Solar Panels and Storage, Explained

Rooftop solar turns daylight into electricity, and home storage saves some of that electricity for later, but neither works alone in a useful way without the parts between them. Panels produce direct current, an inverter turns it into the alternating current a home uses, and a battery, if fitted, stores surplus for evening use or for a cloudy spell. Export is what remains after the home has used what it can, and it flows back to the grid under the tariff and connection rules that apply locally.

The useful question is not how much a roof could produce on a perfect June day, but how much of that production the household can actually use, store or export at a fair value across the whole year. A system sized for summer peaks can disappoint in winter, while a system sized for winter demand can export most of its summer output.

In practice, four factors decide the result: the roof itself, including direction, pitch, shading and structure; the household pattern, including when people are home and when large appliances run; the electrical setup, including the inverter, battery and meter; and the local rules on connection, export payment and planning. Change any one and the best system size changes with it.

Storage adds a further choice: a battery increases self-consumption and can provide backup during outages in some designs, but it adds cost, needs space and ventilation, and degrades slowly over years of cycling. Whether that trade pays depends on daytime use, export value and how much evening electricity the household actually needs.

Start by gathering a year of electricity bills or smart meter data, and note the roof direction, pitch and any shading from trees, chimneys or neighbouring buildings at different times of day. Photograph the roof, the loft structure and the consumer unit, and note the space available for an inverter and, if considered, a battery.

Ask any proposer for a month-by-month production estimate, not just an annual total, with the shading, orientation and weather assumptions stated. A proposal that only quotes a sunny annual figure has not yet answered the seasonal question.

In the EU, solar and storage sit under national building, planning and grid rules within the wider EPBD and renewable energy framework, so connection procedures, export arrangements and support schemes differ by member state. Some countries run net metering or feed-in arrangements, others use market-based export payments, and the difference changes the battery case completely.

In the UK, the Smart Export Guarantee requires larger suppliers to offer an export tariff, while connection to the distribution network follows rules set by the local network operator, with MCS certification commonly required for supported installations. Devolved planning rules and conservation controls add local variation.

A common waste is sizing panels to fill every square metre of roof without checking whether the household can use or store the output, leaving most summer generation exported at a low value. Another is buying a battery larger than evening demand, so much of its capacity is rarely cycled and its cost is never recovered in useful stored electricity.

A third mistake is ignoring shading: a single chimney shadow across one string can cut output disproportionately on some designs, so panel layout and inverter type should respond to the actual shading pattern, not to a tidy symmetrical drawing. A further point worth settling early is the order of decisions, since roof condition, household load pattern and tariff choice each shape the best system size, and a proposal that fixes panel count before those three are known is working backwards from a product rather than forwards from the home it is meant to serve.

Keep the roof survey, the production estimate with its assumptions, the inverter and battery data sheets, the connection approval, the export tariff terms and the commissioning and handover records together. Those papers let a later owner, installer or assessor understand what was promised and what was installed.

Ask a qualified installer: what monthly production do you expect and on what assumptions, how much will we self-consume with and without a battery, what export tariff applies, and what happens during a power cut. Answers tied to this roof and this household pattern are the test of a sound proposal.