Solar batteries

Is now the time to buy a battery for my. 9 Year old system of 8 solar panels?? Or should I wait til the panels die and install a completely new system ? Advice gratefully received!

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I doubt anyone can give you a definitive answer for reasons of: substantial lack of detail about the current system and your current situation, and the impossibility of knowing the future.

However I think the general consensus is that the price differential between electricity buy price and electricity sell price is not high enough relative to the price of a battery to justify a battery purely on those grounds.

Is it possible to add more panels and did you consider that as an alternative investment?

Do you currently not have an EV and did you consider that as an alternative investment in a battery?

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Financially, in most cases, installing a PV battery systems don’t stack up. This could change in the future as the forecast electricity prices rise in the short term due to gas/coal prices and insufficient generation to meet demand - as well in the longer term to move the electricity industry from conventional generation to renewables.

Choice has covered solar battery systems in the past…

and this might be worth reading.

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Many thanks. I did wonder if I should wait until my panels die - how long do they usually last???
cheers
Petrina

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Around 25 years or more. Inverters generally last less than this.

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On a standard contract with most providers it is not worth considering at this stage.With a lot more panels than you have, and with a contract with a company like Amber, then it can certainly pay for itself before the warranty expires.
However, you need to know what you are doing, as you are exposed to wholesale market prices.

The other important consideration is why do you want a battery? Do you want to make (or lose!) money, or do you want it for backup purposes in case of blackouts?

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thanks Gordon. Good question. I think I want it to maximise my use of the sun for environmental reasons, if that makes sense.Maybe I should wait until the inverter dies - how long do they last???

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it also depends on your electricity usage, if you are at home during the day when the sun is out you are using some or most of the electricity you are generating hence the batteries will not be of great benefit.

If no one is home during the day then you may save money with a battery but given your system is probably 1.5kW you are not generating a large amount of power so the payback period may be longer than the life of the batteries. I would try to do things like clothes and dish washing when the sun is out to maximise using the electricity you generate from solar.

The only other way you could save money with a battery is if you are on a time of use electricity tariff, I believe some of the batteries available can be setup to provide power during the peak times and if not enough solar power available to fully charge the batteries, they can charge during the cheapest electricity cost times. (getting a bit complicated now)

While the solar panels may last for 25 years the power output declines each year. Inverters are not likely to last as long hence it may be worth holding off your decision. In the event the inverter fails that would be the time to consider adding more panels and batteries or a whole new system.

Solar equipment is improving all the time, hence the longer you can make do with your existing system the better (and hopefully cheaper) the replacement will be.

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Dear Engineer,

I really appreciate your advice, which I will follow. I use more electricity than most families of two because I am a potter and have an electric kiln . I replaced a gas kiln for obvious reasons and am trying to “midfire” to reduce consumption.
cheers
Petrina

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Depending on your usage pattern and total consumption there may be a benefit in having a larger system. There are other factors including the general area of Oz in which your home is (solar exposure and heating/cooling needs). For SE Qld our retailers suggest approx 5,000kWh annually is typical for a 2 person family. Is your need similar?

If your supply agreement is on an older high value feed in tariff staying as you are may be more valuable than upgrading and being moved onto a current plan. For anyone with a feedin tariff greater than the tariff for supply it is more valuable to avoid consuming power during the day to maximise export. At least until that circumstance changes.

That only makes sense if your financial circumstances provide an excess of funds, to upgrade. The best options for your needs or objectives need more information than a general discussion might discuss. There are those in the community who would argue no one should spend money if it does not add to your personal financial wealth. There are others who accept that the future of the planet has a price to be repaid, that modern economic theory chooses to ignore.

There’s some good advice in this and other community topics concerning battery systems for solar PV. For most of us the value in a battery system is akin to purchasing a new BMW for our next car rather than a Hyundai. The cost of an upgraded/replacement solar PV is less of luxury item. Our smaller quality system was priced at just on $4,000 installed. The larger 5.5kW was closer to $6,000. Just be sure to check what your future tariffs will be before any decision to upgrade is considered.

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Since the grid is still mostly fossil fuel powered (unless you are in Tas or SA), a battery connected to the grid is not really an environmentally sound choice at the moment. The reason for this is that batteries are not 100% efficient.

If you export all your excess energy then 100% of it replaces dirty energy* on the grid- IE, mostly coal or gas fired electricity.
If you instead use it to charge your battery at 90% charging efficiency then only 90% of the energy produced by your panels is replacing dirty grid energy when you use it later, at night for example.

  • The NEM (and WA) has been powered by 66% coal and gas, and 34% renewables over the past 12 months but on a state by state basis Tas and SA pull the average up, the rest have lower renewable energy NSW 28% renewable, Qld 21%, Vic 35%, and SA 70%, Tas 99%

Once the percentage of renewable generation in the grid increases significantly, then home batteries will make more sense environmentally.

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I’m of the understanding that your 2KW system won’t be big enough to charge a battery. Mine’s 3KW but when I inquired about getting a battery I was told to forget it. I think the issue is that a battery requires sufficient input to fully charge it, which won’t be delivered by anything less than 5KW

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There are recommended charge rates for batteries. The minimum depends on the battery type and chemistry. Smaller off grid systems provide a useful point of reference. EG 2kW nominal system (2.35kW panels, 5.5kWh useable battery capacity). I’m not recommending this solution or package. It’s just an illustration of a system that shows what is possible with smaller solar PV. There are even lower powered systems with lithium battery storage targeted at off the grid outback caravaners.

A small battery may be sufficient to offset some or all evening peak demand for consumers in a ToU or Demand tariff. Whatever your objective with a battery, it’s in most instances less expensive to be grid connected and purchase off the grid. Roof top solar PV is a more effective investment providing it is matched to your needs. @gordon has suggested the few scenarios in which a home battery can be beneficial.

Alternatives?
A better alternative might be to put the $15k nominal cost of a modest home battery system (EG Powerwall 2) towards the higher cost of a BEV. At current fuel prices we’d expect to spend $18-22 per 100km for fuel before any other added ICE maintenance costs. It’s looking a better use of our surplus solar generation given the latest drops in feedin tariffs.

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Battery storage in a solar PV system saves energy for use at night. The cost of the night-time energy imported from the grid is much less than the current cost of a battery system. The other issue is seasonal. in southern Australia, the solar energy generated in winter is limited because the days are shorter and the sun is lower in the sky. The night-time load may also be greater in winter. A large PV system is required to fully charge the battery in winter, exporting excess energy in summer. Or, the battery may not be fully charged throughout winter, limiting performance and savings. See Energies | Free Full-Text | Guidance on Implementing Renewable Energy Systems in Australian Homes.

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I agree with you about economics of batteries for environmental purposes. For us the battery is about medical devices running when night time power outages occur. The battery will never pay itself off on the basis of cost saving or even environmentally good reasons, it has paid itself off in terms of life saving.

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It may come to pass sooner than we expect. Having been hit with one price rise by the electricity retailer for the end of August, there is another coming in Dec.
128.46 c/day supply and metering charges
24.61 c/kWh supply tariff
05.0 c/kWh feed-in tariff

Nearly a 20 c/kWh differential to pay for a battery if grid connected. At our current annual consumption we could be paying 36 c/kWh averaged once the supply and metering charges are accounted for.
IE
If we went off grid close to $1200 per year in savings from a battery. This is assuming we can manage through the days when heavy cloud and rain limit Solar PV production. A V2H BEV offers one solution.

Solar quotes latest solar battery only cost estimates start as low as 17 c/kWh. All in one options, start from 30 c/kWh. A Tesla Powerwall 2 comes in at 44 c/kWh. These estimates assume a constant daily demand. From our home useage data over 4 years, this is unlikely. Perhaps a 50-60% utilisation factor is more reasonable. In which instance the suggested costs increase. Up to double for some battery options.

P.S.
I suspect there are better deals to be had post Dec. the problem may be whether what is listed on Energy Made Easy for comparison pricing is also likely to increase in Dec? A different topic, I’ll add comment to when I have an outcome.

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If your existing PV system produces more energy than you use (for example, from one electricity bill to the next), storing the excess energy for your own use will decrease your marginal emissions by the corresponding amount.

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I take it by “your emissions” you mean the emissions that would be produced by the generation of electricity that you no longer need from the network. What about the emissions from the manufacture of the battery and ancillary gear required to run it?

When faced with various approaches to managing your energy use you need to look at all the costs, environmental and financial, for each option. You may decide to trade off financial for environmental savings but not including all the costs doesn’t help make a good decision.

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Thanks. Amended - “marginal” inserted.

People can decide for themselves what’s important to them. We can’t automatically assume that our British culture of “cheapest is best” or “shortest pau-back period is best” automatically apply to everyone.

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Yes it will, but it increases the total emissions from the grid, as I explained earlier. A net negative environmental benefit.

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