Mastodawn

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

The app that controls and reports on the dance that takes place between my solar panels, the battery system, the heat pump, the house and the grid has many simple graphs (usually comparing just two things). I say that because I know that some may complain this one, knitting everything together, is overwhelmingly complex. After a few days, however, I’ve come to appreciate what it does, displaying the phases of operation in a single day. Read on as I explain…

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

The easy one first: The bright green line shows the state of charge of the battery. The SOC was 100% at this time last night. At that time solar generation ended and the house was essentially off grid with the battery meeting all demands. In this graph it had already depleted to about 50% at midnight (far left) and you see it steadily dropping to the 10% safety margin by about 4.50am. It stays there with the house now now drawing grid power until around 9am when the solar comes back on in ..

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

..sufficient strength to charge the battery back up. Solar provid3d enough power to completely recharge the battery by noon. I had hoped the battery would last till the solar came back on for a full 24 hours without the grid but last night was very cold and so the heat pump drew more power to keep the house a constant 19C. Tonight is milder and I hope for success this time. As to the rest of the graph, things above the x-axis are sources of power which we aim to juggle: solar, battery and grid.

Christine Burns MBE 🏳️‍⚧️📚⧖

.. The commodities below the 0kW axis are places using power: grid export, charging the battery and the domestic load, which includes the heat pump. The four pulsing blips on the plot between midnight and 8am are cycles of the heat pump. This draws a variable load accord8ng to how hard it has to work and you see here that the negative excursions are loads of about 1.5-1.75kW heating the radiators. These are mirrored by bursts of battery discharge to provide the power. Each burst reduces the %SOC

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

Just before 5am the battery was depleted so the third and fourth heat pump cycles are powered instead by the grid. Just after 9am solar was ramping up though so the fifth smaller cycle is part powered by solar and part by the grid. After that it’s warm enough outside that the heat pump doesn’t come back on again till later this evening, when the cycle starts again. From 9am the big purple bell shape curve is the typical daily cycle of solar. The power increases rapidly with the rising sun.

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

Below the purple bell shape the rapid 8ncrease in power is being used to recharge the battery (watch the green SOC line). In fact the battery is full by noon so now there is nowhere else for the power to go except onto the grid as an ‘export’. The house continues pushing electricity out onto the grid from noon till around 7pm when I took this screenshot. From here the battery takes over again, powering everything through the night. As I said, tonight I predict the heat pump will need less ..

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

..power and the battery will get to continue running the house till the solar comes back on. The savings are twofold: first there is the money not spent importing grid power. Today I’ve used only 50p worth of power and tomorrow I hope that’s zero. Second, I’m hoping it won’t be long before I get paid the the exported power. Today I sent the grid 14kWh and, whilst I won’t get as much as I pay to import the same amount, the numbers are not that far apart. Over time this will offset what I bought..

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

..in the darker colder months. A third factor is that even in the depths of winter the battery will help me to ensure all the electricity I import is from low price periods of the tariff — roughly half the standard tariff price. Couple in the greater efficiency of the heat pump and you’ll see that there is not one but several factors that combine to maximise the savings. This is why the numbers each day are going into a set of spreadsheets so I can understand how to tune the setup.

Tim Ward ⭐🇪🇺🔶 #FBPE 1d ago

@christineburns "all the electricity I import is from low price periods of the tariff"

If you've got a big enough battery. We haven't - the standard basic domestic battery has doubled in size since we had ours put in.

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

@TimWardCam That’s sad. The Octopus Cosy tariff gives eight hours of half price electricity split through the day into slots of 3, 3 and 2 hours. The 5kW inverter can charge the 10.2kWh battery in each of those slots and so there’s more than enough energy to supply the house even with no solar in the more expensive slots of 3, 6, 3 and 6 hours.

Tim Ward ⭐🇪🇺🔶 #FBPE 1d ago

@christineburns Yes. When we bought our system the standard battery size seemed to be 4.5kWh, now 9kWh or more seems to be the base offer.

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

@TimWardCam To be honest, I would’ve preferred the 14kWh in the Tesla battery option rather than juggling with 10.2kWh but there was no way I was buying from Musk.

Tim Ward ⭐🇪🇺🔶 #FBPE 1d ago

@christineburns Too right.

Mark Koek 1d ago

@TimWardCam @christineburns My battery system can be extended with 3kWh modules. Increasing from 12 to 15 kWh next week.

bees and nature 1d ago

@TimWardCam @christineburns we only got ours last year and that was all we were offered. I would like to double it up

@christineburns you may want to check out the Havenwise app to see if your heat pump is supported. https://www.havenwise.co.uk/ I switched over to using it for our Daikin heatpump and have seen good results. We also have solar, batteries & heat pump using the Octopus Cosy tariff.

Simple Heat Pump App | Havenwise

Stop guessing heat pump settings. Havenwise automatically adjusts your heat pump settings as weather and electricity prices change. Better comfort, lower costs. 1 month free trial.

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

@droyls Thanks, although I’m quite enjoying the Cosy support in the Octopus app. I won’t be staying so hands on forever though. I wasn’t it all to just work in the end. The close study at the moment though is to learn by experiment how it all performs over an entire year. Failing to hit 24 hours with the battery last night is a case in point: I misjudged whether the energy sums added up over the long 16 hour stretch without my usual planned boost at 4am.

David Phd 1d ago

@christineburns I do love a good solar system graph (ours is a simpler system)

Christine Burns MBE 🏳️‍⚧️📚⧖1d ago

@cmsdengl It’s funny how these things tend to look com0licated to begin with and you then get used to reading the story they’re telling. I see your numbers are quite similar to mine. 😄