Tesla Powerwall 3 set up.

JKenH

Currently the NetZero app is sending pricing information to the PW3 without any intervention from me. Yesterday I was a little disappointed with the charging regime. We had had overnight electricity prices in the 14p range but the battery elected only to charge to 60%despite daytime prices being generally in the 18-20p range. It then ended up doing a top up at 1.30pm when the price was 20p.

The problem I believe was the weather we had didn’t match the forecast. Originally on Friday the app had been predicting over 5kWh of solar generation but during yesterday it scaled that down but there was still a shortfall as despite a brief glance if the sun around 9am low cloud rolled in. The NetZero app shows generation only being 45% of predicted with a shortfall of 1.8kWh or 13% of battery capacity. The 1.30pm boost added 5% taking the battery from 47-52%. We then limped through to 21% at 10.15 pm before another small top up. Yesterday, I could have done a better job myself.

Last night, with a similar day expected both in terms of pricing and solar generation we had quite a bit of time at 14.6p but the battery at 6.30am was only at 51%. It then decided to add a further 4% at 15.44 p. There aren’t any cheaper slots later in the day with the afternoon being consistently around 19p before the 30p plus peak slot so either we will limp through with the 57% we have now and use electricity from the grid at these higher rates or it might do a top up at the higher rates. I honestly am not expecting any sunshine to bail us out and neither is the app with a total generation for the day of 0.8kWh predicted.

I accept it’s early days at the moment but I don’t see me sticking with the NetZero app after my first month’s subscription expires and I am anticipating moving to Octopus Go (if I am allowed). 

Edit: I may be maligning the NetZero app as I don’t know if it does anything more than provide pricing data to the PW3 which may then make its own decisions about solar estimates or demand and charging management. 

thevilla

Predbat can get caught out by lower than expected solar generation. It has an option to set a value in kWh which it should not plan to drop the battery below. Does your app have similar? I find it useful in winter now we have a heatpump and there's no chance we'll be exporting if I set the value too high. I'm on IOG so predictable prices help. 

JKenH

I can set a reserve level in the Tesla app. It recommends 20% but it is currently set at 5%. If I up that level then presumably the PW3 will add more charge charge to a higher level.

IOG would be nice to have but I definitely need an EV for that. I had a chat with a Tesla sales rep who was looking bored outside a garden centre and he assured me I can get (standard) Go without an EV. I will definitely move to that within the next month but having spent the money on the NetZero app I am experimenting with it for a bit. We have family staying with us until the New Year so our usage patterns aren’t representative. It’s not a good time to be training the battery software.

JKenH

JKenH said:

Currently the NetZero app is sending pricing information to the PW3 without any intervention from me. Yesterday I was a little disappointed with the charging regime. We had had overnight electricity prices in the 14p range but the battery elected only to charge to 60%despite daytime prices being generally in the 18-20p range. It then ended up doing a top up at 1.30pm when the price was 20p.

The problem I believe was the weather we had didn’t match the forecast. Originally on Friday the app had been predicting over 5kWh of solar generation but during yesterday it scaled that down but there was still a shortfall as despite a brief glance if the sun around 9am low cloud rolled in. The NetZero app shows generation only being 45% of predicted with a shortfall of 1.8kWh or 13% of battery capacity. The 1.30pm boost added 5% taking the battery from 47-52%. We then limped through to 21% at 10.15 pm before another small top up. Yesterday, I could have done a better job myself.

Last night, with a similar day expected both in terms of pricing and solar generation we had quite a bit of time at 14.6p but the battery at 6.30am was only at 51%. It then decided to add a further 4% at 15.44 p. There aren’t any cheaper slots later in the day with the afternoon being consistently around 19p before the 30p plus peak slot so either we will limp through with the 57% we have now and use electricity from the grid at these higher rates or it might do a top up at the higher rates. I honestly am not expecting any sunshine to bail us out and neither is the app with a total generation for the day of 0.8kWh predicted.

I accept it’s early days at the moment but I don’t see me sticking with the NetZero app after my first month’s subscription expires and I am anticipating moving to Octopus Go (if I am allowed). 

Edit: I may be maligning the NetZero app as I don’t know if it does anything more than provide pricing data to the PW3 which may then make its own decisions about solar estimates or demand and charging management. 

Disappointingly, the battery reached its reserve level of 5% at 6.30pm and for the next half hour the house was using between 1.1 and 1.8kW from the grid at 31p. This could have been avoided if the battery had charged to a higher level overnight when prices were 14.6p. Hopefully things will get better with time.

thevilla

JKenH said:

I can set a reserve level in the Tesla app. It recommends 20% but it is currently set at 5%. If I up that level then presumably the PW3 will add more charge charge to a higher level.

IOG would be nice to have but I definitely need an EV for that. I had a chat with a Tesla sales rep who was looking bored outside a garden centre and he assured me I can get (standard) Go without an EV. I will definitely move to that within the next month but having spent the money on the NetZero app I am experimenting with it for a bit. We have family staying with us until the New Year so our usage patterns aren’t representative. It’s not a good time to be training the battery software.

Reserve is a value the battery will not go below I believe. Predbat has one it will try not to go below. 

I suppose you just have to see it it settles down.  It is very easy to get obsessed though isn't it 😃

as96

NedS said:

JKenH said:

I am getting a bit more used to how the PW3 behaves and, perhaps more importantly, it seems to be getting used to me. After the initial disappointment with its response to Agile I programmed in my own”tariff” with four different price bands from super off peak to peak then broke the day up to 7 or 8 time slots and allocated a rate to each. It was necessary though for me to also set separate export rates for each time slot because the PW3 on time based control is focussed on saving money and how it responds to any given import price will depend on the export price at the time. Because the PW3 also takes into account charging losses there has to be a clear margin between import and export. (The rates I entered while reflective of typical time of day pricing are of course are a completely artificial construct and don’t reflect what I pay - I just wanted to programme the PW3 to test how it responds). Over around a 30 hour period the PW3 responded exactly how I wanted it to, charging and discharging perfectly. 

This is essentially how I run my PW3, although I'm on the Cosy tariff which is a lot easier to manage. If I were on Agile, I would do as you have done and manually assigning slots as either 'cheap' or 'mid' or 'expensive' throughout the day. You know Agile is generally cheap from 22:30 through to 5am, higher through to 10 or 11am, cheaper through to 4pm, and then expensive until later in the evening. You can probably work out the slots you'd like to charge in / draw from the grid and manually update each day - or pay the monthly subscription to NetZero and let it manage it for you (but I doubt you will save the subscription fee?) 

I set the 3 Cosy cheap slots as Off-Peak (15p) and set all other times as Peak with an artificially high import price of 200p - in other words DO NOT import outside of the cheap rate slots, only run from the grid or import electricity in the 3 cheap slots. Hopefully this is clear enough that even the Tesla AI can be in no doubt! My average import price is effectively equivalent to the Cosy cheap rate price (~14.8p for me).

If you have enough battery capacity to run your home like this, Cosy may be an easier option than Agile unless you think you can achieve a lower average price on Agile over winter. I keep an eye on the Agile pricing, but mostly the lowest prices have been around the same or higher than Cosy, and mostly only occur overnight when we use least due to overnight set backs on the heating, plus Cosy with it's 3 spaced out cheap slots allow us to recharge 3 times per day and cover 40-50kWh per day usage from a single 13.5kWh PW3. So for us, I think on average Cosy is cheapest in winter and gives certainty of pricing.

You should absolutely consider switching to Intelligent Octopus Flux (IOF) in summer as this is by far the most lucrative tariff when you are a net exporter. Last summer we averaged 25-26p for our excess exported electricity and then import at ~15p in winter giving great leverage. We switch in around April and back to Cosy in October, and the points we become net exporters / net importers, corresponding roughly to the time the heating goes on/off. This arrangement requires virtually no management or input from me and I can just let the PW3 get on with it, plus I do not need to pay any subscription fees for the NetZero app.

Ned, I'm still trying to find the best settings for Back Reserve on my PW3  I'm not exporting and on Octopus Cosy. What do you have yours set at?

NedS

as96 said:

Ned, I'm still trying to find the best settings for Back Reserve on my PW3  I'm not exporting and on Octopus Cosy. What do you have yours set at?

It depends. I move it according to needs.

So far this year, it's been fairly mild so we've not really pushed the battery that hard, and a 20% reserve (Tesla's recommendation) has been fine, but if we were looking like we might hit the reserve I'd just reduce it to 10% or whatever was required to see us through and avoid pulling from the grid outside of the cheap rate slots.

If you do not want to micro-manage like this on a daily basis, just reduce it to 5-10% or whatever is appropriate for your usage. The only point of the reserve is to ensure you always have some battery in the event of a power outage, otherwise you can run your battery right down to zero if that avoids pulling from the grid. If it's a massive issue and you are always hitting the buffers, you probably need a bigger battery, not a lower reserve (accepting the law of diminishing returns).

Like you, I disable battery export (export excess solar only) in winter as it makes no financial sense on Cosy, and it's one less thing to confuse the Tesla AI.

I'm not sure if there's a longevity argument around keeping the battery charge between 20-80%, but I'm not overly concerned given how robust modern batteries are. I bought it to use it, and the harder it works, the quicker it pays for itself.

Screwdriva

as96 said:

Ned, I'm still trying to find the best settings for Back Reserve on my PW3  I'm not exporting and on Octopus Cosy. What do you have yours set at?

When I asked Tesla this, they were vague but did hint that below 10% wasn't "a great idea" on a continuing basis. I would get something in writing to ensure the warranty isn't affected by going below the recommended setting over the longer term.

JKenH

Last night the PW3 fully discharged just before midnight. The PW3 shows the amount discharged as 14.3kWh. I have no means of checking how accurate this is. Overnight the PW3 charged back up to 100% and consumed 14.4kWh doing so. The PW3 app recorded total draw from the gid at 21.7kWh which tallies exactly with my IHD which is presumably accurate. The split is shown by the Tesla app as 14.4 Powerwall/7.4 House (some rounding up there). I have no means of checking the House draw but no reason either to believe that it is not correct as the total tallies with the IHD.

It would seem from this that the amount recorded as discharged is 99.3% of the amount recorded to recharge the battery. I have seen it quoted that the PW3 is 98% efficient but I have also seen elsewhere a figure of 90% efficiency. (I believe the PW3 has a quoted useable capacity of 13.5kWh).

All I can say is that, from the app, it appears to be around 99% efficient. I wonder how the efficiency suggested by the PW3 app compares with other the figures shown by apps for other batteries or indeed with other PW3 users’ experiences.

Despite my reservations about the accuracy of figures seen in energy apps, I am reasonably heartened by what the PW3 app is telling me - could my battery be 99% efficient and could it actually have a capacity of14.3kWh? I will assume so until it is demonstrated otherwise. 

JKenH

Yesterday was another grim day so no daytime charging of the battery. 14.2kW discharged and 14.4kWh overnight to refill back to 100%.