Autonomy scoreLocal analysis
Portsmouth Home autonomy potential in Portsmouth (England)
The strongest asset here is Food growing. It is not, however, what pays your home the most: that is Low-carbon heating.
Annual potential, standard home
£4,231
Four items added up — each one is a separate decision, in whatever order suits you.
Overall score
61 /100
Advanced
Portsmouth: 61/100 achievable autonomy with a recommended setup.
Strong potential — high self-sufficiency in energy, water & food is well within reach.
What you could reach in Portsmouth
A typical home in Portsmouth can reach about 61% self-sufficiency with a right-sized solar, storage, rainwater and low-carbon heating setup — much of it backed by UK grants and 0% VAT. The figure sharpens once you enter your own home.
- ≈218 days a year off the grid — keep the fridge, lights, router and heating pump running straight from your own roof and battery, right through a winter outage.
- Rainwater self-reliance — ≈66,300 L harvested from a 100 m² roof covers the garden and toilet flushing, so hosepipe bans stop mattering.
- A real harvest — ≈320 kg of fresh vegetables over a ≈306-day frost-free season takes a genuine bite out of the weekly shop.
- A warm, low-bill winter — insulation plus a right-sized heat pump turns the local climate into low-carbon comfort and shields you from gas-price spikes.
From the most to the least profitable, here
What you could gain
-
Low-carbon heating60/100
~£2,185/yr
less heating after insulation + heat pump (−7,560 kWh/yr on 90 m², electric heating)
The detail
Realistic outlook
2,420 heating-degree-days: a high-efficiency heat pump is the lowest-carbon way to keep Portsmouth warm.
Watch-outs
A heat pump only pays off in a well-insulated envelope — insulate first, then size the unit.
Grants & tips
Boiler Upgrade Scheme: £7,500 towards an air-source heat pump (England & Wales); ECO4 and the Great British Insulation Scheme fund insulation, plus 0% VAT on heat pumps.
Heating-degree-days (base 18°C) : ≈ 2,420 HDD — Source: PVGIS, hourly ERA5 temperatures 2005–2015 (base 18°C).
-
Food growing70/100
~£941/yr
off the weekly shop — up to ≈320 kg/yr of fresh vegetables from 100 m²
The detail
Realistic outlook
With about 306 frost-free days, a household garden in Portsmouth supports up to three planting rotations a year.
Watch-outs
A productive garden needs space, decent soil and a few hours a week — start small and scale up.
Grants & tips
Council allotments (Allotments Act) give cheap growing plots; RHS and community-garden schemes support home food production.
Frost-free growing season : ≈ 306 days — Source: PVGIS, hourly ERA5 temperatures 2005–2015 (frost dates).
-
Solar energy60/100
~£845/yr
less electricity with 3 kWp on your roof (≈3,381 kWh/yr)
The detail
Realistic outlook
At 1,127 kWh/kWp per year, Portsmouth offers solid potential for residential rooftop solar.
Watch-outs
Roof orientation, shading and DNO connection rules affect real output — get an MCS-certified site assessment first.
Grants & tips
Smart Export Guarantee (SEG): your supplier pays for surplus solar exported to the grid, plus 0% VAT on residential solar PV and battery storage until 2027.
Annual PV yield : 1,127 kWh/kWp — Source: PVGIS 5.2 (EU Joint Research Centre), optimal tilt and local horizon.
-
Rainwater54/100
~£260/yr
less mains water with a 5,000 L tank (≈66,300 L/yr harvestable from a 100 m² roof)
The detail
Realistic outlook
780 mm of rain a year makes rooftop rainwater harvesting worthwhile in Portsmouth.
Watch-outs
Harvested rain is non-potable by default — keep it separate from drinking water and add a first-flush diverter.
Grants & tips
Many UK water companies offer subsidised or free water butts; on a metered supply, harvested rainwater cuts your water bill directly.
Average annual rainfall : 780 mm — Source: NASA POWER, MERRA-2 corrected precipitation.
£4,231
Ranked by annual value. The order of the works themselves does not change: insulate before you equip.
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Estimate your solar system in Portsmouth
Estimate your solar system in Portsmouth
Based on a local yield of 1,127 kWh/kWp per year.
Indicative estimate (production = kWp × local yield). Real output depends on roof orientation, shading and your self-consumption rate.
Climate month by month in Portsmouth
In Portsmouth, a 3 kWp array pitched at 40° and facing 2° west of south — the optimum PVGIS computes for this location — produces about 3,381 kWh a year. July is the strongest month, at about 414 kWh, and December the weakest, at 123 kWh. November to February bring 17% of the year's output — enough for a battery to cover winter evenings on sunny days, not through grey spells.
The heating season runs from October to May: 8 months average below 15 °C, and February is the coldest at 5.9 °C. In a typical year the coldest hours drop to about 1 °C, the point a heat pump has to be sized for: mild conditions, the easiest case for any heat pump.
The last frost comes around early March, and autumn stays frost-free until the year turns — about 306 frost-free days; tender crops go outside after early March. Days above 30 °C are rare, so summer care is mostly steady watering.
Mean wind at 10 m is 4.7 m/s: borderline for a small turbine, which would need an exposed, unobstructed mast to pay off. The southern horizon is open (at most 1.1°) in PVGIS's elevation model, so low winter sun reaches roofs unless nearby buildings block it.
Compared with Southampton, 24 km away, Portsmouth has 4% more solar yield, 60 more frost-free days and a heating need 7% lower. Compared with Reading, 71 km away, Portsmouth has 10% more solar yield, 86 more frost-free days and a heating need 13% lower.
| Month | Mean temperature | Solar output, 3 kWp |
|---|---|---|
| January | 6.6 °C | 129 kWh |
| February | 5.9 °C | 180 kWh |
| March | 7.0 °C | 297 kWh |
| April | 9.6 °C | 384 kWh |
| May | 12.2 °C | 399 kWh |
| June | 15.1 °C | 411 kWh |
| July | 17.1 °C | 414 kWh |
| August | 17.0 °C | 360 kWh |
| September | 15.7 °C | 312 kWh |
| October | 13.5 °C | 216 kWh |
| November | 9.9 °C | 153 kWh |
| December | 7.3 °C | 123 kWh |
Frequently asked questions — Portsmouth
How much could solar panels generate in Portsmouth?
A well-oriented 3 kWp rooftop array in Portsmouth produces about 3,381 kWh a year, worth roughly £845 in self-consumption. A 6 kWp system reaches about 6,762 kWh/yr where the roof allows. Smart Export Guarantee (SEG): your supplier pays for surplus solar exported to the grid, plus 0% VAT on residential solar PV and battery storage until 2027.
Is rainwater harvesting worth it in Portsmouth?
Yes. A 60 m² roof in Portsmouth can capture about 39,780 litres a year for the garden, WC and washing machine. Keep harvested rain separate from drinking water and fit a first-flush diverter. Many UK water companies offer subsidised or free water butts; on a metered supply, harvested rainwater cuts your water bill directly.
What grants help with low-carbon heating in Portsmouth?
Boiler Upgrade Scheme: £7,500 towards an air-source heat pump (England & Wales); ECO4 and the Great British Insulation Scheme fund insulation, plus 0% VAT on heat pumps. Insulate first — a heat pump only pays off in a well-insulated home (2,420 heating-degree-days here), so prioritise the roof and walls before sizing the unit.
How much food can a garden grow in Portsmouth?
With about 306 frost-free days, a 100 m² garden in Portsmouth yields roughly 320 kg of fresh fruit and vegetables a year — a partial share of a household's needs, not full calorie autonomy. Council allotments (Allotments Act) give cheap growing plots; RHS and community-garden schemes support home food production.
When is the last frost in Portsmouth?
The last frost comes around early March, and autumn stays frost-free until the year turns — about 306 frost-free days; tender crops go outside after early March.
How much does solar produce in winter in Portsmouth?
December is the weakest month: a 3 kWp array makes about 123 kWh, against 414 kWh in July. November to February add up to 17% of the yearly total.
How this score is calculated
Public climate data (PVGIS, European Commission) weighted by how vital each dimension is. The score sharpens once you enter your own home. See the full methodology.
Sources
- Solar energy — Source: PVGIS 5.2 (EU Joint Research Centre), optimal tilt and local horizon.
- Rainwater — Source: NASA POWER, MERRA-2 corrected precipitation.
- Food growing — Source: PVGIS, hourly ERA5 temperatures 2005–2015 (frost dates).
- Low-carbon heating — Source: PVGIS, hourly ERA5 temperatures 2005–2015 (base 18°C).
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