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Author Topic: Tesla Powerwall 2, one month in.....  (Read 10146 times)
dickster
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« Reply #15 on: January 23, 2019, 03:15:37 PM »

So to sum up. I'm happy now that I can control the SOC of the PW2 using the Tesla app, thus avoiding leaving it discharged for long periods of time in dull weather.

I'm also very happy that on a sunny January day (today), the system has generated over 60% (3.5 kWh) of our average daily usage, with the excess tucked away in the PW2 for use later on this evening.

I now intend to get a quote for an Economy 7 meter ( I have a cunning plan....), but remain very aware that a trip through a PW2 costs 10% of the electrons.


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linesrg
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« Reply #16 on: January 23, 2019, 04:52:49 PM »

dickster,

I'd consider 10% more than acceptable. When I make calculations for such devices I allow 10% each way............

Regards

Richard
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dickster
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« Reply #17 on: January 24, 2019, 09:55:52 AM »

Another point. Below freezing this morning, what has the PW2 done to look after it's batteries? Warmed them up with 300W at 4 a.m. this morning.

Cheeky, but good to know it's looking after itself without me having to fiddle about.


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oliver90owner
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« Reply #18 on: January 24, 2019, 11:09:53 AM »

For how long was it warmed and how cold was it?
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dickster
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« Reply #19 on: January 24, 2019, 12:17:14 PM »

The app is not accurate enough to give good readings (slidy finger over rough graph), but I reckon maybe half an hour, ramping up to a peak of 300 Watts and then back down again. Most likely a lot less than 300Wh , but gave that figure as I'm a lazy boy.
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dickster
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« Reply #20 on: January 24, 2019, 12:18:08 PM »

Sorry, forgot to say -3 C.
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Tiff
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« Reply #21 on: January 24, 2019, 01:39:23 PM »

Sorry, forgot to say -3 C.

Do you know what temperature the bateries are at and what the target temperature is?
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Scruff
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« Reply #22 on: January 24, 2019, 02:05:55 PM »

What happens when the battery is too discharged to run it's electric blanket and starts charging? I suppose it must prioritise the heater and stay in a discharged state?

Is the 10% round trip losses  figure a marketing number or based on independent metering in real world conditions?

For any energy storage system <20% would be unheard of (NOC)
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dickster
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« Reply #23 on: January 28, 2019, 10:44:28 AM »

Tiff...I don't know,

Scruff, the PW2 took a charge from the grid to look after itself. The 10% is a figure that came from general chit chat amongst Tesla PW2 on the internet. A pinch of salt might be needed.

As time goes on I'll be able to narrow down all figures more accurately and might have more useful information to hand.
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dickster
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« Reply #24 on: January 29, 2019, 02:55:16 PM »

With internet off, a lovely sunny day, got 4.2 kWh solar, but PW2 from 0% SOC then stopped charging from solar at exactly 12 noon with plenty of capacity left, the rest of generation exported to grid. Answers on a post card please.
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dickster
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« Reply #25 on: January 30, 2019, 10:18:14 AM »

So overnight with the PW2 at 0% SOC , -2C and internet off, it stirred itself using 300W of mains electricity at around 2 am.

The app gives running totals for day, week and month, but doesn't store anything beyond this.

I looked at the weekly figures of consumption using the app. It stored 9.1 kWh and gave back 5.9 kWh, so my 10% loss is looking very doubtful, more like 33.3%, which is pretty awful, IF the figures are to be believed.

I suspect that running the PW2 from 0%, loading an average of maybe 1kWh of solar per day, using it at night back down to 0%, all in cold weather is perhaps the most inefficient way of power transfer.

However, the monthly totals, which include me charging fully from the grid on a couple of occasions over a period of warmer weather (less overnight stirring) show 73.2 kWh in and 62.2 kWh out, but I'm not sure what the SOC was to start with. Nevertheless it equates to around 85% efficient, so a more acceptable loss.

There are too many unknowns and it's too early in the day to be really conclusive.

Unfortunately, I am not willing to leave the satellite broadband on all the time, which would remove one of the most obvious dodgy variables from the equation.

Thanks for the suggestions for running android on my laptop, internet alternatives and all the other hints, tips and questions.


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Tinbum
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« Reply #26 on: January 30, 2019, 11:34:50 AM »

My Growatt runs at about 85% efficiency which seems to be the norm. In this cold weather though it shuts down due to battery temp and it doesn't have a heater in it. I've just bought a small 120w tube heater to fix under the battery that I can turn on with an app when needed.
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sbchapman
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« Reply #27 on: January 31, 2019, 03:49:54 PM »

@Tinbum - that's a great idea.

'Energy for free', sort of, or at least energy enhancement ....

AC heater, powered by the battery overnight (PV in daylight), which warms the battery resulting in better energy capacity for other loads. I've been thinking about battery here but no space internally (that SWMBO would approve anway) and really wasn't keen on putting one outside due to temps, but guess you could build an insulated container outside. Will have to check the installation requirements for LiFEPO4 chemistry from the manufacturers.

However if the container were insulated, would also need a fan for cooling in summer, so one of those controller recently shared with heat and cool circuits would work perfectly ...
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dickster
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« Reply #28 on: February 04, 2019, 10:01:54 AM »

Nearly 2 months now, but should have said energy, not power, in last post.

So, PW2 has had another fit on Thursday, under the same circumstances as it's first one.

Bright sunny day, plenty in the battery, put washing machine on, crazy powerflow on the app, basically taking about half the energy from the grid, half from the battery in random seesaw wave pattern making no sense at all, but again, the internet was off. Maybe the PW2 needs to phone home during this type of usage. I'll try again when I have same conditions, but with internet on.

So Saturday, a beautiful day, full sun, pv generated 4.7 kWh and minus house usage, left with 18% SOC (on local gateway app, shows as 13% on app via Tesla). Looked forward to another sunny day on Sunday, hoping to have bridged from one day to another to another without using grid. Internet off overnight.

However, -5C overnight, PW2 didn't stir itself and even with internet on, it won't discharge, house power coming from grid. About 9 am, it started whirring and humming (as it does when it stirs itself), but still no action. Lovely sunny day, but the PW2 won't discharge or charge, now exporting sun power to grid. Nothing seemed to wake it up, so switched off Gateway for a couple of hours and then back on. As the sun went down behind the trees around 4 pm, PW2 starts discharging and feeding the house. So now it will give, but will it take? Down to 0% SOC so decide to give it 2 hours charging from 12 pm to 2 am. It starts charging as requested. Then internet off to see if it will switch itself off at 2 am.

Monday morning, internet on, good news, it charged for 2 hours. Now have to switch it back to self powered to see whether it will discharge and feed the house. More good news, it does.

So it would appear that, for one reason or another, a minus 5 C with internet off overnight is to be avoided, seemingly taking all day to defrost?, but I will be leaving the internet on next time we have a -5 C night to see what happens.


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dimengineer
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« Reply #29 on: February 04, 2019, 10:10:06 AM »

Just as a thought - so many things these days "need" the Internet to function properly that having the Internet off screws with the Powerwall's brain.
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