What amazes me is that the cost is still as high as what we paid 6 years ago. I'd expected that it would have fallen. 

As ever some great detailed explanations, @Transparent.

There’s been a wealth of info shared here, both on the technical considerations and financial implications of installing solar PV - we’re looking to collate these into a seamless overview so would love to know if there’s still any unanswered questions we should look to include?

Notice there’s been a lot of focus on the installations themselves here but not much discussion on the metering side of things. For those who already have PV panels installed how are your export or generation readings measured? Do you have a separate meter or do you find it easy to take the readings from your smart meter? 

Get sharing as we’d love to cover all aspects of your solar setups in this guide!

Oh I’ve got loads of unanswered questions @Jess_OVO 

Here’s one -

Can an electric vehicle travel as fast in reverse as it can in the forwards direction?

… or did you specifically mean questions about solar panels?

Actually I’d quite like to get an answer on this ^^^ @juliamc what’s the top speed of your e208 in reverse? 

Yes good shout, Jess - we don’t have much in the way of metering. My understanding is that there’s always a generation meter fitted, clocking the energy generated (please correct me if I’m wrong people!), so some detail on these would be good. Does it matter what this is? Does it just come with the panels and there’s various different manufacturers and they all do the same thing?

As for export, again my understanding is that this will depend on the tariff arrangement and if it’s a smart meter your export is measured exactly rather then assumed to be 50%. 

Now we need the actual experts (that’s you) to confirm or correct all of that! 

@Tim_OVO @Jess_OVO We have report PV figures manually each quarter (M, J, S, D). The reading from the generation meter indoors, and the EXP KWH from the "smart" meter outside (press 9 and wait for the phrase to show followed by the number). The IHD isn't any use for this. The instructions specifically said we cannot use the export reading from the generation meter. The payment takes almost 2 months. 

Prior to getting the smart meter our export was estimated at 50%. It has actually been around that in winter but over 70% for the two summer quarters. 

Apparently SMETS2 might be able to report the EXP KWH but I'd still have to report the generation reading. The OVO Guide to smart meters states : If you have a SMETS1 meter, a remote software upgrade will enable it to work across the same network used by SMETS2. That means it will be migrated onto the national smart meter network - but I don't imagine it will enable SMETS2 functionality. 

I don't know any technical details of the generation meter, but it was installed with its own big off switch next to the existing consumer unit aka fuse box. I'm not at home so only have old photos. 

SMETS1 meter followed by generation meter. 

@EverythingNeedsAUserNamewrote:

That means it will be migrated onto the national smart meter network - but I don't imagine it will enable SMETS2 functionality. 

The software upgrade applied to SMETS1 meters by the manufacturers should enable the same functionality as any other SMETS2 Smart Meter. That requirement was part of the initial specification dating back to 2013.

I don’t understand why you have to report the Export Reading manually from the display on the meter. Nor do I know if those with SMETS2 Meters have their export read automatically.

The reason I don’t know is because I still haven’t managed to get approval for the Smart Export Guarantee (SEG) from OVO’s in-house SEG Audit Team, seven months after the first application.

So perhaps someone else with a SMETS2 Meter could answer that one.

As for Export Meters, they are a statutory part of the installation for any grid-connected ‘generation device’ under MCS regulations. The same is true for the red & yellow rotary switch to disconnect the device from the grid.

As I have two ‘generation devices’, a PV Inverter and a PowerVault Storage Battery, each has its own AC Disconnector. The one for the battery is inbuilt to the left side of the unit (arrowed), whilst the one for the inverter is a separate device:

What I don’t understand is why the installers had to return to site to fit an over-complicated export meter for the Storage Battery, whilst the very simple display on the front of the inverter is deemed adequate.

I rarely consult my Export Meter - an OB418. It has over 50 different parameters which can be displayed on the screen. For reasons unknown to me it has divided the kWh exported into two separate figures. As I still have no payments for exported energy, I have more important things to concern me!

@Transparent good luck. Back in 2015 my application was November and I got the first payment  for the December quarter in February 2016. It took 23 pages of application form and accompanying documents, including my driving licence as ID! 

Well there's interesting. I've been looking back at the information from our installation. They definitely used their calculations of potential energy generation. Our Inverter (hard to access, fixed to the roof trusses in the loft) is a SolarEdge SE3500. It is rated for Maximum AC Power Output 3500W, which compares to the 3990W of the panels. The peak at any moment that we've seen over the 6 years of about 3100W. Perhaps if it had been south facing we'd have had a bigger Inverter?

I now recall that I had asked the question about more panels so that we could actually generate enough to stand a chance of exporting 4kW. I was told that it was the panel nominal that was limited even though the power company restrictions were based on the export to the grid - which would never match the panel rated power. 

An inverter is positioned between the rooftop Solar Panels and the mains Distribution Grid. Its job is to convert the Direct Current from the Panels into the Alternating Current used for the UK mains electricity.

Almost all domestic installations will use an inverter which has G98 certification. This means that the design has been tested to the G98 standards and the device is already ‘trusted’ by the Electricity Networks Association (ENA). As such it can be installed by a qualified electrician without the need for a site-inspection by the regional Distribution Network Operator (DNO).

It’s important to note that an inverter may not supply the house with power in the event of an outage on the Distribution Grid. It must cease operation in order to avoid electrocution of the engineers who will be working to fix the fault at the substation!

When power is restored, each inverter waits for a random period of time of several minutes before re-starting export. If this were not so, then all inverters in the area would simultaneously supply power, thereby causing a surge.

So how does such a small inverter manage to push power onto the Distribution Grid in opposition to the enormous generation already being supplied from large commercial power stations?

It does so by raising the voltage of its output. The current being exported is continuously monitored, and the voltage adjusted to ensure that it remains within the permitted 16A (for a single-phase property).

The inverter must always ‘fail safe’. So if, for example, exporting at the maximum 16A would take the Grid voltage above 253v, then the current is lowered accordingly.

Clearly this situation is most likely to occur on sites where the normal voltage is already high, such as mine:

Rural areas are more likely to have voltages that run close to the permitted envelope of 216-253v. In my case the voltage is kept ‘high’ by my regional DNO in order to compensate for significant losses on other long feeds across the nearby countryside.

Here’s the high-voltage limitation coming into force on 26th August 2021 mid-afternoon:

You will notice the momentary over-voltage at 15:17 whilst the inverter was ‘hunting’ for how much current it could supply whilst keeping below 253v.

Although I have a PowerVault Storage Battery, that had already been filled to capacity during the morning and was no longer available to take in any further solar generation.

Here’s the corresponding ’live’ display from the PowerVault monitor screen, showing output from the Solar Panels lowered to just 900w during a moment when the inverter had cut all export to the Grid:

The implementation of G98 by the Growatt inverter shows that it is effective at operating within the required parameters. However, doing so is very wasteful of energy.

All excess solar generation during the afternoon was thrown away.

Is there a way in which my Battery could be better used such that the energy wasted was reduced?

Yes. The most promising route to achieve that would be the Flex Platform, which has weather-forecast input.

Given the relevant data, Flex could reduce the amount of electricity being stored during the morning by exporting that portion to the Grid. To do so it must know:

• my geographical location
• the hours of sunlight expected at my site during the day
• the daily pattern of my house base-usage
• the battery capacity

At this moment in time there is no suggestion that Flex is being developed in this direction. However, the theoretical use of a national smart control system would clearly allow greater capture of precious renewable generation.

It would also allow better use to be made of electricity storage on the local grid.

There is still some energy wasted on a site (like mine) with more than 3.6kW of solar capacity. But that wastage is due to the limitations of the G98 certification on inverter design.

If, in future, a Storage Battery was accredited as a Load Diverter, then the level of wasted energy could be further decreased by installation of a larger inverter. At the time of writing (Sept’21) only immersion heaters can be accredited for load diversion use.

Thanks for all your great input and story sharing - @Transparent, @EverythingNeedsAUserName, @sylm_2000, @PeterR1947, @JohnMcG.

I’ve picked out some of your responses and combined them into the guide - check out the edited first comment.

Let me know what you think and if there’s any more insight you think should be included - particularly in terms of the metering side of things and how you went about choosing an installer.

@Transparent - I’ll be moving all your great self-installation comments over to a dedicated DIY guide tomorrow - watch this space!

That’s great @Jess_OVO - Just bear in mind that I have more yet to come on this subject!

So I’ll need to ensure that a future post is either ‘generic’ or ‘self-install’.

I’ve already described the G98 requirements for an inverter to be grid connected, and illustrated this above by showing what happens when the grid-voltage goes too high - above 253v.

So what happens when the grid-voltage goes too low?

This is actually a much more serious situation, and raises the prospect of the Distribution Grid collapsing.

The voltage limits which must be obeyed by a grid-connected inverter are 230v +10% -6% which equates to 216-253v. If the grid strays outside of these limits, the inverter must automatically disconnect.

Once the voltage recovers within the specification, the inverter is required to wait a random period of time before reconnecting (typically several minutes).

Let’s illustrate a low-voltage response by visiting the rural hamlet of March End.

It’s a quiet idyll about 2 miles outside the village of Averley in the West Country. Averley and the surrounding area is served by single 11kV supply from the Primary substation just outside Stannerton.

Whilst Stannerton itself takes the great majority of that electricity, the overhead line to Averley suffers from voltage drop of about 5% during the early-evening period of peak demand.

To alleviate the risk of houses in Averley falling below 216v, the Distribution Network Operator (DNO) has set the Primary transformer taps at Stannerton on the high-side. This delivers around 245v to houses in Stannerton, but no one has complained.

However, the real issue remains the increasing load being fed from the 11kV line running five miles southwards to Averley.

Encouraged by the local Council, many of the houses around Averley have installed roof-top solar panels, including two in March End itself. When the sun shines this helps by raising the voltage locally.

The six houses in the hamlet of March End are supplied from a pole-mounted transformer next to Croft Corner. However the overhead wires onward from there still lose 3 or 4 volts before reaching Figton Cotts or March End House.

We pick up the story on 10th May at 4:30. It’s a sunny day. Mrs Higgins at No.1 has used their new Electric Vehicle to collect the children from an after-school club. Knowing that she will need to use it again in the evening for a long trip to see her sister, she quickly plugs it in for a 2-hour boost-charge.

Next she switches on the kettle for a much needed cuppa and sets the electric oven to 200°C to cook the chips and sausages for tea.

She doesn’t know that solar generation at Croft Corner and March End House has been dropping for the past half-hour as the sun starts to sink, and she is completely oblivious of the chain of events which she has just set in motion.

The additional electricity load at Figton Cotts has pulled the voltage lower for all six houses in March End. It’s most critical at March End House which is now at 217.5v. But the occupants are still out at work and no one monitors it anyway.

At 4:55 a cloud passes slowly in front of the sun. It will be there for just six minutes.

With full sunlight no longer hitting the Solar Panels on the roof of March End House, the voltage falls to 216v. The inverter complies with its G98 certificate and detaches itself from the grid.

The sudden loss of 3.6kW in the small hamlet pulls down the voltage at the other nearby houses. When it detects 216v, the inverter at Croft Corner also disconnects.

The loss of a second source of power momentarily pulls down the EV charger at 1 Figton Cotts. The lights briefly flicker, but Mrs Higgens barely notices. After all, she hasn’t just switched something on or off, so it can’t be anything to do with her can it?

She is equally unaware that her charger has dropped out of Boost Mode. It’s been operating for only 30 minutes out of the 2-hours it was set for.

By 5:02 the sun comes out again, but neither of the PV inverters senses a rise above 216v and both therefore remain off-grid.

At 5:10 the family sit down for tea, after which she goes upstairs to pack and tells the children they can’t watch TV until all the homework is done. The TV doesn’t get used. They don’t yet know about the power-cut.

Just after 6:30 Mrs Higgins and the children pile into their new electric car to make the 3-hour drive to her sister in Wales. In her haste she doesn’t notice that the battery level is only reading 65%.

It’s still daylight as they pass through Averley village, although the illuminated sign outside the village shop appears to be broken.

During the 5 mile drive to Stannerton Mrs Higgins turns on the car radio and hears a news-flash about a major power outage affecting an area of the West Country.

“I expect that’s why the lights flickered just before tea-time,” she thinks to herself.

Only after they pass through Stannerton does she notice the battery level. She’s not too concerned and decides to press on to the M5 where she can pick up a rapid-charge at a service station.

They never make it to her sister’s...

Less than twenty of the 230,000 ground-mounted substations are monitored - all by community energy groups working with Western Power Distribution.

Unless they're doubling up as a depot or office, Primary substations are unmanned.

On the evening of 10th May, Stannerton Primary would've been manned by Bob. But he'd been called out to a reported fault at 4:15 and hadn't yet returned.

All Bulk Supply Points are fully monitored - the first line of defence if the Distribution Grid is under threat.

At Western Power's South West Regional Control Centre, the duty engineer, Steve, is watching the screen displaying data for the 132kV circuits fed by Indian Queens Grid Supply Point. It's the most westerly GSP on the National Grid and also the point at which the commercial wind-turbine arrays on the North Cornwall coast send their power onward to supply the rest of the country.

At 5:09 the wind dropped off, and Cornwall became a net-demand rather than a supply generator. Steve's hobby is hot-air ballooning, giving him a clear understanding of the calm period before sunset.

Just as he was about to call his colleagues at National Grid Control, an alarm sounds and Steve sees the Bulk Supply Point at Landulf is at -4% and falling rapidly.

Before he can decide whether to throw open the breaker or call National Grid first, the decision is taken out of his hands.

The senior duty engineer at National Grid has seen the frequency drop to 49.4Hz with heavy demand down both arms of the grid from Taunton. He releases the load with a second to spare and sends Devon and Cornwall into blackout.

Grid frequency rises to 49.6Hz.

Signals are sent automatically to all standby generation plants to come on-stream.

The two hydro-electric pumped-storage generators at Ffestiniog and Dinorwig in North Wales are first to respond and reach maximum output in less than a minute. That's enough to hold the country at 49.6Hz whilst the slower nuclear and gas-generators build up steam pressure through their turbines. It's an anxious 12 minutes before the frequency rises to the lower operational limit of 49.8Hz.

It will be 4 days before the West Country is fully back on the National Grid, and another day before the Higgins family can return home by train and bus. Their EV remained in Somerset for a fortnight more whilst insurers scrabbled around for break-down trucks to recover customers' vehicles.

Is this realistic?

Yes. The UK suffered a similar outage across a large area of eastern England on Friday 9th August 2019. Power was lost to 1-million consumers. A timeline illustrating the sequence of events has been published for download from National Grid PLC.

What was the precursor to this event?

A lightning strike on the National Grid north of London caused the immediate, short-term loss of 150MW of ‘embedded generation’.

‘Embedded generation’ refers to electricity supplies connected to the Distribution Grid by G98/G100 certified equipment. It includes small-scale commercial sites and houses with PV Solar Panels.

All G98/G99 grid-connected inverters in the area north of London sensed the momentary drop below 216v and detached themselves from the Grid.

Lightning strikes on electricity supplies are common and 150MW is not an enormous amount in the overall energy-budget of National Grid. But in this case the sudden demand made on two other supplies(1) also failed because of the overload.

The Grid frequency fell to 48.8Hz - sufficiently low that it was no longer possible to bring additional generators on-stream. To recover the situation, electricity demand was reduced by totally removing supplies to end-users across a large area of East England.

Could such a grid-outage actually be initiated by a failure of local domestic generation?

Yes. Distribution Network Operators regularly survey the network looking for areas which have inadequate fault-resilience.

These deficiencies are reported to Ofgem and a proposal made for system enhancement and upgrade. This can involve replacing transformers and cabling.

In some instances it is necessary for installers to re-visit individual homes connected to the Distribution Grid by inverters that were certified under the earlier G58 standard. These are upgraded.

In most cases the public remain unaware of these system weaknesses. But I have a report showing how an area of the UK was identified as vulnerable to a cascade of outages initiated from domestic-level generation. For obvious reasons the geographical area will not be identified here.

(1) The supplies failed from both Hornsea offshore wind farm (a loss of 737MW) and Little Barford gas-powered generators in Bedfordshire (244MW loss from plant-1, followed by 187MW from plant-2).

Statistics taken from the ESO Technical Report of 6th Sept 2019, which differ from the figures published in the timeline of 16th Aug.

The threat to our electricity supplies from the million+ homes with single-phase micro-generation would be alleviated to some extent if more of us also installed Energy Storage. This could be grid-connected batteries, a (SunAmp) thermal phase-change device, an EV with a V2G charger, or an off-grid battery.

All these technologies would lower the power-demand during the early evening peak.

However the way in which such devices are currently being deployed is still rudimentary.

For example, my own PowerVault Storage Battery is either charging or not. It has no concept of charging at a lower rate whilst still allowing some export to the Distribution Grid.

The clunkiness of such devices therefore causes sudden changes in Grid supply and demand.

If storage is implemented randomly within houses on a relatively large substation (½MW), then the switching surges have reduced effect. But they can still cause outages when installed in homes connected to a smaller pole-mounted transformer, as shown in the above story.

Here’s the generation/storage graph from my PowerVault installation from a weekday at the beginning of September ‘21

The battery first takes all available power (blue) until 1 o’clock when there is a sudden switch to maximum export (3.68kW) because the battery is full.

However, if there was intelligent control over the amount of charging, the graph should’ve looked like this next one, avoiding any sudden changes but still achieving a full battery before direct sunlight was no longer hitting the Solar Panels:

Of course, this assumes that the control system ‘knew’ in advance how much sunshine was expected for my area throughout the day.

However, such data is already available from my Distribution Network Operator (DNO) for each hour of the day. Each data-set covers the area served by a Bulk Supply transformer - around 20,000 homes:

This is where a national flexible energy system could offer the required scheduling, controlling the proportion of renewable generation from our homes which is to be stored or exported.

Whether OVO’s use of the Flex Platform will ever allow this isn’t known.

However, if I was looking around for a Storage Battery, high on my ‘wants’ list would be the ability to configure the charging rate using some form of external control, such as an App.

This would increase the total amount of grid-export throughout the day, allowing some to occur within the 3.68kW limits whilst the battery was still charging.

Even if setting the charge rate is initially very manual, it would in future also allow Flex to take over and handle it automatically.

Actually a Tesla can except it is software limited to 20mph I believe. It just runs the motor one or the other… so the drive train can. The rest of it no!

… bit off topic but hey!

Hi all,

I am in the process of getting a 10.5KWH battery and 10 x 400W panels installed and these are going onto a Just south of London, due south (2 degrees off) , 36degree pitch roof. 

Question is, given this setup and my 3.6kwh inverter, what energy savings financially am I likely to realise.

Edit: If relevant voltage to house is 253v stable. I am about 5metres from the substation.

Thanks.

A great question, @Jequinlan

Wonder if any of the Solar PV owners above might be able to give you an idea of the energy savings you could make with that setup? @EverythingNeedsAUserName, @PeterR1947, @sylm_2000 

You can search for Solar Estimate databases such as https://ec.europa.eu/jrc/en/PVGIS/downloads/CMSAF these will give you an estimate on your likely generation month by month although I have always found them to be a little under optimistic; this is a graph of my year to year generation, the target from the database is the blue line that is mostly at the bottom but it is at least a starting point

Just having a PV array fited with battery. What do we need to do in terms of changing the meter or do the PV company arrange this with SSE?

@Chris Evans when we had our solar PV installed (and battery storage later) the meter wasn’t changed. Have you been told that it needs to be?

I’m assuming we will Bryan as it’s an old analogue meter!

Oo - wish I still had an analogue version. They used to be driven backwards by solar.

If it’s a Smart Meter, it simply needs to be configured to track exports. This will prevent false Reverse Energy Detected warnings and will actually make it easier to send in export readings.

If it’s any other meter with RED functionality, I’m afraid it’ll trigger RED warnings which you cannot prevent. You can ignore them if you’re doing legitimate exports though.

If it’s an old analogue meter, I’m afraid you will probably need to have it replaced before you install Solar PV equipment. Otherwise you risk being done for accidentally “abstracting electricity” or “meter tampering”. Whoever your current energy supplier is should be capable of booking in a free Smart Meter upgrade for you, which should prevent that problem. You’ll need to arrange that yourself.

Do you know if OVO Energy sell PV system components (as inverter, battery or pv panel) or if it sells for other companies?