The short answer
On a south roof at 35° in Congleton, about 70% of a year’s solar output arrives between April and September, and only about 15% from November to February. Units the house uses directly are usually worth more than units exported. Exports can be paid under the SEG, which needs an MCS certificate and an export-capable meter.
The shape of a Congleton year
The table shows what 4 kWp of panels on an unshaded south roof at 35° makes in each month, from the PVGIS runs for this guide (PVGIS 5.3, PVGIS-SARAH3 data for 2005-2023).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 110 | 185 | 316 | 435 | 463 | 457 | 448 | 404 | 336 | 228 | 149 | 106 |
The best month makes about 4.4 times as much as the worst. Roughly 70% of the year’s output comes in the six months from April to September, and only about 15% in the four darkest months. That pattern drives everything else on this page: panels produce the most when a gas-heated house uses the least, and the least when the house needs the most. The full table by direction and pitch is on output.
Within the day
The same mismatch repeats every day. A south roof peaks around midday, while many households use most electricity at breakfast and from late afternoon into the evening. Fridges, routers, alarms and devices on standby draw a steady background load all day, and that load absorbs part of the midday output. Whatever the roof produces beyond what the house is drawing at that instant leaves for the grid by itself.
How much of the output a home uses directly varies widely. A household where someone is at home in the daytime, or that runs appliances on timers, uses more. One where everyone is out from eight till six uses less and exports more. A roof facing east and west produces earlier and later, which can fit a working household better: see east and west roofs.
Why self-use usually counts for more
A unit used in the house replaces a unit that would otherwise be bought at the import rate. A unit exported earns the export rate. Import rates have generally been well above export rates, so each unit kept at home tends to be worth more than each unit sent out. That is why the questions that matter most are about timing: what the household runs during daylight, and whether surplus can be stored or turned into heat.
This guide does not give bill or value figures, because they depend on tariffs that change and on how each household lives. A firm’s quote should state its assumptions about self-use, so you can test them against your own habits.
Ways to use more of the output
- Timing. Set washing machines, dishwashers and dryers to run in the middle of the day when the panels are producing.
- Hot water. A diverter steers spare output into the cylinder’s immersion element rather than out to the grid. Mains gas is the only central heating for 82.5% of Congleton East households and 82.6% in Congleton West (Census 2021), so in many homes the diverter heats water that gas would otherwise heat. It needs a cylinder; a combination boiler has none.
- A battery. Storage moves midday surplus into the evening. It is the most expensive option, and its case depends on how much surplus there is: see batteries.
- An electric car. Charging at home on sunny days, with a charger that can follow solar output, uses large amounts of surplus.
How export payments work
Under the SEG, larger electricity suppliers have to offer at least one export tariff, paying more than zero, to households with systems up to 50 kW (Ofgem). Smaller suppliers may choose to offer one. To qualify, the installation needs an MCS certificate, which the firm issues on completion, and a meter that can record exports, usually a smart meter.
The rate is set by each supplier. Some tariffs pay a flat rate, some vary with the time of day, and some are only available to customers who also buy their electricity from that supplier. The export supplier need not be the same company as the import supplier, so it is worth comparing both sides together. Firms on the MCS register provide the certificate; keep it safe, because it is needed again if the house is sold.
Summer and winter in the house
Household demand moves in the opposite direction to the panels. In winter the lights are on longer, people spend more time indoors and, in homes with electric heating or a heat pump, heating adds a large load. In summer there is no heating load in a gas-heated home, daylight runs past nine in the evening and lighting use falls. The result is that in June a 4 kWp roof makes about 457 kWh while the house needs comparatively little, and in December it makes about 106 kWh while the house needs much more.
That is why a solar household still buys plenty of electricity in winter, and why summer surplus cannot be banked against winter bills except through export payments. It is also why the months from March to October matter most when judging any plan to use more of the output.
Reading the self-use figure in a quote
Most quotes include an estimate of how much of the output the household will use, often expressed as a percentage, because the value of the system depends on it. Ask how that figure was reached. A firm that has looked at your actual electricity use, by month or by half-hour from a smart meter, can give a much better estimate than one using a standard profile. Be wary of a self-use figure that rises sharply when a battery is added without any explanation of the household’s evening demand.
The performance estimate itself should use Congleton’s sunlight figures. The PVGIS runs for this guide show Congleton a few per cent below the Cheshire plain towns to the west, so an estimate based on a regional average may run high. Choosing an installer lists the other questions for a quote.
When exports are limited
Some systems are not allowed to export everything they make. Where a larger system needs approval from the network operator, the approval can come with an export limit, and the equipment is then set to hold exports below it. Any output above the limit that the house cannot use is simply not generated. If your quote mentions an export limit, ask how much output it is likely to cost in a typical summer: see grid connection.
Applying for an export tariff
Registration is done by the householder, not the installer. The supplier will ask for the MCS certificate, the meter details and the system size. Payments are usually made monthly or quarterly against meter readings. If the house changes hands, the new owner has to register in their own name: buying a home with solar explains the handover.
Sizing with self-use in mind
A larger system raises summer output much more than winter output, and most of the extra summer output is likely to be exported. Where export rates are low, a moderate system matched to daytime use, perhaps with a diverter, can make more sense than covering the whole roof. Where the house plans an electric car or a heat pump, a larger array has more to supply. Costs in Congleton shows how the price changes with size, and the roof and route check gives a starting estimate for your own roof.