[Paultheparaglider]

most "grid tied" solar systems have to shutdown during outages for safety, which many owners don't realise.

Ours certainly does. It is something we are sensitive to because our water supply is pumped from a borehole so we lose the ability to flush loos etc.

That said, apart from minor spikes, I can count the power cuts in the 16 years here on the fingers of one hand. Inconvenient, but not really a significant problem.

[Paultheparaglider]

exported the remaining 25%. #bummer. We've had a 13kWh Powerwall for 2 years now, and have managed to get exports down to perhaps 5%.

CP,

Please correct me if you think I'm missing something here.

Assuming a generation of 5,000 kwh per annum (mine is under 4,000 (but I live in slightly less sunny Wales), that 20% reduction in export means 1,000 extra units used at home so 1,000 less units paid to your supplier.

Assuming 20p per unit, the extra saving from your Powerwall is £200 per annum.

A Powerwall2 and backup typical installation costs £10,200 per Tesla website, so payback of 51 years, and that excludes a cost of capital. Or battery degradation and replacement over time. Even at 40p per unit, the payback period is a long one.

I've been reading through @T67M 's interesting link. The grid smoothing strikes me as very clever, and a very good way to move forward strategically, particularly if we all end up with electric cars that can also be tied into the grid in a similar fashion.

The numbers might not really add up just yet for me, but the future is almost certainly heading in that direction.

[VRB_20kt]

Feed in Tariffs only apply to older installations. You’re lucky if you can get 5p per unit for export now. It’s galling when you generate 3x as much energy as you use but end up paying through the nose for import.

Hence the importance of having a battery and a degree of smartness to the installation.

[Trent772]

To explain the two types in plain speak.

A basic PV install will shut down on loss of mains power to prevent back feed of electricity up the pipe.

An advanced system with storage - such as Tesla has interlocks that isolate the incoming supply and then allows the house to feed from stored power. That way, the maintenance gadges don't get fried from your wanton spewing of solar wind !

Also bear in mind - those little panels produce around 250v DC which will kill you in an instant - do not fiddle with the back side of panels !

[Colonel Panic]

exported the remaining 25%. #bummer. We've had a 13kWh Powerwall for 2 years now, and have managed to get exports down to perhaps 5%.

CP,

Please correct me if you think I'm missing something here.

Assuming a generation of 5,000 kwh per annum (mine is under 4,000 (but I live in slightly less sunny Wales), that 20% reduction in export means 1,000 extra units used at home so 1,000 less units paid to your supplier.

Assuming 20p per unit, the extra saving from your Powerwall is £200 per annum.

A Powerwall2 and backup typical installation costs £10,200 per Tesla website, so payback of 51 years, and that excludes a cost of capital. Or battery degradation and replacement over time. Even at 40p per unit, the payback period is a long one.

I've been reading through @T67M 's interesting link. The grid smoothing strikes me as very clever, and a very good way to move forward strategically, particularly if we all end up with electric cars that can also be tied into the grid in a similar fashion.

The numbers might not really add up just yet for me, but the future is almost certainly heading in that direction.

When looking at whether to get a Powerwall I calculated that I would be effectively "off grid" for a third of the year, and only using cheap rate imported power for the rest of the year. Due in part to the algorithm that Tesla use to predict tomorrow's weather not being perfect, it hasn't quite worked out that way in reality.

That said, the numbers for a battery are not nearly as good as PV (was); IIRC my fag packet calcs showed a payback of 7-8 years for the PV, and perhaps 15 years for the Powerwall. I "only" paid £7,000 inc 5% VAT for my Powerwall 2 years ago, and even that included 2 additional PV panels and a secondary inverter to go with them.

It has been a while since I looked at the numbers, but here is sunny mid-Sussex I "only" manage to generate ~3,900 kWh / year from my nominal 4kW PV system. In the 2 years since installing the battery, exports have dropped from 1,500 kWh / year to 580 kWh / year.

90% of my imported power is at the night rate, which was ~10p cheaper than the day rate, and is now over 20p cheaper than the day rate now. Before the Powerwall we were importing ~3,000 kWh / year, so that makes a saving of ~£300/year. Add in the drop in exports and that goes up to ~£400/year. I accept that these figures don't look like they will get a payback of 15 years, but for the life of me I can't recall how I came to 15 years at the time of purchase anyway!

With the benefit of hindsight, would I install PV again (assuming the rules at the time)? Most definitely. Would I install another battery? Most likely, but I do accept that it is a nice-to-have rather than a no-brainer.

[Dodo]

Thanks all. Lots to think about. I shall investigate costs and report back.
D

[T67M]

One key factor, @Dodo is to decide whether you're going to install something to save you money, betting on tariffs available over a 10+ year timeframe, or do you want to do something that's environmentally "the right thing to do" and affordable. You are likely to get very different answers!

[Flyin'Dutch']

With the benefit of hindsight, would I install PV again (assuming the rules at the time)? Most definitely. Would I install another battery? Most likely, but I do accept that it is a nice-to-have rather than a no-brainer.

The battery was a condition stipulated by Mrs FD, she reasoned that not having one would result in me being grumpy if non-PV-electricity would be used. I think she knows me well...

[dublinpilot]

What is the lifetime of a battery in such an installation?

Are they like regular lithium ion batteries that lose a lot of their capacity after 1000 recharges (3 years)?

Or do they have a much longer life?

[Flyin'Dutch']

I don't know but it is not that everyday counts as a cycle; I cannot remotely log on to the system but IIRC after 2.5 years we have clocked about 150 cycles. WIll check and confirm/Correct when I am at home

[rikur_]

What is the lifetime of a battery in such an installation?

Are they like regular lithium ion batteries that lose a lot of their capacity after 1000 recharges (3 years)?

Or do they have a much longer life?

The warranty on the Powerwall is 70% capacity at 10 years.
For 'self consumption' that's unlimited by cycles/throughput, otherwise it's 37MWh of throughput, which is about 3000 full cycles. In practice you're unlikely to do a full cycle everyday, so 10 years seems to be the limiting factor.

[Flyin'Dutch']

[quote="dublinpilot"]What is the lifetime of a battery in such an installation?

Are they like regular lithium ion batteries that lose a lot of their capacity after 1000 recharges (3 years)?

Or do they have a much longer life?[/quote]

2.5 years 329 cycles.

Just read an article on these batteries which suggest that the lifespan of batteries is more related to age than cycles.

[rikur_]

[usermention=1654]@dublinpilot[/usermention] .... as my reply above didn't survive the migration,
I'll repeat it ....
The warranty on the Powerwall is 70% capacity at 10 years.
For 'self consumption' that's unlimited by cycles/throughput, otherwise it's 37MWh of throughput, which is about 3000 full cycles. In practice you're unlikely to do a full cycle everyday, so 10 years seems to be the limiting factor.

[SafetyThird]

First thing I would do is head over to https://camelot-forum.co.uk/phpBB3/index.php and ask your questions. It was set up after the old Navitron forum closed, that had been the best repository of alternative energy information in the UK for many years. I had been a member there for over a decade and the wealth of knowledgable people is huge, from those with a few grid-tied panels to people who've lived off grid in the Hebrides for over 30 years.

I've had my 6kw of solar panels for 7 years now, generating around 5800kwh annually, with an Eddi diverter pushing any excess into my thermal store to heat our hot water. That, along with a woodburning stove with back boiler has heated all our hot water over the past 7 years. We heated our cottage with two woodburners and a couple of storage heaters while renovated the place but last year put in ground source heat pump central heating. Our electricity consumption hasn't changed but has moved from mostly night time power to day time and a consequent increase in cost. Some of the new inverters can be connected to tarrifs such as Octopus Agile, or Octopus Go and allow charging during very low cost times of day which can vary at different times of day depending on countrywide generation capacity and demand.

I'll be installing a 14kwh battery pack and AC inverter in the next few weeks to hopefully allow me to time shift my consumption, importing night time power and charging the batteries to use during the day/evening. My system will be a LuxPower Squirrel Pod inverter and 4 x Pylontech US3000C batteries. Everything is modular and I can change out individual items if something should fail, which is different to, for example, a Tesla Powerwall where, should it fail, the whole thing needs changing out.

The LuxPower inverter has the option to output 3.5Kw from battery in the event of a power cut, so I will move my lighting circuits and a ring main the covers our home office onto a separate feed for that. At least we can keep working during a power outage. Most Lithium Ion Phosphate batteries are warrantied for 10 years and many can be discharged down to 100% discharge level without being damaged. Battery Technology has come a long way in recent years. I would expect my Pylontech units to be good for at least 80% of their charge capacity after 10 years and, because my system is modular, I can add batteries to it if I need to increase it's capacity or to make up for reduced capacity as it ages.

What I really need is a wind turbine, which would give my power generation during the winter months when my 6kw of solar just can't add much on cloudy days. However, that's expensive, even if I buy a used 6kw Proven turbine (about £5k plus installation, which would be quite substantial) or spend £20k on a new turbine. Even with that, getting planning permission is doubtful and I'm out in the countryside on a farm. Instead, I've just invested into a share in a Ripple Energy turbine (Rippleenergy.com) that will come onstream at the end of next year and for which I'll be paid for my share of it's power generation for the next 20 years, which hopefully will cover a significant chunk of my winter power needs.

Hope that might offer some insights but post over on Camelot forum and you'll get all the information for your specific situation to make the best decision.

[rikur_]

SafetyThird wrote:
> My system will be a LuxPower Squirrel Pod inverter and 4 x Pylontech US3000C
> batteries. Everything is modular and I can change out individual items if
> something should fail, which is different to, for example, a Tesla
> Powerwall where, should it fail, the whole thing needs changing out.

That sounds like what I'm looking for.
I will pop over to Camelot to learn more, but lazy question first .... can that be installed outside, or does it need to be inside? An attraction of the Powerwall was that it could be installed outside.