Solar and Battery Storage in Hampshire

What a Solar and Battery System Does to a Household’s Electricity

Take a 4 kW south-facing array on the Hampshire coast, which PVGIS models at about 4,526 kWh a year, on a medium-use household (Ofgem’s typical 2,500 kWh a year) that is part of the day at home, so 45% of its use falls in solar hours. At the 26.32p price cap and 12p export rate, the model gives:

Benefit = electricity you avoid buying at 26.32p plus export income at 12p. Cost = DESNZ South East solar cost (£1,859/kW up to 4 kW) plus a battery priced from Octopus’s published £3,947 (5 kWh) and £5,336 (10 kWh). Model: monthly average day, PVGIS yields, 90% battery round-trip efficiency, flat demand; no degradation, price changes or standing charges. EU JRC PVGIS 5.3, PVGIS-SARAH3 2005-2023, 14% system loss; DESNZ Solar PV cost data 2025/26 (published 28 May 2026), South East mean; Octopus Energy, battery-only installation (April 2026 prices, read 7 October 2026); Ofgem energy price cap, 1 October to 31 December 2026; Octopus Outgoing, region H (OUTGOING-VAR-24-10-26, from 1 March 2026); Ofgem typical domestic consumption values, from 1 July 2026

Two things stand out. First, a 4 kW array on a medium home uses well under half of what it makes: it cannot use more than the home consumes, so claims that panels and a battery let you “use up to 80% of what you generate” do not survive arithmetic for a modest household. Second, the battery earns the least per pound. A 5 kWh battery adds £133 a year here and takes 30 years to repay itself; a second 5 kWh adds almost nothing. The panels do the heavy lifting.

It depends on who is at home

The biggest variable is how much of your use falls in daylight, which you control and we cannot measure for you. Same array, same medium household, 5 kWh battery:

Daytime share of use is an assumption you can change in the calculator. The less you are home, the more a battery is worth — and the less the panels alone are.

And on how much electricity you use

Same 4 kW array, 45% of use in solar hours. A high-use home gets more from both; a low-use home gets little from a battery.

A Year of a 4 kW Array and a 5 kWh Battery, Month by Month

Averages hide the shape of the year. This is the same 4 kW array, the same medium household and a 5 kWh battery, month by month, from PVGIS yields and the model above (kWh per month):

Same assumptions as the tables above. A monthly average day smooths out cloudy days, so it flatters the battery slightly. EU JRC PVGIS 5.3, PVGIS-SARAH3 2005-2023, 14% system loss

The array makes about 151 kWh in December and about 562 kWh in June — roughly 4 times as much in midsummer. The battery has surplus to store and use in March, April, May, June, July, August, September, October; in no months it is mostly idle, because there is little surplus to charge it from. That is why a battery that charges only from your own panels earns least in the months you most want it, and why a cheap overnight tariff is what keeps one working through the winter.

How Big Should the Array Be? Start With Your Annual kWh

Fill every square metre of roof and you export more at 12p, so each extra kW earns progressively less. The same medium household, solar only, part of the day at home:

DESNZ South East mean: £1,859/kW up to 4 kW, £1,721/kW from 4 to 10 kW. Same model and assumptions as above.

The pattern: smaller arrays use a larger share of what they make and repay slightly faster per pound, while larger arrays earn more in total. Neither is wrong; the right size is the one that fits your usage and your roof. We size from twelve months of bills, not from the roof area.

Smart Export Guarantee, and What It Needs

A Smart Export Guarantee tariff pays for the electricity you export, and it requires an MCS-certified solar installation. Solent Solar’s MCS certificate for solar PV is NIC-40078294 (certified by NICEIC), which you can check on the MCS directory. Outgoing Octopus pays 12.0p/kWh flat from 1 March 2026; other suppliers pay differently, and the lowest rates are only 3–4p, which is why choosing an export tariff matters as much as choosing a battery. Our Smart Export Guarantee rates guide compares them.

What to Check on Any Solar and Battery Quote

A quote is only comparable if it says the same things. Ask every installer — including us — for these, in writing:

• Usable kWh, not just the label. A battery sold as “10 kWh” may deliver less than that; the datasheet states usable energy.
• Inverter rating, and whether it is a hybrid. The inverter limits how fast the battery can charge and discharge, and whether it works with the panels or sits beside them.
• The warranty in the manufacturer’s own document: years, the capacity it guarantees to keep, the throughput floor, and who may make a claim. Our best solar battery comparison shows how to read one.
• Backup. Whole-home or essential circuits only, and whether the hardware is in the price. A battery does not keep the lights on in a power cut by default.
• The export arrangement. Which Smart Export Guarantee tariff, and the MCS certificate for the solar installation that SEG payments require.
• Network paperwork. A G98 notification or a G99 application, prepared and submitted by the installer.
• What is included. Scaffold, mounting, electrical work, certificates, commissioning and the monitoring set-up.
• The VAT rate stated. 0% to 31 March 2027 and 5% after that; a quote that is silent on it is not a quote.
• A fixed written price after a survey, and the deposit terms. For comparison, Octopus asks a £500 non-refundable advance payment.

If a figure on a quote cannot be traced to a document, it is the installer’s promise, not the product’s. That goes for the percentages in a savings projection too — which is why every number on this page shows how it was worked out.