Energy storage with solar PV system

What are the differences between island, hybrid, battery and conventional solar systems? How can energy storage be solved with solar panels?

Different systems and energy storage with solar panels

The European market offers a wide choice of solar systems, both in terms of brands and technology solutions. We strive to provide the most reliable systems possible to meet our customers' electricity needs, and at the same time do something for our land and our environment. There are many ways to do this, here are the differences between the various solar systems.

First, we'll look at the types of systems that can be built, starting with the two perhaps technically simpler, conventional and islanded systems, and then moving on to the more technical subtleties of battery and hybrid systems, where we'll go into a little more detail about the different manufacturers' methods of energy storage and management.

Conventional solar PV system

The operation of a conventional solar system is simple. The solar panels generate direct current which the inverter converts into alternating current. The electricity thus generated is either fully used in the building's electrical grid or the unused electricity is fed back into the grid, i.e:

• solar panels

• inverter

• building electrical system

• service electricity network

With grid connection, net metering, this model is optimal for the population, but it is unsustainable at the system level, in the long term and for many prosumers, and therefore the regulation has been changed in Hungary. Weather-dependent renewable energy is now more time-proof and manageable at the system level than gross metering.

Let's move on to solar systems where we are already integrating batteries.

Island solar PV system

An island solar system provides power without any connection to the grid, for example in case of a complete power outage or deep in the woods in a holiday home.

The direct current generated by the solar panels is then converted into alternating current in the amount needed to meet consumption, or the amount not immediately used is stored in battery packs that can be used later because there is no utility connection. Also in the case of a back-watt solar system, we work with zero export, so we do not feed any kWh into the grid. We try to maximise on-site electricity use by reducing self-consumption. We use smart meters to monitor our property and our consumption profile tries to cover our production profile.

The disadvantage of this system is its dependence on battery power, which can be difficult if we do not have enough capacity because we cannot store 100% of the energy we can produce, or we can be left without electricity if we do not have other power generation options, such as wind or diesel generators. Typically, our typical residential customers have 10-20 kWh battery capacity, and the price of these devices is decreasing and increasing. SolarKit's Deye inverter brand is the market leader in South Africa, Brazil, where power outages can last for several hours and a reliable island or hybrid power system is required.

The advantage of an off-grid solar system is that we are not tied to the service provider in any way (location, grid connection, licensing, equipment used).

This is what our system looks like:

• solar panel

• inverter - battery pack

• building electrical system with integrated smart meter

Solar panel system with batteries

A battery solar system is similar to a conventional system, except that in addition to the solar panels, a charged battery also provides the DC power for the inverter, for example at night.

Newer battery systems have DC-DC (direct current) switching, i.e. the DC current from the solar panels can be charged into the battery (the batteries store DC current), thus avoiding conversion losses (DC-AC-DC-AC), and can also store energy when the DC side is oversized, with the inverter switching current at maximum capacity.

Then our system looks like this:

• solar panel

• inverter - battery pack

• building electrical system integrated smartmeter

• electric meter

• electricity supply network

• zero export (back-watt protection)

The batteries can be configured with different controls, so-called charging profiles, which can be configured to the customer's needs when the system is commissioned:

• Self-consumption - primary battery charging, secondary charging

• Mains supply - primary charging, secondary battery charging, may be of interest for significantly oversized DC side and for balancing

• Time-based configuration - periodic programming of the two profiles mentioned above, recommended for clear energy use patterns with gross settlement and peak and trough settlement

The advantage of a battery-powered solar PV system is that we can bridge the gap between the sale and purchase of electricity by increasing self-consumption in less favourable billing regimes than the balance. Everyone should think about and calculate the return on investment for battery expansion, and smartmeters can be retrofitted to optimise the energy management of your property.

Hybrid solar systems

A hybrid solar system is one that can operate both when connected to the grid and in stand-alone mode (in the event of a power outage).

Then your system looks like this:

• solar panel

• Inverter

• battery pack

• electricity meter

• electricity supply network

• building electricity system with integrated smart meter

• backup box (if needed separately, details below)

• critical loads circuit (if necessary, details below)

Energy storage with solar panels

Let's look at battery solutions from different manufacturers. Batteries are a key component for storing and harnessing solar energy, and there are many different solutions available worldwide.

When choosing a battery, it is important to take all aspects into account and make a decision based on the features that are most important to us, as we can see that different manufacturers are constantly improving their solutions. Warranty period, battery performance retention, efficiency, modular expandability and compatibility are all factors to consider when making your choice. Choosing the ideal battery will ensure efficient and reliable solar energy storage over the long term. At Solar Kit, in our official collaborations, we have strived to bring our customers solutions from which everyone can choose the right one for them, from brands such as Huawei, SolaX or Deye.

In the following, we will first discuss the hybrid system with Huawei L1,M1 (up to 10kW) inverter, and then we will move on to the Deye and SolaX inverters and batteries, also available from Solar Kit.

Huawei LUNA battery

Huawei's solution requires an inverter, a battery, a backup box and a smart meter to create a hybrid system. The battery consists of two parts: the power module handles charging and energy output, and the 5 kWh capacity battery can be easily added with up to 2 extra modules, so you can achieve 5-15 kWh capacity, with 3 in series, depending on your needs.

If you want to draw power from both the grid and the battery, you should also get the Backup Box , which allows Huawei (L1, M1) inverters to run in hybrid mode.

In such a case, the device with two AC (alternating current) connections will still have the primary connection to the building's electrical grid, while the secondary connection will be to a newly created circuit, the critical load circuit (hereafter referred to as the C.C.C.). Depending on the inverter, the grid can be single-phase or three-phase, but the emergency circuit in our case is always single-phase.

In the presence of grid power, the primary and secondary circuits are supplied in the same way as in a conventional solar PV system. If there is no grid voltage, both circuits are de-energised. When our system detects this, after about 3 seconds, it starts generating electricity to the CFC, and not only the kWh in the battery, but also the solar panels that are producing electricity will continue to operate.

When designing the circuit for critical loads, care should be taken to ensure that the maximum output current of the Backup Box is not exceeded under any circumstances.

For these solutions, it is worth thinking of the RCD not as an uninterruptible power supply, but as a secure back-up where we can be sure that the house security system / lights / entertainment electronics / cooling / heating system will be supplied with electricity.

Deye inverters and batteries

SolarKit officially distributes Deye technologies to the public and our partners. Deye's hybrid inverters include a backup box and smart meter as standard, and can be easily connected to their proprietary battery solution, but in addition they can handle dozens of battery brands and even wind or diesel generators. If you opt for a system supported by energy storage, your inverter can switch to island mode in 4 milliseconds, drawing power immediately from the battery, so you get a full-fledged uninterruptible system. So, unlike Huawei's solution, thanks to the inverter's phase asymmetry capability, we can supply not only the RCD in case of a power outage, but also the 3 phases in the building at the same time.

The ease of connectivity can also be an advantage if you may not have a battery connected to the system at the time of installation, but plan to connect it later. Another advantage is that multiple inverters and batteries can be connected together, so we can recommend Deye's solutions for complex solutions.

In 2023, our Managing Director and Wholesale Manager discussed the official SolarKit European market distribution cooperation during a factory visit lasting several days, and you can read more about our experience and Deye's solutions in our more detailed article on this topic.

SolaX inverters and batteries

SolaX is another of our collaborations and they have also developed their own energy storage system. Their inverter is just as capable of the aforementioned uninterruptible power supply thanks to the integrated backup box, so when supplemented with a battery, full islanding can be achieved here too, with a switching speed of 0.01 seconds. Thanks to LFP (Lithium Iron Phosphate) technology, they have a higher temperature tolerance and are safer to install. With a 10-year warranty and a 90% discharge depth, they represent excellent value for money.
You can read more about Solax solutions in our article about them.Overall, energy management of our property and our country is an extremely complex task and issue. That's why we always offer free professional advice, on-site surveys and distribute several world brands. With over 3,500 installed solar PV and heat pump systems, we have the experience to help you.