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carlyhardy avatar image
carlyhardy asked

'Battery In' and 'From Battery' - big difference

Hello, I seem to have a large discrepancy between what my generator provided to my battery and what my battery provided to my site. Victron is telling me that 'Battery In' was 2,975kWh and 'From Battery' to site was 2,329kWh. My system has lost 646kWh somewhere which seems huge (I would have expected 5 - 10% losses maximum). My battery only stores about 60kWh max. Am I missing a trick here or misreading the data?!


from-generator-from-battery-mr-bs.png


system-overview-mr-bs.png

Thank you :)

Carly

battery charging
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Jason - UK avatar image
Jason - UK answered ·

@CarlyHardy THats about right. When you convert from AC to DC, as a rule of thumb, you lose 10%. Then when you convert from DC back to AC, you lose another 10%. I did some quick numbers and the 'round trip' from charge to discharge based on 2,965kWh would give you 2,409kWh. The losses are lost in the form of heat energy.

Other factors affect the charger and inverter efficiency, ambient temperature, ventilation around the unit, the AC voltage being too high, and so on.

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carlyhardy avatar image carlyhardy commented ·
Thanks @Jason - UK ! Wow, I didn't realise the losses would be quite so much! Seems to vary across projects too. This one was 22% losses and another project was 17%. Sounds like a small difference but every kWh counts. They were different battery products, mind: the 17% result was working with a slightly bigger battery (60kW /120kWh instead of 45kW / 90kWh)
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Jason - UK avatar image Jason - UK carlyhardy commented ·
@CarlyHardy For me, my losses are even greater. I have a solar PV array that obviously generates from the panels in DC, to then convert to AC via the solar PV inverter, to then charge my batteries from AC to DC, to then discharge the battries DC to AC again when I actuialy use the energy so my round trip losses are 30%. I am going to change the PV system to charge the batteries directly saving 2/3rds of the conversion losses.
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Alexandra avatar image Alexandra ♦ Jason - UK commented ·
Heat losses are the big one.


Balancing also has losses, particularly passively balanced batteries.

In keeping with what @Jason - UK has mentioned in my personal experience, i have found that not having marginal DC cables helps alot so go bigger. And keeping the room where the install is cool helps alot.

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