Understanding Your Electricity Bill with Solar

Getting your first electricity bill after installing solar can be confusing. The bill looks different, the numbers don't always match what you expected, and new terms appear. Here's how to make sense of it.

The Four Key Numbers

To understand your electricity with solar, you need four numbers:

1. Generation

The total electricity your panels produce. Read from your generation meter or inverter app. This is NOT on your electricity bill.

2. Self-Consumption

The electricity you generate and use yourself. This is the electricity that never hits the grid and never appears on any bill — it's invisible savings. Self-consumption = generation minus export.

3. Import

The electricity you buy from the grid. This IS on your electricity bill. Every kWh of import costs you your tariff rate (e.g., 26p/kWh).

4. Export

The electricity you generate but don't use, which flows back to the grid. You get paid for this via SEG — usually as a separate credit.

The relationship: Generation = Self-consumption + Export

Your bill covers: Import only

Your SEG payment covers: Export only

Invisible but real: Self-consumption — this is where most of your savings come from

Reading Your Bill

What Changed After Solar

Before solar: Your bill showed total household consumption × tariff rate = total cost.

After solar: Your bill shows only grid import (total consumption minus what solar provided) × tariff rate = lower cost.

Your self-consumed solar electricity disappears from the bill entirely — it's as if those kWh never existed. This is the main saving.

Example Bill Breakdown

Before solar (quarterly):

• Consumption: 1,000 kWh
• Rate: 26p/kWh
• Standing charge: 90 days × 50p = £45
• Total: £305

After solar (same quarter, summer):

• Import from grid: 400 kWh (you self-consumed 600 kWh from solar)
• Rate: 26p/kWh = £104
• Standing charge: 90 days × 50p = £45
• Total: £149 (saving: £156)

Plus SEG income: 500 kWh exported × 12p = £60 (paid separately)

Total quarterly saving: £216

Why Your Bill Might Be Higher Than Expected

Several common reasons solar owners are surprised by their bills:

1. Seasonal Variation

Summer bills will be dramatically lower (high generation, high self-consumption). Winter bills may barely improve (low generation, high heating demand). Don't judge solar performance by a winter bill.

2. Low Self-Consumption

If you're out during the day and no one uses electricity while the sun shines, most generation gets exported at 12p/kWh instead of saving you 26p/kWh. Your bill drops less than expected because the expensive evening imports remain.

3. Smart Meter Timing

Some smart meters record import and export in the same half-hour slot. If your generation and consumption happen to be poorly aligned within each half-hour, the recorded import can be higher than you'd expect.

4. New Appliances

Did you add an EV charger, heat pump, or other major appliance around the same time as solar? The new load may offset the solar savings on your bill.

5. Tariff Changes

If your tariff rate increased at the same time as the solar installation, the bill may look similar despite lower kWh usage. Check the unit rate and consumption separately.

SEG Export Payments

Export income typically appears:

• As a separate credit from your energy supplier (Octopus, EDF, etc.)
• Quarterly or annually depending on the supplier
• Based on smart meter export data or generation meter readings

If you haven't registered for SEG, you're exporting electricity for free. See our claiming SEG guide to set this up.

Understanding Import and Export on Smart Meters

If you have a smart meter (SMETS2), it records:

• Import register: Grid electricity you consumed
• Export register: Electricity you sent back to the grid

Your in-home display may show these separately or as a net figure. The Octopus app and most supplier dashboards show half-hourly import and export data.

The In-Home Display

Smart meter in-home displays can be confusing with solar:

• They may show negative usage when you're exporting (some displays don't handle this well)
• The "electricity used today" figure is import only — it doesn't account for self-consumption
• The "cost today" figure also only reflects import costs

For accurate monitoring, use your inverter app or Home Assistant rather than the in-home display.

Calculating Your True Solar Savings

Your true saving isn't just the bill reduction — it includes export income:

Monthly solar value = Self-consumption savings + Export income

Where:

• Self-consumption savings = Self-consumed kWh × import tariff rate
• Export income = Exported kWh × SEG export rate

Example (typical summer month, 4kW system):

• Generated: 400 kWh
• Self-consumed: 180 kWh × 26p = £46.80
• Exported: 220 kWh × 12p = £26.40
• Total value: £73.20

Of this, £46.80 appears as a lower bill and £26.40 appears as SEG income. If you only look at your bill, you're only seeing part of the benefit.

Year-Round Bill Expectations

For a typical 4kW system on an average UK home:

These figures assume 40–50% self-consumption with no battery. Adding a battery increases self-consumption (and bill reduction) while reducing exports (and SEG income), but the total value increases.

Making Sense of It All

The best approach to tracking solar finances:

1. Check your inverter app for generation data (daily/monthly)
2. Check your electricity bill for import costs (quarterly)
3. Check your SEG payments for export income (quarterly/annually)
4. Calculate self-consumption as generation minus export
5. Track annually — monthly variations are large; annual totals are more meaningful

With these five steps, you'll always know exactly how much your solar system is saving you.

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