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Grid v battery when solar available?


shumbaman
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for Axpert type inverters SUB/SBU is  a good option to maximise the use of the available solar. However when solar is not available (particularly at night) are you better off switching to grid or to battery? Using batteries will obviously deplete them but if you have enough PV power they should recharge during the following day and if you have enough battery storage you can see out the night and wait for the solar to start the recharging again in the morning. It all boils down to the economics and the savings derived from less grid usage compared to the the fact that by cycling the batteries they will not last as long. Anyone got some experience or ideas on this? 

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Firstly, batteries are the most expensive part of a PV system, so they're not economical when compared to grid...Unfortunately in SA we need battery backup.

 

I cycle my batteries to 50% DoD every day, starting at 4pm till they get discharged to 50%..It does not make sense to buy batteries and then not use them.....You just need to make sure you don't punish the batteries by discharging too quickly. I have pylontechs, they regularly push 4kW into the inverter from 4 x 3000C batteries.. I hope they will last 10 years by which time the price of batteries will drop significantly. 

Edited by FixAMess
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17 minutes ago, FixAMess said:

Firstly, batteries are the most expensive part of a PV system, so they're not economical when compared to grid...Unfortunately in SA we need battery backup.

 

I cycle my batteries to 50% DoD every day, starting at 4pm till they get discharged to 50%..It does not make sense to buy batteries and then not use them.....You just need to make sure you don't punish the batteries by discharging too quickly. I have pylontechs, they regularly push 4kW into the inverter from 4 x 3000C batteries.. I hope they will last 10 years by which time the price of batteries will drop significantly. 

I do something similar. 

Batteries will degrade over time even if not used so why spend so much money on a lithium battery if you are not going to use them. 

The only time I turn off battery use during the night is when Eskom announces load shedding. Also running 4 x US3000 batteries that I plan to add to every 8 months until I have sufficient to last me through the night. 

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18 hours ago, Achmat said:

Also running 4 x US3000 batteries that I plan to add to every 8 months until I have sufficient to last me through the night. 

How many pylontechs can you run in 1 stack? I read one has to buy another piece of equipment if you go more than 4 batteries?

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10 minutes ago, FixAMess said:

How many pylontechs can you run in 1 stack? I read one has to buy another piece of equipment if you go more than 4 batteries?

The newer C models can be stacked with up to 16 batteries without needing the LV hub even with some of the batteries in my stack being the B models. 

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I run my Pylontech’s down to 20% DOD every night and SOH is now at 99% after eight months of cycling every day, so trying to get the quickest ROI.

 The batteries reach 20% SOC around 4:30 am and grid kicks in and I might use just under 1 kWh by the time pv production picks up, so for my needs, Eskom is cheaper than an additional battery for quite a few years to come

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