When the finance director stared at my chart for 30 seconds in complete silence, I knew something was wrong. The electricity bill was £360,000 per month across 20 line items, ranging from £174,000 for wholesale energy down to £3 for settlement charges.
My stacked bar chart was technically perfect. Every penny accounted for, every proportion mathematically correct.
It was also completely useless.
This commercial user consumes around 2 GWh monthly. The figures vary by region, capacity and demand profile, but these proportions represent typical UK commercial electricity bills in 2025. The bill breaks into six categories: commodity costs, environmental levies, balancing charges, distribution fees, transmission costs and administration.
That £360,000 monthly bill tells a different story depending on how you look at it.
Attempt 1: The Stacked Bar
All 18 charges in one bar — can you see the BSC Charge?
The problem: Wholesale Energy (£174.2k) dominates. The BSC Charge (£12), and several other charges are literally invisible. You'd need to zoom in 10,000x to see them.
Every charge sits exactly where it should, proportionally speaking. But can you spot the BSC Charge? The Settlement Charge? The CM Operational levy?
They exist. You just cannot see them.
Scale becomes the enemy when your largest value towers 58,000 times above your smallest. Linear scales cannot show £174,000 and £3 meaningfully on the same axis. The bottom dozen charges vanish into digital dust.
Attempt 2: The Horizontal Bar
Every charge visible, ranked by cost
Better visibility: Every charge is now readable. You can see that Wholesale Energy (£174.2k) dominates, followed by RO (£66.1k). But you lose the sense of composition - how do these parts relate to the £360.1k total?
Separating each charge onto its own bar solves the visibility problem immediately. Every line item becomes readable. The descending order makes comparison intuitive - you can instantly see that Wholesale Energy dwarfs everything else, and that RO and CfD are the next largest costs.
But something is lost. You can see individual values clearly, yet the relationship to the whole becomes abstract. How do these 20 bars sum to £360,000? The composition vanishes.
Attempt 3: The Logarithmic Scale
Every charge visible, but proportions distorted
Technically correct, perceptually wrong: The £3 Settlement Charge now appears roughly one-tenth the width of the £174k Wholesale Energy. In reality, one is 58,000 times larger than the other. Log scales solve visibility but break intuition.
A logarithmic scale compresses the range. Every charge becomes visible on the same axis. The £3 Settlement Charge finally appears alongside the £174,000 Wholesale Energy.
The mathematics work perfectly. The perception does not.
Humans interpret bar length as proportional to value. When you see one bar three times longer than another, you expect it to represent three times the amount. On a log scale, that same visual difference might represent a thousandfold difference in actual value.
The Settlement Charge appears roughly one-tenth the width of Wholesale Energy. In reality, Wholesale Energy is 58,000 times larger. The visual lies while the numbers tell the truth.
Log scales excel at scientific data where orders of magnitude matter conceptually. For financial data where every pound counts equally, they create dangerous false equivalences.
Attempt 4: The Treemap
Proportional areas — better for seeing relative sizes
Better: You can now see proportions. But small charges are still hard to read, and you lose the sense of how costs flow from total to category to individual charge.
Area replaces height, which helps with the visibility problem. Environmental charges now clearly occupy about one-third of the total space. You can roughly distinguish the larger individual components.
The small charges remain stubbornly illegible. More importantly, hierarchy disappears. You lose the sense of how the total breaks into categories, and how categories subdivide into individual charges.
Attempt 5: The 100 Per Cent Stacked Bar
Percentages show proportions clearly — but what's the actual cost?
Trade-off: Clear proportions, but you've lost the absolute values. Is Environmental 34% of £100k or £1m? Context matters for decision-making.
Percentages solve visibility completely. Commodity takes 49 per cent, Environmental grabs 34 per cent, Balancing claims nine per cent. Every component appears clearly.
But we have traded one problem for another. Absolute values vanish entirely. Is that 34 per cent slice worth £34,000 or £340,000? For someone controlling budgets, this distinction matters enormously.
Attempt 6: Sankey Diagram
Shows hierarchy and flow — Total → Cost Type → Charge
Getting closer: You can now see the full hierarchy — how £360.1k splits into Commodity/Non-Commodity, then into cost types, then into individual charges. But a Sankey implies flow. An energy bill is a composition. Let's try one more approach.
A Sankey diagram reveals flow. Money enters from the left as one total bill, streams through category buckets, and emerges as individual charges on the right.
The story becomes clear: £360,000 splits into commodity costs (48 per cent), environmental levies (34 per cent), balancing charges (nine per cent), network fees (eight per cent), and administration (0.01 per cent). Each category then subdivides into specific charges. Flow width matches monetary value.
Even tiny charges appear as thin streams. They exist visually.
But Sankeys imply movement, like money flowing through a process. Energy bills represent composition, not flow. Money does not travel from commodity to environmental charges. They are parallel components of the same whole.
Attempt 7: Sunburst Chart
Composition + hierarchy + every charge visible
The solution: A sunburst shows composition and hierarchy together. The centre is the total, with cost types and charges radiating outward. Single-charge categories like Wholesale Energy appear directly. Click to zoom, hover to explore.
A sunburst chart shows composition and hierarchy simultaneously. The centre represents the £360,000 total. The inner ring displays categories. The outer ring reveals every individual charge. Arc width matches value proportionally.
You can explore any segment by hovering over it. Even the £3 Settlement Charge appears as a thin slice, but it appears nonetheless.
Unlike a Sankey, the visual metaphor works correctly. These are parts of a whole, not stages in a pipeline.
Think of it like Money for Nothing. The song builds from simple beginnings into complex layers, but every element contributes to the complete composition.
Different questions demand different groupings entirely. Charge type represents just one way to slice this data.
How you group the data changes what questions you can answer
What it answers: How much is market-exposed (Commodity) vs pass-through charges (Non-Commodity)? Commodity costs can be hedged and traded; Non-Commodity is largely fixed by regulation.
The "right" chart depends on the question you're trying to answer.
Asking “where does the money go” suggests grouping by charge type. Asking “what can I actually control” reveals a different structure: 49 per cent depends on trading decisions, 43 per cent scales with volume, six per cent represents fixed costs, and two per cent reflects demand management.
Asking “how are charges calculated” shows yet another pattern: 92 per cent links to consumption (p/kWh), six per cent involves daily standing charges (£/day), and two per cent relates to peak demand (£/kVA).
Same data. Three different stories. The correct visualisation depends entirely on the question being answered.
When data spans multiple orders of magnitude, standard charts deceive through omission. Small values disappear despite their importance for understanding the complete picture.
A sunburst chart succeeds because it shows hierarchy clearly while preserving proportions. Everything remains visible through interactivity. Arc width equals value mathematically. The metaphor matches the reality: composition rather than flow.
Chart selection should match mental models. Are you showing parts of a whole? Use pie charts or bars. Showing flow through stages? Choose Sankey diagrams. Showing hierarchical composition? Pick sunburst or treemap visualisations.
Getting this choice wrong transforms accurate data into misleading stories. The numbers stay the same, but the truth gets lost in translation.
The next article explores which parts of this bill you can actually control and what levers exist to reduce commercial energy costs.