Compare a battery with your existing solar
The starting values are an illustrative example, not current tariffs, a roof prediction or an installation offer. Replace them with your annual statement and surveyed quote. Generation means annual AC energy available to the home.
Your annual estimate
What changes the solar result?
These one-at-a-time scenarios vary direct use by ten percentage points, then each unit rate by 20%. Cautious, central and optimistic refer to the resulting annual benefit at the entered rates, not forecasts. More direct use improves value only when avoided imports are worth more than exports.
Horizon cash flow table
This constant-year projection uses a fixed 20-year display horizon for solar alone, or your selected battery horizon when comparing storage. It includes the purchase at year zero, repeats the entered annual benefit and operating costs, and assumes 0% tariff escalation, 0% degradation and no replacement. It is a scenario, not lifetime return or a discounted forecast. Actual equipment loss or replacement can worsen it.
Inputs and provenance
Model solar-ac-1.0.0; assumption set illustrative-2026-11-01. User-edited scenario inputs are estimates unless supported by your own measured data or quote. Read the equations, source register and limitations.
Non-contact inputs are carried only within this browser session where storage is available.
Gather the existing system records
Find the inverter make/model, array size, commissioning date, certification, generation history and electricity statements. Include any generation meter, export limit, monitoring arrangement and FIT or export-payment documents. These let an installer examine the actual system rather than guess from a roof photograph.
Tell the installer your aim: shifting solar to evening use, backup power or another outcome. Backup equipment and power limits need a specific design and may add cost without increasing annual energy savings.
Ask what stays and what changes
An AC-coupled design may retain the solar inverter; another design may replace or reconfigure it. Confirm the exact supported equipment, metering, protection, cable routes, location and commissioning. Do not assume a hybrid label guarantees a later battery is compatible.
Ask who checks network requirements and whether generation-meter wiring or the existing payment agreement is affected. Read the inverter scope guide and obtain professional assessment before electrical changes.
Use the existing system as the baseline
The original solar purchase is sunk for this decision. Compare no new battery with the additional installed battery, including required inverter work, backup equipment and annual costs. Keep direct solar use unchanged. Count only the extra delivered energy after losses and subtract forgone metered exports.
For deemed FIT, absent or unknown export payment, first clarify which arrangement applies. We withhold a battery financial verdict for deemed/unknown cases because a metered SEG formula is not necessarily valid. Physical energy estimates and compatibility questions remain useful.
Request a battery-specific assessment only when available
Battery-only installer matching is not currently verified for this website. You can use the calculation without submitting your details. Check availability and prepare a battery enquiry; an internal request is not installer acceptance.
Before committing to equipment, compare usable capacity, power, backup scope, warranty provider and support. Compare battery cost boundaries and check a retrofit proposal.
Sources and review dates
Research-based guidance. Source checks do not imply product testing or verification of an individual installer.
- Energy Saving Trust: Battery storage. Storage losses, scope of cost estimates and possibility that savings do not justify battery cost. Scope: UK. Checked .
- Ofgem: Smart Export Guarantee. Eligibility and supplier-set export terms; export payments are not installation grants. Scope: Great Britain. Checked .
- Ofgem: FIT generators. Existing FIT arrangements require agreement-specific checks before storage or export changes. Scope: Great Britain. Checked .
- Ofgem: Co-location storage guidance version 6.2. Existing generation and export metering must be assessed for a storage addition; no blanket FIT preservation verdict. Scope: Great Britain. Checked .
Registry sources-2026-11-01. Tariffs have a 30-day internal review interval. Methodology and assumptions.