The issue of self-storage of energy has been at the center of PV users' concerns since the very beginning of their emergence. Even if they used prosumers and the possibility of storing energy in the power grid, despite the favorable form it still involved a cost of 20/30% of energy. What to do to avoid paying? Store!

(a) Heating water from surplus electricity. For this, there are system solutions such as Wattrouter, or ELWA-E. This is a good solution, but we will not apply it everywhere and it will always be limited to hot water. We won't power a refrigerator or laptop with such "storage".  

b) Pumped storage power plant. Super solution... only we have to build a small mountain next to the house. This is an expensive solution reserved only for the most motivated. 

c) Chemical batteries - this is the default solution that most of us think of when we hear about energy banks/storage. The solution is the most versatile, repeatable, and simple to implement, but also the most expensive per kWh of stored energy. 

The battery of a battery is unequal. So how to choose a battery? Let's perhaps start with what we expect from it: 

(a) Frequent and deep discharge (during the day we charge to the max, in the evening we discharge almost to zero). 

b) High power capacity, so that they power not only for a long time but also many devices at the same time.  

c) Long life, that is, at least 10 years, and even better, 20 years. 

d) Safety, so that you can put them in the house/garage and not be afraid that the dog will drink the electrolyte, and any malfunction will lead to a serious, unstoppable fire. 

e) High energy density, so that the battery is as small and light as possible. 

The most popular "large" batteries, easily available and relatively affordable, are car batteries (acid). One with a capacity of 0.72 kWh (60Ah car battery) costs about 300 PLN gross, so 7.2kWh (x10pcs) is a cost of 3000 PLN. That's not bad, so why do storage systems for PV cost 20-30 thousand PLN, but have 5/7/10kWh after all? This is where we come to the battery technology, thus meeting the assumptions made earlier. Traditional batteries are not designed for deep charging and discharging every day. If we take classic batteries, their capacity will run out after a few months - it is estimated that 6-12 months. In addition, we do not have at our disposal any control of the state of the battery, so if one cell/battery dies, it is likely that the whole system will stop working and we will have to replace the batteries. Admittedly, there are traditional batteries for so-called deep discharge, but it is still not a solution for years.  

The market, knowing the criteria we have already defined for ourselves, 2021 proposes LiFePO4 batteries otherwise known as LFP.  

5. TYPES OF CURRENT STORAGE TOPOLOGIES

Contrary to what you might think, it's not just a matter of installing batteries. You also need power electronics equipment for control and operation. So we come to the clue of the whole trip. We can store it in parallel with the photovoltaic system or on top of it.  

AC Coupling - I have a PV installation and want a battery

The first group interested in expanding PV installations with an energy bank are current prosumers who, having experienced the savings, want more ... savings. If one does not have a special inverter for this, it is said to be impossible. 

Actually, it can, and it's called AC Coupling, or Retro-FIT.

est is a solution in which we connect a second device to the AC grid (home installation) at any point of the installation. Such a second inverter is only connected to batteries, not photovoltaic panels. The kit requires an EnergyMeter, which: 

(a) As it detects the flow of energy to the grid, it starts charging the batteries, so as to overcharge the energy storage. 

(b) When it detects power draw from the power grid, it activates the inverter and puts the energy from the batteries back into its own use.  

In other words, it stores the excess and replenishes the shortage. 

To summarize the advantages:

a) We add, not replace. 

b) It's easy to add batteries to an on-grid system - we mount the kit where it suits us. 

c) It is the cheapest energy storage system on the market. 

Possible drawbacks:

a) Available only in 1 phase variety - for full optimization you need 3 - one for each phase (except for the SolaX solution) 

b) Backup power supply (backup), if any, is only 1 phase and low power up to 16A 

c) It has lower efficiency, because we convert DC from panels to AC, then from AC we charge batteries (AC->DC) and from batteries we make AC at the end - 3 processes of energy conversion - here physics is not overcome. 

d) You need a second inverter 

This is how a Yetti-type device works - TeslaPowerWall. Yetti means everyone has heard, but no one has seen.

After the April 2022 law change, which ends the golden era of the discount system, most new installations will have systems that increase auto consumption (i.e., energy storage, for example), or will be adapted to work with them. Since installations are designed from the beginning to work with batteries, hybrid inverters come into play. They are based on DC Coupling, i.e. the current from the panels supplies our house with electricity, and the top charges the batteries. The systems are equipped with a switching system for emergency power supply, and we can in case of a power outage on the grid side completely supply ourselves with our photovoltaics and energy from storage (e.g. at night). A complete solution! Any but? Well, precisely none, which is why this is a full grazing version.

A word of further commentary

It is possible to do AC coupling systems that work with hybrids and DC coupling, which we pin between the panels and the inverter. Technically there is no contraindication to this, but to the author's knowledge the market and his solutions have adopted the 2 models described above and there are no other implementations. This does not mean that they do not exist. If you know which manufacturers use something different, please contact us.

You need to answer what you need at the moment, and a good and educated installer will help to select the equipment because as the content of the article shows, all this is not one-dimensional, you buy a battery and it just works.

And this is, after all, a demonstration version in one room, because the main switchgear is probably in a different room than the inverter will be.  

We need space, and not just any space - the batteries must stand at a positive temperature, weigh 50-100kg, and are not small. In houses where there is no utility room putting up an on-grid system with storage can be a hassle. 

This problem is solved by SolaX's proposal, the G4 system, where all connections take place in a cable box called a matebox, which is part of the inverter housing. On top of that, only SolaX batteries can operate in sub-zero temperatures, so you can make an outdoor set-up. 

It won't decorate, but at least it won't disfigure. Don't have space at home? Put the inverter with batteries outside. 

Content-based on:
https://www.cleanenergyreviews.info/blog
/ac-coupling-vs-dc-coupling-solar-battery-storage