5kW - what is it really?

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#281358 13-Feb-2021 13:50

Ok, I am being very impatient as I can't wait till Monday to ask the company that send me a quote.

They quoted a 5kW (I suspect this is 5kWh though) 8 panel solar system. But can you run on 5kW AT NIGHT! How long does it last.

Am I wrong in saying if my fridge uses a 1000 watts so 1kWh, it would mean it can run, in theory for 5 hours (without the DoD) at night?

I am so confused lol. Thanks heaps

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#2655649 13-Feb-2021 13:55

I assume your talking about solar, also is the energy being stored in batteries?, also with your fridge it has a starting wattage of 1000+ or so, but an actual running wattage of much less, around 150-200.

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#2655652 13-Feb-2021 14:03

l43a2:

I assume your talking about solar, also is the energy being stored in batteries?, also with your fridge it has a starting wattage of 1000+ or so, but an actual running wattage of much less, around 150-200.

Sorry, yes solar.

The fridge was just an example. I could have just send device A is using 1000 watts. It is just to understand how things work.

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#2655653 13-Feb-2021 14:14

do you know what your base load is? do you know what your normal peak load is and when it is? can you easily time shift usage to times of the day when its sunny?

many things you should know before considering solar.

5kwh is not much in terms of battery storage for a normal house.

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#2655655 13-Feb-2021 14:17

Pinpoint:

Am I wrong in saying if my fridge uses a 1000 watts so 1kWh, it would mean it can run, in theory for 5 hours (without the DoD) at night?

You are wrong.

kWh is a unit of energy (e.g. battery storage). kW is a unit of power (energy / time) i.e. rate of generating/consuming energy. So your panel will generate up to 5kW of electricity at any one instant, and your fridge will use 1kW. If you run your fridge for 1 hour, then it uses 1kWh. An hour at full production would generate 5kWh of electricity from your panel. If you have a 50kWh battery, you could fully charge it in 10 hours from your panel.

So you could run 5 1000kW fridges off a 5kW solar panel (so long as it's sunny), or you could run 1 1kW fridge, and put the remaining 4kW each hour into a battery.

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#2655658 13-Feb-2021 14:21

frankv:

Pinpoint:

Am I wrong in saying if my fridge uses a 1000 watts so 1kWh, it would mean it can run, in theory for 5 hours (without the DoD) at night?

You are wrong.

kWh is a unit of energy (e.g. battery storage). kW is a unit of power (energy / time) i.e. rate of generating/consuming energy. So your panel will generate up to 5kW of electricity at any one instant, and your fridge will use 1kW. If you run your fridge for 1 hour, then it uses 1kWh. An hour at full production would generate 5kWh of electricity from your panel. If you have a 50kWh battery, you could fully charge it in 10 hours from your panel.

So you could run 5 1000kW fridges off a 5kW solar panel (so long as it's sunny), or you could run 1 1kW fridge, and put the remaining 4kW each hour into a battery.

I realize my question was still not asked properly. The battery has a 5kW storage. I am purely looking at night usage.

At night my 1000 watt fridge can run for 5 hours. Yes? No? So confusing.

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#2655662 13-Feb-2021 14:35

Pinpoint:

I realize my question was still not asked properly. The battery has a 5kW storage. I am purely looking at night usage.

At night my 1000 watt fridge can run for 5 hours. Yes? No? So confusing.

kW is a unit for instantiations power. kWh is a unit for storage. As such your statement "The battery has a 5kW storage." doesn't make sense.

If it is a 5kWh battery, yes It would run a 1kW appliance for 5 hours less any loses due to inverter efficiency.(kW times hours gives kWh).

But if it is a 5kW output, this would refer to how much energy it can put out at an instant. (i.e. it could run two 2300W fan heaters simultaneously), but without knowledge of the capacity we can't say for how long.

For reference one of the more common home batteries is the Tesla power wall 2. It has 13.5kWh of usable storage, and maximum continuous power of 5kW (for both charge and discharge).

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall%202_AC_Datasheet_en_AU.pdf

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#2655666 13-Feb-2021 14:47

Scott3:

Pinpoint:

I realize my question was still not asked properly. The battery has a 5kW storage. I am purely looking at night usage.

At night my 1000 watt fridge can run for 5 hours. Yes? No? So confusing.

kW is a unit for instantiations power. kWh is a unit for storage. As such your statement "The battery has a 5kW storage." doesn't make sense.

If it is a 5kWh battery, yes It would run a 1kW appliance for 5 hours less any loses due to inverter efficiency.(kW times hours gives kWh).

But if it is a 5kW output, this would refer to how much energy it can put out at an instant. (i.e. it could run two 2300W fan heaters simultaneously), but without knowledge of the capacity we can't say for how long.

For reference one of the more common home batteries is the Tesla power wall 2. It has 13.5kWh of usable storage, and maximum continuous power of 5kW (for both charge and discharge).

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall%202_AC_Datasheet_en_AU.pdf

Thank you for taking the time to explain things. I still don't get it though. Sorry, guess it is not really my thing.

This is the battery. So it has 5kWh? That's a lot less than the Tesla one?

https://www.sonnensupportaustralia.com.au/uploads/2/9/8/5/29857561/sonnen_-_datasheet_-_australia_-_eco_9.53__-_hybrid_unit.pdf

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#2655672 13-Feb-2021 15:12

it states in the marketing what its KWh is, you are just confusing it with inverter output or a unit of energy, ie a Kw

a 1KWh battery will output 1KW for one hour.

an inverter can output 1KW of energy at any instance. it will take the battery 1 hour to charge to its 1KWh capacity.

*this is overly simplistic and ignores heat, efficiency losses and a slower charging rate when nearly full

a tesla battery has about 13-14KWh so your one is about 2 and a bit times less. so will not last as long.

also this fridge uses 453kWh/year, or 1.25KWh per DAY or about 50W per hour, miles from your 1KW fridge in your example.

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#2655729 13-Feb-2021 16:24

I'm not sure that anyone has really answered your question yet. It's a hybrid system. This 3rd party overview of the Sonnen hybrid system says the 5kWh Sonnen system has a usable capacity of 4.5kWh. See the table about half way down:

https://www.solarchoice.net.au/blog/sonnen-battery-hybrid-review/

So, your original assumption is more or less correct. A theoretical 1kwh fridge will run for 4.5 hours. In practice this may be more or less time depending on how hard the fridge has to work depends on temperature in the room, how often you open it, etc.

Let's go from theoretical to practical now. The estimated yearly or monthly on the fridge ecolabel divided by hours could be a better measure of average hourly consumption rather than the motor rating. It will be realistically lower than the motor rating because the motor does not run all the time.

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#2655731 13-Feb-2021 16:49

Pinpoint:

Thank you for taking the time to explain things. I still don't get it though. Sorry, guess it is not really my thing.

This is the battery. So it has 5kWh? That's a lot less than the Tesla one?

https://www.sonnensupportaustralia.com.au/uploads/2/9/8/5/29857561/sonnen_-_datasheet_-_australia_-_eco_9.53__-_hybrid_unit.pdf

It gets confusing as there are two different type of units here. Kilowatts (kW) and kilowatt hours (kWh).

Kilowatts is an instantaneous unit. It is the amount of power being consumed at a point in time. It's the same as horsepower in a car, it's how much "grunt" your system has. On the datasheet you listed it's called nominal power and is 4.6kW. So that means you can only run up to 4.6kW of load at any time. If you try and run a higher load it will fail.

Kilowatt hours is a measurement of the amount of energy stored. It's how many kilowatts your system can supply for how long, a bit like the gas tank in your car.

You are correct that the battery system can store 5 kWh.

You are also correct in your calculation to figure out roughly how long you can run an appliance. In the case of the fridge example it'll have a 1000w (1kW) compressor so if the compressor was running continuously you'd have about 5 hours of run time. In reality the compressor doesn't run all the time so you would probably get a fair bit longer than that.

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#2655893 14-Feb-2021 08:26

IME, your expectations for what you would get from solar may be way too high. Solar still isn't worthwhile (my opinion of course) unless you are using the energy it is generating while it is being generated unless-

- You don't care about wasting money

- You care more about the environment than you do about money

- You are at home during the day to use the power, because storing it (maintenance for replacing expensive batteries over time) or selling it back to the grid does not make financial sense

- You are aware that it will not power your entire house, instead it will power certain CIRCUITS such as one with a water pump on it etc, therefore it is pretty difficult to use it totally efficiently because you will reach a limitation to what you can run on the inverter at the same time, meaning some things will remain grid-only

- You realise that energy sold back to the grid currently sits at (and has for a very long time) around 8c a unit when you're buying it at 22c+

- You reside in a "tiny home" where you could put all circuits thru the inverter and use it sensibly so that the inverter doesn't crash from overloading

I've seen so many installs where clients do not get what they are expecting. If you are going to be at home to use the energy, that is the only time I'd consider it personally

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#2655897 14-Feb-2021 08:58

Pinpoint:

They quoted a 5kW (I suspect this is 5kWh though) 8 panel solar system. But can you run on 5kW AT NIGHT! How long does it last.

You can't run much on a 5kw solar panel at night... it's dark... doesn't produce or store power 🤣

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#2655920 14-Feb-2021 09:39

snnet:
IME, your expectations for what you would get from solar may be way too high. Solar still isn't worthwhile (my opinion of course) unless you are using the energy it is generating while it is being generated unless-

- You don't care about wasting money

- You care more about the environment than you do about money

- You are at home during the day to use the power, because storing it (maintenance for replacing expensive batteries over time) or selling it back to the grid does not make financial sense

- You are aware that it will not power your entire house, instead it will power certain CIRCUITS such as one with a water pump on it etc, therefore it is pretty difficult to use it totally efficiently because you will reach a limitation to what you can run on the inverter at the same time, meaning some things will remain grid-only

- You realise that energy sold back to the grid currently sits at (and has for a very long time) around 8c a unit when you're buying it at 22c+

- You reside in a "tiny home" where you could put all circuits thru the inverter and use it sensibly so that the inverter doesn't crash from overloading

I've seen so many installs where clients do not get what they are expecting. If you are going to be at home to use the energy, that is the only time I'd consider it personally

You have an interesting look on things. My post was not what I could expect but more to understand how it works after the answers I realized that 5kWh is not enough for us to run everything. But during the day it will as the panels will carry most off the load and the battery get charged and kicks in when needed.

On good days, and we are in the sun capital, I can fully run off solar. So I need to discuss another battery. But thats an extra 3k orso

snnet

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#2655993 14-Feb-2021 10:59

Pinpoint:

You have an interesting look on things. My post was not what I could expect but more to understand how it works after the answers I realized that 5kWh is not enough for us to run everything. But during the day it will as the panels will carry most off the load and the battery get charged and kicks in when needed.

On good days, and we are in the sun capital, I can fully run off solar. So I need to discuss another battery. But thats an extra 3k orso

Yes, sorry, I did not mean to hijack, I have just seen a lot of disappointment from what people do expect :) A main point here is that the whole house generally will not be hooked up to the solar inverter so if you go hard using a dryer etc just be certain it's on the inverter circuit

Another point for having solar of course is redundancy - long as you are aware of the battery life and costs

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#2656109 14-Feb-2021 13:40

A friend has a solar system but it does not work during a power cut, My understanding is it endangers line workers. That seems like a really key feature to make sure you have especially if you have storage.

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