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Feedback on new solar system

Budding Contributor

Feedback on new solar system


Hi all,


We are installing 16 extra solar panels on our roof and adding battery storage.


The battery is a 1.2KW Lithium Iron Phosphate with 10 years warranty made by Enphase.


The installed cost of the panels and battery is $8888. Does that sound reasonable? 


They have suggested that we might need an extra battery in the future - another $2500. They have recommended to monitor use for a few months and then consider adding another. 


I would appreciate any feedback on whether we are doing the right thing.






Community Manager Jason
Community Manager

Re: Feedback on new solar system

Welcome to Workshop @TonyJ. I hope that you find it an invaluable source of information and inspiration for your projects. I also hope that Workshop members can assist with some feedback for you.


You mention that you are installing extra panels. How many do you have currently?



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Budding Contributor

Re: Feedback on new solar system

Sorry, yes we already have six panels which give us 1.5kw. The new panels would be 4.32kw, so we would have nearly 6kw. But the battery is only 1.2kw.

Budding Contributor

Re: Feedback on new solar system

Sorry if this is a 'downer' on your green savings....
Always keep in mind the 'power' of the panels is the maximum possible output in perfect conditions. In saying that, I assume your system feeds into the network as well?
So my guess is that the panels will charge your battery, then when it's fully charged, the power will feed into the network, providing you with your feed in value.
When you use your power, it will drain the battery before you start drawing from the network. (never 100% drain)
Have you done the calculations regarding the possible/average daily usage (from previous electricity bills) and calculated what the battery will deliver to you (in terms of savings)
Let's assume a few things:
Your system is 100% efficient;
Your battery is fully charged every day and it's 1.25kW.

This will give you 1.25kW/h of power each evening when you get home (when most people actually use power)
My last bill shows the cost of electrical power is 16.62c per kW/h
Therefore, your battery will be saving you (1.25*16.62=20.8c per day or $75.83 per annum)
I don't know what your battery cost, but do the calcs and then assess it against it's warranty period. (Especially do these calculations on your bigger battery purchase)
After you do that, then do the calcs on the entire system (cost of panels vs feed in tariff vs warranty period)
Currently, your maximum feed in would be 4.62kW/h in perfect conditions. Not knowing the angle of your panels and where you are, assume you will get 8hrs per day at the full production (4.62*8 = 37kW/h, subtract 1.2kW/h = 35.8kW/h @ 16.6c per hour = $5.94 per day)
I did the calculations on my place and it isn't feasible (unless I got in in the first few months when they were offering the 60c per kW/h, 20yrs guaranteed)
Battery storage isn't worth it yet.
Stay with feed in...
Valued Contributor

Re: Feedback on new solar system

As @Kev says a 1.2 battery will give you next to no savings. If you have an isolator switch in case of a power failure you can have some back up off grid power for a while, just how long that would last depends on your usage.


Some light reading for you that will also give further links.

Experienced Contributor

Re: Feedback on new solar system



I agree with the previous posters. Batteries are not worth buying yet. They are offered to the market at a premium.


Typically power costs you about 45 cents per kW.


The battery you are buying will store 1.2 kWh which means you can run your fridge+freezer+TV+a couple of lights (1.2kW) for an hour or so from your battery every night, then you’re on mains power again. This means you will save about 55 cents a night using your battery and not mains power.


A stand alone 4.5 kW system should cost you about $4k installed meaning the battery is costing you about $4800.


This means that the battery would take you 4800/.055 = 8727 days or approximately 23 years to pay off. A duration longer than the warranty period.


Having said this, electricity is set to double over the next year and some days will be overcast allowing you to draw from the battery and recharge a couple of times, but that's still not enough to justify the battery.


The sales strategy for batteries is flawed at the moment due to the small size available to the market.


Tesla Powerwall is the best value at $11k and 10kWh and a payoff of around 8 years.


You can always retrospectively add a battery to the installation at a later date.


Hope this is helpful.

Trusted Contributor

Re: Feedback on new solar system

Very interesting discussion. I really appreciate the numbers shared, although it's a bit disappointing. But I'm still excited about Tesla Powerwall. I want to install solar panels on the roof and a battery or two to store the electricity generated. Hopefully it will be feasible to go off the grid one day. I guess we just need the technology to improve a little more to get the cost down. Is it currently a chicken and egg scenario? If more people were buying the batteries then their price might fall, making for a faster return on investment.  

Budding Contributor

Re: Feedback on new solar system

Thank you. Very helpful. It looks like we rushed in too soon. We will try to cancel the battery purchase. 

Budding Contributor

Re: Feedback on new solar system

Just to clarify a couple of things, a lot of people don't understand the difference of kW and kW/h (kilowatt and kilowatt hour)

Without going too deep into the theory:

with 240v (AC) if you have a kettle that has a 2400W power requirement (or 10A - 240*10 = 2400 or 2.4k), then if you run it for one hour, it will require 2.4kW/h or 2400W for an hour. Now the kettle will boil long before an hour, usually less than five minutes, but it is a requirement that it has a 2.4kW/h supply and it's accumulative over time. It means, 1000W used for 1hour is 1kW/h - it adds up.

Many kitchen items are 10 Amp items (because of circuit/power requirements)

Toasters, rice cookers, kettles etc are 10A or 2.4kW. This is because of general circuits are rated to 10A. (or are circuits rated to 10A because many items are 2.4kW?) Chicken and egg story

So, the joys of incandescant lighting vs LED lighting - incandescant is usually 60W or 0.25A (60/240) as opposed to LED lighting which is around 15W (lots of inefficiencies, but still better) is 0.0625A (15/240) for the same light output (called lumens) You can't get away from the power needed for heating the kettle (it's inherent for water) but lighting is becoming more efficient.

The short story is, is if you put a kilo of food into the refrigerator, it will take energy to bring the temperature down to five degrees, the hotter the food is, the more energy it will require - therefore, let it cool on the bench for awhile then put it in the fridge. If you have a lot of food, it will require lots of energy to cool it down.

Install LED lighting, Solar hot water, energy efficient reverse cycle air conditioning (18 degrees in winter (wear a beanie), 23 degrees (wear shorts & singlet) in summer) you will start to maximise your power savings & the environment.

One last note:

It does amuse me when people have 'electric and emission free' vehicles but don't realise that they use the cheapest electricity which is usually coal powered electricity... The emissions are somewhere else unless you choose to purchase 'green energy' at exhorbitant costs.

The whole world is a system, and we need to look at the system as a whole

No, I'm not a 'greenie' but I'm aware.





Budding Contributor

Re: Feedback on new solar system

Thanks again for all the feedback. We were able to cancel and will keep investigating other options.

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