Home solar batteries have become the standard for PV power systems, and if your carefully selected storage system does not work properly and is not suited to the characteristics of the PV system, it therefore becomes a bad investment, unprofitable and you lose more money.
Most people, install solar power lithium batteries for the sole purpose of generating savings along with the PV system, but it is often not properly utilized precisely because some manufacturers or battery brands suggest products with unsuitable characteristics.
But what characteristics must a home solar battery have to be efficient? What should you focus on when choosing a storage system to avoid wasting money? Let's find out together in this article.
By definition, the task of a solar power lithium battery is to store the excess energy produced by a photovoltaic system during the day so that it can be used immediately if the system can no longer produce enough energy to power the home load.
The free electricity generated by this home solar battery system passes through the house, powering appliances such as refrigerators, washing machines and heat pumps, and is then fed into the grid.
The home solar battery makes it possible to recover this excess energy, which would otherwise be almost given to the state, and use it at night, avoiding the need to draw additional energy for a fee.
In homes where natural gas is not applicable, everything needs to operate via electricity, so home solar batteries are essential.
The only limitation if sizing a PV system is.
- Roof space
- Available budget
- Type of system (single-phase or three-phase)
For home solar batteries, sizing is crucial.
The larger the capacity of the home solar battery, the larger the maximum amount of incentive spending and the larger the "incidental" savings generated by the PV system.
For proper sizing, I usually recommend a system sized at twice the capacity of the PV system.
Do you have a 5kW solar system? Then the idea is to go with a 10kWh battery.
A 10 kW system? 20 kWh battery.
And so on...
This is because in the winter, when electricity demand is highest, a 1 kW PV system produces about 3 kWh of energy.
If on average 1/3 of this energy is absorbed by household appliances for self-consumption, 2/3 is fed into the grid. Therefore, 2 times the size of the system is needed for storage.
In spring and summer, the system produces much more energy, but the absorbed energy does not grow accordingly.
Capacity is just a number, and the rules for determining battery size are quick and easy, as I just showed you. However, the next two parameters are more technical and much more important for those who really want to understand how to find the best fit.
It sounds strange, but the battery must be charged and discharged, and in order to do this it has a bottleneck, a constraint, which is the power expected and managed by the inverter.
If my system feeds 5 kW into the grid, but the batteries only charge 2.5 kW, I'm still wasting energy because 50% of the energy is being fed in and not being stored.
As long as my home solar batteries are charged there is no problem, but if my batteries are dead and the system is producing very little (in the winter), lost energy means lost money.
So I get emails from people who have 10 kW of PV, 20 kWh of batteries (so correctly sized), but the inverter can only handle 2.5 kW of charging.
The charging/discharging power also reflexively affects the charging time of the battery.
If I have to charge a 20 kWh battery with 2.5 kW of power, it takes me 8 hours. If instead of 2.5 kW, I charge with 5 kW, it takes me half that time. So you pay for a huge battery, but you may not be able to charge it, not because the system doesn't produce enough, but because the inverter is too slow.
This often happens with "assembled" products, so those I have a dedicated inverter to match the battery module, whose configuration often enjoys this structural limitation.
Charge/discharge power is also a key feature to fully exploit the battery during peak demand periods.
It's winter, 8pm, and the house is cheerful: the induction panel is working at 2 kW, the heat pump is pushing the heater to draw another 2 kW, the fridge, TV, lights and various appliances are still taking 1 kW from you, and who knows, maybe you have an electric car charging, but let's take it out of the equation for now.
Obviously, under these conditions, photovoltaic power is not produced, you have batteries charging, but you are not necessarily "temporarily independent" precisely because if your house requires 5 kW and the batteries only provide 2.5 kW, this means that 50% of the energy you are still taking from the grid and paying for it.
Do you see the paradox?
The manufacturer recommends home solar that isn't right for you, but you buy it anyway because you didn't notice a key aspect or, more likely, the person who supplied you with the product gave you the cheapest system where he could make the most money without giving you any relevant information.
Ah, most likely he doesn't know these things either.
Linked to the charging/discharging power is to open the brackets for the 3-phase/single-phase discussion because some batteries, for example, 2 BSLBATT Powerwall batteries cannot be put on the same single-phase system because the two power outputs add up (10+10=20) to reach the power needed for three phases.
Now, let's move on to the third parameter to consider when choosing a home solar battery: the type of home solar batteries.
Note that this third parameter is the most "general" of the three presented, as it encompasses many aspects that are worth considering, but are secondary to the first two parameters just presented.
Our first division of the storage technology is in its mounting surface. AC-alternating or DC-continuous.
A small basic review.
- The battery panel generates DC power
- The task of the inverter of the system is to convert the generated energy from DC to AC, according to the parameters of the defined grid, so the single-phase system is 230V, 50/60 Hz.
- This dialogue has an efficiency, so we have a more or less small percentage of leakage, i.e. "loss" of energy, in our case we assume an efficiency of 98%.
- Solar power lithium battery charges with DC power, not AC power.
Is that all clear? Well...
If the battery is on the DC side, and therefore in DC, the inverter will only have the task of converting the actual energy generated and used, transferring the continuous energy of the system directly to the battery - no conversion.
On the other hand, if the battery is on the AC side, we have 3 times the amount of conversion that the inverter has.
- The first 98% from plant to grid
- The second is charging from AC to DC, giving an efficiency of 96%.
- The third conversion from DC to AC for discharging, resulting in an overall efficiency of 94% (assuming a constant efficiency of 98% for the inverter, without considering the losses in the charging and discharging process, which is present in both cases).
Now it is important to point out that the intersection of these two technologies is mainly the decision to install energy storage batteries while building the PV system, since the technologies on the AC side are the most used when retrofitting, i.e. installing batteries on the existing system, since they do not require significant modifications to the PV system.
Another aspect to consider when it comes to battery type is the chemistry in storage.
Whether it's LiFePo4, pure lithium ion, salt, etc., each company has its own patents, its own strategy.
What should we look for? Which one to choose?
It's simple: each company invests millions in research and patents with the simple goal of finding the best balance between cost, efficiency and assurance. When it comes to batteries, this is one of the most important aspects: the guarantee of durability and effectiveness of the storage capacity.
The guarantee thus becomes an incidental parameter of the "technology" used.
The home solar battery is an accessory that, as we said, serves to make better use of the PV system and to generate savings in the home.
If it is not there, you have to live anyway!
After enduring 10 years, 70% of the benefits are still there and even if it breaks, you don't necessarily have to replace it because in 5, 10 or 15 years, the world could be a completely different place.
Quite simply, by immediately turning to qualified, knowledgeable people who will always put the customer at the center of the project, not their own personal interests.
If you need further support, our BSLBATT home solar battery manufacturer is certainly at your disposal to guide you in choosing the most suitable product for your home.