Solar Savings With vs Without a Battery: UK Calculator Comparison

One of the most common questions is: Should I add battery storage to my plug-in solar system?

A 600Wh battery like the EcoFlow PowerStream adds ~£200–£300 to your system cost. In return, it captures your afternoon generation and lets you use it in the evening, when electricity would otherwise cost 30p/kWh. Sounds smart, but is the payback there?

This article compares savings with and without a battery, shows the real numbers, and helps you decide if battery storage makes financial sense for your situation.

The Battery Economics: Quick Math

Without a battery:

• Daytime solar = self-consumed or exported at 0p
• Evening demand = imported from grid at 30p/kWh
• Annual saving (800W, London): £256

With a 600Wh battery:

• Daytime solar = charged into battery or self-consumed
• Evening solar = stored and used from battery instead of grid import
• Reduced evening import = more savings
• Annual saving (800W, London): ~£300–£320
• Battery cost: ~£250
• Extra annual saving: ~£40–£60
• Payback on battery: 4–6 years

Bottom line: A battery adds £40–£60/year in savings, which takes 4–6 years to pay for itself. After that, it's pure profit. Over a 15–20 year lifespan, total extra profit is £400–£1,000.

The question becomes: Is a 4–6 year payback acceptable for a battery that costs £250? For some, yes. For others, it's marginal.

Real Comparison: Three Scenarios

Scenario 1: Standard Tariff (30p/kWh), No Time-of-Use

User profile: Average daytime load (out 3–4 hours/day during peak solar), evening peak (cooking, heating 6–9pm).

Without battery:

• Daytime solar (850 kWh/year): ~60% self-consumed (510 kWh), ~40% exported at 0p (340 kWh)
• Evening import: ~7 kWh/day at 30p = £2,555/year (baseline electricity cost)
• Solar self-consumption saving: 510 kWh × 30p = £153/year
• Total annual cost without solar: £2,555
• Total annual cost with solar: £2,555 - £153 = £2,402
• Annual saving: £153

With battery (600Wh):

• Daytime solar (850 kWh/year): captures in battery or self-consumed, reduces evening import
• Effective evening saving: ~40% of generation captured in battery = 340 kWh × 30p = £102/year
• Plus daytime self-consumption: 510 kWh × 30p = £153/year
• Total annual saving: £153 + £102 = £255/year
• Extra annual saving (battery): £255 - £153 = £102/year
• Battery cost: £250
• Battery payback: 2.5 years
• Over 20 years: £102 × 20 - £250 = £1,790 extra profit

Verdict: Battery pays for itself in 2.5 years. Worth doing.

(Note: This scenario assumes good evening load and successful battery charging throughout the day—realistic if you work from home or have high evening usage.)

Scenario 2: Time-of-Use Tariff (Octopus Flux, 15p peak, 5p off-peak)

User profile: Same as above, but with Octopus Flux (peak 4–9pm, off-peak rest of day).

Without battery:

• Daytime solar (peak hours 8am–4pm): ~500 kWh/year at 15p saved = £75
• Daytime solar (off-peak hours 4pm–6pm): ~100 kWh/year at 5p saved = £5
• Daytime solar (export): 250 kWh/year at 15p (Flux export reward) = £37.50
• Evening import (peak, 6–9pm without solar): still 3 hours at 15p = baseline £1,500/year
• With solar evening import reduced: savings on some evening peak
• Rough total annual saving: £150–£180

With battery:

• Battery stores afternoon generation and releases 6–9pm (peak time = 15p/kWh)
• Extra 100–120 kWh peak-time avoided = £15–£18/year
• Plus daytime self-consumption and export rewards
• Total annual saving: £165–£200
• Extra annual saving (battery): £15–£20/year
• Battery cost: £250
• Battery payback: 12–17 years

Verdict: On Flux, battery payback is longer (12+ years) because the tariff already makes daytime solar valuable. Battery adds only marginal benefit. Only worth it if you have very high evening usage.

Scenario 3: Standard Tariff + High Evening Usage (Work from Home)

User profile: Work from home, high daytime load (heating, cooking, work equipment), even higher evening load (cooking, heating, electric car charging 6–9pm).

Without battery:

• Daytime solar: 70% self-consumed (595 kWh), 30% exported at 0p (255 kWh)
• Evening import: ~8 kWh/day (higher than average) at 30p = £2,920/year
• Solar self-consumption saving: 595 kWh × 30p = £178.50/year
• Annual saving: £178.50

With battery:

• Daytime solar: 80% captured in battery or self-consumed (680 kWh), 20% exported (170 kWh)
• Evening import: ~6 kWh/day (reduced, some from battery) at 30p
• Solar savings: 680 kWh × 30p = £204/year
• Annual saving: £204
• Extra saving (battery): £25.50/year
• Battery cost: £250
• Battery payback: 9.8 years

Verdict: Better than Time-of-Use scenario (12 years), but still a long payback. Only worth it if battery also serves as backup power (storm resilience, grid outage protection), which adds emotional value beyond ROI.

Premium choice

EcoFlow PowerStream 800W + Delta 2

~£1,099 estimated

• 800W dual-panel kit with 1kWh Delta battery
• Store daytime solar for evening use
• Full home backup mode
• Smart scheduling via EcoFlow app

View on EcoFlow →

BSI-compliant kits expected from July 2026. Prices are estimates.

The Trade-Off: Battery Cost vs Benefit

Here's the universal trade-off:

Key insight: Battery works best with standard tariffs and high daytime/evening usage. Battery is least attractive with Time-of-Use tariffs (which already optimise pricing). The tariff is the bigger lever; battery is a secondary optimisation.

When a Battery Makes Sense

Battery is worth considering if:

1. You work from home or have high daytime load – battery captures afternoon surplus and stores it for evening
2. You're on a standard 30p tariff – you can't optimize with Time-of-Use, so battery is your only way to capture evening value
3. You have high evening usage – electric heating, cooking, or car charging 6–9pm makes evening power expensive and valuable
4. You value backup power – battery provides resilience during grid outages (emotional/safety value beyond ROI)
5. Your payback tolerance is 5–7 years – if you're okay with longer payback, battery can work

When a Battery Does NOT Make Sense

Skip the battery if:

1. You work away all day – daytime solar is mostly exported at 0p; battery can't capture value
2. You're on a Time-of-Use tariff – Octopus Flux already pays 15p/kWh for afternoon generation; battery adds only marginal value
3. You have low evening usage – heating off, minimal cooking, no car charging; evening import is low, so battery can't save much
4. You can't tolerate 5+ year payback – battery is expensive relative to the savings it enables
5. Cost is constrained – battery is optional. Spend on solar first; battery second

An Interesting Edge Case: Battery + Standard Tariff + Work from Home

This is the sweet spot where battery actually shines:

• User: Work from home, high daytime heating/AC, electric car charges 6–9pm (3 kWh/day)
• System: 800W solar + 600Wh battery
• Tariff: Standard 30p/kWh
• Daily scenario:
  • 8am–4pm: Solar generates ~2.8 kWh. You use ~1.5 kWh (heating, work). Battery captures 1.3 kWh.
  • 4pm–9pm: You use 3 kWh (car charging, evening load). Battery supplies 1.3 kWh, grid supplies 1.7 kWh.
  • Evening import: 1.7 kWh × 30p = £0.51/day = £186/year
  • Without battery: import 3 kWh × 30p = £0.90/day = £328/year
  • Battery benefit: £328 - £186 = £142/year
  • Battery cost: £250
  • Payback: 1.8 years ← Excellent

In this scenario, battery genuinely pays for itself quickly. But this requires:

• Work from home (or flexible schedule)
• High evening load (car charging is the key)
• Standard tariff (not time-of-use)

Most people don't tick all three boxes.

The Simple Decision Tree

Do you work from home or have high daytime load?
├─ YES
│  ├─ Are you on Octopus Flux or another Time-of-Use tariff?
│  │  ├─ YES → Skip battery (tariff already optimised)
│  │  └─ NO → Do you have high evening usage (car charging, heating)?
│  │     ├─ YES → Battery payback 4–5 years → Worth considering
│  │     └─ NO → Battery payback 5–6 years → Marginal
│  └─ NO → Skip battery (most generation exported at 0p)
└─ NO (work away)
   └─ Skip battery entirely (not cost-effective)

Real Case Study: London Flat, Work from Home, Octopus Flux

Scenario: Second-floor flat, south-east balcony, 800W vertical panels, works from home, Octopus Flux tariff.

Without battery:

• Annual generation: 663 kWh (vertical balcony = 78% of tilted)
• Daytime self-consumption (home all day): 450 kWh at 15p peak = £67.50
• Afternoon self-consumption (off-peak): 100 kWh at 5p = £5
• Export (off-peak afternoon): 113 kWh at 15p = £16.95
• Total annual saving: £89.45

With 600Wh battery:

• Captures afternoon generation: +80 kWh stored
• Evening use from battery (6–9pm = peak): saves 80 kWh × 15p = £12/year
• Plus same daytime and export = ~£89
• Total annual saving: ~£101
• Extra saving (battery): £12/year
• Battery cost: £250
• Payback: 20+ years ← Not worth it

Verdict: Even with Time-of-Use and work-from-home, vertical balcony panels don't generate enough to make battery worthwhile. Battery payback is too long.

Comparing Battery to Tariff Switching

Here's a question many people miss: Is battery a better investment than switching to a better tariff?

Scenario: Standard 30p tariff, work from home, low evening usage

Option A: Add a battery (£250)

• Extra annual saving: £40/year
• Payback: 6.25 years

Option B: Switch to Octopus Flux (free)

• Extra annual saving: £50–£80/year
• Payback: Immediate
• 10-year benefit: £500–£800 vs battery's £400–£200

Verdict: Switch tariff first (free, 20–30% ROI improvement). Then consider battery if you want to spend extra capital.

Key Takeaways

• Battery adds £40–£60/year in savings – via evening load shifting
• Battery payback: 4–6 years for work-from-home; 12+ years on Time-of-Use tariffs
• Battery works best with: Standard tariff + high daytime load + high evening usage
• Battery doesn't work with: Work away + standard tariff, or any usage on Time-of-Use tariff
• Switch tariff first – free, improves savings by 20–30%, better ROI than battery
• Battery is optional – solar alone (no battery) pays for itself in 3.1 years; battery is a secondary optimisation

Next Steps

1. Check your tariff – are you on standard (30p flat) or Time-of-Use (Octopus Flux)?
2. Assess your daytime load – work from home or work away?
3. Calculate without battery – run the calculator without battery
4. Estimate with battery – add £40–£60/year and subtract £250 cost to see payback
5. Decide: If payback <5 years, consider it. If >7 years, skip it and invest elsewhere

Ready to calculate your exact scenario? Run the calculator with and without battery to compare.