Imagine I have a large south facing roof inclined at 30 degrees, and I'm weary of paying £250 a month for electricity (no gas)..

Feed in tariffs have gone, but apparently if I pay a large sum of money for a Tesla powerwall and join octopus I get paid the same 28p to export to the grid as I do to import

Do I have to get some particular certification to have this deal, i.e. does the TPW have to be installed by some particularly approved person who will sell it to me at some wallet-searing rate?

How does the payback look against some other battery storage system and a strive to self-generate and use as much myself as possible, minimise grid imports? Do I use lithium or lead batteries?

In terms of charging these battery storages up, I'd imagine that most of the world has gone bananas for solar, with the ever spiralling upwards costs of electricity so the costs of panels are probably higher than what they were..

..looking around ebay I see various kit secondhand and new - seems that 450 to 550 watt panels come in at around 225 to 275 quid so the wattage is about double the money.. Used kit is e.g. a 260watt panels for a hundred quid so perhaps slightly better value at watts that are 2.5 times the money, but do they wear out? Are these older lower wattage panels worth considering or are they approaching end of life already?

Then we have other stuff like inverters and mounting systems. Inverter per panel is reckoned to be the best way to go, but there's a premium for it, and it might be hard to justify for me as I don't really have a lot that could shade any panels I install - no trees etc. Mounting rails might be something I can build myself; i've never looked to see whather they're expensive for what they are.. Do we have full and free flex to pair any inverter with any panel and mount in any way? Or are things sold as paired up systems and you're better off getting all the bundled kit together? If microinverters are used do they phase align themselves so they "just work" when all connected together, even from different manufacturers?

Can I install panels myself and get them MCS signed off? Do I need them to be signed off if I'm in "minimise taking from the grid" mode? Do I need them to be signed off if I'm securing an SEG tariff and exporting (the export part is Tesla's problem, I think - who cares how the Tesla is charged up)?

What sort of ratio of panels power to battery storage kwh capacity do I need? How do I translate the kwh eon say I used in the last N years into a sensible kw sizing of an array?

Imagine it's ridiculously windy where I live too - can domestic wind turbines usefully add to this system? How do they rate, £ per watt, compared to panels and do they feed into the same/similar inverters?

So many questions.. What I'm looking for ultimately a relatively easy route to minimising electricity bills as something of a curiosity about whether I could get e.g. a 2 year payback on an install cost in light of energy costs having risen to be 3x a month what they were when I first started living in this house - some of that is increased usage, the rest is a doubling in price per kwh

Averaging it out over the last 3 years it looks like I get through 34kWh a day; it's been fairly consistently that year on year (about 12MWh a year).

When you say 14, is that you're aiming to reduce usage to 14kWh a day, or you're aiming to install 14kW of panels? Is the rule of thumb 2/3 the daily use goes into panel capacity? (Yikes! Still, I've got enough roof space for 30kW..)

When you say "your supplier is the one that cares about MCS" that means electricity supplier, not panel or battery supplier ?

Hi tychwarel

True, but micro inverters make it easier to extend the system? Or would you say put 10 panels on one inverter, and then put another 10 on another same inverter, rather than using micro's and enabling some ability to add any number of extra panels?

There's some other thing as well, not an inverter, that is supposed to help with maintaining efficiency if some panels are shaded.. I think it has to be used per panel along with a central inverter

-

True about the Tesla, though I read that they weren't actually that ridiculously priced for the capacity and they do work well. And they're the only system to have engineered a good contract with a supplier (octopus) to ensure a good price for exported energy (its symmetric apparently; 26p for export or import)

We are not worthy. tony's one line deepeties are without equal - all hail tony the font of all wisdom

Posted By: cjardTrue, but micro inverters make it easier to extend the system? Or would you say put 10 panels on one inverter, and then put another 10 on another same inverter, rather than using micro's and enabling some ability to add any number of extra panels?

Haven't looked much into micro inverters, partly as we have a PV and battery system where the PV output is to the DC side of the system. We have two PV arrays, each are wired to an MPPT charger, which knows about the battery voltage and state of charge. Charging batteries is a (surprisingly) complex operation which will be much more efficient if there's no inverter involved and charging is controlled by the batteries own BMS (i.e. for lithium).

Seems to me that micro inverters are not suited to a PV and battery system (unless you have a v shady and awkward for panels location).

Remember that 'shading' in a conventionally wired system comes in a variety of guises- a dollop of seagull s**t, a bit of saharan dust, a perched bird, a bit of algal growth, faulty panel.

Adding micro inverters or optimisers also allows for individual panel monitoring so if one panel or optimiser fails the monitoring platform can notify you. Without individual monitoring it could take years to notice a drop in output followed by what could be quite extensive roof top fault finding.

If the array is split over differing facing roof pitches then each pitch needs wiring separately back to separate MPPT inputs on the inverter. With micro inverters or optimisers they are just series wired over whichever pitch you want.

Certainly for a Solaredge system if you want to add panels, just break into the existing loop and plug in your new optimisers/panels. Hit the pairing button, wait a few minutes and the new panels are up and generating. The other thing to consider with optimisers is they allow you to use differing output panels on the same string without the lower rated panels pulling the string output down.

Potentially add a bit of cost so theres a bit to consider

Octopus are paying 30p/unit for exports at lunchtime today, but 108p at tea time (yes £1.08). A few weeks ago it was windy and prices went negative. Batteries starting to look like a better idea! (I make no predictions about whether this continues or not...)

OEM EmonTX4

https://shop.openenergymonitor.com/6-channel-energy-monitoring-bundle-emontx-v4/

Posted By: WillInAberdeenOctopus are paying 30p/unit for exports at lunchtime today, but 108p at tea time (yes £1.08). A few weeks ago it was windy and prices went negative. Batteries starting to look like a better idea! (I make no predictions about whether this continues or not...)

But do you get to decide when to export (I.e. when it's sunny turn off everything in the house) or is it dictated by Tesla's software? (No demand; no export)

No smart meter but considering sticking a light sensor on a Pi I do have, to count the flashes from the normal meter :)

Posted By: renewablejohnI know we are a low user at an average 7kwh per day but 34kwh seems exceedingly high

I'm going through similar plans myself, I want to go big for 10 to 14kw array but that only worth it if can store battery AND export back to grid, so i guess i need to check with DNO if i can get permission first?

For usage comparison we use 9500kwh a year, 26kwh a day av, , and that is our 4 bed house, a 3 bed holiday let and and another 1 bed holiday let combined. 3x electric induction hobs, 3x ovens, 3x mvhr systems etc

So 34kwh on a single house sounds quite alot... something must be a BIG energy hog, are you EV charging as well? multiple chest freezers, multiple computers/ games consoles, old non LED lights, huge electric range cooker, electric aga?

I also think that 34kWh per day is a hell of a lot. More than twice my output for a family of x4 and an EV.
Although everyone is different and a couple of electric heaters or underfloor heating alone could swallow up a large amount of leccy and skew the numbers.
Begs the question though as to whether is would make more sense to focus on reduction. Every £ spent on eliminating those peaks and items heavy on electric could save ££ on PV and batteries.
I have a plug-in monitor that is handy for recording usage from anything with a plug. I once found that my old outdoor fridge was haemorrhaging electric and a new A++ fridge payed for itself within a year!

On batteries, I looked into them for my new PV set-up and I couldn't get the numbers to work. I think it helps that I have an EV and can charge during the day on PV. They are good bed-fellows.

Posted By: WillInAberdeenIf you are interested in the tariffs which reward off-peak consumption or peak-time exports, then you're going to need a smart meter sooner or later. We were surprised how useful it is, for a freebie. Good to get involved with R-Pies, but also get a smart meter too while you're waiting for stock!

EPCs are being reformed to show: total energy consumed; net energy imports (IE net of self-generation); cost of energy (electricity costs more); and carbon emissions (electricity emits less). And a meaningless number about primary energy. These can all be in kWh, or in kWh per m².

Focusing in on just one of those measures (such as kWh of electricity purchased) can be a bit misleading without also quoting the others - eg if using more electricity means using less fossil fuel, then that's a good thing, and one kWh of electricity used can be much better/worse than another, depending on when exactly it is consumed. Plenty of opportunity for spreadsheets!

Just to get back to the thread topic, are issues with batteries outweighed by enabling consumption when grid electric is lower carbon? Of course, that largely depends on accepting the difference between transmission and distribution (which is another story!). Also, depending on which inverter manufacturer you decide on, some offer a data portal for your system with hour-by-hour consumption and generation data - much better than a spreadsheet. Eventually, you might expect EPC's to allow that data to be part of the picture.

Re raspberry pi availability, haven't tried one yet but there are new alternatives such as 'OKdo ROCK' (nice name). One small issue with smart meters being 'free' - think we need to be a bit more critically aware given we're all paying an extortionate amount for each meter!

Not in the UK, Bot, different kind of meters over here - the energy co is liable for consequences if they remotely cut off the power eg to someone who is using a medical device, or to someone's fire alarm. They don't want to to take on that liability so they use different approaches. Apparently such as moving people onto pre-payment meters, which (for decades) have always had the ability to cut users off without an official coming to visit, if they aren't able to pay.

But a smart meter is necessary to access the kind of battery tariffs being discussed above, where you get paid more for exporting after the sun has gone down, or on days that aren't windy. Yesterday Octopus paid 36p for daytime solar, or 56p for the same electricity in the evening, so 20p uplift for using your battery. Don't know how long that would take to pay for the battery.

<blockquote><cite>Posted By: WillInAberdeen</cite>Not in the UK, Bot, different kind of meters over here - the energy co is liable for consequences if they remotely cut off the power eg to someone who is using a medical device, or to someone's fire alarm. They don't want to to take on that liability so they use different approaches. Apparently such as moving people onto pre-payment meters, which (for decades) have always had the ability to cut users off if they aren't able to pay.</blockquote>

Are you sure about that Will?

There is a SM thread somewhere from a while back where I warned that is what was going to happen.


"A rise in the so-called 'switch by stealth' of people being forced onto pre-payment meters has been branded "alarming" amid calls on energy watchdog Ofgem to intervene.

Ofgem has said it has received reports of vulnerable customers being left without power for days or even weeks.

According to data from Ofgem, more than 152,000 households with smart meters were remotely switched to more expensive prepayment plans for gas or electricity last year.

But Citizens Advice has predicted that 450,000 people could be forced onto a prepayment plan this winter - with 180,000 of them expected to be remote switches via a smart meter."

https://uk.news.yahoo.com/smart-meter-cut-off-prepayment-meter-switch-by-stealth-warn-campaigners-142534893.html?guccounter=1&guce_referrer=aHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS8&guce_referrer_sig=AQAAAMB8upAMgeh52Iup-GLyabPlmdbZn6WkXsXWSLCpUVLxMGrQc9mRY0mPbAQOgKrE_169yoksoLamSs94PoUlpVXPBY7ahtTfsmU8l1BGog20t05Vup7Q7QtKNkFLvQA-UluQkyzDtMGFEvwknRfN0a-W9tSz1ZYjIqFlcLIsP4Ab

<blockquote><cite>Posted By: WillInAberdeen</cite>Er, that's what I said! So the 450k-180k =270k people who didn't have a smart meter, still were moved onto pre-payment. So SM or no SM, it doesn't protect you from moving to pre-payment.</blockquote>

It says "could" be forced. The SM people dont get a choice , it will just happen at the press of a button. And it is leaving some without power. Nothing they can do about it. Good luck getting through to cusomer sevices and persuading them to turn your elec back on.

The none SM people still have some power as customers that the SM ppl dont dont.

Sorry, but if you willingly hand over total control to power companies, you are asking for it.