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Exiled_Tyke

Sterlingtimes wrote: »

In considering a long-term investment decision for batteries if may well be appropriate to consider that all exported electricity will be metered in due course.

Currently I am compensated for my export at 4.85p/11.04p = 44%.

I currently use 62% solar generated electricity (before immersion diversion). I would expect to increase this upon retirement. I cannot see that batteries would be a good investment.

Presumably, batteries could work better for those who export most of their production.

And there lies the issue: Will we get export meters? Currently I can't see it happening as the cost is high and overall I reckon the utility companies are benefitting from the very many exporters who use less than 50%. (The fact that most can't get a meter even if they want one supports this view). Only if battery storage becomes common can I see export meters being imposed.

Perhaps though we are still all being rather premature in even discussing the topic. Prices need to fall quite a bit further for battery storage to make economic sense in most cases.

EricMears

Martyn1981 wrote: »

Nope. As the leccy is discharged by the batt, it will flow through the inverter and then the TGM, before reaching the CU and being consumed by the household.

Mart.

[Edit: Sorry Eric, that reads really snotty, or really snooty, apologies. Hi by the way. M.]

No offence taken. However, I'm not completely convinced that wiring up a house such that electricity not directly generated by solar panels is fed to the TGM would comply with any 'small print' in the FIT scheme.

As described, I wouldn't consider it 'cheating' but I can see that there is potential for the unscrupulous to arrange for some additional batteries (charged up with bought in power) to be temporarily attached and boost the 'real' generation.

Martyn1981

EricMears wrote: »

As described, I wouldn't consider it 'cheating' but I can see that there is potential for the unscrupulous to arrange for some additional batteries (charged up with bought in power) to be temporarily attached and boost the 'real' generation.

That's a good point, a system directly linked to the inverter, doesn't lend itself to an E7 use.

The diverter system would work fine, but that does then mean the PV leccy goes from DC to AC to DC to AC with greater losses than the DC to batt to AC PV set up.

Quite a lot to think about going forward. For me I've got 3 inverters, 2 TGM's and 2 different FiT tariffs, so an AC excess batt system would be my preferred option, with the potential to store cheap evening leccy, if the margin* is worth it.

*Daytime rate - night rate - storage cost (batt cost/life expectancy number of cycles). Eg 15p - 7p -7p =1p saving!

Mart.

michaels

There is a suggestion that putting the DC thru the batteries on the way to the export meter would see losses of order 10% - Is this realistic? I presume the loss must be via heat generated in the batteries during charge/discharge.

Is there any data on losses when staying entirely in DC?

Martyn1981

michaels wrote: »

Is there any data on losses when staying entirely in DC?

Hiya.

Yep, there is data, I was referring to Tesla's claim of 92%. There will also be conversion losses through the inverter, but those would exist anyway, however, if low demand is being bled in from the batteries, with no PV generation to boost it, then the inverter may be running at a lower efficiency.

Here are the specs. Scroll to the bottom.

Mart.