Daytime vs evening electricity use: why self-use matters more than kWp
Most UK homes use electricity in the evening. Solar produces it at midday. This guide explains why that timing mismatch matters, how self-use drives savings, and what to do before you simply buy more panels.
Daytime vs evening electricity use: why self-use matters more than kWp
If you only remember one thing about home solar, remember this: timing is the hidden boss.
Solar makes most of its energy around midday. Most UK homes use most of their electricity in the evening. That mismatch is why self-use often matters more to savings than squeezing in another kWp.
If you want a quick baseline for what “normal” solar output looks like where you live, start here: Find your postcode
In this guide we will talk about kW, kWh, and kWp (see Glossary) and why the value of an extra panel depends far more on when you use electricity than on the panel itself.
- Self-use is the valuable bit. A kWh you use at home avoids buying a kWh at your import rate, while exported energy is usually paid at a lower SEG rate (see Glossary).
- More kWp can reduce your self-use percentage. If your usage stays evening-heavy, extra midday generation often becomes extra export.
- Small behaviour and control changes can beat extra panels. Timers, smart plugs, and running flexible loads at midday can move the needle.
- A battery helps timing, not annual yield. It can shift midday solar into evening use, but it does not create winter energy.
Assumptions and variability
- We assume a typical UK household where electricity use is higher in the morning and evening than at midday.
- We assume you are comparing the value of self-used solar versus exported solar under SEG export (see Glossary).
- What varies most in real homes: occupancy (work-from-home vs away), cooking habits, hot water setup, and big flexible loads (EV charging, immersion heater, heat pump).
- We do not assume a specific tariff or SEG rate in this guide, because prices change. The principle is stable: self-use is usually worth more than export.
- For how SolarByPostcode estimates output and savings by outcode, see: Data sources and methodology
What “self-use” means (in plain English)
Solar gives you electricity when the sun is up.
Your home either:
- uses it immediately (self-use), or
- sends it to the grid (export)
The key point is that these two kWh are usually not worth the same amount of money.
If you want the bigger sizing framework (beyond this timing topic), the flagship guide for this cluster is:
Why most UK homes are evening-heavy
A common pattern looks like this:
- Morning bump: kettle, toaster, showers, heating controls, school run routine
- Midday lull: house emptier, fewer appliances running
- Evening peak: cooking, lighting, TV, laundry, dishwashers, showers, device charging
That general shape is true across very different places, whether you are in a dense outcode like SE1 (Southwark) or a smaller coastal area like TR1 (Truro).
The problem is simple: solar is a midday engine.
The core mismatch: solar peaks when you are least likely to be using power
Here is the “why self-use matters” picture in one glance.
Why “more kWp” is not always the right next step
It is tempting to think:
If I add more panels, I solve the problem.
Sometimes you do, but often you just create more export.
If your daytime demand is low, adding panels increases midday generation first, and the extra energy has nowhere to go except the grid.
That is why self-use percentage often falls as systems get bigger, unless your household has daytime load or you add something that shifts timing (like a battery or smart EV charging).
This is also why “oversizing” can be smart in some homes and pointless in others:
A practical way to think about value: the “two prices” model
You do not need perfect numbers to think clearly. You need the structure:
- A self-used kWh is worth roughly your import price avoided.
- An exported kWh is worth your SEG export price.
- These are usually not equal.
So the question becomes:
Will the next chunk of solar generation be mostly self-used, or mostly exported?
If you want to sanity-check your local generation potential before you think about timing, run your outcode page first, then come back to this:
Three household patterns where self-use can be high (and three where it is usually low)
This is the “cast a wider net” part: the same solar system can behave very differently across household types.
The simplest self-use upgrades (often cheaper than more panels)
You do not need to become a “solar lifestyle” person. You need a few default behaviours that move flexible loads into the overlap window.
1) Put the boring stuff on timers
- Dishwasher
- Washing machine (when safe)
- Tumble dryer (if you use one)
- Dehumidifier
A one-hour shift into midday can matter more than you expect because it stacks with whatever else is already running.
2) Make hot water a solar sponge (when you can)
If you have an immersion heater, it can act like a simple “storage” load when controlled well.
This is not automatic savings in every home, but it is one of the most common ways to turn midday surplus into something you actually use.
3) If you have a heat pump, you can still shift some demand
Heat pumps and solar are not a perfect seasonal match, but timing still matters. The pairing guide goes deeper:
When a battery is the right answer (and when it is not)
A battery is a timing tool:
- it can turn midday surplus into evening self-use
- it can smooth your import pattern
- it can increase self-use in evening-heavy households
But it does not solve:
- winter low generation
- shading or poor roof geometry
- fundamentally low electricity use
If your household is away all day and your evenings are heavy, a battery may be rational. If your household already has strong daytime demand, you may get most of the value with timers and smart control first.
(There is a full battery cluster coming, but for now the safest rule is: fix timing before buying capacity.)
A quick diagnostic you can do tonight
1) Look at your last few days of usage in your supplier app or smart meter display.
2) Ask: “Is midday naturally low, or do we have meaningful daytime load?”
3) Then ask: “Can we move any flexible loads into 10:00–16:00 without making life worse?”
If you want to anchor this to real solar output where you live, start with your outcode page. For example, compare a dense urban pattern like SE1 (Southwark) with a different housing mix like LE2 (Leicester) or a smaller city centre outcode like AB10 (Aberdeen).
How this changes sizing decisions
Once you understand your timing, sizing becomes less mysterious:
- Evening-heavy household with low daytime demand often benefits from a “not too big” system unless you add a battery or flexible load.
- Daytime-heavy household can justify bigger systems because extra generation is more likely to be self-used.
- Big future loads (EV, heat pump) can justify sizing up, but only if the timing works or you plan for it.
For the full sizing logic, including roof constraints and the “waste money vs leave savings on the table” balance, read:
Bottom line
- Solar savings are driven by value per kWh, not just annual kWh.
- Self-use is the high-value path for most households.
- The easiest wins are usually timing and control, not extra panels.
- Once you know your usage shape, the right kWp choice becomes much clearer.
Next reads
- How much electricity does the average UK home actually use?
- Self-consumption vs export in UK solar: how the Smart Export Guarantee changes the maths
- Solar batteries in the UK: who they make sense for (and who should skip them)
- How big should a home battery be? Avoiding the most common sizing mistake
- Solar payback periods in the UK: what actually drives the number