WHAT DOES THE 3.68KW LIMIT PER PHASE MEAN WHEN INSTALLING SOLAR PANELS?

solar inverter’s maximum output DOES NOT relate to the solar capacity able to be installed.

Getting AC output confused with the DC capacity of the solar array could cost you £000’s in the long run by not using the solar panel inverter to it’s full potential.

The 3.68kW limit per phase (before permission is required) relates to the AC OUTPUT of the solar panel inverter not the CAPACITY of the solar panel system. 

The DNO (grid) has a limit on the amount of output you can connect to the grid without needing permission. Output and PV capacity are not the same or directly comparable. It’s important to understand the difference to ensure you get the most productive system possible and avoid missing out on £000’s in lost generation. We explain below. 

Ensure that your system designer or salesman understands the difference to avoid ending up with a significantly underperforming system.

First, let us explain what the capacity of a solar panel system means…

The capacity relates to how much energy the solar panels would produce under standard test conditions (Irradiance: 1000W/m2 at a temperature of 25 degrees celsius).

The headline figure is not a maximum or a rating. Remember – solar capacity tells lies.

Therefore a 4kW solar array operating within an environment of constant irradiance of 1000W/m2 @ 25 degrees would generate 4000Wh during those conditions (before any system losses).

In the real world, especially in the UK, irradiance fluctuates significantly. Here in Hove, we can expect irradiance to fluctuate from 0W/m2 (night) to 1200W/m2  (clear sky at midday around the height of summer).

Which is why choosing a solar panel with good low light efficiency is key – don’t just look at the headline figure.

 

“By following bad advice regarding output limits you could be costing yourself £000’s.”

— Thomas Moyes, Director of Leoht Ltd

 

What does this mean in practice?

In the example shown (right),we have a south-facing, unshaded 16-panel, 6.2kW system with a good quality 3.68kW solar inverter.

According to the weather station at Birmingham airport, the maximum irradiance the array will receive is 1006W/m2. Irradiance fluctuates significantly throughout the day/year.

Therefore, during the summer we can assume, on a clear day from 12-1 pm the array will produce 6.23kWh. (for illustration purposes, excludes system losses).

The solar panel inverter can deliver 3.68kWh to the AC side.

2.55kWh is ‘AC clipped’ – lost as heat via the inverter and/or module or the maximum power point trackers (MPPT) will turn the amps down.

The simulation software calculates the yearly losses to ‘AC clipping’ for us:

190 kWh is lost per year to AC clipping – worth £6.65 – £32.30 depending on whether or not you can use the energy.

Total output of 6.2kW array (after AC clipping) = 5908 kWh

What if we installed a 4kW solar system instead “because 4 is closer to 3.68”
The same model (right) but with a 4kW system installed with the same inverter.

AC clipping: 0 kWh

Total output: 4095 kWh

Resulting in 1813 kWh less production per year.

Or enough energy to power an average family home for 11.9 YEARS over the lifetime of the system.

Is a 3.6 kW inverter limited to producing 3.6 kW?

No. A good 3.6 kW hybrid inverter can also charge the battery directly using DC generated by the solar panels. This is called DC-coupling, and it allows for more efficient charging of the battery as it does not require the energy to be converted to AC and back to DC again. DC-coupled systems can also provide better performance in low light conditions, as the energy from the solar panels goes directly to the battery, rather than being converted to AC and losing some energy in the process.

The maximum energy generated by a good 3.6 kW inverter, such as Q Cells Q.CORE.HOME or a GivEnergy hybrid inverter is the maximum AC output plus the maximum battery charge capacity.

Make sure your designer is aware of the capabilities of the proposed system and how AC clipping works or you might miss out on a lot of energy.

The image to the right was taken from a 7 kW solar array with a 3.6 kW GivEnergy hybrid inverter at 11.37 am on 18.03.2023. Because there was capacity left in the battery, the system was able to take full advantage of a sunny spell in the winter.

How many solar panels do I need? Try our calculator and find out in 30 seconds.

faq’s about solar panel systems

One for the zoom family quiz!

In 1921, Albert Einstein won his first and only Nobel prize for his work on describing the photoelectric effect.

In a nutshell, light (a beam of particles) knocks off electrons from the solar cell; the solar cells direct these electrons along a current – creating electricity. In theory, solar panels could last forever as there are no moving parts.

 

Find out more

Solar power panel efficiency has increased significantly over the last ten years so you might be surprised at how much electricity even a small roof could generate.

The smallest system we would recommend would be 9 x 380W panels, covering an area of 17 square meters. (4m x 4.25m).

 

How many solar panels do I need?

No. It’s a common myth. Whilst south facing is the most optimum facing position, as a rule of thumb – an identical East or West facing roof would generate 85% as much energy as the south-facing roof.

You may prefer to have an east and west facing roof than the south and north-facing roof as you could fit twice as many electric residential solar panels on the east/west roof than just south facing.

Even a North facing roof will generate approx 55% as much energy as a south-facing roof. For example, a 20 year old 10% efficient south-facing solar panel would generate approximately the same amount of energy as a modern north-facing solar panel.

 

How do solar panels generate electricity

The installation of solar panels on residential buildings are considered permitted development so you do not require planning permission if they comply with the following conditions.

There are necessary limits and conditions which must be complied with to benefit from permitted development rights.

  • Solar panels should not be installed above the highest part of the roof and should not project more than 200mm from the roof slope or wall surface.
  • Installers should not install solar panels on a building that is within the grounds of a listed building or on a site designated as a scheduled monument.
  • If your property is in a conservation area, or a World Heritage Site, you must not install solar panels on a wall that faces a highway.

Feel free to reach out to us to buy solar panels in the UK & switch to a sustainable lifestyle. Give us a call at 01273 286 627 and request for a free design and quote.

 

Planning Portal

The district network operator (DNO) is the company responsible for distributing electricity from the national grid to your home. Installers must inform the DNO of your installation within 28 days after the date of installation. Leoht will handle this for you.

You do not require permission for systems under 16 amps per phase (3.68kW single-phase or 11.04kW three-phase supply). All of the residential solar panel systems that we install fall into this category. System sizes are based on the AC inverter rating rather than the peak DC output of the solar system.

“By following bad advice regarding output limits you could be costing yourself £000’s.”

 

Find out more

Not on their own. But it is possible when combined with a time of use tariff and energy storage – depending on the time of use tariff and smart export guarantee rates.

For example, Octopus Go tariff pays 5.5p/kWh for every unit exported and charges 5p/kWh for off-peak use from 00:30 – 04:30. You could install solar panels that generate the equivalent of 100%+ of your electricity consumption and earn 5.5p/kWh for every unit exported to pay for topping up the batteries in the winter at 5p/kWh.

Your bills could even go negative if you can generate more than you use!

Time of use tariffs are why we have smart meters so expect them to become more common in future.

Yes. Solar panels are worth the cost. We believe that solar pv panels systems are an excellent investment for both you and the environment.

Our solar power panels systems cost between £5000 to £9000+ VAT, depending on the size and location of your home. This may seem expensive, but by installing a solar system we aim to reduce your electricity bill by up to 100%. Where else could you earn 9-13% per year tax-free on a low-risk investment, whilst protecting against rising energy prices and helping the environment at the same time.

Our solar panels are durable and come with a 25-30 year warranty. If well maintained, our solar panels can last for more than 30 years. Our solar panels are modern and blend well with any roof. A premium solar panel installation acting as your home’s own energy supply is likely to increase the value of your property.

Solar panels are largely maintenance-free. Over time, however, they may be affected by environmental factors – dead leaves, for example, may block sections of the panel. We recommend that solar panels are checked every few years to ensure maximum efficiency and cleaned once or twice a year.

Solar panels need sunlight to generate energy, so they do not work at night. However, you can install a battery to store excess electricity generation during the day to then be used later at night.

Negative electricity bills

Generating more energy than you use could turn your electricity bills negative.

The marginal cost of adding panels to a 4 kW solar system is negligible, you may as well use the space available and go larger.

Find out how much you could save with solar

Our cost and savings calculator can help you find the right solar specification for you and how much you could save!

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