Solar storage batteries: Tesla Powerwall and 17 others put to the test

Energy
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Grid connected batteries actually increase emissions slightly, in our mostly fossil fuel powered grid. That will change once it is mostly renewables powered, but with our current government delaying that day as much as they can, it’s a long way off.

The reason being that charging them is not 100% efficient. Say they are 90% efficient, then 11% extra of your PV power would be required to charge them, versus all of it (111%) going to load somewhere else on the grid, displacing the need for coal or gas fired electricity.

In other words, you get 10kWh usable energy from 11kWh of PV charging, vs someone else powering 11kWh of loads with your exported energy.
There are benefits, but emission reduction is not currently one of them, unless you live in Tasmania, which is almost entirely powered by renewables now.

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Hi Gordon,

I was intending the investment to refer to both panels and battery, resulting in emissions reduction. I agree the panels cut emissions, the battery cuts costs, so makes the whole thing more cost effective.

:slightly_smiling_face:

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Choice refers members to a number of sources of good solar advice. One such source is Solar Quotes.

Perhaps others reading here might like to consider the following.

Batteries Do Not Pay for most home owners.

Apologies, the information provided as follows does not make any economic sense for our household.

Savings for most can only be invested in super post tax, and not pre tax. There is no provision to pay back the increase in household mortgage costs in the commentary. Importantly there is no illustration of how a battery saves $2,000 per year when a solar PV system alone can save just as much without spending all that extra on a battery. And a further point is I’m not 30 and no longer working. It appears a very narrow argument that has been presented.

By all means if you have money to burn, buy a battery to go with your solar PV.

But if you are on a budget, the science and maths says you are better off buying just a solar PV system and maximising the number of panels you can install.

One view is that Tesla suppliers in particular mask or con customers by selling systems and offsetting the waste and disadvantages of the expense of battery with the savings created by the PV panels.

The simple proof. Compare the financial outcome of a PV system only to a PV plus battery. There is no one answer, but this simply requires two quotes to know half the answer. The other 50% of the answer is what is the best supplier deal you can do with your retailer.

P.S.
I had one of those every other day give you the best deal on electricity supply phone calls again today. When I told them who our retailer was and our current deal, they could not wait to end the call. There is in my experience a lot of misinformation out there and as many shonks including sellers of solar and battery systems.

I’m not against solar nor battery storage.
We’ve put our money on the table and secure in the knowledge that a small investment is helping us save 100% of our electric power bill. No need to blow the household mortgage to achieve it.

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Indeed - the only ‘advantage’ for me would be the possibility of going off-grid, but I’m not sure a single battery would allow that with certainty. I’ve had solar for a little over 2 years - the system has paid for itself based a little roughly on my bills for the previous year or so and some rough calculations I’ve done on generation and feed in - I haven’t paid a bill in 2 years now and just shy of $1k in credit (which I should convert into motorcycle parts) … am I missing something?

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“The short answer is that for most Australian homes, solar panels make economic sense but batteries don’t”

So you are saying (strongly) for most Australian homes batteries do make economic sense.

So do you accept that while your experience has been good others may not share your good fortune, for for some it might make economic sense and others not. You only have your outcome to go on, you have not attempted to model the whole market. If you ask the experts who have modelled the situation I don’t think you will find them saying no households would be economically better off with a battery.

Which still leaves open the original statement that for most homes batteries are not worth it at present.

I am not playing word games for the sake of it just trying to head off the situation where naive buyers might be lead to follow the exception rather than the rule.

As for having more detailed modelling to try to tease out who might or might not benefit I wonder if that is practical. Having just been through the experience of selecting a solar system I can vouch for the complexity of the data, opinions and alternatives that are presented. I suspect that there are some questions that have no answer except for the technically minded few who are prepared to put a great deal of effort into it. For many, generalisations may be the best thing even if not applicable in all situations.

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Hi Mark

I was just trying to give an example of how cost and benefits could be presented for people in a specific situation with a set of assumptions clearly defined. The word ‘net’ was intended to imply that the difference between the gross savings and additional mortgage payment would be invested.

Regarding payments to superannuation additional contributions can be made by most people up to $25,000 — use a Notice of Intent form to inform your fund that you wish it to be treated as a concessional contribution, which will reduce your taxable income, but be taxed at 15% within the fund.

It sounds as if in your situation a battery would not provide significant benefits — for a rough estimate of what you might save take a look at how much electricity you buy from the grid and calculate the difference if it cost off-peak rate.

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Yes, I guess if you have space for enough panels and can minimise power from the grid that is probably a cheaper option. We have limited space for panels, and use most power in the evening so the battery works well for us.

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Any potential saving is actually the difference between the cost of power and our feed in tariff. Every one kW of power sent to a battery is one kW less sold to the retailer. The battery storage has a charge, discharge and generation loss of at least 10%.

For us this might save 42c per day on average, or approx $150 per year. A 100 year pay back for a PowerWall.

It has been much more cost effective to spend $2,000 on a larger PV system and feed sufficient surplus into the grid to cover what we bought in.

This is a 100% saving compared to previous annual bills of $1400, and typical of most smaller Australian households.

P.S.
Additional contributions pre tax to super are subject to the work test and by retirement status. Not everyone thinks super is a wise investment. General financial advice often suggests paying down the home mortgage as a priority, and not to increase it?

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The following is a really useful calculator that allows an estimate of savings of simple solar PV systems and upgraded systems with battery storage.

I ran our data through it for a 5kW system in SE Qld.

The calculator forecast 7637kWh of annual PV generation. Our rolling average after 16 months 7630kWh. That is our actual inverter data!

A $5,500 investment in solar PV generates cumulative savings over 10 years of $17,708.

With an added Tesla PW2 the investment required increased 4 fold to $20,850. The cumulative savings over 10 years $20,083.

For a simple PV system the net savings over ten years assuming a personal loan for the purchase at 12.5% variable interest will be approx $10,000.

For the upgraded battery option the net savings over ten years are effectively zero. There are plenty of loan calculators around for those who like to practice accounting skills.

Finance options for Battery System
The interest ($2,500 pa ) is greater than the savings if the Powerwall 2 option is financed with a personal loan. No go!

For homeowners with a redraw on the home loan, (approx 30% of Aussie households) there will be a residual of approx $7,000 owing after ten years. That is if all the savings in electricity bills go to repaying the extra borrowings. Alternately allowing the debt on the home to balloon would increase. The total debt on the system to more than $35,000 owing after ten years.

Alternately if you have a spare $21,000 in cash spending it on a solarPV + battery system will give you back approx $21,000 over the ten years. A very similar return to the current zero% bank cash rates.

Or a Special case for those with a spare $20k in cash.
A better outcome using just $5,500 to buy only a solarPV. That would leave more than $15,000 up front to invest as needed. You could even add that into super if you are eligible. Plus a further averaged $1,800 per year of genuine savings including up to $300 in real cash credits to add to your investments. One great way to save for that new battery electric car. Just don’t let P Dutton find out you are going to pay with cash. :wink:

(Edit)
P.s. Just finished reading the updated battery test progress report. Hope they more funding in the future to continue testing new products as they become available.

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12 posts were split to a new topic: Fred’s Solar system - Predicted vs Actual Output

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A post was merged into an existing topic: Fred’s Solar system - Predicted vs Actual Output

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SolarQuotes latest blog entry on the Battery Testing Centre report, which is not a good one!

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Its disastrous and would put one off buying one, unless one is a very high risk taker and has money and time (sorting out problems) to burn. Not only is the reliability terrible, but degradation after cycling is also high. Imagine after 6-8 years of operation, only 50% storage capacity remains (Tesla Powerwall 1).

Also, it is interesting that they also observed that battery prices have remained relatively static (not getting any cheaper) over the past 3 years when there has been much media and blog hype about holding off ihstalling battery systems as they will become cheaper and cheaper, like PV cells have in the past decade. Looks like battery prices may have reached a floor with little prospect or them becoming cheaper.

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Actually, retail prices have gone up quite a bit since I put together my LiFePO4 battery in 2012, I suspect mostly due to the lower $AU. I too am waiting for the long promised price reduction, but as the prices keep going higher, any reduction on 2012 prices disappears further into the future.

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The $AUD has been from $USD 0.4775 (Aug 2001) to $USD 1.1080 (July 2011). Multinationals set transfer prices for their businesses to stabilise exchange issues, usually annually looking forward. It might not go above parity again for a l.o.n.g time but if and when, our prices should adjust downwards.

Warning: currency speculation can be damaging to one’s accounts by waiting or not waiting. :wink:

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Storage as part of the infrastructure. Like shock absorbers for the network.

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To be fair, the original statement may have been intended to apply only to “homes”.

Good neighbour!

That of course is true but there are losses everywhere in the system. If your panels produce 1 kWh and you send that to the grid for someone to use, that doesn’t end up being 1 kWh either. You lost some in your inverter, some in transmission losses, some in grid transformers - and that’s before the someone else’s highly inefficient appliance adds to the losses.

Maybe SA too now

That figure may be a slight exaggeration i.e. based on an inflated cost - depending on whether you did a proper time-value-of-money calculation or just straight out multiplied it.

Also feed in tariff’s are quite variable (differ from state to state and retailer to retailer and plan to plan).

Also your usage pattern makes a difference. If you generate more than you use during the day and have no battery then it can make sense to do things during the day that you would otherwise do overnight. Some people may be unwilling or unable to alter their usage pattern.

All of which shows that no one calculation applies to every household.

Another factor to consider is what the actual lifespan of the inverter and/or battery is. The panels may be rated to minimum 80% performance after 25 years (if the company is still around to warrant that) but it is unlikely that the inverter and battery are still going after 25 years.

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Ten years is around the most common guesstimate for either.

If the payback was anywhere close to ten years it is reasonable to put the effort into a discounted cash flow and derive an NPV result for the option. In my example it would seem hardly worthwhile. Even if there is some error in the simplification.

For a more viable example it would need a more complex sensitivity analysis. Several of the key assumptions are open to speculation. Uncertainty over electricity market changes and inflation, EG future competition, carbon related taxes, government policy/incentives, changes in battery technologies and costs. A common business strategy in such circumstances is to base a purely financial decision on the short term outcomes. IE 2-5years. If it does not make a positive return in the short term, it fails the key toll gate.

Alternately others might see the decision as a strategic one that they can afford. It does not need to generate a positive cash outcome. There are other community or personal goals delivered by the decission.

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The Test Centre has a comprehensive and navigable web page at, https://batterytestcentre.com.au/

A number of new battery technologies and brands have been added to the program including the Zenaji Aeon with a 20 year 22,000 cycle warranty at 100% dod.

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Victoria ups tha ante on network battery storage.

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