Inverter and batteries

Jaws677

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I am aware of that. However, running high draw appliances drains the batteries very quickly - it still takes me by surprise each time it happens (we do try and run things like washing machines during sunlight hours)
With a bit of common sense most households will be able to shift at least 90% of their usage off grid with a battery pack that size if the OP has sufficient solar panels
 

Dairyfarmer

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I spoke to an electrician ..... he says inverter don't handle it
Find another electrician. This guy doesn't have a clue.

There are simple devices that you can use to measure the actual requirements of an appliance. Don't rely on the manufacturer's specs. You need to know both the average AND maximum Kw/Kva.

The average is used to spec the storage capacity you will need. Like if you are going to drive from Jhb to CT. You need to know if your fuel tank is big enough or if you will need to refuel along the way.

The maximum is just as important. If the average is 2000W a 3000W inverter would run it. But the appliance may spike at 3500W, in which case your inverter will not handle the load. Inverters do allow a certain time for an overload before they shut down. Also you may have multiple devices that have 2000W and your inverter is 3000W. You can't run them both at the same time.
 

Tinuva

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You can get inverters to handle any size load. If your main circuit breaker is 60 amps then a 15 kva inverter will be able to provide that.

However, your batteries...
5 x 3.5 pylon techs is 17.5kwh. What is their max dod? 80 percent? So that leaves 14kwh usable.

A 5 kw load will flatten that in under 3 hours. To go off grid that battery needs to last you at least 15 hours. Assuming no clouds and sufficient solar that the battery is at 100 percent at 5pm.
Those pylon techs can easy go to 20% without being damaged.
 

Dairyfarmer

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For my grid tied system I made the following rules when installing my system. There are so solar inputs yet. Designed to run for a 2 hour loadshed.

1- You will be using 50% of total load 100% of the time, but your inverter must be 1.5x more than your total load.
2 - Have enough storage capacity to handle 100% of the load for 100% of the time (so actually 200% as you run your batteries down to a maximum of 50%).

1 - 2Kva total load will run at 1Kva minimum all the time, so you need a 3Kva inverter.
2 - 24v 400Ah will run 2Kva for 2 hours (8 x 12v 100Ah = 24V x 400Ah x 0.85 efficiency / 2000W / 2 for 50% DoD).

In real life my load is usually only 0.8Kva. I have 4 x 12v 100Ah batteries. I have yet to get to 50% DoD even after 3 hours.
 
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InternetLuddite

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Thanks Folks,

I thought he was talking a bit of bollocks. So definitely, I know what my house runs, during day, idle is 450w, and about 700w at night when sleeping .Difference in 'idle' load is external lights.

The plan is for solar to drive all appliances (washing machine, pool pump, geyser heat pump - max load if all on simultaneously is 4.5kw) during day, so would spec for 8kw inverter, just to be safe. But even then, they all don't run daily.

At night it would be dishwasher and oven as high load and heaters (for winter) but need to sort that out, right now, load is around 2-3kw if blankets and two heaters on.

Batteries , starting small and then increasing capacity - ideally I want 30kwh of energy so I never have to worry about what to turn on ;)

So takeaways, don't deal with that electrician that was recommended ...

Thx again
 

TheChamp

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Thanks Folks,

I thought he was talking a bit of bollocks. So definitely, I know what my house runs, during day, idle is 450w, and about 700w at night when sleeping .Difference in 'idle' load is external lights.

The plan is for solar to drive all appliances (washing machine, pool pump, geyser heat pump - max load if all on simultaneously is 4.5kw) during day, so would spec for 8kw inverter, just to be safe. But even then, they all don't run daily.

At night it would be dishwasher and oven as high load and heaters (for winter) but need to sort that out, right now, load is around 2-3kw if blankets and two heaters on.

Batteries , starting small and then increasing capacity - ideally I want 30kwh of energy so I never have to worry about what to turn on ;)

So takeaways, don't deal with that electrician that was recommended ...

Thx again
My advice, I wouldn't connect everything on one inverter, it's better to split the load into a couple of inverters with their own battery banks, you talk about expanding the system over time but you don't want to be mixing new batteries with old ones, same with the panels.

Space for panels and shading are all going to affect your 30kwh capacity, there's a lot to consider for such a massive system and it costs a pretty penny, that's why most people settle for removing the power guzzlers of the system.

Your electrician guy was probably thinking along those lines, I doubt he doesn't know what he is talking about, it is just bad that he assumed it was not worth it to try and explain the complexity to you.
 

Dairyfarmer

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The plan is for solar to drive all appliances (washing machine, pool pump, geyser heat pump - max load if all on simultaneously is 4.5kw) during day
Sounds very low. I think you should retest those to find their peaks.

Also remember to take the Kva and Kw into account. The easiest way to explain it is how efficient the inverter is. A good inverter will have very similar Kva and Kw values, say the Kw will be 90 to 95% of the Kva value. Generally pure sine wave inverters are above 85%. Those "cheap" 1000W modified sine wave inverters can be as low as 60%.
 
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Sinbad

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Sounds very low. I think you should retest those to find their peaks.

Also remember to take the Kw and Kva into account. The easiest way to explain it is how efficient the inverter is. A good inverter will have very similar Kw and Kva values, say the Kva will be 90 to 95% of the Kw value. Generally pure sine wave inverters are above 85%. Those "cheap" 1000W modified sine wave inverters can be as low as 60%.
My victron 5KVA is 4.5KW.
 

Tinuva

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I have 2x 3.5KW geysers in this house. Makes for difficult planning. Considering I am starting off with a 4.5KW inverter. While a great inverter, 2x geysers are insane. So they will be Eskom with the Oven.
Gas stove can be on the inverter to make sparks :ROFL:
 

Sinbad

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I have 2x 3.5KW geysers in this house. Makes for difficult planning. Considering I am starting off with a 4.5KW inverter. While a great inverter, 2x geysers are insane. So they will be Eskom with the Oven.
Gas stove can be on the inverter to make sparks :ROFL:
Time to switch to gas geysers too ;)
 

Dairyfarmer

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I have 2x 3.5KW geysers in this house. Makes for difficult planning. Considering I am starting off with a 4.5KW inverter. While a great inverter, 2x geysers are insane. So they will be Eskom with the Oven.
Gas stove can be on the inverter to make sparks :ROFL:
Geysers are the red haired stepchild.

Solar heated water supplying a gas water heater is about as efficient as you can get.
 

InternetLuddite

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Sounds very low. I think you should retest those to find their peaks.

Also remember to take the Kva and Kw into account. The easiest way to explain it is how efficient the inverter is. A good inverter will have very similar Kva and Kw values, say the Kw will be 90 to 95% of the Kva value. Generally pure sine wave inverters are above 85%. Those "cheap" 1000W modified sine wave inverters can be as low as 60%.

I did check peaks.

Pool Pump is 1.1Kw
Heat Pump is 1.1kw
Washing Machine : Max 3Kw (depending on hot water temp) We never use 60 Degrees.

Lots of valuable info from you and everyone else. #educated :)
 

Tinuva

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just a quick question, if i had to get a pure sine wave inverter and a 100ah AGM battery, does the inverter charge the battery aswell or do i need some sort of charger, im a little confused in regards to how it works

for example something like this, maybe not this extreme, but https://www.takealot.com/inverter-pure-sine-sine-wave-2000w-12v/PLID68909188

any input will be appreciated.
that one doesnt look like it has a built-in charger, so you will need a charger.
 
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