Energy consumption is usually linked to the expected consumption of the home, so there are three models that broadly group together the most common models of energy consumption for homes of all sizes:
– Low-consumption homes that require from 200Wh/day to 2,000Wh/day. The power of the inverter will be from 250W to 1000W and with 12-volt batteries with deep cycle type from 70 to 250Ah.
– Medium consumption homes that require from 2,000 Wh/day to 8,000 Wh/day. The power of the inverter will be between 2,400W and 4,000W and the appropriate 6V or 12V batteries, with 24V batteries from 400 to 1,200Ah.
– High consumption homes that require from 8,000Wh/day to 12,000Wh/day. The power of the inverter will be from 4,000W and the appropriate 12V batteries from 400 to 1,200Ah with 48V battery banks.
The elements that define a solar kit and most condition its production, autonomy, and power are monocrystalline solar panels, 12v inverter, and batteries. The rest of the elements, although they are also important, define to a lesser extent the autonomy and energy potential of the kit. The following explains how the choice of each of these elements of the solar kit affects.
Solar panels are responsible for obtaining photovoltaic energy. They are one of the most sensitive parts of the installation, since rainy days, with little sun and night hours will not obtain the expected energy, hence the importance of having a battery and/or generator power supply system (in this case isolated installations) or to have an electrical connection to maintain the usual consumption of the home (for grid connection installations).
Another factor included in photovoltaic production is the area where the photovoltaic installation is carried out. The power of the inverter is linked to the power required by the photovoltaic installation, hence the importance of knowing the consumption and appliances that will be connected at the same time. This value is defined by the power needed to supply the installation. If the necessary power is 1500W we will go to inverters of 2400-3000W at 24V. If it is necessary to service instantaneous consumption of 500-700W, we will install an inverter of about 1000W at 12V. Or, if the required power is about 3500W, we will usually choose 4000-5000W inverters at 48V.
The batteries will allow energy autonomy at times when the energy needs are greater than the real-time production of the solar panels, something very common on rainy days or with little sun, as well as during night hours.
Usually, the batteries found on the market tend to guarantee an energy autonomy of 2-3 days of autonomy, although this value also changes according to the type of use, since the energy autonomy needs of a habitual residence are not the same as those of a weekend house.
Monoblock batteries are prepared to work in photovoltaic installations with low power and unusual or discontinuous uses. Therefore they would be limited in most cases to 12V or 24V solar generator systems with sporadic consumption. Hence, monoblock batteries are cheaper and have a shorter useful life than stationary batteries.
While stationary batteries are designed for permanent consumption, they have a higher quality and a greater number of life cycles. To cover medium and high consumption and power, 24V and 48V installations are usually chosen.
The most common mistakes in the composition of a solar kit
Properly sizing a solar kit is essential to cover the expected consumption. Not taking into account the autonomy of the batteries, recommending the wrong number of solar panels, and offering undersized systems are some of the mistakes when creating a kit.
The result of poor sizing of a kit is systems that show short-term performance problems and low production that barely covers the expected needs. As a general rule, in a photovoltaic solar kit, apart from the solar panels, there are 3 usual components: batteries, inverters, and charge controller.
Now, what are the most common errors in the composition of the photovoltaic solar kit?
Regarding the kit charge controllers
It is essential to correctly choose the type of charge controller based on the solar panel to which it will be connected. There are companies in which grid connection panels are called 24V solar panels, which is not correct. Hence the difference between isolated solar kits and grid connection kits. The problem with grid connection panels is that due to ignorance, they are installed with a PWM charge controller. Although this type of connection will not cause immediate short-term problems, it will cause damage to the system.
The connection of the panels must be in accordance with the charge controller and the power they deliver. You must keep in mind the connection in series vs parallel to guarantee the durability of the charge controller.
Regarding the batteries of the solar kit
Lead-acid batteries affect them very negatively and they break down much sooner when they do not frequently reach the floating state (+95% of their charge). If we put in excessively large batteries, yes, we will have a lot of autonomy, but we will not be able to use the solar installation regularly, they will be discharged and it will be an investment that is difficult to amortize.
There are many types of batteries for every use. If you want an economical system with monoblock batteries, keep in mind that their useful life is also shorter.
Sizing the batteries according to consumption is essential. A 250Ah battery whose usual consumption is 200Ah (80% discharge) wears out more than a 500Ah battery from which the same 200Ah is extracted (40% discharge). The paradox can occur that the 250Ah battery, even though it is of higher quality, has a shorter useful life than the 500Ah battery due to the demand for use.
Finally, it is the parallel connection of the batteries. Although in an ideal environment the parallel connection should not cause problems, the reality is that this type of connection significantly damages the batteries and at no time is the real installed capacity enjoyed.
Regarding the inverters of the solar kit
The inverter, due to the fact that it is turned on, has its own consumption, and this consumption must be taken into account to size the solar kit correctly. In systems that have been dimensioned without taking into account this small usual consumption of the inverter, in times of low solar radiation, if there are few panels, the energy needs of the inverter itself can hardly be supplied. Thus, for example, a 5000W inverter in Standby consumes what a 320W panel produces on a full, sunny winter day.
The battery inverter extracts energy from them, so opting for an excessively powerful inverter in a small battery bank implies overexertion for the batteries that in the medium term will shorten their useful life.
In the market there is a wide variety of inverters that can be attractive, the specific model of square wave inverters spoils those devices into which they are plugged. The only type of inverters that can be used in a photovoltaic installation and expect optimal results are pure sine wave inverters, and any solar kit that includes a modified wave inverter can negatively affect the connected devices.