When it comes to solar-powered air conditioning and heating, understanding how your system uses energy is key to maximizing performance and savings. Two common operating modes, solar-only and hybrid, offer different advantages depending on your setup, energy availability, and comfort expectations, as well as different solar power requirements.
What is Solar-Only Mode?
Solar-only mode means your heat pump runs exclusively on solar energy, using direct DC input from your solar panels, no inverter nor battery needed as solar panels are plugged in directly in the heat pump. There is no connection to the grid or generator in this mode.
This mode is a good fit for:
- Off-grid cabins, lodges, and remote buildings
- Eliminating grid or generator usage
- Daytime operation where solar production is strong
The key consideration is that operation depends entirely on available sunlight. If solar production drops below the unit’s requirement, the system will reduce output and eventually stop when solar power is unavailable.
What is Hybrid Mode?
Hybrid mode combines solar energy with grid (AC) power to ensure continuous operation. The system always prioritizes solar energy first and automatically supplements with grid power when needed.
This mode is a good fit for:
- Grid-connected homes or buildings
- Users who want reliable, 24/7 operation
- Installations with variable solar production
Hybrid mode combines solar and grid power (AC/DC), using available solar energy first and relying on the grid to ensure continuous operation under varying conditions.
Solar Power Requirements: Solar-Only vs Hybrid
One of the key differences between these two modes is how much solar power is required, and how your solar system behaves under real-world conditions.
Important, voltage limits are critical when designing your solar array:
Maximum VOC (open circuit voltage):
- Solar-only mode: 350 VOC max
- Hybrid mode: 380 VOC max
- Panels must be installed in series.
Exceeding these voltage limits will damage the heat pump and must be strictly avoided when configuring your panel strings. Always refer to the specifications of the solar panels you select. The sum of the open-circuit voltage (VOC) of all panels connected in series, adjusted for cold weather, must not exceed the maximum allowed voltage above.
Here’s how to calculate it:
- Take the VOC of one panel
- Apply a winter correction factor (typically ×1.21) to account for higher voltage in cold temperatures
- Multiply by the number of panels in series
Example:
- VOC of one 500 W panel = 39.58 V
- Adjusted VOC with winter correction = 39.58 V × 1.21 = 47.89 V
- Maximum allowed = 350 VDC
350 V ÷ 47.89 V = 7.30
This means you can install a maximum of 7 panels in series, for a total array size of approximately 3500W.
Always round down to stay within safe limits.
Solar-Only
In solar-only mode, your system relies entirely on solar input. This means your solar array must be sized not only for average conditions, but also to operate reliably during less favorable sunlight periods (cloud cover, early morning, late afternoon, seasonal variation), while accounting for higher power demand when the unit is running in heating mode.
Another key factor is startup power. When the unit starts, it requires a short burst of higher power. Startup requirement: approximately 900W to 1300W, depending on the model (see full technical details in the spec sheet here). If your solar array cannot meet this startup demand, the unit will fail to start or operate inconsistently in solar-only mode.
- 12,000 BTU unit: requires a minimum of 1400W of solar panels
- 18,000 BTU unit: requires a minimum of 1800W of solar panels
It’s strongly recommended to oversize your solar array, while staying within voltage limits, to account for less favorable weather conditions. Having more solar power ensures smooth operation and avoids system interruptions as well as startup failures.
Hybrid
In hybrid mode, the system can rely on the grid when solar production is insufficient. This gives you much more flexibility in sizing your solar array.
- The system uses solar power first whenever available
- The grid can automatically supplements any shortfall (including during startup)
- You can operate with less solar capacity while still benefiting from solar savings
Because the grid acts as a backup, hybrid mode can maintain stable operation during cloudy or variable weather, periods of lower solar production, and during startup when higher power is required.
In terms of solar sizing, hybrid mode allows for a smaller array while still delivering meaningful solar contribution:
- 12,000 BTU unit: typically effective with around 900W of solar panels
- 18,000 BTU unit: typically effective with around 1300W of solar panels
Key Differences at a Glance
| Feature | Solar-Only Mode | Hybrid Mode |
| Energy Source | Solar only (DC) | Solar (priority) + Grid (backup) |
| Operation Time | Daytime / solar-dependent | 24/7 operation |
| Reliability | Weather-dependent | Consistent |
| Solar Requirement | Higher | Lower |
| Best For | Off-grid applications | Grid-connected homes |
Which Mode Should You Choose?
Your choice depends on your priorities:
- Solar-only mode is best if your goal is energy independence and you’re operating off-grid. Just make sure your solar setup is properly sized.
- Hybrid mode is ideal if you want uninterrupted comfort with the flexibility to use solar whenever it’s available to save a great deal on energy costs.
Final Thoughts
Both modes are designed to maximize the value of solar energy, but they serve different needs. The main difference comes down to how much you rely on solar versus having a grid backup available.
By understanding these modes and their solar requirements, you can design a system that fits your lifestyle, your energy goals, and your environment.