't very efficient because you throw away half your generated electricity. So you would use other electronics, not a dynamo, in an energy-efficiency sensitive application like a turbine.

There used to be dynamo-powered bicycle lights but the lights went out when you stopped pedalling so I imagine they're not allowed any more.

Morning all - dicussion of electrical theory is an interesting diversion while I wait for the call from PowerVault who are going to do some work calibrating my batteries today - more on that later, and other battery plans

In the meantime, I think the article Reed links to is a bit misleading and Joe's description is better. If you Google "split ring commutator" you'll see loads of explanations of how current is reversed, e.g.

http://www.gcsescience.com/pme13.htm

On the bicycle dynamo/magneto question, you can still get them. Mine charges a capacitor that drives a LED so the light doesn't dim as you go uphill or go off when you stop at a junction, which is what used to happen in the old days.

Reed_Richards · 19 September 2019 at 12:51PM

joefizz wrote: »

Are you sure you arent confusing the operation of a commutator with a half wave rectifier? Commutator changes a sine wave output from positive and negative peaks to just positive only. Half way round, it reverses the direction of the current going to the load, it doesnt switch off for half the circuit. Thats of course a description of just a 2 section commutator

Yes, your'e right; I was thinking of something very basic but reversing the direction of current is much better. This was O-level physics and O-level physics was a long time ago. But the point I have been trying to get across the whole time is that all these doohickies take electricity from a turbine that would be a form of AC if left unfettered by electronics (or electro-mechanics) and turn it into DC. Whereas the natural inherent behaviour of a solar panel is to produce DC, no conversion required.

joefizz wrote: »

Again slightly pedantic but technical point the wee generators on bikes were magnetos not dynamos..

Again I'm sure you are right. As kids we always called the dynamos but what do kids know?

Exiled_Tyke · 19 September 2019 at 12:59PM

joefizz wrote: »

Are you sure you arent confusing the operation of a commutator with a half wave rectifier? Might just be my reading of the above.

Commutator changes a sine wave output from positive and negative peaks to just positive only. Half way round, it reverses the direction of the current going to the load, it doesnt switch off for half the circuit. Thats of course a description of just a 2 section commutator.

Half wave rectifier only uses one side of the AC (as opposed to full wave rectifier - a commutator is like a physical rectifier).

Again slightly pedantic but technical point the wee generators on bikes were magnetos not dynamos. Dynamos use coils for the magnetic field magnetos used magnets (if you ever broke one open you would see the curved magnets). You can still get them, IIRC they are mostly built into bike hubs now.

A full wave rectifier (I think a 'bridge rectifier') uses an arrangement of 4 diodes (in a rather clever configuration I've always thought) to handle both sides of the sine wave. (A half -wave uses one diode). Capacitors are used to smooth the sine wave out.

This has got me thinking about how large scale hydro plants (such as Dinorwig) produce AC. Is it possible to manage the water flow to create a well governed AC or are efficiencies lost by converting AC to DC to AC as is being suggested for wind turbines. Which leads to a further thought - how on earth is the AC 'wave' regulated across the whole of the country? And then what about 3-phase supplies. GULP!

joefizz · 19 September 2019 at 3:13PM

Reed_Richards wrote: »

Again I'm sure you are right. As kids we always called the dynamos but what do kids know?

We called them dynamos as well (think they are still referred to as dynamos). Magneto was a character in the x-men comics ;-) A/O level electronics examiners liked the proper terms used though ;-)

'Which leads to a further thought - how on earth is the AC 'wave' regulated across the whole of the country?'
Ahh, thats the big question going forward, with so much of renewables being generated from DC then its becoming more and more of a problem. The losses are just a given, at the minute my PV is producing DC, going through the inverter to AC, down the cable to my computer and monitors then back to various forms of DC again. Later on tonight add the battery in and the 2 way conversion from AC to DC back to AC and out again and its changed many times over.

On-grid domestic battery storage

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