Installer tools · Battery storage

What does a battery actually change?

Generating electricity and using it are two different problems. This answers the second one, by the recognised method, in kilowatt-hours rather than promises. Take me through it instead →

The roof

3,948 kWh a year

4.32 kWp in BS1 1AA. Change the roof →

Or a metered figure, if you have one

kWh/year

Only from an MID-approved generation meter, over a full 12 months — that is the one alternative the method allows.

The household

When is anyone in?

How much electricity does the house use?

Or the figure from your bill

kWh/year

Twelve months from actual meter readings. Leave it blank and the method assumes 3,500 kWh.

The battery

How big?

Or usable capacity in kWh

kWh

Usable, not nominal. If the datasheet gives only a nominal figure, multiply by the depth of discharge — 90% for lithium, 50% for lead acid.

What is it for?

The battery's job

There is a power diverter, heat pump, electric heating or EV chargerNone of them are in the figures above — the method excludes them. Ticking this shows how much room is left under the ceiling.

What the battery changes

	Solar only	With the battery
Solar you use yourselfof everything the roof generates	23%	69%
Your electricity that solar coversof what the house uses in a year	26%	78%

What that is worth in a year

£760 – £858

First year, at today’s prices. The spread is almost entirely about which export tariff you are on — not about your roof.

Electricity you don’t buy: £711; The solid half. Valued at 26.11p, the Ofgem price cap — which is capped, published and moves once a quarter.
Paid for what you export: £49 – £147; The loose half. Ofgem sets no export rate and caps none — it requires only that a rate is above zero, so suppliers differ by a factor of 3.0.

What each export tariff would pay you, on these numbers

1,227 kWh exported a year. Rates checked 30 August 2026; a supplier may change one on 30 days’ notice.

Tariff	Rate	A year
OVO Energy SEGwhoever supplies your electricity	4p	£49
Octopus Energy Outgoing Octopusif you move your electricity supply	12p	£147
OVO Energy SEG Beyond Exclusiveif you move your electricity supply	12p	£147

Switching your electricity supply would take you from £49 to £147a year on exports alone — a bigger difference than anything you could change about the roof. This comparison is Minute Solar’s own guidance: no part of the recognised MCS calculation involves tariffs, prices or switching supplier.

These money figures are ours, not the standard's. MCS 032:2025 puts no price on anything — it stops at kilowatt-hours, and the tariffs here come from Ofgem and from suppliers.
The export rate is the biggest single lever on this number — a factor of 3.0 between the cheapest and dearest, against about ±10 % on the generation estimate. Ofgem neither sets nor caps export rates; it requires only that they are above zero.

Show the arithmetic and the prices

Solar used in the home2,722 kWh
From the self-consumption method. This is the half that is worth the most.
Import price avoided26.11p / kWh
Ofgem price cap, July to September 2026 — England, Scotland and Wales (average), Direct Debit. Includes VAT at 5 %.
Money not spent on electricity£711
2,722 kWh × 26.11p
Solar exported1,227 kWh
Everything generated that the house did not use at the time.
Paid for what you export£49 – £147
4p (OVO Energy SEG, available whoever supplies you) to 12p (OVO Energy SEG Beyond Exclusive, needs you to move your electricity supply).
A year's worth, all in£760 – £858
Money not spent, plus money paid for exports. First year, at today's prices.

Assumptions

Import price: 26.11p / kWh: Ofgem price cap, July to September 2026. The cap is set a quarter at a time and this is 2026-07-01 to 2026-09-30, applied to a whole year — no published price covers twelve months.
Standing charge: Not counted: 57.19p a day is payable with or without solar, so counting it as a saving would flatter the figure.
Price inflation and degradation: None: First year only, at today's prices, matching the scope of the kilowatt-hour figures this is multiplied by.

Where the prices come from

Ofgem — Energy price cap (default tariff) level, 1 July to 30 September 2026 — electricity, Direct Debit open
OVO Energy — Smart Export Guarantee Tariff (SEG) — tariff rates and conditions open
Octopus Energy — Outgoing Octopus — export tariff open

Money figures are Minute Solar's own and are outside the MCS standard entirely — MCS 032:2025 sanctions no tariff, price or saving anywhere in its method, and the kilowatt-hours these are multiplied by are the only part with a recognised source. Import prices are the Ofgem default tariff cap, which changes quarterly. Export rates are set by each supplier: Ofgem neither sets nor caps them and requires only that they are above zero, which is why a range is shown rather than a figure. First year only, with no allowance for price inflation, tariff changes or system degradation.

Annual consumption was not supplied, so 3,500 kWh has been assumed. Consumption moves this figure more than almost anything else — a real meter reading from twelve months of bills is worth getting.
Occupancy was not supplied, so the "in half the day" table has been used, as the method directs. A household home all day self-consumes noticeably more, and one out all day noticeably less.

Show the calculation

What the battery is forRaising PV self-consumption
Clause 4.1 routes this to the procedure in clause 4.2.
Source: MCS 032:2025 — The MCS Charitable Foundation
Usable capacity10 kWh
Established per clause 5.2.5, from the datasheet's usable figure or nominal capacity × maximum depth of discharge.
Source: MCS 032:2025 — The MCS Charitable Foundation
Occupancy archetypeIn half the day
Occupancy was not established, so the method's own fallback table is used — Table 2 says to refer to "in half the day" where typical occupancy is unavailable.
Source: MCS 032:2025 — The MCS Charitable Foundation
Annual electricity consumption3,500 kWh
Not established, so the method's default of 3,500 kWh is used — the mean, non-population-weighted British domestic consumption.
Source: MCS 032:2025 — The MCS Charitable Foundation
Annual generation from the PV system3,948 kWh
Row used: 3,900–4,199 kWh. Estimated by the Section 3 method.
Source: MCS 032:2025 — The MCS Charitable Foundation
Self-consumption without storage23%
910 kWh of the 3,948 kWh generated, from the "PV Only" column.
Source: MGD 003 — The MCS Charitable Foundation
Grid independence without storage26%
910 ÷ 3,500 kWh of demand.
Source: MCS 032:2025 — The MCS Charitable Foundation
Usable storage capacity10 kWh
Column used: ≥ 9.1, < 10.1 kWh. This is the capacity allocated to solar PV self-consumption, not necessarily the whole battery.
Source: MCS 032:2025 — The MCS Charitable Foundation
Self-consumption with storage69%
2,722 kWh of the 3,948 kWh generated.
Source: MGD 003 — The MCS Charitable Foundation
Grid independence with storage78%
2,722 ÷ 3,500 kWh of demand.
Source: MCS 032:2025 — The MCS Charitable Foundation

Assumptions

Cycles per year: 730: Two per day, which MCS sets as a limit rather than an expectation — the note to clause 4.3.1 says more cycles raise the benefit but shorten the battery's life, so the assumed number is capped.
What is not modelled: Money, degradation, changing allocation: The method produces kilowatt-hours only. It models no battery degradation, and clause 4.4.1's note accepts that the split between self-consumption and other services will move across a year — an average is to be assumed.
What this figure is: An average across similar homes: The standard is explicit that this is not a performance prediction for an individual property, but the average self-consumption for a sample of homes with similar occupancy, consumption and PV. Behaviour varies more than the table can.
Loads not included: EVs, heat pumps, diverters, electric heating: Electric space heating, hot water, swimming pools, heat pumps, power diverters and EV charging are outside the method (clause 5.1.4). A house with any of them will self-consume more than this says, by an amount the tables cannot give.
Period: First year: No PV or battery degradation is modelled, and the figure does not reflect the behaviour change that often follows an installation (clause 5.1.8, clause 5.1.13).
Battery operating mode: Self-consumption: The tables assume storage operated primarily to raise self-consumption. Time-of-use charging, backup reserve or grid services all reduce that benefit, and clause 5.1.11 requires the reduction to be calculated and communicated separately.
Annual consumption: 3,500 kWh: The method's own default where consumption cannot be established — the mean, non-population-weighted British domestic figure from UK Government sub-national statistics.

Where the numbers come from

The MCS Charitable Foundation — MCS 032:2025, Solar PV & Battery Pre-sale Information and System Performance Estimate Standard — Section 4, Electrical Energy Storage Systems (Issue 1.0, 01/01/2025) open
The MCS Charitable Foundation — MCS Solar PV Self-Consumption Lookup Tables (MGD 003) open
The MCS Charitable Foundation — Permission from MCS to use the published Irradiance Datasets in this tool
The MCS Charitable Foundation — MCS 032:2025, Solar PV & Battery Pre-sale Information and System Performance Estimate Standard — Section 5, Solar PV Self-Consumption (with and without EESS) (Issue 1.0, 01/01/2025) open

Self-consumption estimated by the method in MCS 032:2025 Section 5, using the lookup tables published by MCS and used with permission. This is not a performance prediction for this property: it is the average self-consumption across a sample of homes with similar occupancy, electricity consumption and PV system, for the first year, and it excludes electric vehicle charging, heat pumps, power diverters and electric space or water heating.

The pre-sale document you should be given

MCS 032:2025 Section 6 requires an installer to give you these figures, in this format, before you award the contract — together with the wording quoted underneath. It is reproduced here so you know what to ask for, and so you can hold a quote against it.

A. Solar PV installation data

Installed capacity of PV system – kWp (stc)	4.32kWp
Orientation of the PV system – degrees from south	45°
Inclination of system – degrees from horizontal	30°
Postcode region Bristol — the location MCS computed this zone's column for.	Zone 5E

B. Performance calculations

kWh/kWp (Kk) from table	914kWh/kWp
Shade Factor (SF)	1.00
Estimated annual output (kWp x Kk x SF)	3,948kWh

C. Estimated PV self-consumption – PV Only

Assumed occupancy archetype Not stated. Clause 5.2.2 Table 2 answers an unknown archetype with the “in half the day” table, and this is that table's figure.	Home half day
Assumed annual domestic electricity consumption Not stated. Clause 5.2.3(e)'s default of 3,500 kWh, the mean British domestic consumption.	3,500kWh
Expected solar PV self-consumption (PV Only)	910kWh
Grid electricity independence / Self-sufficiency (PV Only)	26%

Section 6 permits this section to be left out here: “Where occupancy archetype is not known (e.g. new build) then both sections C & D in the above table can be omitted (or marked as N/A).” It is shown anyway, because the method does have an answer and a stated assumption is more use than a gap.

D. Estimated PV self-consumption – with EESS

Assumed usable capacity of electrical energy storage device, which is used for self-consumption	10kWh
Expected solar PV self-consumption (with EESS)	2,722kWh
Grid electricity independence / Self-sufficiency (with EESS)	78%

E. Additional benefits from PV and EESS

EESS capacity not used for self-consumption	0kWh
Total energy discharged per annum	Not stated

The wording that must accompany the estimate

“Important Note: The performance of solar PV systems is impossible to predict with certainty due to the variability in the amount of solar radiation (sunlight) from location to location and from year to year. This estimate is based upon the standard MCS procedure is given as guidance only for the first year of generation. It should not be considered as a guarantee of performance.”
MCS 032:2025 clause 6.2.1 — every solar PV estimate is accompanied by this text.
“This system performance calculation has been undertaken using estimated values for array orientation, inclination or shading. Actual performance may be significantly lower or higher if the characteristics of the installed system vary from the estimated values.”
MCS 032:2025 clause 6.2.3 — orientation, inclination or shading are estimated rather than measured.
“Important Note: The energy performance and benefits of EESS is impossible to predict with certainty due to the numerous functions a system can be programmed to perform. This estimate is based upon the standard MCS procedure and is given as guidance only. It should not be considered as a guarantee of performance.”
MCS 032:2025 clause 6.3.1 — a second, separate Important Note wherever an EESS is installed.

What this calculation does not give you

Clause 6.2.4 and clause 6.3.2 require these in writing too. They describe the specific products quoted, so only the installer can supply them — this page is not a complete pre-sale pack and should not be presented as one.

Manufacturer's datasheet for the proposed solar modules (clause 6.2.4 b)
Manufacturer's datasheet for the proposed inverter (clause 6.2.4 c)
Manufacturer's datasheet for the Module Level Power Electronics Device, if applicable (clause 6.2.4 d)
Manufacturer's datasheet for the proposed EESS, if applicable (clause 6.2.4 e)
A drawing with the proposed module layout (clause 6.2.4 f)
The classification of the system, per MIS 3012 clause 2.2 (clause 6.3.2 b)
The battery type and any special precautions such as ventilation and fire safety (clause 6.3.2 c)
The physical characteristics of the system — size and weight (clause 6.3.2 d)
The proposed location of the system (clause 6.3.2 e)
Whether AC or DC coupled, and if using an existing in-situ inverter (clause 6.3.2 f)
Maximum power output in kilowatts, and maximum continuous current output in amperes (clause 6.3.2 g, h)
The usable storage capacity in kWh, accounting for the maximum allowable depth of discharge (clause 6.3.2 i)

The kWh in sections C and D are the full-precision lookup values, per clause 5.2.6(g). MCS's printed worked examples multiply by the rounded whole percentage instead, so a hand-check against the standard's examples will differ by a few kWh. The percentages match exactly.
Annual consumption was not supplied, so 3,500 kWh has been assumed. Consumption moves this figure more than almost anything else — a real meter reading from twelve months of bills is worth getting.
Occupancy was not supplied, so the "in half the day" table has been used, as the method directs. A household home all day self-consumes noticeably more, and one out all day noticeably less.

Where the numbers come from

The MCS Charitable Foundation — MCS 032:2025, Solar PV & Battery Pre-sale Information and System Performance Estimate Standard — Section 6, Pre-sale Information for Solar PV and EESS Systems (Issue 1.0, 01/01/2025) open
The MCS Charitable Foundation — MCS Irradiance Datasets — kWh/kWp (Kk) by postcode zone, inclination and orientation open
The MCS Charitable Foundation — Permission from MCS to use the published Irradiance Datasets in this tool
The MCS Charitable Foundation — MCS 032:2025, Solar PV & Battery Pre-sale Information and System Performance Estimate Standard — Section 3, Standard Estimation Method (Issue 1.0, 01/01/2025) open
The MCS Charitable Foundation — MIS 3002, The Solar PV Standard — clause 4.1 and Appendix B, Performance Estimation Method (Issue 6.0, 18/03/2026) open
The MCS Charitable Foundation — MCS Solar PV Self-Consumption Lookup Tables (MGD 003) open
The MCS Charitable Foundation — MCS 032:2025, Solar PV & Battery Pre-sale Information and System Performance Estimate Standard — Section 5, Solar PV Self-Consumption (with and without EESS) (Issue 1.0, 01/01/2025) open

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An estimate for the first year, not a guarantee. What a battery saves depends on the household's actual pattern of use — check the workings, and verify against your accreditation scheme's requirements before quoting from them.