It Is Not Solar or Battery — It Is About Timing

This is the question we get asked more than almost any other: should I get solar panels first, battery storage first, or both together?

They are not competing technologies. Solar generates free electricity. A battery stores it for later. The real question is which order makes the most financial sense for your home, your budget, and how you use energy.

Here is the honest breakdown.

Option 1: Solar Panels Only

What You Get

A typical 4kWp solar panel system generates around 3,600 kWh per year in Milton Keynes. Without a battery, you will use about 50% of that directly and export the rest to the grid via the Smart Export Guarantee (SEG).

Pros

  • Lower upfront cost: £6,500–8,500 for a fully installed 4kWp system (0% VAT until March 2027)
  • Immediate bill savings: Around £62–67/month average from day one
  • 50% self-consumption: Every kWh you use at home saves 28p at current grid rates
  • Fastest payback: 5–7 years, then 18–20 years of pure savings
  • SEG income: Export surplus at 7–15p/kWh — not as good as using it yourself, but still money coming in

Cons

  • Export at low rates: The 50% you export earns 7–15p/kWh rather than saving you 28p/kWh
  • No evening coverage: Peak household usage (5pm–9pm) happens after the sun goes down — you are back on the grid
  • Seasonal mismatch: Generates most in summer when you need least heating

Real Savings Example: Solar Only

  • Self-consumed: 150 kWh/month × 28p = £42 saved
  • Exported: 150 kWh/month × 10p (avg SEG) = £15 earned
  • Total: ~£57–67/month (£800–900/year)
  • System cost: £7,500 → Payback: ~6 years

Option 2: Battery Storage Only (No Solar)

What You Get

A standalone battery (typically 5–10kWh) that charges from the grid during cheap off-peak hours and powers your home during expensive peak hours. No solar generation — purely tariff arbitrage.

Pros

  • Time-of-use tariff savings: Buy electricity at 7–10p/kWh overnight, use it during peak at 28p+ — saving 18–21p per kWh shifted
  • Backup power: Some battery systems provide emergency power during grid outages
  • No roof requirements: Works for flats, north-facing roofs, or shaded properties

Cons

  • No free generation: You are still buying every kWh — just at a lower rate
  • Limited savings: A 5kWh battery shifting 5kWh/day saves roughly £25–35/month on a time-of-use tariff
  • 15+ year payback: At £2,500–4,000 for a standalone battery, the numbers are slow without solar feeding it free electricity
  • Tariff dependent: Savings disappear if your energy supplier changes their off-peak rates

Real Savings Example: Battery Only

  • Tariff arbitrage: 5 kWh/day × 18p saving × 30 days = £27/month
  • Total: ~£25–35/month (£300–420/year)
  • System cost: £3,000 → Payback: ~8–10 years on tariff alone, 15+ without a time-of-use tariff

Option 3: Solar + Battery Together

What You Get

A complete solar and battery package — panels generate free electricity during the day, the battery stores excess for evening use. This is where self-consumption jumps from 50% to 70%+ and the real savings stack up.

Pros

  • 70%+ self-consumption: Most of your solar generation is used in your home rather than exported at low rates
  • Best long-term savings: £78–88/month average (£115–150 in summer)
  • One installation visit: Cheaper than installing separately — you save on scaffolding, labour, and electrical work
  • Evening coverage: Battery powers the 5pm–9pm peak when grid electricity is most expensive
  • Double benefit: Free solar generation plus tariff arbitrage with overnight charging
  • Future-proof: Ready for EV charging, heat pumps, and rising energy prices

Cons

  • Higher upfront cost: £9,000–13,000 for a 4kWp solar system with 5–10kWh battery
  • Longer payback: 8–11 years (vs 5–7 for solar alone), though total lifetime savings are higher
  • Battery replacement: Batteries are warranted for 10–12 years. You may need one replacement over the 25-year life of your panels

Real Savings Example: Solar + Battery

  • Self-consumed: 210 kWh/month × 28p = £59 saved
  • Exported: 90 kWh/month × 10p (avg SEG) = £9 earned
  • Tariff arbitrage gains: £10–20/month
  • Total: ~£78–88/month (£1,000–1,150/year)
  • System cost: £11,000 → Payback: ~10 years

Side-by-Side Comparison

Solar Only Solar + Battery Battery Only
Upfront Cost £6,500–8,500 £9,000–13,000 £2,500–4,000
Monthly Savings £57–67 £78–88 £25–35
Annual Savings £800–900 £1,000–1,150 £300–420
Payback Period 5–7 years 8–11 years 15+ years
Self-Consumption ~50% 70%+ N/A
Evening Coverage No Yes Partial
25-Year Net Savings £14,000–16,000 £16,000–20,000 £3,500–6,500

When Battery Storage Makes the Most Sense

Adding a battery (alongside solar) makes the biggest difference if:

  • High evening usage: Families with kids home from school at 4pm, cooking dinner at 6pm, running the washing machine at 8pm. That is 60–70% of your daily usage happening after the sun drops off — exactly when a battery delivers
  • Time-of-use tariff: Tariffs like Octopus Flux or Intelligent Octopus let you charge from the grid at 7–10p/kWh overnight and avoid 28p+ during the day. A battery makes these tariffs work
  • EV charging overnight: If you have an EV charger, a battery can store cheap overnight electricity and feed your car without hammering your peak-rate bill
  • Backup power priority: If your area experiences frequent power cuts, or you work from home and cannot afford outages, a battery with backup capability is worth the premium
  • Planning to stay long-term: If you are staying in your home 10+ years, the combined system pays for itself and then some

When Solar Alone Is Enough

Solar without a battery is the right call if:

  • Daytime usage: You work from home, or someone is in the house during the day using appliances. Higher natural self-consumption means a battery adds less incremental value
  • Tight budget: Solar at £6,500–8,500 delivers the fastest payback. You can always add a battery later when prices drop or your budget allows
  • Small household: A couple with low evening usage may not store enough in a battery to justify the extra £2,500–5,000
  • Already on a good fixed tariff: If your evening electricity rate is already reasonable, the arbitrage savings from a battery are smaller

Our Recommendation

We have installed hundreds of systems across Milton Keynes and Buckinghamshire. Here is what we tell every customer:

If budget is tight, start with solar. It is the engine. Without panels generating free electricity, a battery has very little to store. Solar alone pays for itself in 5–7 years and delivers strong savings from month one. You can always retrofit a battery in 2–3 years when prices have dropped further.

If your budget allows, get both together. Installing solar and battery at the same time saves £500–1,000 on installation costs versus doing them separately (one scaffold, one electrician visit, one MCS registration). The combined savings of 70%+ self-consumption are significantly better than either technology alone.

Battery alone rarely makes sense. Without solar feeding it free electricity, a standalone battery is limited to tariff arbitrage — and the payback stretches beyond 15 years. The exception is if your roof genuinely cannot take panels (heavy shading, north-facing, listed building restrictions). In that case, a battery on a time-of-use tariff is better than nothing.

Use our free solar calculator to see which option makes the most financial sense for your specific home. It takes two minutes and gives you real numbers.

Can You Add a Battery Later?

Yes — and plenty of our customers do. If you start with solar-only, adding a battery later is straightforward. Here is what to know:

  • Compatibility: Most modern hybrid inverters are battery-ready. If your system has a hybrid inverter, adding a battery is a half-day job. If you have a string inverter, you will need an AC-coupled battery (like the Tesla Powerwall), which works alongside your existing setup
  • Cost: Retrofitting a battery typically costs £500–1,000 more than installing it alongside solar, due to the second site visit and additional electrical work
  • Timing: Battery prices have dropped 40% in the last five years and are expected to continue falling. Waiting 2–3 years could save you money on the battery itself

If you are considering this route, let us know when we install your panels. We will fit a battery-ready inverter so the upgrade is simple when you are ready. Read our full solar battery storage guide for more detail on how batteries work alongside solar.

Frequently Asked Questions

Is it worth getting a battery without solar panels?

Rarely. Without solar, a battery can only save money through time-of-use tariff arbitrage — buying cheap overnight electricity and using it during peak hours. This saves roughly £25–35/month, giving a payback period of 15+ years. Solar panels should almost always come first.

How much extra does a battery add to a solar installation?

A 5kWh battery adds approximately £2,500–3,500 to a solar installation when fitted at the same time. A 10kWh battery adds £4,000–5,500. Retrofitting later costs an additional £500–1,000 on top of these figures.

Should I get a bigger solar system or add a battery?

If your roof can take more panels, increasing system size from 4kWp to 5–6kWp (extra £1,500–2,500) often delivers better value than adding a battery — you generate more free electricity and the payback is faster. But if you already have a well-sized system and export heavily, a battery is the next logical step.

Do I need a battery for the Smart Export Guarantee?

No. The SEG pays you for electricity you export to the grid, whether you have a battery or not. In fact, a battery reduces your exports (because you store and use them instead), so your SEG payments will be lower with a battery — but your overall savings will be higher because self-consumed electricity is worth 28p/kWh vs 7–15p/kWh for exports.

What size battery do I need with solar panels?

For a typical 4kWp system, a 5kWh battery covers most evening usage for a 3–4 bedroom home. Larger households, homes with EV chargers, or those on time-of-use tariffs may benefit from 10kWh. We size every battery based on your actual usage data — get a personalised recommendation here.