- 1Hot tubs cost £500-£1,500/year to run, making them one of the most expensive home appliances. Solar can cut this by 50-70% with good scheduling.
- 2Hot tubs and solar are an excellent match: the constant heating demand absorbs surplus solar generation, boosting self-consumption from 35-45% to 50-70%.
- 3You’ll typically need 2-4kW of additional solar capacity on top of your household needs to offset hot tub running costs.
- 4The key strategy is to heat your hot tub during solar hours (10am-4pm). Treat it as a thermal battery that stores daytime energy for evening use.
Hot tubs are wonderful, until you see the electricity bill. A typical hot tub adds £500-£1,500 per year to your energy costs, making it one of the most expensive appliances you can own. That ongoing expense is why many hot tub owners start looking at solar panels.
The good news: solar and hot tubs are an excellent match. Hot tubs maintain temperature 24/7, creating a constant baseload that can absorb solar generation throughout the day. Unlike appliances that only run occasionally, your hot tub is always ready to use surplus solar, making self-consumption rates significantly higher than for households without one.
This guide covers everything you need to know about pairing solar with a hot tub, from understanding your hot tub’s electricity consumption to sizing a system, maximising self-consumption, and calculating realistic savings.
Understanding Hot Tub Electricity Consumption
How Much Electricity Does a Hot Tub Use?
Hot tub energy consumption varies significantly based on size, quality, usage, and climate:
| Hot Tub Type | Annual Use | Annual Cost (28p/kWh) |
|---|---|---|
| Small inflatable (2-4 person) | 2,000-3,500 kWh | £560-£980 |
| Mid-range portable (4-6 person) | 3,000-4,500 kWh | £840-£1,260 |
| Premium portable (5-7 person) | 3,500-5,000 kWh | £980-£1,400 |
| Large/luxury (7+ person) | 4,500-6,500 kWh | £1,260-£1,820 |
| Swim spa | 6,000-10,000 kWh | £1,680-£2,800 |
What Drives Hot Tub Energy Use
| Factor | Lower Consumption | Higher Consumption |
|---|---|---|
| Insulation quality | Full-foam insulated cabinet | Basic/partial or inflatable |
| Cover quality | Thick, well-fitted thermal cover | Thin, worn, or poorly-fitted |
| Set temperature | 36-37°C | 40°C |
| Usage frequency | 2-3 times per week | Daily use |
| Location | Sheltered, sunny spot | Exposed, windy, shaded |
| Season | Summer months | Winter (50-100% more) |
| Jet pump size | Smaller/fewer pumps | Multiple large pumps |
Daily Consumption Pattern
Understanding when your hot tub uses electricity helps with solar planning:
| Component | When It Runs | Power Draw |
|---|---|---|
| Heater | Cycles throughout day to maintain temp | 2-3kW when active |
| Circulation pump | Runs 4-24 hours daily | 0.1-0.3kW |
| Jet pumps | Only when in use | 1-3kW per pump |
| Ozonator/UV | Cycles with filtration | 0.01-0.05kW |
| Lights/controls | When in use | 0.01-0.1kW |
The heater is the main energy consumer, typically running 4-8 hours per day in cycles to maintain temperature. This creates an excellent baseload for absorbing solar generation.
Seasonal Variation
| Season | Hot Tub Energy Use | Solar Generation | Match Quality |
|---|---|---|---|
| Summer | Lower (less heat loss) | High | Excellent |
| Autumn/Spring | Moderate | Moderate | Good |
| Winter | Higher (more heat loss) | Low | Challenging |
The seasonal mismatch is the main challenge: hot tubs use most energy in winter when solar generates least. However, the summer surplus and year-round daytime heating cycles still make solar worthwhile.
Why Solar and Hot Tubs Work Well Together
The Self-Consumption Advantage
Hot tubs significantly boost solar self-consumption because:
- 24/7 heating demand: The heater cycles throughout the day, including peak solar hours
- Flexible timing: Modern hot tubs can be set to heat preferentially during the day
- Thermal storage: Heat the water during the day, use it in the evening
- High baseload: Creates constant demand to absorb solar generation
Self-Consumption Comparison
| Household Type | Typical Self-Consumption |
|---|---|
| Standard home, family out during day | 30-40% |
| WFH household | 45-55% |
| Standard home + hot tub | 50-65% |
| WFH household + hot tub | 60-75% |
| Home + hot tub + EV | 65-80% |
Key insight: Adding a hot tub can boost self-consumption by 15-25 percentage points, a significant improvement that directly increases your solar savings.
System Sizing
Additional Capacity for Hot Tub
If you’re installing solar partly to offset hot tub costs, you’ll need additional capacity beyond your household baseline:
| Hot Tub Type | Annual Use | Additional Solar Recommended |
|---|---|---|
| Small inflatable | 2,500 kWh | +2-2.5kW |
| Mid-range portable | 3,500 kWh | +2.5-3.5kW |
| Premium portable | 4,500 kWh | +3.5-4.5kW |
| Large/luxury | 5,500 kWh | +4-5kW |
| Swim spa | 8,000 kWh | +6-8kW |
For more guidance on system sizing, see our guide to how many solar panels you need.
Total System Sizing
Combine household needs with hot tub requirements:
| Scenario | Household | Hot Tub | Total | System |
|---|---|---|---|---|
| 3-bed + mid-range tub | 3,500 kWh | 3,500 kWh | 7,000 kWh | 6-7kW |
| 4-bed + premium tub | 4,500 kWh | 4,500 kWh | 9,000 kWh | 7-9kW |
| 4-bed + tub + EV | 4,500 kWh | 4,000 kWh | 11,000 kWh | 9-11kW |
| 5-bed + swim spa | 6,000 kWh | 8,000 kWh | 14,000 kWh | 11-14kW |
Costs and Savings
Installation Costs
| System Size | Panels | Cost | Suitable For |
|---|---|---|---|
| 5kW | 12 | £6,500-£7,500 | Small home + inflatable tub |
| 6kW | 14-15 | £7,500-£8,500 | 3-bed + mid-range tub |
| 7kW | 17 | £8,500-£9,500 | 3-4 bed + premium tub |
| 8kW | 19-20 | £9,500-£10,500 | 4-bed + tub + some EV |
| 10kW | 24 | £11,500-£12,500 | Larger home + swim spa |
For a full cost breakdown, see our solar panel cost guide.
Savings Calculation
Let’s calculate savings for a typical scenario:
System Details
Solar System
Hot Tub Cost Breakdown
| Hot tub cost before solar | £1,064/year |
| Solar allocated to hot tub (~40% of self-use) | ~1,224 kWh |
| Hot tub cost after solar | ~£721/year |
| Hot tub running cost reduction | ~32% |
With optimised timing (heating during day), the hot tub reduction can reach 50-60%.
25-Year Value
| Total savings (with 3% inflation) | £38,300 |
| Net profit after system cost | £30,300 |
| ROI | 379% |
Maximising Solar Use for Your Hot Tub
1. Schedule Heating for Daytime
Most modern hot tubs allow you to set heating schedules. Configure yours to heat primarily during solar generation hours:
- Main heating window: 10am-4pm (peak solar)
- Avoid overnight heating: Unless using cheap overnight rates
- Pre-heat before use: If using in the evening, boost temperature during afternoon
Some hot tubs have “economy” modes that only heat during set periods. Use these aligned with solar hours.
2. Use the Hot Tub as Thermal Storage
Water retains heat well. Strategy:
- Daytime: Heat water to higher temperature (e.g., 39-40°C) using solar
- Evening: Temperature drops slightly during use but started higher
- Overnight: Let temperature coast down (good cover reduces loss)
- Morning: Temperature has dropped to perhaps 36-37°C
- Next day: Solar reheats during the day
This approach maximises solar heating and minimises overnight grid electricity use.
3. Consider a Hot Tub Timer/Controller
Some aftermarket controllers can optimise hot tub heating for solar:
- Basic timer: £20-£50. Set heating schedule manually
- Smart plug (for smaller tubs): £15-£30. App-controlled scheduling
- Solar diverter integration: Some systems can prioritise hot tub heating
4. Improve Hot Tub Efficiency
Reducing total consumption makes solar go further:
| Improvement | Cost | Energy Saving |
|---|---|---|
| Replace worn cover | £200-£500 | 10-20% |
| Add floating thermal blanket | £30-£80 | 5-10% |
| Improve cabinet insulation | £100-£300 | 10-15% |
| Shelter from wind | Variable | 5-15% |
| Lower set temperature 1-2°C | Free | 10-15% |
| Reduce filtration cycles | Free | 5-10% |
5. Align Usage with Generation
If you’re flexible about when you use the hot tub:
- Weekend afternoons: Use while solar is still generating
- Summer evenings: Long daylight means solar generation continues
- Avoid late night sessions: These require heating with grid electricity
Solar Immersion Diverters and Hot Tubs
Can You Use a Diverter with a Hot Tub?
Standard immersion diverters (like the Eddi or iBoost) are designed for hot water cylinders with simple immersion heaters. Hot tubs are more complex:
Challenges:
- Hot tub heaters are controlled by the tub’s own system
- Most hot tubs won’t accept external power control to the heater directly
- Safety systems (temperature limits, flow sensors) must remain in control
Options:
- Timer-based approach: Schedule hot tub heating to match typical solar generation times
- Smart controller: Some newer hot tubs have smart features that can integrate with home energy systems
- Whole-circuit diversion: Power the entire hot tub from diverted solar (complex, requires electrician)
For most hot tub owners, a smart heating schedule aligned with solar hours is the practical approach rather than active diversion.
Battery Storage and Hot Tubs
Do You Need a Battery?
With a hot tub already providing a flexible load that can absorb daytime solar, the case for batteries changes:
| Scenario | Battery Value |
|---|---|
| Hot tub heating during day (good scheduling) | Lower: hot tub already absorbs surplus |
| Hot tub + high evening household use | Moderate: covers non-hot-tub loads |
| Hot tub + EV charging overnight | Higher: store solar for overnight EV |
| Time-of-use tariff | Higher: arbitrage opportunities |
A hot tub essentially acts like a “thermal battery,” storing energy as heat. This partially substitutes for an electrical battery, reducing (but not eliminating) the case for battery storage.
If You Do Add a Battery
Focus on sizing for non-hot-tub evening loads:
| Battery Size | Cost | Best For |
|---|---|---|
| 5kWh | £2,800-£3,800 | Covering evening household use |
| 8-10kWh | £4,000-£7,000 | Evening use + some overnight EV |
| 13kWh+ | £6,500-£8,500+ | Maximising self-consumption with EV |
Use our solar battery calculator to see if adding a battery makes financial sense for your situation.
Already Have Solar? Adding a Hot Tub
If you already have solar panels and are considering a hot tub, here’s how it affects your system:
Impact on Existing Solar System
| Metric | Before Hot Tub | After Hot Tub |
|---|---|---|
| Self-consumption | Lower (35-45%) | Higher (50-65%) |
| Export | More at lower rates | Less: more valuable self-use |
| Annual savings | Moderate | Higher |
Example: Existing 4kW System
Before Hot Tub
After Hot Tub
Your existing solar system becomes more valuable when you add a hot tub. You capture more benefit from the same generation.
Should You Expand Your System?
If your existing system is small relative to your new total consumption, consider expanding:
- Current generation covers old usage: Add 2-3kW for hot tub
- Current system was already undersized: Add 3-4kW or more
- Roof space available: Marginal cost of extra panels is low
- Planning future EV: Add extra capacity now
Adding panels to an existing system typically costs £800-£1,200 per additional kW (cheaper than initial installation due to shared costs).
Already Have a Hot Tub? Adding Solar
If you already have a hot tub and are considering solar specifically to reduce running costs:
The Case for Solar
- High baseline consumption: You’re already using 3,000-5,000+ kWh/year just for the hot tub
- Guaranteed self-consumption: Hot tub provides reliable load to absorb generation
- Strong payback: High usage = faster ROI
- Future-proofing: Solar benefits all electricity use, not just hot tub
Minimum Viable System
If budget is tight and you’re primarily focused on hot tub costs:
| Hot tub only focus | 3-4kW system |
| Cost | £4,500-£6,000 |
| Generation | 2,550-3,400 kWh/year |
| Hot tub cost reduction | 40-60% |
| Payback | 8-11 years |
However, we recommend sizing for total household needs. The marginal cost of additional panels is low, and you’ll benefit from solar on all electricity use.
Worked Examples
The Wilsons have a 4-bed house and have owned a premium hot tub for 3 years. They’re installing solar partly to reduce hot tub running costs.
Current Situation
Solar System
The Nguyens are building an extension and adding a hot tub, EV charger, and solar simultaneously.
Projected Use
Solar System
The Hendersons have a swim spa with much higher energy consumption.
Current Situation
Solar System
High-consumption swim spa owners see excellent solar returns due to the massive baseload for self-consumption.
Inflatable Hot Tubs: A Special Case
Inflatable hot tubs are increasingly popular but have different characteristics:
Inflatable vs Hard-Shell Hot Tubs
| Aspect | Inflatable | Hard-Shell |
|---|---|---|
| Purchase cost | £300-£800 | £3,000-£15,000+ |
| Insulation | Poor | Good to excellent |
| Annual electricity | 2,500-4,000 kWh | 2,500-5,500 kWh |
| Electricity per litre | Higher (poor insulation) | Lower (better insulation) |
| Seasonal use | Often summer only | Usually year-round |
| Heating time | 12-24 hours from cold | 8-12 hours from cold |
Solar Strategy for Inflatable Hot Tubs
If you have an inflatable hot tub:
- Summer-only use: Solar generation peaks when you’re using the tub, an excellent match
- Heat during the day: Start heating in the morning for evening use
- Don’t keep heated continuously: Poor insulation means high standby losses
- Consider upgrading: If you love your hot tub, a well-insulated hard-shell will cost less to run
Summary
Hot tubs and solar panels are a natural pairing. The hot tub’s constant heating demand creates an ideal load to absorb daytime solar generation, boosting self-consumption from typical rates of 35-45% to 50-70% or higher. This improved self-consumption accelerates payback and increases lifetime returns.
If you already have a hot tub, solar can cut your running costs by 50-70% with good scheduling. If you already have solar, adding a hot tub makes your existing system more valuable by capturing more generation for self-use. And if you’re planning both together, you’re setting yourself up for excellent economics.
The key is to heat your hot tub during solar generation hours. Treat it as a thermal battery that stores daytime solar energy for evening enjoyment. With this approach, your hot tub becomes not just a luxury, but a smart energy asset.
For general solar information, see our guide to solar panel systems. For cost details, see our solar panel cost guide.
Ready to get started? Use our UK solar panel calculator to estimate your costs and savings.
