Base it on a rough £1k per kw, this will give you an idea
Thats quite manageable, would love 10KW in total if possible as we do have the roof space for it!
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Reward Powerwall UK
- Thread starter stigmeister
- Start date
-
- Tags
- powerwall 2 rewards
Thats quite manageable, would love 10KW in total if possible as we do have the roof space for it!
MrBadger
Badger out
WannabeOwner
Well-Known Member
They've permitted mine but (can't exactly remember what the installer said) there may yet have to be some restriction device on Export ... not that I'm planning to do any of that ... which makes it a bit moot.
An I right in thinking that a set of solar panels AND a powerwall is seen by DNO as potentially being capable of exporting both lots at max
jimbo_hippo
Member
My advanced appeared the day after. Haven't used it yet as we're on fixed tariff until Octopus swap out our smart meter for another smart meter..... yeah, I know.... I've read about why but I don't get it either!Just the standard 4KW FIT stuff, I was surprised to see even in the gloomy weather today at one point the panels hit 0.5KW.
We are doing a house extension soon, am certainly going to get more solar PV, another 4KW would be nice, but no idea on cost yet. Shame Tesla solar roof is no where near ready in the UK.
@jimbo_hippo When does the 'advanced' controls appear on the App, is it roughly 1 week after the install?
^Thanks, just checked and whoo hoo the option is there, now the PW is charging using 8p per kWh electricity. Good to see the 5KW limit, I wasn't home during the install so wasn't sure if DNO had limited the PW to 3KW .
Really amazing bit of kit, the tech is so advanced but so easy to use. Cannot quite believe Tesla were giving these things out for free!!
@jimbo_hippo Whats the time frame for your delay with Octopus? I might think about switching from Bulb which I current pay 8p off peak to the 5p for 4 hrs deal from Octopus, but don't want to end up for months on their fixed tariff.
.Really amazing bit of kit, the tech is so advanced but so easy to use. Cannot quite believe Tesla were giving these things out for free!!
@jimbo_hippo Whats the time frame for your delay with Octopus? I might think about switching from Bulb which I current pay 8p off peak to the 5p for 4 hrs deal from Octopus, but don't want to end up for months on their fixed tariff.
Last edited:
MrBadger
Badger out
When I inquired a few years back, DNO needed a G83? (I think it was actually a G5x? application) application for a Powerwall install - so was effectively being treated as a separate PV install and permission had to be granted in advance, so not a done deal - part of the reason that the high install cost was being justified. Apart from being compliant with technical regs, I'm really not sure why DNO needs to approve loadings of a device that does not export. However, I guess they may argue that, just like a EV charging, it may put an import load on the grid.
Would like to know what DNO's permissions and notifications are for wrt small scale energy storage?
Last edited:
WannabeOwner
Well-Known Member
jimbo_hippo
Member
Octopus called this week. Sparky coming round next week. Not sure if he’s going to fit a new meter or not. Will keep you informed.^Thanks, just checked and whoo hoo the option is there, now the PW is charging using 8p per kWh electricity. Good to see the 5KW limit, I wasn't home during the install so wasn't sure if DNO had limited the PW to 3KW
Really amazing bit of kit, the tech is so advanced but so easy to use. Cannot quite believe Tesla were giving these things out for free!!
@jimbo_hippo Whats the time frame for your delay with Octopus? I might think about switching from Bulb which I current pay 8p off peak to the 5p for 4 hrs deal from Octopus, but don't want to end up for months on their fixed tariff.
Yes both have to be include in the DNO application, recently waited 45 days for a response to my application to get 10kwp solar + powerwall 2 (5kwp) fitted which had to go down as a 15 kwp in total. They said NO which peeved me off considerably and said if I wanted to go for that size install I would need to pay £3500 to upgrade some power lines, and then pay for someone to dig up the road, lay new cables and then put it back together again all at my own cost (estimated at approx £5000). They also had the cheek to say if they did the first part it would be £3500...if I organised another company to do it the price doubles. Basically they are con artists, I have referred them to Ofgen and am waiting to see what happens.
Anyway, you can get as others mentioned something that will limit export so you can put whatever size Solar PV system you want on the roof. I do not plan on exporting anything If I can anyway (which is why the powerwall is getting installed). In the end I toned it down to 7.4kwp on the roof, 6kw inverter and the powerwall 2. Install happening this month so will see it at it's worse the next few months!
WannabeOwner
Well-Known Member
My installer said if DNO objected that is what they would advise.
Exactly. nuts isn't it.
I'm not really an expert on this topic, but I'll share what I know.
AC-connected storage is treated as a generator 'connected in parallel with a distributor’s network', just like a solar inverter, since that is how it is connected and behaves - you may not be intending to use it for export, but the device itself is connected in parallel with the network and you are just controlling the output so that it approximately balances the consumption elsewhere in the house. So with solar you have two generating devices connected.
DC-connected storage (ie. connected behind a common inverter used for the solar or the battery depending on the situation) would be different: the network can't see the storage in that case and it's just acting like a solar installation that works even though the sun isn't shining. DC-connected storage used to be at an artificial disadvantage in the UK due to FIT payments: with the storage connected on the DC side and the generation meter connected on the AC side, all the losses through the storage process subtract from your FIT payments. It also doesn't straightforwardly allow import from the grid, so your storage becomes strictly solar timeshifting rather than also being able to do tariff arbitrage with it. Nonetheless, some DC-connected systems are available, and indeed Powerwall 1 was advertised as available in AC- or DC-connect versions. Powerwall 2 seems to be mainly advertised as AC-connect, though it is possible a DC-connect version exists as well.
Anyhow, assuming AC then it's another generator, and the law (in the form of the ESQCR) makes a hard distinction between systems below 16A/phase which merely have to meet technical requirements and then inform the DNO when you connect them, or systems above 16A/phase where you need to agree "specific requirements" with the DNO. These regulations date from 2002, so probably didn't have domestic storage particularly in mind, but are written in terms of "a source of energy" so that they cover everything. One implication of this (I believe - I haven't looked up chapter-and-verse) is that any reinforcement work required on the network has to be paid for by the DNO for the <16A systems, while for >16A systems they can make you pay for a share of it.
Then you have the ENA documents that codify best practice and are used to show how you have complied with the rather open-ended requirements in the law.
G98 (previously G83/2) is the technical specification for the <16A devices that are permitted to be connected with just post-notification. In particular, it defines the type-test procedures that the manufacturers have to perform and issue test certificates so that installers know the equipment is permitted to be connected. They must now also record their test results in a register of tested devices maintained by the ENA. Note that the rules allow more than one item to be connected if the total output is less than 16A (as might typically be the case with solar PV using microinverters). It is permissible to have the equipment software-locked to a lower output than its physical capability, 'provided these settings are not accessible to the Customer'.
For anything that doesn't fit into that there is G99 (used to be G53) - which applies to anything from your little bit of solar PV up to huge power stations! However, there is a special simplified procedure for 'Integrated Micro Generation and Storage' where the individual units meet G98, the total doesn't exceed 32A, and there's an export limiting device to limit export to 16A.
G100 is the spec for export limiting devices, including both the Integrated Micro Generation and Storage case and more general cases of larger systems, for which it provides formulae to calculate how much generating (and consumption) can be installed. This is based on the export control taking up to 5 seconds to respond, and ensuring that bad things don't happen during those 5 seconds. So you can't have an arbitrarily large installation even if you have the load control.
Most of the 'ordinary' requirements in these documents are simply references to standards (eg. EN61000 for harmonics) that any CE-marked equipment would be expected to conform to: the stuff actually defined in G98 itself is mostly about when the unit must (or must not) shut down for safety reasons in response to voltage or frequency deviations of different types. The key safety feature is 'anti-islanding' - ensuring that if the DNO's supply is switched off (either by a fault or because they deliberately want to work on the line) your generator doesn't continue energizing the network and electrocuting the DNO staff trying to repair the fault. This is not as easy as it might first appear, since if you have generation and load that happen to be well balanced (or you are deliberately export limiting to keep them in balance) then there might not be any current flowing in the DNO connection and so no immediate effect if it is cut off.
That much is the facts about what is allowed, as to why things are like this I am now speculating without solid sources or personal knowledge, so the following may not be entirely accurate.
The main reason why you have to count PV inverter + powerwall against the 16A limit (rather than just considering the export limit setting) seems to be this assumption that the export control will have a time lag - up to the permitted 5 seconds. So you then ask whether that's a reasonable assumption - could you make an export control that responds in milliseconds rather than seconds? At first glance that seems quite easy - many inverters nowadays are software driven (ie. the 50Hz sinewave is generated by software almost like a big DAC), so you can generate any output waveform you like and the software is recalculating it at sub-1ms intervals already. The snag is knowing what you want to do - if the sensor tells you (moment by moment) that the export current is increasing, you don't know whether that's because the PV inverter has increased its output, or the supply voltage has dropped due to a neighbour switching loads, or the grid frequency is shifting etc. I suspect the end result is that you can't do it in your primary (fast) control loop, you have to have a primary control loop that does the ordinary 50Hz behaviour and then a secondary control loop operating over multiple cycles to implement the export control.
Of course if the powerwall and the PV inverter were directly connected and knew what each other were doing at a very low level then you could do it - but now you've made them effectively into a single piece of kit that has a 16A output, and that's already allowed. It's only when you split them into two boxes working indirectly via an export sensor that the difficulty arises.
As to why there's the 16A limit in the first place and why generally the DNOs are more restrictive on generation than they are on extra demand, there's a number of factors at play:
- Obviously the 16A limit itself is an arbitrary round number for regulatory purposes, picked such that it's big enough to be actually useful but small enough that one or two systems suddenly installed on an individual supply main are unlikely to cause immediate trouble. Obviously we as consumers would prefer it larger, but indications are that even the 16A level is causing trouble to some DNOs.
- One of the major sources of trouble is overvoltage at times of light load in the daytime. The DNO is required to deliver to every customer 230V+10%-6%, so between 216V and 253V at all times. The way this is usually managed is that the transformer serving a group of customers is set to deliver the full 253V under no-load conditions, with the voltage then drooping (mainly due to the cable resistance/impedance) as you get further away from the transformer and as the load increases. So if the network has been built like that, as soon as the amount of PV generation exceeds the amount of actual load, then the 'droop' is in the opposite direction and the voltage at the customers will be greater than the legal limit. Since PV is generating during the middle of the day, and residential demand is often very low at that time, it doesn't take very much PV for the problem to occur. If you bear in mind that networks are planned on the basis of average demand per house of only about 2kW, PV at the rate of 3kW per house almost guarantees trouble if everybody installs PV. And they can't just tap down the transformer to less than 253V to give a bit more headroom, as it's still got to work on winter evenings when there's no PV output and load is maximum: unless there was already spare capacity in the network (ie. the worst case droop didn't go down as far as 216V). So in effect, adding PV to a residential network eats up extra capacity - either the network was already at maximum load and adding the PV broke it, or else the network had spare capacity and adding the PV caused you to tap down the transformer and now you haven't got the spare capacity you used to have for adding more houses, supporting EV charging or whatever. So a customer adding generation capacity costs the DNO money even if the generation power is lower than the notional rating of the supply . There has been discussion about relaxing the legal limit on voltage to help with this. It was originally intended to go to 230+/-10% for European harmonisation, but the UK stuck with +10%/-6% out of concern for existing appliances not tolerating the lower voltage; with so many modern appliances being electronically controlled and/or manufactured for EU-wide use it is arguable that it would now be OK to go to +/-10% and so allow a bit more headroom for PV (we'd see the 'typical' voltage drop a bit to allow room for the generation to push it back up again).
- DNOs are concerned with fault current, both for their own equipment and to tell consumers what grade of switchgear they need to install to withstand the worst-case fault current under a heavy short circuit. As an aside, domestic consumer units are typically built up out of MCBs etc with a 6000A maximum fault rating, but the overall CU has a 16,000A fault rating - essentially, the box guarantees to catch the pieces of the exploding MCB once you go above 6000A. DNOs have to publish the maximum fault current their network can deliver, so that you know it's safe to use a standard CU and you don't need to go for something more industrial. Typically, for domestic connections DNOs just make a blanket statement that it's "less than 16kA", and they can do this because they can calculate the maximum fault current a given transformer design can deliver, allow for the effects of a few metres of cable, and then know that the worst case at any customer can't be worse than that. However, once you've got extra generation on the network, those generators can supply extra current in parallel with the transformer. The short-circuit current of an individual powerwall is probably quite small, but put a hundred of them in the area supplied by a single transformer (think one housing estate) and it can add up. If you've got powerwall + PV inverter, then that's (roughly) double the extra fault current compared to one or the other.
- System stability is a concern. This embedded generating equipment (inverters) has to shut down if the voltage or frequency goes out of spec, in order to implement the anti-islanding protection (among other reasons). So if there is an overload situation causing the voltage to droop, all the embedded generators will shut down - causing the voltage to droop even further and lead to a cascading failure. A taste of this was given in the big national power failure on 9th August: as a result of two generators failing simultaneously, the grid frequency drooped and as a result a total of 500MW of embedded generation across the country (so that's everybody's domestic PV nationally and some larger scale systems). The total of the big generators that actually failed was 981MW; the total reserve capacity was approximately 1000MW, so the loss of embedded generation might have been critical.
So all in all, if you want a really big domestic PV+storage system it's probably best to plan it with at least part of the storage DC connected, or perhaps make part of the system 'off grid'. Planning for more than 16A (3.3kW) of PV to 'float' across the grid into the storage is tricky (though you can treble that if you have three-phase).
WannabeOwner
Well-Known Member
WannabeOwner
Well-Known Member
Problems whatever route we head down it seems ...
I am envisaging some scenarios:
#1 Everyone in a street gets PV (and exports some/lots)
#2 Everyone in a street gets PV as per #1 but also e.g. DNO installs a Battery locally (rather than centrally)
#3 Everyone in a street gets PV and PowerWall (and exports nothing)
I had thought that #2 was best (and, indeed, better than Central Storage, close to generation, as it would better safeguard supply locally)
But I now wonder if #3 is best, notwithstanding the possible problems of "fault current"
I am envisaging some scenarios:
#1 Everyone in a street gets PV (and exports some/lots)
#2 Everyone in a street gets PV as per #1 but also e.g. DNO installs a Battery locally (rather than centrally)
#3 Everyone in a street gets PV and PowerWall (and exports nothing)
I had thought that #2 was best (and, indeed, better than Central Storage, close to generation, as it would better safeguard supply locally)
But I now wonder if #3 is best, notwithstanding the possible problems of "fault current"
There's no obvious winner, as it's swings and roundabouts - do the economies of scale of your communal battery outweigh the costs of reinforcing the network? Answer is likely to vary according to circumstances.
I don't think fault current is a big issue - it can be managed easily enough, the point was that it does actively require managing and doesn't just look after itself.
Land use/cost is a significant factor - one justification for domestic rooftop solar is that it is making use of otherwise wasted space (compared to putting it in a field somewhere that it displaces agriculture). Similarly your one-per-house powerwalls might slip into an unused attic while the communal one will need to find space somewhere - tricky in a city, maybe less trouble elsewhere.
Then there's the question we've debated before about whether solar has any purpose in the UK in a zero-carbon world (if you've built something else to cover the winter, why not carry on using it in the summer too and forget the solar?). I'm happy to continue installing solar now because I don't see us getting all the way to a zero-carbon grid within the useful lifetime of the kit, and it's usefully displacing gas in the meantime.
WannabeOwner
Well-Known Member
That's @arg, all good food for thought as always
I'm doing Excess PV too ... but in two minds whether CO2 released in manufacture of PV panels is acceptable (during the CO2-critical period for the planet) compared to buying my Leccy from North Sea Wind instead (lower CO2 in production installation of that, than from me sticking some PV panels on my roof).
I'm doing Excess PV too ... but in two minds whether CO2 released in manufacture of PV panels is acceptable (during the CO2-critical period for the planet) compared to buying my Leccy from North Sea Wind instead (lower CO2 in production installation of that, than from me sticking some PV panels on my roof).
The real question is how soon you think they are going to get around to building that wind for you.
For the next few years at least, that energy you buy from the grid is 100% gas (on the basis that wind is hardly ever curtailed even at night, certainly not on winter nights, so the difference between you installing solar and drawing less from the grid vs. not installing solar and drawing more from the grid will be balanced by burning more or less gas).
Some years later, and assuming they keep on building of wind (but don't build anything else interesting), your extra solar will sometimes cause wind curtailment and so impact the profitability/amortised carbon footprint of the wind generators. If they keep on going (highly questionable assumption) you eventually get to the point where your solar is completely pointless, always causing wind curtailment whenever you have a good solar day.
We really need a coherent national policy about what the long-term mix is (long-distance interconnects from places with different weather? Storage capable of season scale? Building a huge amount of wind 10 years ago so we could keep some gas in our back pocket for days when the wind doesn't blow?). Then we could make informed decisions about installing our solar.
However, I'm not optimistic about that happening any time soon - I think the balance of probabilities is that government will continue punting on the hard decisions and we will still be burning a fair bit of gas for electricity generation in 10-20 years time so installing solar now is a good bet.
WannabeOwner
Well-Known Member
Hmmm ... interesting to hear you say that, but wouldn't we have a ready market to export juice if we can roll out right across the North Sea shallows? installation will get cheaper / more affordable for more difficult locations (presumably ... as North Sea Oil did).
I mean ... there is always Hydrogen
Many of the net-zero commitments seem to be 2050. Seems a long way off to me, and "too late". Lots to do in the meantime of course, but as economies-of-scale benefits start to arrive maybe the target will be moved nearer / reached earlier. Flip-side after all the the low hanging fruit is gone the target will become harder
Probably far greater creators of CO2 that could be avoided before not installing PV. [New] Bricks / Concrete / etc., as other building materials are available.
I'll send you a dinner invite next time I'm having a dinning room full of Range Rover school-run parents ... could do with some backup!
If there is major work on long-distance interconnects (so we can export when we have excess and import when there's no wind), then that's a plausible solution, but it requires substantial international cooperation. Turning it into hydrogen (and then possibly turning the hydrogen into something else that's less inconvenient to store) is a possibility if you accept that you end up with only a third of the energy you started with.
The reason I said that indefinite wind expansion is questionable is that at some point the economics take a hit. At the moment, you put up a turbine and you can count on selling close to 100% of what it can generate (albeit some of it at low prices). Once the gas burn is getting close to zero on 'good' days, the investment case for your next turbine has to allow for it standing idle some of the time, or for some storage, or for interconnect to somewhere that can use it, or bribe some consumer to use more on windy days.
Given good government policy, the pain is shared around, the price of energy goes up (which is a good thing - make people take more care of how they use it - but politically difficult) and continued investment in renewables works out. But I think at the moment there's a bit of a trap: cost of wind has gone down, so people are looking at the cost per kWh and saying "wind now cheaper than conventional! Job done, no more subsidies required!" when those costs don't take account of intermittency. There's a desire to leave things to sort themselves out in the market (a sentiment I'm politically disposed to agree with), but ignoring the fact that the market can't justify the investment case without some certainty on how things are going to play out. If you knew for sure that no more gas would be burned after some date, you could make an investment case on the basis that your incredibly expensive turbine-plus-hydrogen-storage plant will still make money as it will be the only electricity left to buy and you can sell at a high price. However, you don't have to be much of a sceptic to realise that government targets are bound to be missed, and faced with the rising cost of electricity concessions will be made to allow burning of gas past the deadline (like how the petrol tax escalator got switched off 'temporarily' and never started up again).
The other part of the problem is that it needs international cooperation. One of the alternatives to storage is for energy-using industries to invest in more plant so that they run at double rate on windy days and shut down when electricity is in short supply. If the cost of duplicate steel furnaces/aluminium smelters etc is cheaper than storage units, then the variable market price for electricity ought to make this a viable investment for these plant owners. Unfortunately in the real world, their rational investment decision is to shut the plant in the UK altogether and go build a new one in China fueled by coal.
We are all doomed....
What ever happens to power generation been able to smooth out 'peak' demand has to help the overall grid balance. The PW has enabled us to turn a very busy/demanding evening use - when I suspect everyone else is doing the same, to virtually no demand.
I assume Nuclear is almost 'free' to run at 100% versus 50% power generation, so even is a small number of house holds were able to shift their 'peak demand' in a similar fashion balancing the grid surely will be easier?
I assume Nuclear is almost 'free' to run at 100% versus 50% power generation, so even is a small number of house holds were able to shift their 'peak demand' in a similar fashion balancing the grid surely will be easier?
Yes, Nuclear currently runs almost constantly at 100% (subject to maintenance etc) and is not generally throttled up and down to match demand - it is capable of doing so to some extent, but as you say there's no point as the cost has all been spent already, much like the wind case. The presence of those nuclear-powered generators does help with the very shortest term aspect of grid stability (over fractions of a second) where the mechanical inertia of rotating generators keeps the frequency stable for long enough that other measures (like turning up the gas) can be taken.
It is fairly clear that battery storage for short-term demand management is cost-effective - dramatically so for the grid reserve function, arguably so for covering the evening peak. The only question is whether it makes more sense for these to be small units installed at individual households or larger communal units.
The unsolved problem is what to do about seasonal variations - the risk of having a whole week with not much wind, or the fact that UK solar generates almost nothing in december/january. Batteries are too expensive for this job (or at any rate the sort of batteries in a powerwall etc). There's lots of alternatives, but none a clear winner.
