For homeowners seeking true energy autonomy, an off-grid solar and battery system offers unparalleled benefits. Moving beyond grid-tied setups, an off-grid system, particularly one centred around robust Victron Energy components like the 10kVA MultiPlus and SmartSolar MPPT chargers, empowers you to generate, store, and manage your own electricity.
Why Off-Grid Means No DNO Notification (Usually)
One of the significant advantages of a truly off-grid system in the UK is the reduced, and often eliminated, need to inform your Distribution Network Operator (DNO). The key distinction lies in the system’s ability to operate entirely independently of the national grid.
A Victron MultiPlus inverter, configured for off-grid operation, typically has a completely isolated output for your home’s electrical loads. It does not export power back to the grid. If the system is designed to never feed power into the DNO’s network, then there’s no technical interaction requiring their notification or approval (like G98/G99 applications, which are for grid-connected generation).
Important Note: While a fully isolated off-grid system generally doesn’t require DNO notification, it’s always prudent to consult with a qualified electrician or installer who is well-versed in current UK regulations. They can ensure your specific installation design truly meets the criteria for exemption and provides the highest level of safety.
Off-Grid in the Home, Grid-Connected for Charging
This is where Victron Energy excels in offering flexibility. While your home operates primarily off your solar and battery power, the MultiPlus inverter/charger has an AC input that can be connected to the grid. This allows for:
- Grid Charging: In periods of prolonged low solar irradiance (e.g., deep winter, extended cloudy spells), you can use cheap off-peak grid electricity to top up your batteries. This provides a crucial backup and significantly enhances system resilience.
- Grid Assist/Passthrough: The MultiPlus can also act as an intelligent transfer switch, allowing grid power to bypass the inverter and supply your loads directly if your battery is low or if you have exceptionally high momentary demands that exceed the inverter’s capacity. This prevents system overload and ensures continuous power.
This hybrid functionality gives you the best of both worlds: energy independence for daily operation and the security of grid access when needed.
Unlimited Solar and Inverter Size: A Freedom for Off-Gridders
Unlike grid-tied systems that often face limitations on inverter size (e.g., 3.68kW export limits for G98 installations) and solar array capacity dictated by DNO regulations, an off-grid system offers remarkable freedom.
- Solar Array: You can install as many solar panels as you deem necessary to meet your energy demands, ensuring ample generation even in challenging conditions.
- Inverter Size: The inverter size is solely determined by your household’s peak power requirements. A 10kVA MultiPlus, for instance, provides a substantial 8kW continuous power output (at 0.8 power factor), capable of running most domestic appliances simultaneously.
This freedom allows for highly customised and robust systems, perfectly tailored to your energy consumption profile.
RenewSolar 50kWh Battery: The Heart of Your Off-Grid System
A significant battery bank is crucial for off-grid living, and RenewSolar’s 50kWh battery provides the necessary storage capacity. With a nominal capacity of 50,000 Wh, and given that Wh=V×Ah, if we assume a common Victron system voltage of 48V, then 50,000Wh/48V≈1041.67Ah. Let’s assume a 980Ah battery at 51.2V nominal for the 50kWh capacity.
Charging a 50kWh (980Ah) Battery with Victron’s AC Charger:
The Victron MultiPlus 10kVA has a powerful built-in AC charger. While the 10kVA model typically has a much higher charge current than 140A (often closer to 200A or more at 48VDC for a 10kVA unit), let’s calculate based on your stated 140A DC charge current.
- DC Charge Power: Power(W)=Current(A)×Voltage(V) Assuming a battery voltage of 51.2V (common for a 48V nominal LiFePO4 battery at around 50% SoC): 140A×51.2V=7168W=7.168kW
- Charging Time (from empty to full, theoretical): Time(hours)=Battery Capacity(kWh)/Charge Power(kW) 50kWh/7.168kW≈6.97 hours
Important Considerations for AC Charging:
- Efficiency Losses: There are always efficiency losses in the charging process (inverter conversion, battery internal resistance). Account for 10-15% losses, so actual charging time will be longer.
- Charge Curve: LiFePO4 batteries have a specific charge curve. The 140A will be sustained during the bulk phase, but the current will taper off during the absorption and float phases, extending the overall charge time.
- Grid Connection Limits: The actual AC power drawn from the grid for charging will be limited by your home’s mains fuse and the MultiPlus’s configurable input current limit.
Basic Summary of Kit Needed for an Off-Grid Victron Energy Installation:
- Victron MultiPlus 10kVA Inverter/Charger: The central brain, converting DC to AC and managing battery charging from solar or grid.
- Victron SmartSolar MPPT Charge Controllers: To efficiently harvest power from your solar panels and charge the battery. The size and number depend on your solar array.
- RenewSolar 50kWh LiFePO4 Battery Bank: For energy storage.
- Solar Panels: The array generating DC power.
- Battery Management System (BMS): Essential for LiFePO4 batteries to monitor cell voltages, temperatures, and ensure safe operation. Often integrated into modern battery packs or as a separate Victron Lynx Smart BMS.
- Victron Cerbo GX (or similar GX device): For comprehensive system monitoring, data logging, and remote control via the Victron VRM portal.
- DC Distribution & Fuses: For safe connection of batteries, MPPTs, and the MultiPlus. (e.g., Victron Lynx Distributor or similar).
- AC Distribution & Circuit Breakers: For safe connection of loads and grid input.
- Cabling: Appropriate DC and AC cabling, sized correctly for current and length.
- Safety Disconnects: DC isolators for solar and battery, AC isolators for grid and inverter output.
- Mounting Hardware: For solar panels and system components.
Solar Array Sizing and Performance (UK)
To achieve a 5-hour charge time from solar in summer and account for winter performance, we need to size the solar array carefully.
- 50kWh Battery Capacity (usable): We aim to recharge this amount.
- Summer Peak Sun Hours (PSH) in UK: Approximately 4-5 hours (average peak production equivalent).
- Winter Peak Sun Hours (PSH) in UK: Can be as low as 1-2 hours (average peak production equivalent).
Required Solar Array Size (for 5-hour summer charge):
- Solar Array Power(kWp)=Battery Capacity(kWh)/Desired Charge Time(hours)×Efficiency Factor
- Considering system losses (inverter, MPPT, cabling, battery efficiency), let’s use an overall efficiency factor of 0.8 (80%).
- 50kWh/5 hours/0.8=12.5kWp
A 12.5 kWp solar array would be a good target for a 5-hour summer charge. In reality, you might install more to account for sub-optimal days or future expansion.
Performance and Charging Times:
Let’s look at how this 12.5kWp array performs with varying loads and seasons.
| Scenario | Daily Load (kWh) | Season | Solar PSH (hours) | Solar Production (kWh/day) (12.5kWp * PSH) | Battery Charge from Solar (kWh) | Grid Charge Needed (kWh) | Grid Charge Time (hours) @ 7.168kW |
|---|---|---|---|---|---|---|---|
| Example 1 | 7 kWh | Summer | 5 | 12.5×5=62.5 | 50 (battery full) | 0 | 0 |
| 7 kWh | Winter | 2 | 12.5×2=25 | 7 (to cover load) + 18 (to store) = 25 | 0 | 0 | |
| Example 2 | 15 kWh | Summer | 5 | 12.5×5=62.5 | 15 (to cover load) + 35 (to store) = 50 | 0 | 0 |
| 15 kWh | Winter | 2 | 12.5×2=25 | 15 (to cover load) + 10 (to store) = 25 | 0 | 0 | |
| Example 3 | 25 kWh | Summer | 5 | 12.5×5=62.5 | 25 (to cover load) + 25 (to store) = 50 | 0 | 0 |
| 25 kWh | Winter | 2 | 12.5×2=25 | 25 (to cover load) + 0 (to store) = 25 | Need 25kWh for battery for next day, 0kWh produced | 7 hours (for full battery) |
be aware that this view is singular and does not account for longer periods, or mixed use and loads.
Analysis of Winter Performance and Grid Charging:
As seen in the table, winter dramatically impacts solar production. With only 2 peak sun hours, a 12.5kWp array yields 25kWh.
- For a 7kWh daily load, this is more than sufficient.
- For a 15kWh daily load, you’ll meet your daily consumption and still have 10kWh to put into the battery.
- For a 25kWh daily load, your solar will meet the day’s consumption, but there will be no surplus to charge the 50kWh battery for the next day’s autonomy. In this scenario, you would rely on grid charging to replenish the battery, requiring approximately 7 hours of grid charging to fill the 50kWh battery from empty (assuming no solar contribution or continuous load during charging).
This highlights the importance of grid charging in winter for off-grid homes with higher consumption to maintain battery levels.
Cost Savings and Annual Benefits
Let’s calculate the savings based on current electricity prices and a low grid charge rate for the off-grid system.
Assumptions:
- Grid electricity purchase price: £0.2654/kWh
- Grid electricity charge price (off-peak): £0.07/kWh
- Battery efficiency (round trip): 90% (LiFePO4)
Average Annual Solar Production Calculation: A 12.5kWp system in the UK can produce approximately 10,000 – 12,000 kWh annually in good conditions. For these calculations, let’s assume a conservative 8,000 kWh average annual production to account for real-world conditions and partial self-consumption.
Explanation of Savings:
The savings are primarily derived from avoiding the high retail electricity price. Even with grid charging in winter, the cost of that charging is significantly lower (£0.07/kWh) than the standard import rate (£0.2654/kWh). The more you rely on your solar and battery, the greater your savings.
An off-grid Victron Energy system with a substantial battery bank like the RenewSolar 50kWh battery offers not just financial savings but also unparalleled energy security and independence. While the initial investment is significant, the long-term benefits in terms of reduced bills and resilience against grid fluctuations make it a compelling solution for those seeking true energy autonomy.
NOTES:
Victron systems are modular and can cost more than other units available. the installation and set up of the system is longer. The use of average is not very real world and therefore there can be a large difference in saving as well as available power and performance. For the most part, 275 days of “good solar” apposed to 90 winter days. the power use and charge times will vary from install to install as well as the users use of the power, and what is stored.
Hardware: 10kva Victron inverter charger. 50kWh RenewSolar battery. Victron TR solar mppt (450/100) with multi array.
consider the array size and positions – this can account for charge time periods from the solar and should be off set for the best performance and winter bias can also assist.
Project management and installation and consultancy is available from RenewSolar.
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