On-grid domestic battery storage

1961Nick

Reed_Richards wrote: »

Thanks @1961Nick, I am sure you have correctly interpreted my description. At present I don't have an Economy 7 meter so charging from the mains is looking to some hypothetical future; I just wanted to know how feasible it would be.

I'm in the process of moving to Octopus GO. I'll charge my batteries between 00.30 & 04.30 @ 5p/kWh. Peak rate is only 13.31p which is virtually what I'm paying Bulb (13.2p/kWh). The standing charge is 4p/day more.

Reed_Richards

I'm in the process of moving from "Bulb" to "Outfox the Market". I like Bulb and Outfox has acquired a poor reputation for customer service but Bulb had a standing charge of slightly more than 20p per day whilst with Outfox it is slightly less than 10p a day. This is significant because I pay more in standing charges than I do for electricity, now that I have solar PV plus battery.

mmmmikey

The last 2 posts certainly highlight the need to choose a tariff to suit your own usage pattern. I pay 21.97p standing charge (ouch) and 19.81p per kWh for peak usage (ouch again) but this is an absolute bargain tariff for me. I only pay 4.7p per kWh overnight on the E7 tariff, and because I have night storage heaters and an annual consumption of ca. 6000kWh of which 95% + is night usage I'm quids in despite the horrific day rate and standing charges.

My goal is to reduce day usage to <1% through careful use of my battery and panels.

Reed - in relation to your eralier posts, I think some (or possibly all) energy supplier have restrictions on providing new E7 meters and may only do this if you have storage heaters, so if you do decide to go down the overnight charging route you may find that a time of use tariff's such as Octopus GO is your only option.

1961Nick

Reed_Richards wrote: »

I'm in the process of moving from "Bulb" to "Outfox the Market". I like Bulb and Outfox has acquired a poor reputation for customer service but Bulb had a standing charge of slightly more than 20p per day whilst with Outfox it is slightly less than 10p a day. This is significant because I pay more in standing charges than I do for electricity, now that I have solar PV plus battery.

I also like Bulb & have found them very easy to deal with - just one price & no contract. Their prices are at the lower end of the market & they're reasonably fast to react when wholesale prices drop. The only reason I'm changing is because they're lagging behind the smart meter roll out & therefore tariffs tailored to EVs - I haven't got an EV yet, but my battery usage mirrors having one.

Martyn1981

Reed_Richards wrote: »

No I am sure I am correct. But the AC that is the immediate output from a wind or hydro turbine I have seen described as "wild AC", not the domesticated type that you use in your home. So it must be immediately converted to DC, possibly just using something simple like a rectifier. But I cannot tell you why the AC to DC conversion is done at the turbine end of the cable that carries electricity to the end user rather than at the user end.

Right. So do we both now agree that they output DC, and the inverter is DC to AC?

Sorry to be a pain about this, but I've never heard of AC output (for these small units), they all seem to me to be DC rated, which is why I was so baffled at your original post.

I'm with outfox the market. They have good customer service and are easy to use.

Reed_Richards

Martyn1981 wrote: »

Right. So do we both now agree that they output DC, and the inverter is DC to AC?

If you like, Martyn. Fundamentally a turbine output is "Wild AC" but if your research shows that it is always converted to DC at the point of generation then so be it. Why it is thought better to transmit the electricity as DC rather than Wild AC I don't know.
My inverter can swing both ways. Most of the time it converts the DC from my solar panels and battery to domesticated mains AC (as you say) but it can also charge the battery from the mains, which is AC to DC.

Martyn1981

Reed_Richards wrote: »

If you like, Martyn. Fundamentally a turbine output is "Wild AC" but if your research shows that it is always converted to DC at the point of generation then so be it. Why it is thought better to transmit the electricity as DC rather than Wild AC I don't know.
My inverter can swing both ways. Most of the time it converts the DC from my solar panels and battery to domesticated mains AC (as you say) but it can also charge the battery from the mains, which is AC to DC.

Total guess, but perhaps DC for off-grid as it would go (via a charge controller) to batts?

There's probably a logical explanation and one of the electrical engineers might know?

Reed_Richards

mmmmikey wrote: »

Reed - in relation to your eralier posts, I think some (or possibly all) energy supplier have restrictions on providing new E7 meters and may only do this if you have storage heaters, so if you do decide to go down the overnight charging route you may find that a time of use tariff's such as Octopus GO is your only option.

That sounds like a catch 22. You wouldn't dream of having storage heaters unless you had an Economy 7 tariff but you can't have an Economy 7 meter unless you have storage heaters.

Can you not use a Smart meter (which I personally don't yet have) in Economy 7 mode? I did this in my old house when my Economy 7 meter (no idea why the house had one) was replaced by a first generation Smart meter.

joefizz

Martyn1981 wrote: »

Total guess, but perhaps DC for off-grid as it would go (via a charge controller) to batts?

There's probably a logical explanation and one of the electrical engineers might know?

AC is easiest to generate by rotation but cant be stored.
Electronics etc run on DC. If standards were to start again from scratch I would wonder if it would be dual voltage in houses (230v for cooking, washing machines, kettle, toaster, immersion etc and 12v/5v for everything else). I would guess that probably everything outside of my kitchen runs on lower DC.



If you think about your 'wild ac' example it will vary in frequency, amplitude and phase so conversion to DC makes it constant.


At higher voltages DC transmission is used over longer cables as it is less lossy but we are talking hundreds of miles or undersea cables.

zeupater

Reed_Richards wrote: »

... Fundamentally a turbine output is "Wild AC" but if your research shows that it is always converted to DC at the point of generation then so be it. Why it is thought better to transmit the electricity as DC rather than Wild AC I don't know.

Hi

Could it be that the issue is one of consolidation of generation, transmission efficiencies & grid synchronisation?

Think about a cluster of turbines (consisting any integer >1) of same design in a general area (field, hill ridge etc) with each turbine spinning at a moderately different rate because of topological, immediate locality airflow or turbulent conditions. AC generation related to revolutions would create power at varying frequencies, however, in order to best consolidate the power for useful onward transmission the frequencies must be aligned .... presumably the most straightforward solution is immediate conversion to DC to a standardised voltage within the turbine, consolidate the output from various DC sources and then convert the total sum DC output to grid synchronised AC ...

To provide an analogy of what & why .... although the nominal grid conditions between France & the UK are equal, in reality there are both operational & spot-load based voltage & frequency differences between the two grids, therefore the two cannot be directly interconnected using AC to create a single entity, with the additional issue of not being able to control the flow direction or power requirements across the connection. This is essentially why the interconnectors operate as DC with AC conversion & frequency synchronisation performed at each end-node .... this is effectively being done for the same reason.

Make sense?

HTH
Z