EEVblog 1502 - Is Home Battery Storage Financially Viable?

[EEVblog]

Running through the numbers to see if home battery storage is viable on my home.

[furmek]

Could someone with a battery please tell me how much cycling a day one should expect.

In Dave's case - 10kWh battery - would you expect close to 10kWh in and out every day or more or less?

The other way of looking a the cost of battery is to compare it to "storing" energy with the network.
I get paid $0.05 for 1kWh exported and pay $0.25 for 1kWh used which would mean that "storing" 1kWh would cost me $0.20 - and it's a infinite capacity "storage".
Where as if you assume $1k per 1kWh battery over 5 years (1826 days) you are looking at $0.55 and that does not have infinite capacity. Am I wrong here?

* yes I know that you can't store energy within the grid but I'm considering here the financial aspect.

edit:
let's run the numbers on the whiteboard:
let's assume you can fill up the 10kWh battery everyday and use all of that energy every night over 5years 1826days
you will be saving: 1826days * 10kWh = 18260kWh * $0.3 = $5478
but you won't get paid for export 18260kWh * $0.079 = $1442
so total savings is $4035
Looks like none of the options would paid itself off within 5years.
And the question of limited capacity remains open.

[ssander]

Hi,

While watching this video, I was thinking about bi-directional charging, in other words using the battery in the EV at night to power the house. It seems there are a few different type and dependent on the make model of the EV. Unfortunately this solution seems to be just as expensive at the moment as installing a dedicated battery.

Link: https://www.carsguide.com.au/ev/advice/bidirectional-charging-explained-a-guide-to-v2l-v2g-and-v2h-technology-86820

[boB]

Probably don't want to wear out your EV battery by cycling it a bunch !

Once in a while for when the power goes out is probably just fine though.

Charging your EV during the night is good and for self consumption use when sun isn't shining are probably the best uses for having a battery... And of course, if your power goes out enough, keeping the lights on and the beer cold.

boB

[NiHaoMike]

let's run the numbers on the whiteboard:
let's assume you can fill up the 10kWh battery everyday and use all of that energy every night over 5years 1826days
you will be saving: 1826days * 10kWh = 18260kWh * $0.3 = $5478
but you won't get paid for export 18260kWh * $0.079 = $1442
so total savings is $4035
Looks like none of the options would paid itself off within 5years.
And the question of limited capacity remains open.

A battery system that costs $400/kWh would break even in 5 years at that rate, the cells go for about $100/kWh in bulk, there's plenty left for other stuff like the BMS, inverter, and setup/assembly time.

[EEVblog]

Could someone with a battery please tell me how much cycling a day one should expect.
In Dave's case - 10kWh battery - would you expect close to 10kWh in and out every day or more or less?

Daily use fluctuates a lot. I think I mentioned that some days can be like three times the consumption of the day before.

So daily fluctuations impact the cycling of the pack.
And combine a bad solar day with excess usage on any particular day and it's going to
But I believe you can set the limits in the battery so you don't actually 100% cycle it, it will just take from the grid instead.

[EEVblog]

Hi,

While watching this video, I was thinking about bi-directional charging, in other words using the battery in the EV at night to power the house. It seems there are a few different type and dependent on the make model of the EV. Unfortunately this solution seems to be just as expensive at the moment as installing a dedicated battery.

Link: https://www.carsguide.com.au/ev/advice/bidirectional-charging-explained-a-guide-to-v2l-v2g-and-v2h-technology-86820

Yes, I believe the only bi-directional charger approved in oz at the momment costs around $10k. That's just the charger!

[furmek]

I was more interested in how much the battery helps to save you money and less in how fast it wears out.

Leaving the wear aside and going by the numbers you've presented and assuming just one full cycle a day you are looking at 10years before this thing pays itself off.
I may be very wrong about it and the battery may be helping a lot during the day when it fills in the gaps on a partly cloudy day.

BTW: do you live in the Hills district? there is a gov rebate program for a battery install up to $4k.

[EEVblog]

Leaving the wear aside and going by the numbers you've presented and assuming just one full cycle a day you are looking at 10years before this thing pays itself off.

Depends on the cost, could be half that.

BTW: do you live in the Hills district? there is a gov rebate program for a battery install up to $4k.

Link?
Only one I am aware of is a loan program, not a rebate.

[furmek]

point 2 on that site.
https://naturalsolar.com.au/nsw-solar-battery-rebate/
I'm not in hills district so i did not go into details.

[EEVblog]

point 2 on that site.
https://naturalsolar.com.au/nsw-solar-battery-rebate/
I'm not in hills district so i did not go into details.

Note the date, 2019 
https://naturalsolar.com.au/shbs/

[bartpl]

Hello, this is my first post here so I greet all members and of course Dave - Great Respect!

I tried to comment this movie on youtube, but my comments were vanishing around 1 minute after posting. I wonder why is it like this. Therefore I decided to post a reply here...

I would recommend buying lifepo4 cells directly from china (Aliexpress/alibaba), plus a BMS (i recommend JK-BMS with active balancing) - this will cost you around 2kAUD for 200Ah@48v (so around 10kWh). One just has to invest rather lot of time not to get ripped off by low reputation sellers selling used/damaged cells. I think however this price difference makes it really worth looking into! It is not a brand with support etc, but for someone who knows electronics/electrics like you this should be no biggie! Connecting is like just attaching wires to right places. Even if this (as being 48v) would not be compatible with enphase, you can get a 5-4kW inverter with built-in charger and even mppt/pwm solar input for charging for 650AUD (ISolar SML 5.5K) this is really worth looking into! you can (but not have to) connect it directly to PV - it can charge batteries also from AC. Smart controlling it to charge battery with the excessive power (requires bidirectional energy meter with instant readout like Shelly 3EM - pushes every 3s data to mqtt) and you are all done AC-coupled!

I bought similar setup myself, it was under half of the price what I could find to be the cheapest on the market. Really had to pay a lot attention to seller reputations (not a single negative feedback, huge number of possitive feedbacks ideally with pictores of received goods, internal resistance measurements etc.) This worked for me exceptionally got, as I got brand new cells, without any usage marks nor bulges. There is also an awfull lot about this topic in a YT channel I can really recommend to anyone considering self assembly of the battery - https://www.youtube.com/c/OffGridGarageAustralia. It can be done all on one weekend, what is considering the savings exceptionally worth looking into!

[free_electron]

BEFORE you jump into any of these things you need to do an analysis of what power you use.
- do you have natural gas (street supplied) or propane (tank)
- what do you use for heating the home ?
- electric car ?

Make a list : what are your largest power loads : HVAC , Car , water boiler , oven , cooktop , microwave, washer , dryer , dishwasher ,pool equipment. Write down the power ratings. of course, only the ones that are electric.

In many cases, when you have other forms of energy, it is very difficult to recuperate the investment , even over 10 to 20 years.
Things change when you go full electric. But even then there may be additional costs because you may have to switch out some other equipment in the house.
So it is not easy to come up with a solution.

My case :
- 1800 sq ft home , summertime can hit 100F for weeks. No other power sources. Only electric
- Electric car. No other non-electric cars

Installation : 48 panels (17Kw system) , two inverters + gateway and 4 Tesla powerwalls.

Daytime production yesterday was 70KWh. Home consumption was 20KWh and 50 KWH was dumped into the batteries. (they can hold 56, so they were not completely full , because i had dumped them the day before into the car)
During the night i used about 8 KWH off the batteries , so they are now at 60% and will be full again by noon

On an average day (no car charge the day before, so only nighttime use)
Last week wednesday : 77 KWH produced , 20 kwh to home , 11kwh into battery , 46kwh to grid

My water boiler is electric and is set on a timer. It will only get power from 1pm till 4pm . It only needs about 2 hours if starting from ambient to 65C for a 250 liter (80 gallon) tank.  Water bollers are another for of "battery" . Do not fall for those flow-thru boilers : their instantaneous power draw is enormous and you will need to grid to run them. Your solar + battery cannot deal with such a load.
My HVAC is an atmospheric heat-pump with VFD drive (continuously variable speed scroll-compressor) and speed controlled inside unit as well. Recirculation inside is always running. 5 TON system ( on average runs at 3.5 TON level. during peak summer it climbs into 4...4.5 TON mode
Pool pump is also a VFD drive. 1HP , runs on average 9 hours a day.
Cooking is induction.
The car is programmed to adapt its charge current depending on what is available as "rest" energy. The car only charges starting at night 2AM using leftover in the storage battery , or i let it charge daytime when the batteries are full. 40KWh that goes to grid goes into the car. 40Kw gives me 120 .. 150 miles. more than my daily use. My car is always full.

Don't buy bits and pieces. inverter/array from x , battery from y , car from z. It doesn't work together.
My system regulates power flow to the battery by looking at the house draw , solar output and only instructing the battery to charge at "leftover power" level. It can talk to the car as well ( yeah everything is TESLA. Disclaimer : i WAS an employee , no there are no incentives )

Winter power bill : 300..400US$ a month
mid-season ( spring fall + "indian summer")  : 400$
peak summer : 700..900$

With this system :
The whole system was 60K . Assuming 15 years of life . That's 4000$ a year. or , just below 400$ a month.
I have no other energy bills. No gas, no gasoline. Both my house and transportation needs are covered for a fixed price. My monthly payment is actually less since i paid the tax rebate directly towards the loan, bringing down the principal down to 40-something.

Dave has done very detailed calculations to "ride" the profit point. My approach was different : look at my electricity bill over a year span and divide by 12 to get average monthly cost. Look at what you can get in terms of system that would cost you less a month ( not even taking into account what you sell to the grid. That is unpredictable. See that as a "bonus" ). Turns out I could go for the largest setup 48 panels and 4 powerwalls, and still be cheaper.

Now, if you need to change other equipment in your house you need to take that into account too. Switching from a power hungry bang-bang AC and a gas heater to a heat pump also costs money. So you need to look at other power sources. if you can convert those to electric, scale up the powerplant and ditch the gas you may be able to tip the balance even further.

[EEVblog]

Hello, this is my first post here so I greet all members and of course Dave - Great Respect!
I tried to comment this movie on youtube, but my comments were vanishing around 1 minute after posting. I wonder why is it like this. Therefore I decided to post a reply here...

Welcome. Youtube does stupid mysterious stuff with comments sometimes 

[EEVblog]

BEFORE you jump into any of these things you need to do an analysis of what power you use.
- do you have natural gas (street supplied) or propane (tank)
- what do you use for heating the home ?
- electric car ?

Make a list : what are your largest power loads : HVAC , Car , water boiler , oven , cooktop , microwave, washer , dryer , dishwasher ,pool equipment. Write down the power ratings. of course, only the ones that are electric.

In many cases, when you have other forms of energy, it is very difficult to recuperate the investment , even over 10 to 20 years.
Things change when you go full electric. But even then there may be additional costs because you may have to switch out some other equipment in the house.
So it is not easy to come up with a solution.

IONIQ EV that is charged from excess solar from the Zappi.
Currently gas hot water but moving to a heat pump hot water shortly that will take about 2kWh/day extra.
4x reverse cycle aircon units, IIRC around about 1kW each.
Electric induction cooktop and electric stove.
Electric dryer gets used sometimes, but she wants a heat pum version of that too.
Poll coming this year and will have heat pump heating.
Highest consumption I've seen in the house at peak is around 8kW IIRC.

But yes, battery systems should be optimised for the peak currents if you want total 100% grid independence.

Here in Sydney heating and cooling is not the big deal it is in other parts of the world.
In winter it's more than enough to just use an extra blanket, but Mrs EEVblog gets paranoid and sets some of the aircon timers to come on about 5am or something.
Some aricon in summer to cool down, but not nearly as much use as winter time.

[EEVblog]

Don't buy bits and pieces. inverter/array from x , battery from y , car from z. It doesn't work together.

Problem is, as I explained the video, my system is already "bits and pieces".
I already have a 5kW Enphase system, a 3kW string system, and a Zappi solar EV charger system. Not to mention the independent Solar Analystics monitoring system
Plan on addding 4 more 400W+ panels, and at the moment it makes the most sense to go with a hybrid inverter for that plus the existing 3kW string + adding a matching battery to that.
That mean the Enphase system remains inpedendent.
Although Enphase have offered to give me more microinverters for free, from a battery expansion cost point of view it almost doesn't make sense to take them up on that offer.

[free_electron]

That bits and pieces is the big issues. none of such systems really work together. You may be better off ditching the frankenstein contraption.

Even if you forget a car charger, the tesla system is way better than others. ( note again : my only interest in tesla are my shares , i am no longer an employee. just for the sake of disclaimer ). Throw in the car and the entire system becomes adaptive.

The key is in the gateway. The gateway can dynamically regulate the power flow between solar, grid, battery and home. if home consumption goes up it slows down the battery charging . it is really a power tracker and will do anything possible to prevent you pulling power from the grid.

If you get a SPAN fuse panel (US only) the system becomes really smart as SPAN can turn off loads in the fuse panel and has per fuse energy reporting.
https://www.span.io

That company was started by ex-tesla employees. The span panel can work with non-tesla equipment as well.

But even without such fancy panel you can put the boiler on a time clock so it runs only at peak production, after the main batteries have collected some charge. ( 1pm the solar output is highest so you will have collected all morning , and the cooking for lunch is done. I notice that 1pm is the point where i start feeding the grid. so then i kick on the large loads like pool pump , water boiler and the electric dryer. i have a simple wifi connected lg washer and dryer. I can program a start time for both, and i get a notification when the washer is done. Get up : transfer from washer to dryer and hit start. If there is washing to be done this runs after the water boiler has reached temperature.

I have literally no grid cost except the mandatory connection fee (it is illegal NOT to be connected. you have to have grid connection , so they charge you some fee for the meter ). Anyway, the grid is nice. if you need extra power it is there. My consumption is more than offset by my production

[EEVblog]

That bits and pieces is the big issues. none of such systems really work together. You may be better off ditching the frankenstein contraption.
Even if you forget a car charger, the tesla system is way better than others. ( note again : my only interest in tesla are my shares , i am no longer an employee. just for the sake of disclaimer ). Throw in the car and the entire system becomes adaptive.
The key is in the gateway. The gateway can dynamically regulate the power flow between solar, grid, battery and home. if home consumption goes up it slows down the battery charging . it is really a power tracker and will do anything possible to prevent you pulling power from the grid.

I already have the Zappi that dynamically regulates the EV charging.

But even without such fancy panel you can put the boiler on a time clock so it runs only at peak production, after the main batteries have collected some charge. ( 1pm the solar output is highest so you will have collected all morning , and the cooking for lunch is done. I notice that 1pm is the point where i start feeding the grid. so then i kick on the large loads like pool pump , water boiler and the electric dryer. i have a simple wifi connected lg washer and dryer. I can program a start time for both, and i get a notification when the washer is done. Get up : transfer from washer to dryer and hit start. If there is washing to be done this runs after the water boiler has reached temperature.

A "boiler" isn't a thing here, but the plan is to run the new heat pump hot water system on a timer during peak solar hours, so maybe 11am to 4pm. That's built into the system we are getting quoted now.

[Black Phoenix]

Dave, just a tangent: did you have any knowledge about this?

https://youtu.be/1SXNjsSsmq0

Is this claims (and tests) as good as this YouTuber claims?

[kripton2035]

for me the return $$$ you can make on a battery system is nothing in front of the potential failure of the grid coming...
the resilience of your house is the primary goal. so I will buy a solar system with the batteries there is no doubt about it.
I know that we will have more and more bad weathers conditions in the future. big tempests can cut grid power for some days it's sure.
a house with some power in these times is better than a house that returns money like a financial plan.

[thm_w]

Dave, just a tangent: did you have any knowledge about this?

https://youtu.be/1SXNjsSsmq0

Is this claims (and tests) as good as this YouTuber claims?

You can read the specs:
https://signaturesolar.com/canadian-solar-445w-bifacial-solar-panel-cs3w-445mb-ag/?ref=SALE

- 59c/watt vs ~50c/watt for their regular panels
- So you are paying 20% more for 15% more solar power (thats the number he used in the video, their claim is "up to 30%" though).

In certain scenarios that will make sense, maybe where you have limited roof space. In other scenarios they won't be worth using.

I like the idea though, as it encourages use of reflective/white rooftops.

[Bud]

With such strong gusty winds as we occasionally have in Ontario, mounting the panels higher above the roof is just asking for troubles IMHO.

[manicdoc]

At my place, I have the microinverters and via a raspberry pi set up I query the ajax endpoint every minute and send out the net power on a MQTT message, this is picked up by controllers on the hot water heater and pool to decide when to power. The hot water is able to percentage heat - so if 2kw going spare and the hot water is cold, about 1800w is used by the hot water. The hot water controller has about 4 'modes' it switches into depending on the time of day, the energy available, pricing, etc. The aircon is also under control, which will only be allowed to turn on when needed (with a weighting towards spare power going) or directly commanded via Alexa to do so. The hot water can also be commanded via Alexa.

As a result of this, my power bill has crashed.

I'm going to get some more panels and go up from 5kw to 8kw.

In effect, I'm using the hot water as a time-shifting device - I know my two lads will have showers in the evening, right during the peak charge period. So shunting spare solar power into the hot water saves me the peak rate cost, as the system won't allow anyone to run the hot water during peak charge periods (not even via Alexa). Once I have the additional panels, I will see what else is worth time shifting.

Although doing this has caused a secondary effect, the lads spend inordinate time in the shower, as they think it is 'free', so in the morning, even with overnight heating, there was a high chance I'd have a cold shower in the morning - so in response, the bathroom air extractor got a controller and a humidity sensor, so I know the usage... fixed that.

[EEVblog]

At my place, I have the microinverters and via a raspberry pi set up I query the ajax endpoint every minute and send out the net power on a MQTT message, this is picked up by controllers on the hot water heater and pool to decide when to power.

Nice. Is this Enphase?
I've wanted to do something like this.

[manicdoc]

At my place, I have the microinverters and via a raspberry pi set up I query the ajax endpoint every minute and send out the net power on a MQTT message, this is picked up by controllers on the hot water heater and pool to decide when to power.

Nice. Is this Enphase?
I've wanted to do something like this.

Yep, Enphase. BTW have you had the controller box 'freeze' yet?  Mine does this every few months or so and needs the power cycling on it...