On-grid domestic battery storage

Grandad2b

EcoScruples said:

Alnat1 said:

We generally use around 0.3-0.5kWh a day from the grid. I call them "leaks" but it happens when the inverter takes a few seconds to change to battery power when something is switched on.

Worst days are when hubby is messing with some kind of plug in power tool and uses lots of short bursts of electricity, grrrr 

I have slowly started to move all my power tools (circular saw especially) to battery power to avoid the spikey pull on the grid.

If you're pulling just 300Wh per day from the grid I can't imagine it's cost effective to splash out on battery tools for that reason alone... the DeWalt 54V chop saw is a mere £672 at toolstation. 6720 days is a long time.

EcoScruples

Very true, I suppose the convenience of not having wires is more the reason.
If I'd have known about the current export prices and slight drop in kwh price I'd have gone for more solar and no battery.
Quicker payback for sure.

Grandad2b

I totally get the joy of not trailing wires around.

The thing about a battery is what would you have done with the money you spent? If it sits in a current account then in a year it loses 10% of its value. Even in the best deposit account it's still not keeping up with inflation.

The energy market has been hit by a number of shocks in the last few years but the climate emergency isn't going away.
Should I look at a battery as a way of decarbonising the grid? Is it a purely financial decision?

If I buy a 10kWh battery then for much of the year I would expect not to import any electricity apart from those hysteresis losses caused by the inverter not switching quickly enough. But just at the time when the generated supply is likely to be at its most carbon intensive (winter) I'd probably be importing in the evening peak so the necessary gas fired capacity wouldn't decrease. Are TOU tariffs an answer to this (fill the battery overnight)? 

Exiled_Tyke

Grandad2b said:

I totally get the joy of not trailing wires around.

The thing about a battery is what would you have done with the money you spent? If it sits in a current account then in a year it loses 10% of its value. Even in the best deposit account it's still not keeping up with inflation.

The energy market has been hit by a number of shocks in the last few years but the climate emergency isn't going away.
Should I look at a battery as a way of decarbonising the grid? Is it a purely financial decision?

If I buy a 10kWh battery then for much of the year I would expect not to import any electricity apart from those hysteresis losses caused by the inverter not switching quickly enough. But just at the time when the generated supply is likely to be at its most carbon intensive (winter) I'd probably be importing in the evening peak so the necessary gas fired capacity wouldn't decrease. Are TOU tariffs an answer to this (fill the battery overnight)? 

Time of use tarriffs are definitley the answer. Fill up overnight in winter when hopefully more of the electricity is generated from wind.

Grandad2b

Exiled_Tyke said:

Grandad2b said:

I totally get the joy of not trailing wires around.

The thing about a battery is what would you have done with the money you spent? If it sits in a current account then in a year it loses 10% of its value. Even in the best deposit account it's still not keeping up with inflation.

The energy market has been hit by a number of shocks in the last few years but the climate emergency isn't going away.
Should I look at a battery as a way of decarbonising the grid? Is it a purely financial decision?

If I buy a 10kWh battery then for much of the year I would expect not to import any electricity apart from those hysteresis losses caused by the inverter not switching quickly enough. But just at the time when the generated supply is likely to be at its most carbon intensive (winter) I'd probably be importing in the evening peak so the necessary gas fired capacity wouldn't decrease. Are TOU tariffs an answer to this (fill the battery overnight)? 

Time of use tarriffs are definitley the answer. Fill up overnight in winter when hopefully more of the electricity is generated from wind.

Great! Would you care to run through the costs? 

1961Nick

Grandad2b said:

Exiled_Tyke said:

Grandad2b said:

I totally get the joy of not trailing wires around.

The thing about a battery is what would you have done with the money you spent? If it sits in a current account then in a year it loses 10% of its value. Even in the best deposit account it's still not keeping up with inflation.

The energy market has been hit by a number of shocks in the last few years but the climate emergency isn't going away.
Should I look at a battery as a way of decarbonising the grid? Is it a purely financial decision?

If I buy a 10kWh battery then for much of the year I would expect not to import any electricity apart from those hysteresis losses caused by the inverter not switching quickly enough. But just at the time when the generated supply is likely to be at its most carbon intensive (winter) I'd probably be importing in the evening peak so the necessary gas fired capacity wouldn't decrease. Are TOU tariffs an answer to this (fill the battery overnight)? 

Time of use tarriffs are definitley the answer. Fill up overnight in winter when hopefully more of the electricity is generated from wind.

Great! Would you care to run through the costs? 

Do you have an EV?

Exiled_Tyke

This will depend on your circumstances.    The savings will be calculated as follows:

Take the best available daytime rate for electricity you can get (maybe varaible or fixed?)

Deduct the cost of the night time electricity available on your time of use tariff. 

This is the saving per unit cost. However we also need an adjustement for 'round trip losses' i.e. the fact that you get less back from the battery than you put in.    My system is reported to have a round trip effeciency of 96%. So we multiply the saving by this figure. 

To calculate the saving for a complete cycle of the battery multiply this number by the useable capacity of the battery.  By battery is quoted as being 6.3kWh but discharges to 10% so 90% useable.   Also bear in mind that the battery will deteriorate over time.  

If you have to use some daytime electricty then you will need to reduce the cost by the amount of this electricity mulitplied by (your daytime rate minus the best available rate (as above))

1961Nick

Exiled_Tyke said:

This will depend on your circumstances.    The savings will be calculated as follows:

Take the best available daytime rate for electricity you can get (maybe varaible or fixed?)

Deduct the cost of the night time electricity available on your time of use tariff. 

This is the saving per unit cost. However we also need an adjustement for 'round trip losses' i.e. the fact that you get less back from the battery than you put in.    My system is reported to have a round trip effeciency of 96%. So we multiply the saving by this figure. 

To calculate the saving for a complete cycle of the battery multiply this number by the useable capacity of the battery.  By battery is quoted as being 6.3kWh but discharges to 10% so 90% useable.   Also bear in mind that the battery will deteriorate over time.  

The round trip loss is actually around 20% for AC coupled battery storage.

I've metered my inverter for over a year now & the 10.3% loss reported by the inverter is being understated by 4.2% charging & 6.3% discharging. My 10p/kWh Intelligent Octopus actually costs 12p/kWh when it's cycled through the battery.

Grandad2b

@1961Nick No EV. I expect one will eventually enter the mix but at the moment it makes no sense from either financial or environmental perspective. Real life round trip efficiencies very welcome, thank you.

@Exiled_Tyke Of course, it depends on circumstances: as I said, with a 10kWh battery I wouldn't expect to be importing any energy for 9-10 months of the year so we're looking at 60-90 days. Without any generation figures for the winter quarter I'm not in a position to make any decisions but I have looked at the cost per cycle of storage on the bimblesolar website and it's not tremendously encouraging - 3.3p/kWh/cycle for LTO is the cheapest. The issue then is spending £10k for 10kWh capacity, the 3.5kWh Pylon is much more affordable at about £3k for 10kWh and 4.7p/kWh/cycle but it still looks like spending an awful lot for very small returns. 

You may have guessed I'm not going to rush into this

Grandad2b

A couple of things I forgot to factor in 1) the effect of temperature and 2) rate of charge/discharge.

AIUI battery capacities are standardised at 25˚C (77˚F) and can be pretty severely affected if the temperature is different. Is this a real life issue? I wouldn't expect to have the battery in the roof space but I guess a garage can get quite cold in winter.
If the inverter/charger can supply 13A at 230V that's more like 65A at 48V - in a 10kWh battery is that about C/3? Do LFPs cope with this or does it reduce their capacity? The sources I've found are quite old and seem to be mostly dealing with other chemistries.