Every person who is thinking about installing a photovoltaic installation on their roof sooner or later encounters a problem in the form of storing surplus energy produced, so today we wanted to explain a few intricacies related to this topic.
Contrary to the misleading name, photovoltaic batteries are not the equivalent of popular fingers inserted into the TV remote control. Photovoltaic panels are interchangeably called batteries, and there are several types of them:
Thin film batteries also called 2nd generation cells. The cheapest, but also the least durable in its category. Made of materials such as cadmium telluride, amorphous silicon, or a mixture of copper, indium, gallium and selenium, which cover e.g. stainless steel or glass with a thin layer, hence their name. There are several types of thin-film panels: CIGS, CdTe and CIS. Their efficiency is estimated at about 5%, which is also the lowest result among all cell types.
Polycrystalline batteries belong to the so-called thick-layer panels, also called 1st generation cells. Due to the good price-quality ratio, they are the most frequently chosen type of panels, characterized by quite high resistance to temperature changes, which in turn translates into their greater efficiency on hot days compared to second-generation cells. Polycrystalline batteries are mainly made of heat-treated silicon, and their service life is estimated at about 25 years. The efficiency of polycrystalline cells is around 16%. They are characterized by blue color.
Monocrystalline batteries are the highest quality thick-film panels available on the market, but also the most expensive of them. Their price is influenced by the long production process. Their efficiency is maintained at around 19%, which gives them the first place in this comparison. They are made mainly of single crystal silicon, and their service life, similarly to polycrystalline batteries, is about 25 years. They are distinguished by their characteristic black color.
Now that we know what choice we have regarding the material from which our installation will be built, let’s move on to its use. A well-designed installation tailored to your needs will produce much more electricity than you actually need at the peak of production. This situation occurs especially in summer, as we wrote about recently.
Namely, during the period when the sun’s rays reach the panels without interference, the efficiency of the installation increases and it usually produces significant surpluses of electricity, which helps compensate for those periods of the year when there is less light. And this is where the way of managing this surplus is particularly important.
The first is to transfer it to the general power grid and collect it when the cells do not consume energy from light or its amount is insufficient to power your household. An agreement with an electricity supplier to connect and store energy in the general grid gives the owner of the PV installation the status of a prosumer.
The second method is to store electricity yourself in devices specially designed for this purpose.
The only time throughout the year when photovoltaic panels really do not produce any energy is at night – then the complete lack of access to light translates into their inactivity. And mainly at night and in winter, we need access to the surpluses that we produced during the energy boom. This is where home energy storage units come in handy, allowing you to fully meet the daily demand for electricity in your home during periods of increased sunlight. What are they?
The explanation is quite simple – these are commonly known batteries with appropriately selected capacity, and they work in a quite simple way. Namely, if during the day the amount of energy is higher than demand, the surplus will first be stored in the battery and used at night or in the immediate event of a drop in efficiency due to, e.g., bad weather, and only then transferred to the grid for collection, e.g. . Winter.
It is also possible to completely disconnect from the general grid and use only your own installation additionally equipped with energy storage batteries. Many of you are discouraged by this method of using the installation due to the relatively high, although usually one-time, cost of the initial investment. However, this configuration of the installation allows you to save an additional 20% of energy, which in the case of prosumer dependence is transferred to the supplier as a kind of payment for maintaining the network.
However, the way warehouses work means that this is not an ideal solution, although it may seem like it. The additional cost of batteries is not the only expense in an off-grid installation (without connection to the general grid). The main disadvantage of this solution is, unfortunately, the inability to store energy throughout the year, and what we usually care about most is that the summer surplus compensates for winter shortages.
To use your own PV installation and home energy storage more effectively in this situation, it will be necessary to install more panels to increase their energy-generating potential, which naturally generates higher costs. Therefore, it should be remembered that despite the higher price of the entire investment, with a properly designed installation, even in winter, the panels will produce enough energy to meet current needs and store surpluses for the night, thus making us completely independent from the general energy network.
There are actually four types of batteries available on the market, which differ in their chemical composition:
Lithium-ion batteries are particularly known as durable batteries for mobile phones, resistant to performance drops even when completely discharged. Their great advantages in the context of energy storage are low weight in relation to capacity and relatively quick charging time. Lithium-ion batteries are the most common in PV installations. Currently, batteries of this type charged by photovoltaic panels are also available in mobile versions that can be taken, for example, camping, as your own power source.
Lead-acid batteries are quite cheap, because compared to lithium-ion batteries, the difference is almost 50% in price. These percentages are also important for their efficiency. Acid batteries lose their performance when they regularly use more than 50% of their charge, so one might even go as far as to say that they do not like cyclical operation. As a result, warehouses using them should contain a relatively large number of batteries, and it is also necessary to store them in ventilated rooms.
Gel batteries designed to operate in a slow charging and discharging system are particularly suitable for powering devices such as TVs, tablets, and home lighting. They are not harmed by negative temperatures, provided that they have been exposed to them while charged. In their case, it should be remembered that lowering the temperature affects the capacity of gel batteries – however, it returns to normal after “heating”.
AMG batteries are characterized by high tolerance to sudden changes in charge level. They can be used to power devices that require a large and constant load, such as a refrigerator or even an electric car.
When it comes to the prices of photovoltaic batteries, the average cost is around PLN 25,000 for a 10 KWH battery, depending on its type. However, you should not be discouraged by this price, because as we constantly remind you – the Moje Prąd program starts on July 1, under which you can obtain significant funding for photovoltaics in your homes, and the refund from the program also covers energy storage.
So, is it worth it? As lawyers like to say, “it depends.” Additionally, to make you think more carefully about the topic, we suggest that both storing and exchanging energy within the general energy network are not the only possibilities of using energy surplus. It can also be used to power a heat pump or additional devices, such as air conditioning for the entire house.
What to choose? This issue is completely determined by your individual needs, so it is important to seek professional advice when deciding to install photovoltaics.
