Solar and Battery Systems

One system, not two products

Solar and storage are often sold as separate purchases that happen to arrive on the same lorry. Designed properly they are one system, and the design decisions interact from the first hour of the survey.

The array determines how much surplus there is to store. The battery determines how much of that surplus you keep. The inverter sits between them and sets the limits on both. Get the sizing of one wrong and the other spends its life half-used.

Why the inverter choice comes first

A hybrid inverter handles the panels and the battery in a single unit. The panels produce DC, the battery stores DC, and a hybrid converts once, on the way out to the house. An AC-coupled arrangement converts twice — DC to AC at the solar inverter, AC back to DC at the battery — and loses a few per cent each way.

That efficiency difference is real but modest. The bigger reasons to specify a hybrid when both are installed together are practical:

• One set of controls. Charge windows, discharge limits, export behaviour and tariff schedules configured in one place rather than two systems negotiating with each other.
• One warranty conversation. When something misbehaves, there is no argument about which manufacturer owns the problem.
• Headroom for later. A hybrid sized with spare battery capacity lets you add a second battery module without touching the rest of the system.

The constraint is that hybrids tie you to a battery range the manufacturer supports. We would rather tell you that at design stage than have you discover it in four years.

Sizing the two against each other

We start with your consumption, ideally from half-hourly data rather than an annual total. An annual figure tells you almost nothing useful; the shape of the day tells you everything.

From that shape we work out three numbers. The daily surplus the array is likely to produce in spring and autumn — not midsummer, which flatters everything. The evening and overnight draw the battery has to cover. And the peak power the house pulls when the oven, shower and car charger overlap, because a battery with plenty of capacity and modest output will simply hand the rest back to the grid.

Where those three numbers disagree, the honest answer is that some capacity will be underused in some seasons. That is normal. What we avoid is specifying capacity that is underused in every season.

Notification and approval

Combined systems cross the G98 threshold more often than solar alone. Where total capacity is 16A or less per phase — around 3.68kW on a standard single-phase supply — the installation is notified to the network operator under G98 after commissioning. Above that it is a G99 application, and G99 must be approved before any work happens.

Approval timescales sit with the network operator, not with us. Where a design is close to the threshold we will tell you what the choice costs you in either direction, because occasionally the sensible answer is to apply export limiting and stay simple.

Commissioning is where the value appears

A combined system that is installed correctly and configured lazily performs like a cheaper one. Commissioning sets the charge and discharge windows against your actual tariff, decides what the battery does with a forecast sunny day in April, and sets whether surplus goes to the battery, the car or the grid first.

We set that up with you, show you how to read the monitoring, and revisit it if your tariff or your household routine changes.