The home appliances we use at home only work with “alternating current”, but the electricity generated by the photovoltaic power generation system is “direct current”, so we cannot use it as it is. Therefore, it is a power conditioner (power-con) that converts direct current to alternating current.
In other words, a power conditioner is a power supply device that converts the power generated by a solar cell (DC Direct current) into alternating current (AC100V / 200V) used in homes and factories. Generally, DC 320-400V generated by solar cells is converted to AC100V for homes and AC200V for factories. It becomes DC / AC and works in the opposite way to the switching power supply. A power conditioner is an inverter because the power supply that converts DC (direct current) to AC (alternating current) is called an inverter. In English, it is called PCS (Power Conditioning System), and it seems that the power conditioner (Power Conditioner) that we generally call does not work.
Before explaining the power conditioner, let’s talk about the photovoltaic power generation system.
What is a photovoltaic power generation system?
The national average capacity of solar panels installed on the roof of a house is 4.5kW. Depending on the manufacturer, the output capacity of one solar panel is 200 to 250W, and 4kW requires 16 to 20 panels. The cost is 1.2 to 1.5 million yen. This is the price of only the solar panel, and in addition to this, a stand and junction box for installing the power conditioner, power conditioner, breaker, monitor, construction cost, etc. are required separately. The breaker itself is already installed in the house, but if you want to incorporate it into a PV system, you need to change it to a dedicated breaker. It may cost 1.5 million to 1.8 million yen or more in total. If you add a storage battery to this, it will cost an additional 700,000 to 800,000 yen.
In addition, 4kW solar panels always generate 4kW, but they rarely generate 100% of 4kw. 4kW is the amount of power generated at the optimum solar radiation angle when the panel temperature is 25 ° C. Every time the panel temperature rises by 1 ° C, the amount of power generation drops by about 0.5%, depending on the model. Imagine the roof of a car shining in the middle of summer. The panel temperature should be at least 65 ° C. Since it is 25 ℃ to 40 ℃ higher, 0.5% × 40 = 20% 4kW × 0.8 = 3.2kW The amount of power generation will be 3.2kW. In addition to that, it may not generate electricity in the worst case due to dirt on the panel, shadows of buildings and electric wires, and the direction of the roof to be installed.
The DC voltage generated by the solar panel changes depending on the “maximum output voltage” of the panel and the “number of connected units in series”. Simply put, if you have 4 series of 36V panels, it will be 36V x 4 = 144V, and if you have 5 series of 45V panels, it will be 45V x 5 = 225V. Collectively increase the capacity in 3 parallels or 4 parallels.
* Actually, the optimum voltage changes depending on the MPPT function of the power conditioner, but it is explained here in an easy-to-understand manner. MPPT (Maximum Peak Power Tracking) is a function that “adjusts to the optimum power generation voltage of the solar cell that changes depending on the intensity of sunlight”.
The electricity generated by these solar panels is sent to a ” connection box” where the electricity is combined into the input voltage of the power conditioner. For example, Panasonic’s power conditioner has an input of 320V DC, so it is boosted to 320V DC in the junction box and sent to the power conditioner. Of course, the input voltage of the power conditioner differs depending on the manufacturer.
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What is a power conditioner?
The power conditioner converts the DC power sent from the junction box into AC power AC100V or 200V and sends it to the breaker (distribution board). At this time, the conversion efficiency from DC power to AC power is not 100%, and energy loss (heat) occurs during conversion. Since it is about 95%, 5% becomes heat, so it gets hot when the power conditioner is operating.
The role of the power conditioner has the following three roles.
- Converts the direct current generated by the solar panel into alternating current.
- Match the voltage, frequency, and phase of the AC of the electric power company and the converted AC so that the power can be sold to the electric power company. By the way, the purchase price of residential solar power generation by electric power companies in 2020 is 21 yen per 1kW.
- The amount of solar radiation received by a solar panel changes depending on the weather, and the optimum combination of current and voltage differs depending on each weather (solar amount). Therefore, we are constantly tracking the optimum point of the combination of current and power (the point where the most power generation is obtained) so that the power generation voltage that can obtain more output with the solar panel that changes depending on the intensity of sunlight is obtained. increase.
The control function is called MPPT (Maximum Peak Point Tracking), and in Japanese it is called “Maximum Power Point Tracking Function”.
Domestic power conditioner manufacturers include Panasonic, Omron, Mitsubishi Electric, Daihen, Fuji Electric, Yaskawa Electric, Sansha Electric, Meidensha, Toshiba Mitsubishi, Nissin Electric, Tabuchi Electric, and GS Yuasa. Overseas, there are Delta Electronics, Power One, etc.
Renewable energy purchase system（Feed-in Tariff）
For solar power generation, the feed-in tariff (FIT) for renewable energy started in 2009 after the Fukushima nuclear accident. Initially, the purchase price was 48 yen per 1kwh for 20 years, but now it has dropped to 21 yen.
According to the photovoltaic power generation information, there is actual data that a 1kW solar cell generates an average of 1,234kWh per year. There are differences depending on the prefecture, and the prefecture that can generate the most power is Yamanashi prefecture at 1,436kWh, and the prefecture that cannot generate power is Akita prefecture at 902kWh. The national average is 1,234kWh.
And there is data that 30% of the 1,234kWh is sold for self-consumption and 70% is sold.
How much do you earn annually if you install 4kW of solar power?
First of all, by selling electricity, 1,234kW / h x 4kW x 70% x 21 yen = ① 72,559 yen will be the income.
Also, 30% of the electricity consumed in-house is counted as income because it is not necessary to purchase it from an electric power company. 1,234kWh x 4kW x 30% x 28 yen = ② 41,462 yen Many people forget this and calculate. The price plan for 28 yen varies depending on the power company, but it is approximately 25 to 28 yen.
The total of ① and ② is about 114,000 yen. In other words, we saved 114,000 yen a year in electricity charges. This is just “profit” by installing solar panels. Actually, there are cloudy, rainy days, and nights, and during that time, electricity from the electric power company will be used.
The installation cost of the solar power generation system of 1.5 million yen (lowest price) will be paid by 1.5 million yen ÷ 114,000 yen = 13 years. Thirteen years later, 114,000 yen a year will be profitable as it is, but it is a time when both the panel and the power conditioner are nearing the end of their life. In particular, the panel is less than 80% of the initial power generation, so the initial power generation cannot be expected. If it doesn’t break down, it will still be a profitable calculation of 80,000 yen a year.
By the way, the electricity bill we pay is about 20 to 25 yen per 1kwh, and 10 to 15 yen at night. Electric power companies can generate 1kwh of electricity for about 10 yen, but the FIT system buys it for 21 yen. The loss is as it is, but the power company does not hurt or itch because the general consumer is liable for the electricity bill under the name of “levy”. It is estimated that the electricity bill for a standard household of 8,000 yen / month will be about 100,000 yen / year, which will be 110,000 to 120,000 yen / year. It is a profit of the contractor (individual) who installed the sunlight as much as 10,000 to 20,000 yen per household per year. Since the cumulative total is 2 trillion yen, it is no wonder that interests will be generated
Finally, it would be nice if solar power was more efficient than thermal power, but unfortunately that is not the case. In order to generate solar power, a solar panel, a power conditioner that converts the generated DC electricity into alternating current, a control device, a stand for installation, land (roof), etc. are required.
Solar power is free, but a huge amount of electricity (oil) is used to make these solar power generation facilities. Especially silicon used for solar cells. The calculation method is complicated and there are many ways of thinking. It seems that they are making equipment for solar power generation using about four times as much electricity as thermal power generation. This is the result of smoothing out the lifetime life of photovoltaic power generation, not just when building photovoltaic power generation equipment. To put it simply, 4kwh of electricity generated by thermal power generation is used to generate 1kwh of electricity via solar power generation.