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Maximising Savings: Navigating My First Year with Octopus Energy and Heat Pump Running Costs

Steve D · 2024-03-03T10:36:08Z

To provide some context, we moved into a property in 2019 and selected Bulb as our gas and electricity provider. The property, constructed in the 1960s, features good insulation in both the loft and cavity walls, and is equipped with solar panels on the south-east facing roof. A couple of years later, after the COVID lockdowns, we expanded our home with a large extension/annexe. During the renovation, we decided to remove our gas combi boiler and transition the entire property to an air source heat pump (ASHP). We also added more solar panels and installed a small (4.5kWh) battery. More recently, we updated our kitchen, replacing our freestanding gas stove and eliminating all gas appliances from our home. This allowed us to say goodbye to the gas standing charge, which was a significant win. As the energy crisis began to impact the market, causing many smaller suppliers to go out of business, we were hopeful that Bulb would survive. However, we also decided that if Bulb were to fail, Octopus Energy would be our preferred alternative. Unfortunately, Bulb did eventually fall victim to the crisis, and as a result, we were automatically transferred to Octopus Energy in March of the previous year. Initially, we were placed on Octopus Energy's default Flexible tariff after being transferred. Aware of their variety of smart tariffs, I quickly started exploring the options. The range of choices was overwhelming—there were so many! While navigating my Account page, I discovered the option to download a CSV file of my smart meter data. This marked the beginning of my deep dive into understanding our energy consumption and evaluating different tariffs. With a heat pump installed, I found the Cosy tariff appealing, and the Agile tariff also caught my attention. The Agile tariff was especially interesting because of its plunge pricing feature. During certain short periods, the cost per kWh can become negative, allowing you to effectively get paid to import electricity from the grid. I started to track my energy consumption data weekly, monitoring daily costs on my initial Flexible tariff and comparing these with potential costs on the Cosy and Agile tariffs. I attempted to gather as much historical consumption data as possible. However, I was disappointed to find significant gaps in the data, particularly for periods more than a few weeks old, which was before the transition from Bulb to Octopus. During my research, I discovered energy-stats.uk, an excellent resource for accessing both current and historical tariff data. I quickly observed that both the Cosy and Agile tariffs could potentially be more cost-effective than the standard Flexible tariff. The Cosy tariff offers three different rates: a discounted rate (40% less than the Flexible tariff) during 04:00-07:00 and 13:00-16:00, a peak rate (60% more than the Flexible tariff) between 16:00-19:00, and a rate equal to the Flexible tariff for the remaining 15 hours of the day. As we were exiting the heating season and had the added advantage of some battery storage, switching to Cosy seemed like an obvious choice. By minimising our grid electricity usage during peak hours (utilising the battery as much as possible), switching to Cosy was bound to save us money, since its rates outside of peak hours are lower or equal to the Flexible tariff. Although Agile appeared to potentially offer greater savings, the lack of sufficient historical consumption data and the risk of very high rates during winter made me cautious. Consequently, I opted for the safer choice of switching to Cosy, where the rates are fixed. I programmed the ASHP for hot water cycles (including the occasional Legionella cycle) during the morning and afternoon low-rate periods. I also made sure it wouldn't operate during peak hours. Additionally, I leveraged the low-rate periods for charging the battery and running energy-intensive appliances like the washing machine and dishwasher, shifting as much consumption as possible to these cheaper periods. When the heating season returned in the autumn, I started to experiment with the scheduling of the ASHP's flow temperature to shift heating loads as well. Knowing that the ASHP operates most efficiently at a lower and slower rate, I was curious about the impact on its Coefficient of Performance (COP) when increasing the flow temperature during the cheaper tariff periods. I also wondered if we would notice a difference during the three peak hours when the ASHP wasn't heating at all. Deciding the only way to find out was to try, I adjusted the settings and found that on milder days, the ASHP only needed to run during the low-cost periods for both Domestic Hot Water (DHW) and heating. This approach provided sufficient warmth throughout the day. On cooler days, the ASHP required some operation between the cheapest periods to maintain comfort, but I ensured it never ran during the peak hours. Surprisingly, the house retained enough warmth during these three hours wit...

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Old_Scientist

(@old_scientist)

Honorable Member Member

Joined: 2 years ago

Posts: 414

02/07/2024 12:55 pm

I am so relieved to find this thread and discover that I am not the only person obsessed with this - Like Steve, I have no issue with looking at the day ahead Agile pricing every day to work out when to schedule usage to get the most out of it.
Thanks @steve81uk for the detailed analysis. As mentioned in @toodles other thread, I too am now looking at the new Cosy tariff and wondering if it may now be better than Agile for us (12kW ASHP, 3.6kWp solar array. Great to have so many choices.

Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.

👍

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Jack

(@Jack)

Joined: 2 years ago

Posts: 1

18/11/2024 2:37 pm

Really interesting stuff. We're on the octopus cosy tariff and we have underfloor heating with screed... I'm experimenting with the set back temperatures, but it's hard to decide how hard to run the system during the off-peak period Vs the standard period. We've got the set back during the 3 hour 1600 peak period as minus 10 to ensure it coasts through. But for the 10am to 1pm period I'm not sure if it's best to run it with a bit of a set back, made up for by running it very hard during the half price 1300 to 1600 period. Or keep it pretty much on the curve until 1300 and then only need to bump it up a few degrees during the off-peak.... Any thoughts?

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Toodles

(@toodles)

Famed Member Contributor

Joined: 4 years ago

Posts: 2767

18/11/2024 3:50 pm

I suppose in a way the UFH fabric is effectively a heat battery. I use an electrical battery (27kW/h capacity) to ride through the 16 hours of Cosy that aren’t at the cheapest rate. Would your floor screed mass provide you with a large enough buffer to do do anything similar perhaps?
Obviously you don’t want to overdo the heating during the 8 cheapest cosy hours but might this go some way towards covering the rest of the day/night. The 16:00 - 19:00 is the real killer but if your heat battery can do those 3 hours, this would be a good start. Are these the lines upon which you are thinking perhaps?
I have a Homely controller in my system and that (unless instructed otherwise) will ‘stock up’ during the 8 cheapest hours of my Cosy tariff and had I not had battery storage, I would be making even more use of that then I do! I use the grid directly as much as I can as obviously I don’t suffer the ~10% AC-DC then DC-AC losses from using the battery. Regards, Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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AllyFish

(@allyfish)

Prominent Member Contributor

Joined: 4 years ago

Posts: 520

18/11/2024 6:35 pm

Posted by: @toodles

↑

I suppose in a way the UFH fabric is effectively a heat battery.

Yes, this! Thermal mass is key. Ancient civilisations knew a thing or two about using solar reflecting lighter buildings, natural ventilation for cooling & high thermal mass to dampen the diurnal temperature swing in hot climes.
Seems we’ve lost the plot with timber framed buildings finished in solar absorbing colours with architects even scorching naturally light timber cladding to make it dark! They have very low thermal mass translating to very low thermal lag.

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Toodles

(@toodles)

Famed Member Contributor

Joined: 4 years ago

Posts: 2767

18/11/2024 7:53 pm

@allyfish If there is one thing we learn from history, it is that we don’t bother to learn from history! 😉 Regards, Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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