On-grid domestic battery storage

zeupater

1961Nick wrote: »

Here's the battery inverter..

Hi

Isn't the referenced data effectively saying that the spot efficiency of the battery inverter at the time the readings were captured was <90%? ... ie it was discharging the batteries (DC) at 360W & supplying 320W (AC), so measured supply efficiency would be 88.9%(320/360), excluding internal battery resistance losses which wouldn't be measured due to occurrence prior to DC current readings!? ... :think:

HTH
Z

1961Nick

zeupater wrote: »

Hi

Isn't the referenced data effectively saying that the spot efficiency of the battery inverter at the time the readings were captured was <90%? ... ie it was discharging the batteries (DC) at 360W & supplying 320W (AC), so measured supply efficiency would be 88.9%(320/360), excluding internal battery resistance losses which wouldn't be measured due to occurrence prior to DC current readings!? ... :think:

HTH
Z

The charge side seems to be fairly steady at 4-5% loss. The discharge side is all over the place & it's difficult to see a pattern without recording lots of snapshots & all the variables at that time - SOC, power, temp, generation, grid import, ramp up/down.

The cumulative totals for battery charge 435.94 kWh & discharge 387.24 kWh suggest a round trip loss of 11%. The percentage was climbing but has now been static for a week. Metering the in/out will provide a definitive answer. It's on my to do list but not a priority at the moment.

zeupater

1961Nick wrote: »

The charge side seems to be fairly steady at 4-5% loss. The discharge side is all over the place & it's difficult to see a pattern without recording lots of snapshots & all the variables at that time - SOC, power, temp, generation, grid import, ramp up/down.

The cumulative totals for battery charge 435.94 kWh & discharge 387.24 kWh suggest a round trip loss of 11%. The percentage was climbing but has now been static for a week. Metering the in/out will provide a definitive answer. It's on my to do list but not a priority at the moment.

Hi

I follow what you're saying but at the time that the data screen referenced was captured the loss on discharge alone looks to be 11% if it's being read correctly ... and that's likely only the loss through the inverter (ie monitoring power - DC.in vs AC.out)

The definition of 'charge' & 'discharge' probably could do with clarification as it depends on where/how it's measured ... for example, are both measured on the AC (as in to & from the solution) or DC side (as in to & from battery storage) as this is quite important to what the data is actually conveying (ie battery round trip losses vs storage solution round trip losses!)

As you say, accurately metering the AC ins & outs should give you a decent idea of what's actually happening (+/- the meter's tolerance!)

HTH
Z

1961Nick

zeupater wrote: »

Hi


The definition of 'charge' & 'discharge' probably could do with clarification as it depends on where/how it's measured ...

HTH
Z

I know!

The difference between charge & discharge at 11% is too high to just be the battery loss alone, and according to your calculations, too low to be the inverter & battery loss combined. Battery + discharge loss is the current favourite.

zeupater

1961Nick wrote: »

I know!

The difference between charge & discharge at 11% is too high to just be the battery loss alone, and according to your calculations, too low to be the inverter & battery loss combined. Battery + discharge loss is the current favourite.

Hi

Agree, but at the time of the screen capture, the data suggests that the system was discharging at 360W but only supplying 320W, hence, if the collected data was accurate at the time in question, an actual power loss of 11.1% on the discharge cycle alone was coming from somewhere ...

... all I'm highlighting is a technical observation, because that's all that the data on the captured screen really seems to convey regarding power efficiency & losses.

HTH
Z

mmmmikey

A thought that has occured to me, haven't really worked it through yet. Slightly tangential to batteries, but wasn't sure where to post this and the PowerVault aspects makes it relevant....

I've opted for an ac connrection for my PowerVault, meaning that I have the facility to connect addtional panels without affecting metering, FIT, etc. directly to the inputs on the PowerVault. So I could add a second 4kW array alongside my existing 4kW array for just the cost of the panels and installation, i.e. I will already have the inverter capacity in the PowerVault.

Although pretty much all of the power generated would be offloaded to the grid in the peak of summer, off the top of my head there's probably something like £150 per annum value to me for winter use and heating in the shoulder months, which I could realise through some fairly simple changes to the way I run the heaters. My decision would be based on having reasonable confidence on seing my money back in the life of the panels - say 20 years?

Could anyone give me a rough idea of the cost of 4kW of panels installed and connected, it would be a fairly simple installation, with the panels all on the same, unshaded elevation of a bungalow roof, and simple wiring through to the battery? Don't have any experience to go on myself as the current array was on the house when I bought it.

1961Nick

zeupater wrote: »

Hi

Agree, but at the time of the screen capture, the data suggests that the system was discharging at 360W but only supplying 320W, hence, if the collected data was accurate at the time in question, an actual power loss of 11.1% on the discharge cycle alone was coming from somewhere ...

... all I'm highlighting is a technical observation, because that's all that the data on the captured screen really seems to convey regarding power efficiency & losses.

HTH
Z

It can be as high as 20% at very low discharge power & down to 5% at around 750w+.

zeupater

1961Nick wrote: »

It can be as high as 20% at very low discharge power & down to 5% at around 750w+.

Hi

Thanks, that level of performance range would certainly make a difference to anyone with a generally low energy usage profile ...

I reckon it'd be pretty interesting for manufacturers to have a mandated requirement to publish charge & discharge power loading performance curves similar to torque or COP curves ....

Z

1961Nick

zeupater wrote: »

Hi

Thanks, that level of performance range would certainly make a difference to anyone with a generally low energy usage profile ...

I reckon it'd be pretty interesting for manufacturers to have a mandated requirement to publish charge & discharge power loading performance curves similar to torque or COP curves ....

Z

It doesn’t work out too badly for my usage profile. Most of the battery consumption is at or close to 5% and it’s just the 2.5kWh from midnight to sunrise that suffers a larger loss.

The charge side seems very consistent at around 5%.

If the app figures are accurate, I anticipate an overall round trip loss of about 11.5%. I think I may move the meter up the to-do list...

mmmmikey

1961Nick wrote: »

It can be as high as 20% at very low discharge power & down to 5% at around 750w+.

My (limited!) experience of playing with energy monitors is that the accuracy is questionable at low currents. I don't have the data to hand, but I did a check with 2 plug in monitors of one type and another from a different manufacturer some time ago, the outcome of which was they showed readings within a few % of each other for higher currents (> 1A or so if I remember correctly ?) but widely different readings for lower currents. So it wouldn't surprise me at all if the hard-to-explain results you're discussing is simply down to measurement accuracy at different ranges.