Solar 3kW + Tesla PowerWall in Auckland -> Started to Publish Stats as promissed

Forums › Home Workshop DIY › Solar 3kW + Tesla PowerWall in Auckland -> Started to Publish Stats as promissed

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#1624690 6-Sep-2016 16:23

KrazyKid:

I think buying a eclectic or hybrid car is a greener move in my situation ATM.

From a pure reduction in Co2 point of view, moving to an electric car is NZ's best bang for its collective buck,

Moving from a 82% (and increasing) renewable grid , to local solar does not even come close in a $ per Carbon Unit comparison.....

RUKI

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#1624828 6-Sep-2016 21:51

Jase2985:

so going off your info you are charging up your battery storage and using that completely every day? how many recharge cycles do the batterys have in them? what sort of output do you get from the batteries?

Battery is charged automatically when generation exceeds demand. Warranty is 10 years. I would assume usual degradation for Li is expected. Same modules are used in Tesla Car. I am curious myself..

@ 21:44 - still on battery - it is showing 45% (It never goes below 6% though)

Re: output => system is limited to 3KW. For example: if hot cylinder, oven and microwave are operating simultaneously - solar panels alone or battery alone will not be able to provide for that demand ... grid will top up the demand

Jase2985

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#1624873 7-Sep-2016 05:32

ok thanks for that. just considering options for a future build so i may have more questions

SumnerBoy

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#1624901 7-Sep-2016 08:28

RUKI:

Battery is charged automatically when generation exceeds demand. Warranty is 10 years. I would assume usual degradation for Li is expected. Same modules are used in Tesla Car. I am curious myself..

@ 21:44 - still on battery - it is showing 45% (It never goes below 6% though)

Re: output => system is limited to 3KW. For example: if hot cylinder, oven and microwave are operating simultaneously - solar panels alone or battery alone will not be able to provide for that demand ... grid will top up the demand

Hey @RUKI - do you have bespoke system for charging your battery via solar, or is it part of the Tesla Powerwall control system? How does the battery *know* you have excess solar generation and divert to the battery, rather than export to the grid? And how does the charging work in this scenario - i.e. if you only had an excess of 100W for example will the battery get that or is there a minimum threshold before it can actually start charging?

Very interested in one of these potentially - my current solar diverter works great in the winter months for diverting excess to my HWC but in summer there is far too much excess so another dump load is necessary to avoid exporting to the grid and getting a paltry 7c/kWh credit!

RUKI

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#1624924 7-Sep-2016 09:25

Incerted numbers to answer your questions:

SumnerBoy:

1)..... Hey @RUKI - do you have bespoke system for charging your battery via solar, or is it part of the Tesla Powerwall control system?

2) ....How does the battery *know* you have excess solar generation and divert to the battery, rather than export to the grid?

3) ....And how does the charging work in this scenario - i.e. if you only had an excess of 100W for example will the battery get that or is there a minimum threshold before it can actually start charging?

......Very interested in one of these potentially - my current solar diverter works great in the winter months for diverting excess to my HWC but in summer there is far too much excess so .....

4) .....another dump load is necessary to avoid exporting to the grid and getting a paltry 7c/kWh credit!

1) Re: Tesla PowerWall - It is Solar Edge Inverter which does the control function. RS485 Protocol is used between Inverter and Tesla Battery. Tesla is not the only one which can be used with the Solar Edge - surely someone will look at it it in the future and hopefully publish to allow third party batteries be used/controlled.

2) Inverter, not battery. Inverter has 7 settings.

3) I did not find details in the available Technical Docs (from Solar Edge) about thresholds, but Inverter has 7 settings: one of them currently activated in my System is "Maximum Self-Consumption" which implies "Give me all you have and do not export unless I am full..". There is another setting - maximize export. FYI - I do not have control over changing those settings, I can only see on the panel which is active now. System allows scheduling of those. Potentially in Summer they (Vector) can change it.

4) Sure thing. For that reason and because Vector's set up does not have back up in the event of blackout I have another 6KW battery independent from SolarEdge/Tesla Set up. Which has it's own charger and can provide my fridge, lights and some other equipment for a few days in the event of power outage.... It also can power up my High Voltage Battery Analyser + Charger to complete full test on Prius/Camry Hybrid Battery - in that sense I am off the grid for testing purposes..

SumnerBoy

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#1624937 7-Sep-2016 09:46

Ah I see - so the SolarEdge inverter is what has the smarts. It must have some sort of current/voltage sensor to measure the grid connection point - i.e. whether your house is importing/exporting.

The difficult bit for me is working out how to accurately match the excess PV, which would otherwise be exported, to what is being sent to the battery charger.

My current solar PV diverter works great with the HWC, since it is a simple resistive load. I can switch it very fast (using a SSR) in order to exactly match the excess solar to the power being sent to the HWC element. This means I both never import nor export when I have excess solar - everything is sent to the HWC.

I am not sure if this will be possible with something like a Powerwall - as the load won't be as _simple_ and probably won't appreciate being switched like that. The alternative would be some sort of current limiting control, which is probably what the solar edge is doing.

Will be keeping an eye on your updates!

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#1624943 7-Sep-2016 09:53

I was wondering if that PWM signal that EV chargers have to limit their power input would be able to be used to similar result. Mine would be in a garage where the supply is small, so I would want it to take whatever the differece between what is being used and 32A is, allowing for there being some solar on the garage as well. Things I dont have to worry about untill I see if I will actually get a model 3 or not.

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SumnerBoy

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#1624946 7-Sep-2016 09:57

Yeah these guys have something which can adjust the charging rate (http://openevse.com/). But I don't think it would support the kind of switching speeds to ensure you _never_ exported/imported - i.e. it would only be able to change the charging rate relatively slowly, and in large increments. But I think that is just the nature of the beast. It is very hard to exactly match solar excess, considering you have changes in solar (i.e. clouds passing over) and changes in your household usage (i.e. kettle boiling), unless you have a very simple resistive load.

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#1624960 7-Sep-2016 10:08

Yeah, none of the solutions are really made to deal with solar going into sub panels in different buildings to where the power is actually being used. Will be looking at sticking 4 or 6 panels on the shed at some stage as well, which would be an export from the shed to the house almost all the time, since the only load in there is a NAS and sometimes power tools.

Richard rich.ms

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#1624966 7-Sep-2016 10:14

As long as you have a single connection to the grid (which I think you have by the sounds) then my solar PV diverter would work - it just measures the energy direction at the grid supply point - if it is importing then the diverter is idle, if it detects an excess it beings switching the load (HWC in my case) at a rate which ensures that excess is being _used_ by the house. That load can be anywhere inside your home since the diverter is only measuring the overall house usage.

So in your case you could have the solar panels anywhere, as long as they were being fed into the main house wiring.

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#1624971 7-Sep-2016 10:20

Thats great as an overall thing, if the load is in the house, but I would be wanting diversion to a car in the garage or beside it, which would be off the garage DB. Does the diverter need a connection to the measuring device physically or is it wireless/IP based? Ontop of that I would want to ensure I dont trip out the garage breaker by going over 32A which might happen if it is charging and then clouds go over and other situations. I am yet to see a solution that can allow for that sort of control, and particually without things having to be directly wired to current transformers etc.

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#1624974 7-Sep-2016 10:26

My diverter is very much a custom built device. It is based on the Mk2PVRouter (http://mk2pvrouter.co.uk/) which was built with the guys from www.openenergymonitor.org. I lives in my house DB and has a current sensor around the main incoming phase from the street (as well as a voltage sensor to get accurate power measurements). This measures the energy flow in/out of the house by detecting the current direction.

It is all running on an Arduino and samples at 50Hz. Then depending on the current flow it will begin switching my dump load. This is the custom bit I did, it does this switching via MQTT over IP (ethernet). I have another Arduino sitting next to my HWC connected to a bit SSR which subscribes to the MQTT topic and switches the HWC element on/off. So that dump load could be anywhere you have IP connectivity.

But as I mentioned above, this probably won't play very nice with an EV charger since flicking it on/off like that is not going to end well..just showing the level/granularity of control needed to ensure there is no import/export when you have excess solar.

RUKI

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#1625131 7-Sep-2016 15:48

SumnerBoy:

Ah I see - so the SolarEdge inverter is what has the smarts. It must have some sort of current/voltage sensor to measure the grid connection point

It does

MikeAqua

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#1625171 7-Sep-2016 16:47

wellygary:

From a pure reduction in Co2 point of view, moving to an electric car is NZ's best bang for its collective buck,

Moving from a 82% (and increasing) renewable grid , to local solar does not even come close in a $ per Carbon Unit comparison.....

Arguably to increase the electric fleet we should increase our clean generation capacity as well. If we convert the national fleet of small and medium cars to electricity will need more electricity per year. The less carbon we have to burn to generate the extra electricity, the more carbon output is reduced.

Mike

RUKI

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#1625747 8-Sep-2016 14:51

What's going on I wonder - i.e. not charging? Snapshot @ 14:40 today. One of the disadvantages of not having full control of the system:

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