Earth Notes: Statscast - Energy Storage Stats Special (2022-05)

Statscast

Hi, I'm Damon Hart-Davis, and welcome to Earth Notes podcast on all things eco and green and efficient @Home!

7th June 2022, for energy storage stats up to and including May.

Many things have happened since the last statscast!

Upgrades and new systems have gone in here at EOU Towers, and there is now a new unified way to look at the various energy data streams collected too.

[00:36]

16WW energy series dataset

One thing that I'm happy with, and that did not involve splashing out on expensive equipment, is the new energy series dataset and page.

All just a SMoC (Simple Matter of Coding)! In fact, some slow careful thought, a couple of major scripts, a couple of generic ones, and a decent handful of very specific simple data extractors for each data source.

This provides one place to find most of the energy stats from 16WW. The data are provided in a simple uniform CSV format. Where there are multiple sources for the same data, they are consolidated side-by-side in a single CSV file also.

Historically, the gathered data have been in many formats, particularly dates and times, and this dataset largely smooths that wrinkle. (There are still some data that use local time rather than UTC, and that is not entirely fixed yet, but could be.)

I have already spotted a few errors (eg from entering wrong values manually) with this, and have been able to quickly correct them. Hurrah!

Anyway, please go and marvel at the new page and the dataset's CC0 licence.

[01:44]

Off-grid battery upgrade

My off-grid battery bank was getting old and tired after a decade, so at the start of September I replaced it. The new one is lower nominal capacity than previously, but I think a better fit to energy available and required, especially mid-winter.

I stuck with lead-acid gel, since I have everything set up for it, my Morningstar MPPT controller is great, and I still don't see any believable lithium-chemistry solar controllers / BMS.

One aside: this would be the first time that I'd recycled any lead-acid gear. I still had my very first gel battery moping on a shelf. And it's not the sort of stuff that I could easily walk to the local council's recycling point the best part of a mile, and which is in any case massively unfriendly to visit on foot.

I found on-line a recycler who came and collected, including my old LiFePO4 pack, though he was unsure what to do with it, and paid a small amount for it all. He should have made bank on the lead in those heavy batteries, over 100kg. The new one is a mere 66kg!

I also tweaked the battery management to be a little more aggressive in 'dumping', ie taking the optional loads off-grid more often.

The dump load is currently just the Internet router at ~12W. But that's 12W free to spill to grid or charge the Enphase or Thermino.

Overall, I'd say the system has been working more effectively, eg keeping the 'dump' load off mains more of the time. Maybe 10% or more extra delivered energy, but I'll keep watching.

[03:11]

Grid-tied battery quadrupled

A little after refreshing the off-grid storage, and after much indecision, the Enphase AC Battery capacity was doubled.

Though the ~250W power was enough to carry most (non-heating) loads, energy capacity (Wh) was probably on the low side. Against expansion were cost and additional 'vampire' load especially in winter.

The additional power did allow me to, eg bring water to the boil (slowly, on 6, on the small induction spot front right) without need for PV generation or grid imports, and contribute up to about 25% of dishwasher or washing machine or oven demand.

But hardly had that new battery settled in before I was made an offer of two further (second-hand) units at a nice price.

So I caved and doubled capacity again at the end of October, more than I think is actually optimal!

The vampire draw is now ~400Wh/d, and we rarely fully cycle the increased capacity (~5kWh) in any one day. But the ~1kW power covers half the typical high heating loads mentioned above, which is good. It is now much easier to avoid drawing any significant power to cover them if it's at all sunny.

So far I have stuck with firmware version 5 (D5.0.34), because version 7 cuts off unrestricted local read access to system stats. I do not want to round-trip across a sometimes-flaky Internet more than I need, nor 'reauthorise' manually periodically, since I will forget and lose data.

In reality we need about half the capacity (~2kWh+) and twice the power (~2kW) to more cost-efficiently cover our loads. But that implies a battery charge and discharge rate of C/1 rather than the current C/5, which is a tough call.

I think a significant reduction in grid flows, especially at evening peak, is useful for the grid, but we won't be receiving any medals. And even at current elevated retail prices (~35p/kWh import vs ~5p/kWh export) the financial return is still likely insignificant.

[05:23]

Heat battery, gas cut

A significant entirely new subsystem is the long-chewed-over heat battery charged by solar DHW diversion (and tactical mains boost).

Given that dramatically reducing gas demand seemed like a good idea because of events in Ukraine, we turned off the central heating sooner than usual in early March. The Thermino went in a couple of days later. Gas demand for March was ~160kWh compared to ~450kWh the previous March. Indeed, our typical 4kWh/day hot water use was trimmed to around 0.5kWh/day!

No we won't save money, since the loss of payment for an exported kWh of electricity is similar to the saving from not importing that kWh of gas.

Is it a guaranteed carbon saver? Not absolutely clear for diversion, since often grid carbon intensity of a kWh that we could have exported is higher than the 190gCO2/kWh of burning gas locally. But reducing flows of both is probably good.

The system is also designed to allow top-up from the grid when grid marginal intensity is significantly lower than burning gas for heat, usually in the wee hours of the morning. In general, that helps support a market for such electricity out of hours, expensive though it is for us on our pricey green all-day tariff!

The system simply falls back to gas if the heat battery runs empty, since at that point it will be our lowest-carbon option.

Complicated, but from the point of view of my family largely invisible: they never run out of hot water. I am nagging them a bit to modify how they use hot water to push down gas use a little further (and reduce some waste), but we'll see...

And though the predecessor of this unit, the UniQ 6, was suggested as holding ~6kWh, I have seen this Thermino absorb 9kWh or more in a day. Sometimes because there is drawdown during the day, but also, charging from mains cold to well over the phase-change temperature does indeed store well over that rather conservative 6kWh. The unit is currently branded a Thermino "150". 150l of water raised through 70°C is ~12kWh.

[07:31]

Coming soon

I'm keen to look at some more of our load profiles through the seasons, showing the effects of our electrical and heat storage!

Also, I'd like to sonify some of the 1-minute data available from the eddi solar diverter of divert/boost, but also grid import/export.

There's more on my "Earth Notes" Web site at Earth.Org.UK.