Home solar energy systems can be a worthwhile investment, but they are not all made equal. Factors like panel orientation and the angle at which they meet the sun make a real difference. In this series I will explore the advantages and disadvantages of each roof direction and help you select the right system for a NW/SE split roof.
A NW/SE split is a common roof configuration in UK terrace and semi-detached housing, and one that is widely misunderstood.
You have a 4-bedroom house with a NW/SE split roof. The SE face catches morning and midday sun; the NW face gets late afternoon light in summer and very little in winter. This is not ideal for solar, but it is far from hopeless.
The SE face does most of the work, generating around 85% of what a south-facing roof would produce. The NW face contributes roughly 60%. Combined, you are looking at about 75% of south-facing output. That sounds like a penalty, but the SE face aligns well with morning and midday demand, and with the right system design, a NW/SE roof can still deliver strong returns.
What This Roof Must Optimise For
- Self-consumption over export. You generate less than a south-facing home. Every kWh you use directly saves 27.69p. Every kWh you export earns 5p. The gap is massive. Size the system so you consume as much as possible.
- Dual MPPT inverter. The two roof faces produce at different levels throughout the day. You need an inverter with two independent Maximum Power Point Trackers so each string operates at its own optimal voltage. A single-MPPT inverter would drag both strings down to the weaker face.
- Load more panels on the SE face. Put more of your panel budget on the stronger face. The NW panels are supporting actors.
- Battery storage is essential, not optional. With a NW/SE split, your generation peaks while you may not be home to use it. A battery captures that midday SE surplus and shifts it to your evening demand. Without one, you are exporting at 5p what you will buy back at 28p. The only roof orientation where going without a battery is less painful is an east/west split, because the generation spread naturally covers morning and evening demand peaks. On a NW/SE roof, you do not have that luxury.
Opportunities
The SE face generates power from early morning through early afternoon. If anyone is home during the day, works from home, or runs a heat pump, this generation profile matches your demand curve well. The NW face adds a small afternoon contribution in summer that extends your generation window. With a battery, the combination works surprisingly well because the spread of generation across the day means less clipping and a more even charge profile.
Your 4-Bed Consumption Profile
Low to Mid Consumption: 3,500 kWh/year
A 4-bed household using gas central heating and no electric vehicle typically consumes around 3,500 kWh of electricity per year (Ofgem Typical Domestic Consumption Values). That is roughly £970 at current rates. Your base loads are lighting, fridge/freezer, cooking, washing, and entertainment. Most demand concentrates in the morning (7-9am) and evening (5-9pm), with a dip during the day unless someone works from home.
High Consumption: 7,500+ kWh/year
If you run a heat pump, charge an EV at home, or have an electric oven alongside other high-draw appliances, you are in this bracket. A heat pump alone adds 3,000-5,000 kWh/year depending on your home's insulation. An EV adds 2,000-3,500 kWh/year depending on mileage. Your annual bill could hit £2,100+.
At this consumption level, your base load during daytime is significant. The heat pump cycles throughout the day, the hot water tank heats, and these loads overlap with SE face generation. This is actually good news for solar because you will self-consume a much higher proportion of what you generate. Your inverter needs to be at least 5kW to handle the base loads.
Budget Option
Solar Energy Concepts System Rating
| Metric | Score | Why |
|---|---|---|
| Cost | 4/10 | Accessible. DIY with battery around £3,500. Installed under £7,500. |
| Consumption Fit | Mid | Good match for 3,500 kWh homes. Undersized for heat pump households. |
| Tariff Exposure | 2/10 | Battery boosts self-consumption to 66%+. Very little depends on export rates. |
System Specification
Inverter: Solis 3.6kW 5G Hybrid EH1 (£575-653)
- AC output: 3.6kW (G98 compliant, notification only)
- 2 independent MPPTs, 1 string each
- Max DC input: 600V / 15A per MPPT / 5.7kW total
- MPPT range: 90-520V
- Hybrid design allows battery addition later without replacing the inverter
Overpanelling target: 140-150% of the 3.6kW AC rating = 5,040-5,400W DC. In UK conditions with a NW/SE roof, you will rarely clip. The extra panels pay for themselves in shoulder-hour generation (early morning, late afternoon, winter).
Panel Options
| Strategy | Panels | Total DC | Overpanel % | String Check |
|---|---|---|---|---|
| Best value | LONGi Hi-MO X6 455W x 12 (7 SE + 5 NW) — £73/panel | 5,460W | 152% | SE string Voc: 7 x 39.15V = 274V. NW string: 5 x 39.15V = 196V. Both within 90-520V MPPT range and under 600V max. Isc 14.79A under 15A limit. |
| Smallest footprint | Aiko Neostar 490W x 11 (7 SE + 4 NW) — 24.5% efficiency | 5,390W | 150% | SE: 7 x 40.98V = 287V. NW: 4 x 40.98V = 164V. Isc 14.93A under 15A limit. Saves one roof position. |
Battery
Target: ~6.4kWh usable (2/3 of daily low-mid consumption). This captures the SE face surplus and covers a typical evening peak without oversizing.
2x Pylontech US3000C (7.1kWh usable, £1,200-1,600) — a widely available option. Two modules stack easily alongside the Solis EH1 and share its BMS protocol. Alternatively, the Pylontech H48074 (7.4kWh, £900-1,100) is a newer single-unit option where it is available. Both hit the 6.4kWh target with a small headroom. Include a battery from day one: on a NW/SE roof the generation window is compressed, and without storage you will export most of your SE face output at 5p/kWh then buy it back at 28p in the evening.
Total system cost:
- DIY: £3,200-4,100 (panels £876 + inverter £615 + 2x Pylontech US3000C £1,200-1,600 + mounting/cables £500-1,000)
- Installed: £6,000-7,500
DIY Feasibility
A 3.6kW system is one of the most DIY-friendly setups. At 3.6kW AC output, it falls under the G98 threshold (3.68kW), which means you only need to notify your DNO, not apply for permission. The notification is a simple online form and takes 5 minutes. Most DNOs process it automatically.
You can mount the panels, run the DC cabling, and install the inverter yourself. You will need a qualified electrician to make the final AC connection to your consumer unit (Part P of building regulations). Budget £150-300 for this. No MCS certification is needed for the install itself, though you will not be eligible for SEG export payments without MCS. For a system sized for self-consumption, losing SEG income of £60/year is negligible.
Expected Performance
| Metric | Low-Mid (3,500 kWh) | High (7,500 kWh) |
|---|---|---|
| Annual yield | ~4,121 kWh | |
| Self-consumption (with 7.1kWh battery) | 66% (2,722 kWh) | 100% (4,121 kWh) |
| Export | 7% (309 kWh) | 0% (0 kWh) |
| Grid savings | £754/year | £1,141/year |
| Export income (SEG 5p) | £15/year | £0/year |
| Total annual saving | £769/year | £1,141/year |
Premium Option
Solar Energy Concepts System Rating
| Metric | Score | Why |
|---|---|---|
| Cost | 6/10 | Meaningful investment. Battery and MCS install add to the bill. |
| Consumption Fit | High | 5kW inverter + large battery handles heat pump and EV households comfortably. |
| Tariff Exposure | 2/10 | Battery maximises self-consumption. Very little ROI depends on export or tariff games. |
System Specification
Inverter: Solis 5.0kW S5 Smart Hybrid (£707-770)
- AC output: 5.0kW (requires G99 application, not just notification)
- 2 independent MPPTs, 1 string each
- Max DC input: 600V / 15A per MPPT / 8.0kW total
- MPPT range: 90-520V
- 8kW DC headroom gives excellent overpanelling potential
Overpanelling target: 140-150% of 5.0kW = 7,000-7,500W DC. The Solis 5kW accepts up to 8kW DC input, so you have headroom.
Panel Options
| Strategy | Panels | Total DC | Overpanel % | String Check |
|---|---|---|---|---|
| Best value | LONGi Hi-MO X6 455W x 16 (9 SE + 7 NW) — £73/panel | 7,280W | 146% | SE: 9 x 39.15V = 352V. NW: 7 x 39.15V = 274V. Both within range. Isc 14.79A under 15A. |
| Smallest footprint | Aiko Neostar 490W x 15 (9 SE + 6 NW) — 24.5% efficiency | 7,350W | 147% | SE: 9 x 40.98V = 369V. NW: 6 x 40.98V = 246V. Isc 14.93A OK. One fewer panel saves ~1.7m² roof space. |
Battery
Target: ≥14.4kWh usable (150% of daily low-mid consumption). Winter heat pump households need overnight cover — 13.5-14.4kWh bridges a full cold night. A smaller battery exports at 5p what you will pay 28p for the next morning.
Pylontech Force H2 14.3kWh (~£3,500-4,200) hits the target with 14.3kWh usable capacity and pairs natively with the Solis S5 via CAN bus. This is the recommended choice. Alternatively, Tesla Powerwall 3 (13.5kWh, £8,000-9,000 supply and install) and GivEnergy All-in-One 2 (13.5kWh, £5,500-6,500) are 0.9kWh short of the 14.4kWh target but are the go-to choices in this class — the difference is negligible in practice. The Powerwall 3 is installed-only; the GivEnergy AiO 2 includes its own inverter, so if you choose it, replace the Solis inverter line with the GivEnergy unit and adjust costs accordingly.
Total system cost (with Pylontech Force H2):
- DIY: £5,900-6,900 (panels £1,168 + inverter £740 + Pylontech Force H2 £3,500-4,200 + mounting/cables £500)
- MCS installed: £9,500-12,500
G99 and MCS
At 5kW AC output, this system exceeds the G98 threshold of 3.68kW. You must apply for G99 permission from your DNO before connecting. This is a formal application, not a notification. Most DNOs approve residential G99 within 45 days, but some regions (notably SSEN in Scotland and parts of Southern England) can take longer if the local grid is constrained.
MCS certification is recommended for the premium option because: (a) you qualify for SEG export payments, which become meaningful at this generation level, (b) the battery enables time-of-use tariff strategies that require a certified installation for some suppliers, and (c) it protects your home insurance and property value.
When This Makes Sense vs Overkill
Worth it if: you have a heat pump, charge an EV at home, or your annual consumption exceeds 5,000 kWh. The battery earns its keep by time-shifting generation to match your evening demand peak. At 7,500 kWh consumption, the premium system pays for itself in 6-7 years and delivers strong returns over 25 years.
Overkill if: your consumption is under 3,500 kWh and you have no plans to add a heat pump or EV. In that case, the budget option covers most of your demand and the extra spend on battery and larger inverter does not earn a proportional return. Start with the budget system and upgrade when your consumption justifies it.
Expected Performance
| Metric | Low-Mid (3,500 kWh) | High (7,500 kWh) |
|---|---|---|
| Annual yield | ~5,629 kWh | |
| Self-consumption (with 13.5kWh battery) | 53% (2,973 kWh) | 88% (4,957 kWh) |
| Export | 4% (202 kWh) | 12% (672 kWh) |
| Grid savings | £823/year | £1,373/year |
| Export income (SEG 5p) | £10/year | £34/year |
| Total annual saving | £833/year | £1,407/year |
Tariff Strategy and DNO Notes
Budget option: A flat-rate tariff is simplest. Your savings come from self-consumption, not clever tariff timing. If you want to optimise, Octopus Flux offers a reasonable export rate (~15p during peak hours) without requiring complex automation. Avoid Agile unless you enjoy monitoring half-hourly rates.
Premium option: Octopus Go or Intelligent Go is the natural fit. Charge your battery overnight at 7.5p/kWh, use it during the morning, then let solar take over from mid-morning through afternoon. The battery handles the evening peak. If your consumption is very high (EV + heat pump), Octopus Flux gives you better export rates during 4-7pm when the grid pays a premium.
DNO Region Considerations
G98 (budget, 3.6kW): Notification-only. All DNOs process this within days. No practical regional variation.
G99 (premium, 5kW): Application required. Turnaround varies by DNO:
- UKPN (London, South East, East): Generally fast, 20-30 working days
- WPD / National Grid ED (Midlands, South West, Wales): Moderate, 30-45 days
- NPG (North East, Yorkshire): Generally fast, 20-30 days
- SSEN (Scotland, parts of South): Can be slow, 45-60+ days. Known for grid constraint issues in rural areas
- ENW (North West): Moderate, 30-45 days
If you are in an SSEN area and planning a 5kW system, submit your G99 application early. Do not wait until the panels arrive.
Generation Estimates: PVGIS Source Data
Yield figures are sourced from the EU Joint Research Centre PVGIS tool. Location: 52.308N, 0.717W (mid-England). Slope 28deg, 14% system loss, crystalline silicon, building-integrated.
ROI Comparison
| Budget DIY | Budget Installed | Premium DIY | Premium MCS | |
|---|---|---|---|---|
| Low-Mid Consumption (3,500 kWh/year) | ||||
| Upfront cost | £3,650 | £6,750 | £6,400 | £11,000 |
| Annual saving | £769 | £769 | £833 | £833 |
| Payback | 4.7 years | 8.8 years | 7.7 years | 13.2 years |
| 25-year return | £15,575 | £12,475 | £14,425 | £9,825 |
| High Consumption (7,500 kWh/year) | ||||
| Upfront cost | £3,650 | £6,750 | £6,400 | £11,000 |
| Annual saving | £1,141 | £1,141 | £1,407 | £1,407 |
| Payback | 3.2 years | 5.9 years | 4.5 years | 7.8 years |
| 25-year return | £24,875 | £21,775 | £28,775 | £24,175 |
Assumes flat electricity rate of 27.69p/kWh, SEG at 5p/kWh, no energy inflation, and 0.5% annual panel degradation. Real returns are likely higher as energy prices tend to rise over 25 years.
Yield figures sourced from PVGIS (European Commission JRC), location 52.308N -0.717E, elevation 100m, slope 28 deg. SE face: azimuth -45 deg, 931 kWh/kWp/year. NW face: azimuth +135 deg, 644 kWh/kWp/year. 14% system loss, crystalline silicon, building-integrated mounting. Self-consumption calculated using a daily energy model: daily export = max(0, daily_generation – daily_consumption – battery_capacity). Consumption varies seasonally (+10% Nov-Feb, -5% May-Aug).
Related Guides
- Home Solar System Guide UK – Compare all roof orientations and house sizes
- Solar Panel Directory – Full specs and pricing for UK-available panels
- Are Solar Panels Worth It in 2026? – The complete ROI breakdown
- Choosing the Right Inverter – String vs hybrid vs micro
- Battery Storage Guide – Sizing, chemistry, and economics
- DIY Solar Installation Guide – Step by step
