Energy blackouts

[vtsnowedin]

Not far as I know.
Wind turbines are in practice EITHER grid tie to reduce carbon emissions and utility bills, OR stand alone battery charging systems for premises without grid service.

Well there is room for improvement there wouldn't you agree?

[adam2]

It would no doubt be possible to design a system whereby a wind turbine is normally grid tied but can also be used as a stand alone battery charger.
Someone may well have done this already on a "one off" DIY basis.

I am not aware of any ready made solution, and so doing would add very considerable cost and complexity.
Most modern wind turbines produce 3 phase AC at a voltage and frequency that varies continually as the wind varies. For grid tie use the AC out put is rectified to DC and feeds a grid tie inverter that produces line voltage and frequency. Some sophisticated power electronics monitors the power fed into the grid and optimises this to make best use of the available wind.

For battery charging, the rectified AC would have to be electronically converted into a regulated DC voltage suitable the battery voltage, with adjustable limits on voltage and current. Any surplus power would have to diverted to a dump load.
If standard AC appliances are to be used, then one or more inverters would also be needed to convert the battery voltage into line voltage AC.

Note that the battery, dump load, and inverters are not normally used but must be provided and held in readiness for power cuts. The battery must be kept charged and periodically replaced.
There are also strict rules on grid tie equipment and modifications may render the installation non compliant.

[vtsnowedin]

It would no doubt be possible to design a system whereby a wind turbine is normally grid tied but can also be used as a stand alone battery charger.
Someone may well have done this already on a "one off" DIY basis.

I am not aware of any ready made solution, and so doing would add very considerable cost and complexity.
Most modern wind turbines produce 3 phase AC at a voltage and frequency that varies continually as the wind varies. For grid tie use the AC out put is rectified to DC and feeds a grid tie inverter that produces line voltage and frequency. Some sophisticated power electronics monitors the power fed into the grid and optimises this to make best use of the available wind.

For battery charging, the rectified AC would have to be electronically converted into a regulated DC voltage suitable the battery voltage, with adjustable limits on voltage and current. Any surplus power would have to diverted to a dump load.
If standard AC appliances are to be used, then one or more inverters would also be needed to convert the battery voltage into line voltage AC.

Note that the battery, dump load, and inverters are not normally used but must be provided and held in readiness for power cuts. The battery must be kept charged and periodically replaced.
There are also strict rules on grid tie equipment and modifications may render the installation non compliant.

I can see where it would take at least two double throw double pole switches to disconnect the wind mill from the grid and then to the grid isolated house wiring. But I was thinking of something more sophisticated and computer controlled that would dump unneeded power into the batteries and would then feed the grid from batteries and the mill if the wind was blowing during peak demand hours. Something similar may eventually come into play if plug in electric cars become common. All those large batteries sitting there waiting to get charged off peak. If the grid could both give and take as needed they could become the mass storage that intermittent wind a solar require.

[fuzzy]

All options are possible, but in the UK you have the unbridgeable gulf between what the homeowner may well understand, and what the people who are allowed to actually install something understand - which may sadly be basic recipe construction hindered by subsidy regs etc, unless you have boutique design from a costly company.

A while ago, the bloke who wrote the chapter on renewable install regulations for the US National Electrical Code pointed out that he was not qualified to install his own system - just about sums up the UK as well..

[Catweazle]

Hacking a grid tied inverter shouldn't be too difficult.

[vtsnowedin]

Hacking a grid tied inverter shouldn't be too difficult.

Maybe for you but I'd have to get a nine year old to do it for me.

[adam2]

Hacking a grid tied inverter shouldn't be too difficult.

I suspect that it might be difficult, they are designed to prevent exactly what you are trying to achieve.
Also you will need a battery to cater for both short term and longer term fluctuations in wind output, and to supply the start up current of say a fridge.

[vtsnowedin]

Hacking a grid tied inverter shouldn't be too difficult.

I suspect that it might be difficult, they are designed to prevent exactly what you are trying to achieve.
Also you will need a battery to cater for both short term and longer term fluctuations in wind output, and to supply the start up current of say a fridge.

Why wouldn't they want you to feed in power to the grid only when it was most useful to them?

[adam2]

I doubt that the utility would object to receiving power just when it was most needed, but they almost certainly would object on general principles to ANY modification of a grid tie inverter.

And anyway at present a flat rate is paid per KWH fed back into the grid, no premium is payable at times of special need. Therefore the consumer would gain nothing by storing wind generated power in a battery and feeding it back later. Indeed the consumer would be paying for the extra losses and for battery replacement.

As regards any attempt to use a grid tie wind turbine and related grid tie inverter as a standby source of power in a power cut, I doubt that this is possible for the reasons already given.

[Mr. Fox]

Spot on, Adam.

To elaborate a bit at the risk of getting too technical... In the UK, what are known as the 'G83' (or 'G59') regulations demand that any 'generation equipment' (turbines, PV, hydro and power stations) must completely disconnect from the mains in the event of a mains failure (or the quality of the supply falling outside of certain limits) - and then wait a minimum of 180 seconds before reconnecting once grid power is restored within those limits.

The main reason for this is simply to protect line workers from getting killed - for instance, if they're up the road repairing a damaged line, they've disconnected 'their' end from the grid, we don't want your wind turbine/PV sending current back up to the fault site.

Similar regs exist in the US, I'm sure.

Re-purposing a grid-tied system for off grid isn't easy. If we take PV, the panels are likely to be wired together (in 'strings') so as to deliver the highest possible voltage that the inverter (plus cable and switching) can cope with (~400V).

With an off-grid (battery charging) system, you're generally looking at less than 100V (probably a lot less). That means you're working with at least 4x the current for a same sized array (so your cables need to be 4x bigger, etc)

So... lift your panels, re-cable, make a bigger hole in the roof, fit a string-fuse box... you now have a voltage that's not too scary.

Hacking a grid tied inverter is theoretically possible - access to the firmware source would probably be essential. As they are, they all conform to the G59 / G83 regs, so they have to 'see' a nice 50hz between 207 and 264Vac for 3 mins before they'll even think about giving you any power, then they will try to maintain a slightly higher voltage output than they 'see' on the mains. Good luck maintaining that without the grid - unless you can exactly match the load to the (varying) supply, the inverter's just going to push the output voltage up until it hits ~264Vac, then shut down.

There may be some barbaric and dangerous hacks you could do with patience, a logic analyser and a soldering iron (or a hammer with SMAs).

But... If we take a 1kWp inverter, to produce/handle that 1kW, it's going to be pumping out just over 4 amps at ~235 Vac. Let's say we've scavenged 4 car batteries to give us a 48V system, meaning about 54 Vdc would be required to charge them. That means that the hacked inverter can only deal with around 230W, as it's still only designed to cope with around 4 amps. At 12Vdc you'll have about 50W.

For the price of a cheap charge controller (£5?), sad to say: it ain't wurfit.

With regard to hybrid (grid-tied with battery) systems, you'd start with an off-grid system, then install a grid-tied inverter as the dump load (so once the battery is full, excess power goes to the grid). In the UK, you'd still get the feed-in tariff for *everything* produced, plus the buy-back rate for what's exported.

Fronius inverters have a secret ninja key press sequence that disables the 'maximum power point tracking' on the input side (so you can feed it a fixed voltage, e.g. from a battery), but I'm sure there are other inverters out there specifically designed for the task.

More likely (IMO) than a prolonged total blackout is 'rota load disconnection' (rationing to a few hours per day). A degree of protection from that can be built quite cheaply - just a battery, charger and low-voltage lighting, etc.

[adam2]

Yes, very well put.
If you want an off grid inverter than buy one, rather than attempt to modify a grid tie inverter.
That still leaves the problem of trying to charge a low voltage battery from a much higher and variable voltage from a wind turbine or PV array intended for grid tie use. There are ways around this, but all add costs complexity and losses.

And as for the CAUSE of loss of grid power, in MOST non TEOTWAWKI situations then rota power cuts are more likely than a complete shutdown, these could vary from just a few hours a week, to it only being on for a few hours a week.
However the scenario being discussed at the beginning of this thread was the complete absence of grid supply for a few weeks due to extreme weather damage to infrastructure.

[emordnilap]

Here's a small step towards coping with renewables' intermittent delivery.

The Smarter Network Storage project by UK Power Networks has seen a 6MW/10MWh “big battery” installed at one of Leighton Buzzard’s main substation sites at Woodman Close.

It is large enough to:

> Power about 6,000 homes for 1.5 hours at peak times, or

> Power about 1,100 typical UK homes for a whole day during average or low demand times, or

> Power more than 27,000 homes for an hour.

The building itself is about 760sq metres – about the size of three tennis courts – and is divided into two main rooms.

One houses the transformers and inverter units that convert electricity from direct current to alternating current. The other room houses the battery racks and modules where the energy is actually stored.

Is this a viable option? What's its lifespan? Is it worth it?

[adam2]

Here's a small step towards coping with renewables' intermittent delivery.

The Smarter Network Storage project by UK Power Networks has seen a 6MW/10MWh “big battery” installed at one of Leighton Buzzard’s main substation sites at Woodman Close.

It is large enough to:

> Power about 6,000 homes for 1.5 hours at peak times, or

> Power about 1,100 typical UK homes for a whole day during average or low demand times, or

> Power more than 27,000 homes for an hour.

The building itself is about 760sq metres – about the size of three tennis courts – and is divided into two main rooms.

One houses the transformers and inverter units that convert electricity from direct current to alternating current. The other room houses the battery racks and modules where the energy is actually stored.

Is this a viable option? What's its lifespan? Is it worth it?

Neither needed nor economic at present I believe, but still a worthwhile experiment for a future when it might be needed.
There is little point in utility scale battery storage at present, in most circumstances it makes more sense to simply reduce the amount of FF generation at times of plentiful RE production.
Then when we have so much renewable energy input to the grid that NO gas is burnt for base load generation, we should look at reducing imports of electricity at times of plentiful renewable production.
The at demand side control to shift consumption to times of plentiful supply.

Only after exhausting these and other options should battery storage be considered.
Batteries are expensive and involve losses and need regular replacement.

[emordnilap]

Batteries are expensive and involve losses and need regular replacement.

What I thunk. But of course, it's not about common sense, it's about continuing with present lifestyles.

[kenneal - lagger]

Batteries are expensive and involve losses and need regular replacement.

What I thunk. But of course, it's not about common sense, it's about continuing with present lifestyles.

And about people selling their current technology while they can still make a bit of money from it, whether it is apt or not!