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My Tesla Powerwall: Tales of an early adopter

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One Step Off The Grid

As per the tweet I sent the other day, my solar system has now generated over a MWh (Megawatt Hour) since it was installed in late January with the Powerwall. Essentially that means my panels have generated…

wait for it…

zoom in to close up …

drevil

One Million Watts!

Yep, that’s lame, but I’ve been waiting to kick that off for weeks now. And some would say that picture has a striking resemblance to me.

On average that makes it a bit over 25kWh per day solar power generated, which is quite good considering we had a few cloudy days. Record day so far is about 33kWh generated, which might get broken around the summer solstice next year when the days are a bit longer.

March in Australia generally resembles February, but at this stage it is even warmer than usual in Sydney. You can read a really good summary at The Conversation about why its happening this year in particular.

I’m also following 9th Dan Chart-Master, Ketan Joshi on twitter, to see what statistical wizardry he’ll come up with next in terms of climate science and weather patterns.

This record period above 26oC (79oF) has certainly provided some amazing solar power statistics for the first week in March, as follows:

MarchWeek1-e1457422150844

Fairly healthy rates for import and export, and its just a shame I’m yet to take advantage of feed-in tariff. I’m still awaiting changeover to Diamond Energy so I can take full advantage of Reposit Power with the Powerwall later this month. SO excited. GridCredits!!!

If I was on my current provider’s plan (which I’m not because I’d have to sign a new agreement), I’d have imported about $1.70 worth of power after all discounts, and made about $4.40 in feed-in tariff. Throw in 7 days of connection charges of $4.94 after discounts, and I’m $2.24 in the red, theoretically.

However, I’ve consumed 110.17kWh of my own making, or nearly 16kWh per day. That is actually pretty low against the household average over the year (~20) and if I didn’t have solar panels, that 110.17kWh + connection fees would be somewhere in the order of $31.70.

So really, when you think about it, I’m almost $30 to the good!

Importing just over 1kWh per day looks pretty spesh, but I’m here to tell you it could have been even better, and will be once this warm spell expires. Let’s go to the chart…

MarchWeek1-2

Right at the start of you can see a little red block. This was an anomaly where the battery management firmware was confused by 29th February (Leap Day). Yeah, as a developer I can tell you it happens, occasionally. I’m assured its fixed, and because we’re on daylight savings time right now it started at 1AM on the 29th Feb and went through until 1AM on 1st March. Cool.

There is a big spike on 3rd March which was air conditioning going on for a very warm afternoon. On the morning of 7th March the battery finally went to sleep after the previous evening’s efforts cooking dinner and dessert.

Why burn stored energy doing all that baking in the evening? Firstly, it was a work day, but mostly, let’s just say that you can’t put obsessive battery monitoring ahead of my wife’s roast chicken, followed up by chocolate cake. You just don’t.

Our electric oven is running a bit out of kilter at the moment, judging by the noise coming out of the fan assembly. I’m getting that rectified next week, which should decrease duration of usage, by providing a more efficient cooking cycle. Moar cakez!

I recently added a new network attached storage (NAS) for backup duties, after the old one finally threw a shoe – i.e. one of its RAID partitions. The new one has power recovery so can handle being on a timer, along with the TV and games console running from that outlet. Only a few watts saved, but every bit counts when you’re trying to get the battery through the night as often as possible, under varying circumstances.

Powerwall Zen

As I’ve learned a bit more about the Powerwall, I’ve also tweaked some of the larger hardware pieces to exist in harmony with each other and the solar system in general.

For example, the pool pump needs to be running for a certain number of hours per day to ensure cleanliness, and takes about 0.8kWh at standard operation. I’ve worked out the pump capacity (Qmax) and rate of flow correctly, to ensure I use only the minimum hours per day. I also figured out that running it later in the day allows the battery to top up earlier as the panels start cranking up the flow mid-morning.

In partnership with this, the timer on both our washing machine and dishwasher are set for the early afternoon, when the sun is at its highest. I leave a gap in the pool timer of 2 hours in the middle of the day so both these devices can run without issue, even when the sun isn’t so bright.

As always, a solidly overcast day can throw some of these plans out of whack, and that’s why a grid connection is a must. Beyond keeping the warranty of the Powerwall at 10 years (off-grid is only 4), in suburbia there is simply no reason to disconnect, with the grid as your fallback.

And I’m only a couple of weeks away from generating GridCredits, getting the battery topped up before the 2PM peak boundary makes sense both financially, and from the data it will provide to advance our knowledge of micro-grids in a modern urban environment.

Now, if you’ll excuse me, I smell cinnamon cupcakes baking…

The Pfitzner household is equipped with 20 x 250W Phono Solar panels in two arrays of 10 panels, for a generation capacity of 5kW. Both arrays address a north-west aspect, with the western set slightly shading the other in the late evening. There is no shading during prime generation hours, and summer hours are expected to keep the array at or above 1kW between the hours of 0900-1800, based on readings to date.
The panels connect to a SolarEdge SE5000 inverter, with P300 Power Optimisers on all panels, providing maximum throughput of 5kW to match the PV array. The inverter, in turn, connects to the StorEdge battery controller that controls flow between the Powerwall and the house. The Powerwall is a “Daily” model, Lithium-Ion store of 6.4kW capacity, which from full will provide the house enough power to get through most nights, depending on use.

This article was first published in One Step Off The Grid, where you can read more stories about people’s experiences with solar, storage, energy efficiency and other technologies, both on and off the grid. To sign up for the weekly newsletter, click here.

  

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  • MorinMoss

    I wonder what NAS he’s using?

    • Pfitzy

      I got a SeaGate Personal Cloud – single bay, 3TB. Nothing fancy, just simple backup, on a network, with gigabit and power recover. I had a 2-bay RAID 1 but it just made it slow and tedious. The backup to the backup is another Seagate – the GoFlex model, which I’m slightly less enamoured with.

      The point is, both drives are 3TB which is more than enough, and gives me mutiple points of failure 😉

      • MorinMoss

        Thank you. Might I know how much the PowerWall cost fully installed?

      • MorinMoss

        I messed around with backing up to multiple devices for years but finally got myself a LaCie 5-bay NAS Pro over a year ago and it’s been smooth sailing so far.

  • Andrew Woodroffe

    One Million Watts!
    ?
    Surely you mean one million watt hours?

  • Eric Milligan

    What software are you using to graph your data? How do you measure your import/export?

    I have an SE5000 as well, and while their monitoring portal is fine I haven’t found a way to measure import/export/total electrical usage without buying some form of add-on. I’ve been considering CURB/Neurio/Sense but don’t love any of them.

    I export my production data to PVOutput.org:
    http://pvoutput.org/list.jsp?userid=32916

    • Pfitzy

      I looked at pvoutput and its a great site, but I wanted to pull my data into my own site and slice it the way I want for blog entries.

      I’m an IT developer by profession, mostly in database development, dabbling occasionally in PHP with MySQL. More recently I’ve moved into NodeJS and associated tech around API development.

      As a result, I’ve started building data around the SolarEdge API:

      http://www.solaredge.com/files/pdfs/se_monitoring_api.pdf

      First big point: you only get 300 requests per day – or one request every 4m48s 😉

      Last week I started building custom PHP/MySQL routines to pull out a few of the endpoints here (mostly /powerDetails and /currentPowerFlow) then transform them into what I want. I still find JSON a bit meh, but I’m a hardcore SQL guy 😉

      I’ve only published two basic graphs at the moment, both of which you can see here – one in the body for power flow, one in the right panel for battery level:

      http://unleashthepowerwall.com/

      I’ve scheduled retrieval for every 15 minutes, which runs off a google spreadsheet if you can believe that (I couldn’t, until I saw it work).

      The result is, I’m putting through about 190 requests per day, modifying it into half a dozen tables, and using WordPress charting plugins for output. Only two so far, but I’ve had to squeeze this in around my paying job, and learned a lot.

      I might blog about it some day once I’m more on the “mad skillz” side and less on the “amateur dinosaur SQL bloke” side.