The All-Electric Household: A Data-Driven Analysis of Costs and Savings

You’ve probably heard it all before:
“Solar panels will save you a fortune!”
“Heat pumps are the future!”
“You’ll never pay an energy bill again!”

Sounds amazing, right? But how much of that is actually true under real-world conditions?

In this article, I take a deep dive into the real numbers from our household’s transition to an all-electric setup, giving you a clearer picture of whether it could make financial sense for you.

Tracking our energy costs and savings turned into an oddly addictive hobby. Who knew optimising energy usage could be so thrilling? From harnessing “free” solar power and driving oversized “golf carts”, to figuring out if heat pumps are magic or just expensive fans, I diligently measured the impact of each change.

To make navigation easier, I’ve structured this article into key sections:

• Approach — how I became an energy geek
• Tariffs — because not all electrons are priced equally
• Solar & battery — sun-powered savings or just a pricey roof decoration?
• Heating — gas boiler vs aircon & immersion vs heat pump — extra money or extra jumper?
• Driving — the battle between petrol stations and superchargers
• Monthly costs & savings — show me the money!
• Return on investment — was it worth it?
• Summary — finally!
• Further reading & links — graphs, spreadsheets and more!

By the end, you’ll have a data-driven perspective on whether an all-electric household is just clever marketing hype or a genuine financially win.

Approach

To get a large enough historical baseline, I dug out old meter readings all the way from 2017(!) and car mileage recorded during service or MOT visits. I then interpolated everything to monthly data points going back to January 2021. While not 100% accurate from month to month, the reconstructed data points should be good enough to draw meaningful conclusions.

As soon as we switched to Octopus Energy in October 2022, I started tracking monthly usage more rigorously, while also steadily increasing the number of different data points collected to get a more detailed picture.

For temperature data, I pulled readings from our Tado smart thermostats, which we installed a few years back (code available on my GitHub). Since installing the heat pump, we now also have forecasted outdoor temperatures from the Open Energy Monitor, along with actual outdoor temperature readings from a weather compensation sensor.

Gas usage for space heating vs. hot water was tricky to separate, but summer meter readings helped estimate how much went into keeping our showers hot (a lot!) versus heating the house. In winter, some of that hot water heat did sneak back into the house. In summer however, it was mostly just wasted energy — keeping the airing cupboard nice and toasty for absolutely no reason!

Tariffs

Our house originally came with a SMETS1 smart meter, but for years, we treated it like a regular dumb meter — paying a flat rate for electricity and not really caring when we used it. If that sounds familiar, you might be in for a surprise when you see how our average electricity import costs changed over time.

To make sense of our energy journey, I’ve broken it into four overlapping phases, each focusing on a different strategy for optimising costs and usage:

• Phase 0 — Establishing Baseline Usage
• Phase 1 — Maximising Self-Consumption
• Phase 2 — Load Shifting
• Phase 3 — Maximising Export

Phase 0 — Establishing Baseline Usage

To measure the impact of the improvements made to our house, we first established a baseline.

Overall, our energy habits remained very consistent all the way from 2018:

• Gas central heating was highly dependent on outside temperatures (obviously).
• Indoor target temperature of 21.5°C.
• Consistent hot water demand throughout the day for a family of four (please note hot water estimation based on summer months).
• Small variations in electricity usage throughout the year.
• Increasing car mileage post-COVID.

The cost trend was clearly upward starting from late 2021 when energy prices started creeping up, culminating in the energy cost crisis caused by Russia’s war against Ukraine.

Please note that the cost calculations during the energy crisis use the price cap rates applied to our standard tariff, not the much higher wholesale prices at the time.

Key takeaway: before making changes, our energy costs were predictably rising — so anything that could stop it was worth exploring.

Phase 1 — Self-Consumption (November — September 2023)

Without an export tariff for almost five months, I focused on maximising self-consumption of the ‘free’ energy we were generating.

With the first month spent on getting familiar with the solar & battery system, we only really kick-started changes to our energy usage in December 2022. We then moved to a Smart Export Guarantee (SEG) tariff, paying 4p/kWh, but that was still much lower than any import rates until September 2023.

With such low export rates, I obsessed probably too much trying to use as much of the solar energy we were generating. This reached its peak in June 2023:

• 87% self-consumption (730kWh) of generated energy (835kWh).
• 85% self-sufficiency (only 60kWh imported at home, plus 70kWh at Tesla Superchargers).
• Powered the entire house, hot water, heating/cooling, and drove 1285 miles.
• All for just £32.58 (excluding standing charges).

Key takeaway: would I recommend this extreme self-sufficiency approach with significant behavioural changes and advanced Home Assistant automations to the average person? Most likely not. But it was a fascinating experiment and highly satisfying to pull off.

Phase 2 — Load Shifting (January 2023 — Onwards)

After approximately two months of having the solar & battery system in place, we switched from a flat rate to time-of-use tariff. This meant the off-peak electricity was dramatically cheaper than standard or peak rates, incentivising moving all shiftable load to the late night/early morning off-peak period.

Over time, we successfully shifted more than 95% of usage to off-peak for the following:

• Dishwasher (despite no built-in functionality to delay the cycle, we used a smart plug instead).
• Tumble dryer (with built-in timer feature).
• Immersion heater for hot water (scheduled via a Wi-Fi switch).

The impact was immediate — our average import rate dropped off a cliff in early 2023. If you look at the cost graph, you can practically see the moment we said goodbye to flat-rate pricing:

Key takeaway: this is where having a smart meter became incredibly useful. Not because of the in-home display (which mostly exists to remind you that putting on an oven or boiling a kettle costs money), but because it unlocked access to time-of-use tariffs. Thanks to those, our average unit cost dropped below pre-energy-crisis levels.

Phase 3— Maximising Export (September 2023 — Onwards)

In September 2023, Octopus switched us from the SEG tariff (paying 4p/kWh) to the Outgoing tariff (paying 15p/kWh). Making off-peak electricity cheaper than export, had a very substantial impact:

• Simplified Home Assistant automations — no more complex solar-diversion logic or predictive battery charging.
• Easier car charging experience — just plug it in for the night, rather than trying to look at the weather forecast for upcoming days.
• Further load shifting — now from solar to off-peak, prioritising off-peak charging and exporting excess solar.
• More financially viable solar PV & battery systems — with more credit accumulated during summer months.

Key takeaway: this approach aligned with wholesale electricity prices, where night-time is usually cheapest and evening peaks are most expensive. A win-win for both our wallet and the grid!

Final Thoughts on Tariffs

Despite common misconceptions, time-of-use tariffs and smart meters aren’t just gimmicks. They have the potential to radically reduce energy costs while allowing for smarter energy use. By shifting consumption to off-peak hours and making the most of lower rates, we can use more energy for less money.

Solar PV and Battery

Although solar PV and batteries can be installed separately, a hybrid system often reduces installation costs (fewer components) and improves efficiency by charging the battery directly with solar-generated direct current (DC), avoiding unnecessary DC-AC conversions.

Our system consists of:

• 16 solar panels (6.48kW total)
• 6kWh battery storage (5kW usable)
• 5kW hybrid inverter (5.5kW peak AC output)

“Nothing’s Free”

To fairly allocate savings, I followed the cheapest available energy source at any given time:

• Until September 2023, the cheapest was self-generated energy (4p/kWh) — any devices running during peak time “bought” electricity at that rate, with the same value allocated as solar saving — resulting in split saving between production and consumption.
• From September 2023, the cheapest was off-peak energy (7p/kWh) — any devices running during peak time would buy at the peak rate (approx. 25p/kWh), assuming solar was completely separate — this meant all costs avoided through self consumption were allocated to solar production only.

I believe the outlined methodology is the fairest in order to appropriately credit savings to the right system.

A Year in the Sun

Despite not being particularly close to the equator, our south-ish facing solar panels still harvested just over 6000kWh in 2024.

Financially, this breaks down as follows:

• Self-consumed energy savings: 2600kWh (43%) × 22p/kWh (assumed avoided import cost) = £572
• Exported energy: 3400kWh (57%) × 15p/kWh (export rate) = £510
• Total estimated annual payback: £1082

On top of that, our battery helped optimise energy usage in two key ways: storing excess solar energy for later use and charging from the grid at cheaper off-peak rates. In 2024:

• Total battery charge: 2200kWh
• From grid (off-peak charging): 1500kWh
• From surplus solar: 700kWh

Without the battery, our self-consumption rate would have dropped from 43% to 31% (a 25% reduction), lowering our savings by £49. Additionally, by charging 1500kWh during off-peak hours at a 14p/kWh discount compared to peak rates, we saved an extra £210.

• Total battery benefit: £259
• Revised total payback: £1292 (just £0.03 off from my detailed cost analysis — see Energy Usage Google Sheet)

Key takeaway: having a battery can definitely help with utilising much cheaper off-peak electricity and aid self consumption. By how much, depends strongly on how big the battery is and how much electricity you typically consume.

Saving Sessions to the Rescue

To manage peak-time demand, Octopus Energy and other suppliers introduced Saving Sessions, rewarding customers for reducing consumption during high-demand hours.

For us, it meant avoiding the most power-hungry devices (yes, the lights were still on!) at the specific times. While initially it was all done manually, with a few more sessions, all was run by Home Assistant — from pre-charging the battery, switching off all controllable devices (car charger, immersion heater) and forcing battery discharge to maximise export.

Some argue that pre-charging and discharging during Saving Sessions gives an unfair advantage to home battery owners, but this is no different from large-scale grid storage solutions like hydroelectric or industrial battery systems.

The rewards were high, totalling £119.59 for 2023–2024 winter period. Due to Ofgem/NESO changes, the payback is much lower during 2024–2025, but in my view it’s still worth participating and supporting the collective effort.

Final Thoughts on Solar

Solar PV and batteries probably won’t cover all your electricity needs or make your bills disappear entirely. But what they can do is change the way you use energy — giving you more control, reducing reliance on the grid, and lowering costs.

Heating

Heating is by far the most complex part of the all-electric transition, not only to accomplish but also to analyse. Fortunately, I had a few years of gas usage data to establish a solid baseline, making meaningful comparisons possible:

Combined with historical temperature data, a bit of Python wizardry and unnecessarily complex Google Sheets, I developed formulas for monthly space and hot water heating with gas:

For 2021-2024, the estimated average yearly gas consumption was 12540kWh, very closely matching the actual usage.

Transition

Our heating transition timeline was as follows:

• February 2023 — July 2024: used an immersion heater for hot water and air conditioning units to supplement space heating.
• August 2024 onwards: fully transitioned to a Vaillant Arotherm+ heat pump, replacing our gas boiler entirely.

Gas usage estimates can only go so far, so once the heat pump was installed, I started relying on highly accurate data from the Open Energy Monitor’s Level 3 Heat Pump Monitoring kit, publicly available at HeatpumpMonitor.org:

Note: there is also electricity, heat and COP data available in the Vaillant app, but due to errors in flow rate measurements, I don’t consider them reliable enough (exaggerated heat generation and efficiency).

Heating Costs

The chart below breaks down our heating costs across different categories:

With gas prices still double their 2021 levels, our heat pump’s running costs (from August 2024) look promising in comparison. By default, the presented heat pump costs exclude benefits of our solar and battery.

Heating in Low Temperatures

The internet is full of myths about heat pumps struggling in the cold. So, how did ours perform during the January 2025 cold snap?

• Whole of January (average temperature 2.5°C)
  Electricity used: 614kWh (216kWh consumed directly at off-peak hours)
  Heat generated: 1922kWh
  COP: 3.13 (OK, that’s pretty good — but 2.5°C isn’t THAT cold)
  Space heating COP: 3.34
  Hot water COP: 2.20
• 10 coldest days — 3rd to 12th January (average temperature -0.2°C):
  Electricity used: 242kWh
  Heat generated: 721kWh
  COP: 2.98 (OK, that’s still pretty good — but it’s barely below 0°C!)
• 4 coldest days — 8th to 11th January (average temperature -1.4°C):
  Electricity used: 107kWh
  Heat generated: 303kWh
  COP: 2.83 (Yeap, still wearing a t-shirt indoors while it’s freezing outside!)

The Ultimate Cost Battle: Heat Pump vs. Gas Boiler

For the cost calculation I’ve used the following assumptions:

• Heat pump (Intelligent Go+Battery) shows what we spent, helped by the battery (no solar) and the Intelligent Go rates — assuming average rate of 14.24p/kWh, which is total cost of space heating (£77.55) and hot water (£10.03) divided by the number of days (31)
• Heat pump (Intelligent Go) shows what we spent, assuming no use of battery, and only relying on time-of-use Intelligent Go tariff only, with average rate of 17.14p/kWh, which is total cost of space heating (£95.40) and hot water (£10.03) divided by the number of days (31)
• Heat pump (Cosy) assumes 50/50 split between two non-peak time rates (25.44p/kWh & 12.48p/kWh) on the Cosy tariff
• Heat pump (standard/flat) — using the standard tariff (also known as Flexible), with a flat rate throughout the day
• Gas boiler (estimated) — based on historical usage & taking into account outdoor temperature; this estimate might be too pessimistic due to minor drought proofing & insulation improvements, daily standing charge not included
• Gas boiler (90% efficient) — based on the heat produced by the heat pump and divided by assumed boiler’s running efficiency, daily standing charge not included
• Gas boiler (90% efficient+standing charge) — based on the heat produced by the heat pump and divided by assumed boiler’s running efficiency, plus the daily standing charge for gas (not needed for the heat pump)

So, are heat pumps expensive to run in winter? Yes — higher heat demand increases running costs. But the real question is — are they more expensive than gas boilers?

In our case, even with an older, non-optimised radiator system and microbore pipes, our heat pump — combined with a time-of-use tariff (Intelligent Go) — proved cheaper than running a gas boiler, even during the coldest days of January, which itself was pretty cold overall. This would also have been the case with another popular time-of-use tariff called Octopus Cosy, designed specifically for heat pumps.

Total House Rebuild?

Now you’ve seen heat pumps not only work in the cold, but can even beat gas boilers on cost! However, installing one can sound like a major building project — do you really need a full plumbing makeover? Maybe not!

Our heat pump installation was a basic like-for-like swap:

• Outdoor unit: wall-hung, freeing space inside.
• Hot water cylinder: upgraded to 250L, designed for low temperature heating (replacing the original 210L one).
• Pipework & radiators: used without modifications (originally designed for 55–65°C gas boiler).
• Controls: single SensoComfort thermostat (replacing two-zone Tado — now used for monitoring only).

Final Thoughts on Heating

While I’m not a heating expert myself, I would like to think a more comprehensive installation (with radiator, under floor heating or pipe upgrades) should give you an even better performance. Well, as long as you don’t accidentally add a buffer, extra pump and zoning that could cannibalise your efficiency. With that in mind, you could easily consider our system as a reasonably worst case scenario (performance-wise), as we’ve been optimising for comfort and costs (Octopus Intelligent Go off-peak times), rather than performance. Specifically:

• Only using the heat pump for hot water (up to 58°C at night to charge-up the hot water tank; day-time top up to 48°C) — note that a proportion of systems out there would be using immersion for legionella control, and this would typically be excluded from SCOP/SPF calculations.
• Keeping toasty 21.5°C throughout the day — how many people would go higher than that?!

Surprising insight — homes with higher heat demand can actually achieve better overall heat pump performance — as long as the heat pump, radiators and pipework are properly sized. For real-world data see HeatpumpMonitor.org.

Driving

With so many different opinions about electric vehicles, how does driving on electrons actually stack up in terms of cost?

To assess this, I used interpolated monthly mileage and average petroleum prices to estimate what we would have spent had we continued driving internal combustion engine (ICE) cars. For comparison, I assumed a fuel efficiency of 50 miles per gallon (mpg) for ICE vehicles.

Calculating home charging costs was straightforward once we stopped using our charger’s solar diverter. However, accurately measuring solar-fed energy required additional metering via Home Assistant.

Our Nissan LEAF never required public charging, as we typically stayed within 130 miles between top-ups.

With our Tesla, we relied primarily on the Tesla Supercharger network, which cost us between £0.35–£0.46 per kWh. We occasionally used third-party chargers, with the highest rate we ever paid being £0.52/kWh (be wary though — there are some really expensive ones out there!).

Below are the monthly costs since 2021:

For all our driving in electric vehicles so far (23614 miles) our total bill was £664.31, averaging less than £0.03 per mile — take that, petrol prices!

Please also note the efficiency comparison between the models:

Key takeaways:

1. Public chargers can be expensive — some companies charge up to £1 per kWh, compared to just £0.07/kWh at home.
2. Solar panels & home batteries don’t reduce EV charging costs — the cheapest way of charging in the UK is currently overnight at off-peak rates (e.g. Octopus Intelligent Go at 7p/kWh).
3. EV efficiency varies significantly — just like ICE cars, different battery-electric vehicles (BEVs) have varying efficiencies, especially in winter months. When choosing your next vehicle, pay attention to its energy consumption.

Monthly Costs and Savings

Now that we’ve reviewed all the individual elements, we can bring everything together to see the total costs and savings. The chart below is quite detailed, so here are a few key points to help interpret it:

• Anything above £0 → cost
• Anything below £0 → savings / payback
• What we actually paid each month → total (net)
• The estimated combined savings from all categories → total (saving)
• Expected costs for gas, electricity and fuel → total (est. without savings)
• Monthly car mileage → right-hand vertical axis & dotted line

Key takeaways from the data:

• EV savings depend on mileage —the more we drive, the more we save (especially when avoiding public chargers).
• Solar & battery savings are seasonal — higher in summer, lower in winter (although helped by additional payback from Saving Sessions and off-peak charging).
• Heat pump savings are emerging — as expected, heating demand rises in colder months, but so do the savings (despite the slight loss of efficiency). Please note that the heat pump costs assume no solar or battery usage.
• Total monthly savings in 2024 → a whooping £238.31! — based on like-for-like heating, electricity and car usage.

Would you like even more detailed breakdown? Please see the Detailed Costs Chart in Energy Usage Google Sheet.

Return on investment (ROI)

While monthly savings give a snapshot of the financial benefits, they don’t fully answer the big question: “Is it worth it?”

To assess this, I compare savings vs. initial investment — in other words, how long it takes for each system to pay for itself.

Below is a chart depicting annualised return on investment (all costs include hardware and installation):

Smart immersion heater (£75):

• Paid for itself in under a year!
• No longer needed since the heat pump is far more efficient at heating water.

EV charger (£1200):

• Biggest savings overall — initial cost fully recovered.
• Cars excluded as costs for ICE/BEV with similar specifications are comparable.

Heat pump (£4500 net cost; £12000 minus £7500 BUS grant):

• Over 9% annualised ROI after just a few months, solely on Intelligent Go time-of-use tariff (with battery benefit included, ROI would have been above 12%, and even higher by adding solar).
• Compared to a £2500–£3500 gas boiler replacement, ROI difference recovered in 3–5 years (assuming no battery benefit).
• With our old gas boiler, we were due an annual service (~£100) and replacement of faulty pressure vessel (~£100) — both excluded from cost analysis.
• Cost of the optional Open Energy Monitor kit also excluded.

Solar PV & battery (£12000):

• Largest initial outlay, lowest ROI.
• Installed during a high-demand period, which inflated prices.
• Higher solar and off-peak charged battery consumption increases ROI (e.g. by adding a heat pump, we increased peak-time solar self-consumption and battery utilisation).
• Today, same investment could get 50% more solar panels, twice the battery size and much higher ROI.

While all these calculations might have inaccuracies and gaps, they should hopefully give you a better understanding of the financial impact it could have on your budget.

In our transition to an all-electric household, we also made upgrades to enhance comfort and convenience:

• Induction hob (£1048 in 2021) — impact on gas and electricity usage wasn’t even noticeable — for more info, please see our home improvement adventures.
• Air conditioning (£8000 in 2023) — while it helped save us money in spring/autumn, the primary purpose was to provide greater comfort (cooling), hence it’s excluded from the ROI analysis.

Yes, other investments may offer better short-term returns. But these upgrades are more than just financial decisions. They provide:

• Protection against rising energy costs (think of it as insurance), with long-term savings & stability.
• A positive impact on both the economy & environment.

Attributing costs and savings can be complex, especially when multiple systems provide mutual benefits. For example, should savings be split equally between the heat pump and the solar/battery system, or allocated entirely to one? While the total savings remain the same, the ROI for each system will vary depending on the chosen methodology.

Summary

Our transition to an all-electric home wasn’t just about saving money — it was about enhancing comfort, convenience, and reducing our environmental impact. From an induction hob and solar panels to battery storage, EV charging, and finally a heat pump, each upgrade brought us closer to that goal. While the upfront investment was significant, the long-term rewards — lower bills, greater efficiency, and a more sustainable home — make it all worthwhile.

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Further Reading & Links

• Our Torturous Journey to an All-Electric Household — my blog post focusing on the journey and the overall experience
• Energy Usage Google Sheet — contains all the data used in this analysis
• HeatpumpMonitor.org — hundreds of heat pumps with live and historical data, including ours
• Visit a Heat Pump — hundreds of heat pumps to visit, including ours
• Energy Stats UK — great collection of blog posts about tariffs and the Vaillant heat pumps