What makes a battery report survive the CFO

Why storage gets cut

A UK installer and co-founder of Solar4Good, writing in POWER Magazine in September 2026, describes how solar clears the client's hurdle rate on its own while storage is the line removed to make the numbers work. In his order book, 2 of 16 jobs above £30,000 included storage — a small sample, as he notes. His advice: size the battery on the site's half-hourly demand, and quote it as a separate line with its own business case (POWER, 23 Sep 2026).

Trust is the other half. In Zorowatt's review of 50 statements by users and practitioners, mostly from public forums (October 2026), results that users could not explain were the most frequent complaint, in 12 of the 50. In one thread a solar-plus-battery run with almost no solar showed about $20,000 a year in savings; the cause turned out to be a tariff entered wrongly (SAM forum). In another, a user found the peak-shaving dispatch ignored monthly and ratcheted demand (SAM forum).

1. The baseline bill, reconciled

Before any saving, show that the model reproduces what the site actually paid: the bill rebuilt line by line from the meter data and the tariff, next to each month's invoice. A finance reader who sees the baseline match within a couple of percent will believe the difference the battery makes; one who cannot see it will not.

• Zorowatt proposes ±2% on the total excluding VAT and ±5% per line as default tolerances (an estimate, to be calibrated on real bills).
• Every deviation gets a stated cause. Sometimes it is an error on the invoice — a finding that earns the client's attention before the battery is even discussed.

2. A data appendix

One page on the meter data: the period, the share of intervals measured, the share filled and by which method, the problems found and what was decided. It answers the question every careful reader asks: what is this based on?

3. The expected case, not the best case

Headline the savings a real controller would achieve: rule-based dispatch that does not know the future. Show the perfect-foresight optimum only as the upper bound, with the ratio between the two. A report that headlines the optimum promises money the battery will never earn, and the first year's bills will show it.

4. Sensitivities and break-even values

Show what would make the case fail. In the illustrative example in NPV, IRR and payback for a C&I battery, raising the installed cost from €450 to €536 per kWh turns an NPV of about +€25,550 into about −€10,953. A finance reader wants that before approval, not after.

Break-even values are often clearer than a table. Illustrative: an office battery with €7,763 a year gross savings and maintenance at 2% of the cost pays back in 10 years only if cost C satisfies C = 10 × (7,763 − 0.02 × C), so C = 77,630 ÷ 1.2 ≈ €64,692 — about €259 per kWh for 250 kWh. If the quote is far above that, the case needs another value stream.

5. The battery as its own line

Bundled into a solar quote, a weak battery hides behind strong solar until the CFO removes it. Quoted separately — its size, its cost, its savings by bill line and its own payback and NPV — it either stands or it does not, and the client can decide with open eyes.

6. Every assumption in one place

• Tariff versions, with their source and the date they were read.
• Known tariff changes and how they were treated (for example the Dutch 2028 draft or the German AgNes reform, as scenarios).
• Installed cost and its source; maintenance; warranty cycles and end of life; replacement cost.
• Discount rate, price escalation and project life.
• Dispatch mode, and what the battery is assumed not to do.

7. Say what it is not

A feasibility estimate from past data, not a guarantee of savings and not investment advice. Saying so plainly costs nothing and protects you when a future year differs from the past one. Zorowatt's disclaimer is a starting point.

A one-page summary a CFO reads

1. The investment: battery size, installed cost, what is included.
2. Year-1 net saving, split by bill line (peak charge, energy, taxes on losses) and by value stream.
3. Payback, NPV and IRR at the client's discount rate.
4. The two or three changes that would make it fail, and the break-even values.
5. What is not included, and the date the tariffs were checked.

Zorowatt's report is built this way: the rebuilt bill against the invoices, the data-quality appendix, the tariff versions with their sources, the assumptions and the limits. Run a site in the Workspace; your first site analysis is free.

Related guides

• NPV, IRR and payback for a C&I battery
• What a battery feasibility study contains
• The ten data problems that size a battery for you

Sources

• POWER Magazine, The commercial storage gap is not technical, it is what survives capital approval, 23 Sep 2026
• SAM forum, PVWatts with almost no PV and batteries yields large net savings
• SAM forum, standalone battery peak-shaving dispatch

Last checked: 2026-10-30. Every figure in this guide comes from the source linked next to it, with the retrieval date Zorowatt's research recorded (28–30 October 2026), or from arithmetic shown step by step. The forum review and the office break-even example are from Zorowatt's own research notes; the office is illustrative, not a real customer.