On August 17, 2022, at the Agency for Natural Resources and Energy, the “(44th) Subcommittee on Massive Introduction of Renewable Energy and Next-Generation Electric Power Networks”, the theme of which was “Toward Massive Introduction of Renewable Energy (50 pages in total)”, a review of current rules (draft) for “Panel Replacement/Installation of Solar Power Generation Facilities” was presented on pages 37~43.

The following is a summary of the results of a comparative evaluation of panel expansion and repowering using a model PV power plant (low-voltage, single-phase) as an example.

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A. Model PV power plant (single-phase, low-voltage):

(a) Photovoltaic panel: polycrystalline 250 watt, 288 panels, total panel output 72,000 watts. First year degradation rate: 2.5%, annual degradation rate (after 2nd year): 0.7%.

(b) PV inverters: 9 units, single-phase 5.5 kW (4 input circuits and 1 MPPT circuit). Conversion efficiency: 96.0%.

(c) System requirements: 8 series x 4 input circuits, 32 units, 8,000 watts, DC/AC ratio 145.45%.

(d) Others: direction 0-deg facing south, tilt angle of 10-deg or 30-deg, system efficiency 97%.

Table 1. Annual power generation in Japan (49 locations) over a 20-year period:

We estimated and evaluated three proposals for a model PV power plant (single-phase, low-voltage) after 10 years of operation, and for the case where the plant is renovated or expanded in the 11th year.

Renovation proposal A-1:

• Replacement of all (288pcs.) high output panel monocrystalline 315watt of the same size (1640mm x 992mm x 35mm).
• Total panel output increases from 72,000 watts to 90,720 watts.
• Panel degradation: first year 2.5%; annual degradation (after 2nd year) 0.7%.
• PV inverters, system configuration, and mounting structures remain unchanged.
• Continued capacity at current FIT price: 72,000 ÷ 90,720 = 79.37%
• Capacity at new FIT rate: 18,720 ÷ 90,720 = 20.63%.
• Additional cost: 288pcs. of monocrystalline 315watt panels + panel replacement cost

Table 2. Renovation proposal A-1 (Average, 49 locations in Japan)::

The simulation results show that the amount of electricity generated over the remaining 10 years will increase by approximately 30%. On the other hand, the increase generation of the current FIT price is approximately 3%, and the increase generation of new FIT price is approximately 27%. In case of the current FIT price is 40 yen/kWh and the new FIT price is 10 yen/kWh,

the income from electricity sales increased by approximately 2.95 million yen, or 9.8%.

In the case of Obihiro in Hokkaido, where power generation is still favorable after the 11th year, the evaluation showed that the amount of electricity sold at the current FIT price will decrease as shown below. We can assume that the reason for this is that the PV inverter’s rated capacity (49.5 kW) is sufficient to generate enough power even after the 11th year, so the ratio of the increase in power generation due to the expansion of the system is small.

Table 3. Renovation proposal A-1 (Hokkaido, Obihiro):

The amount of electricity generated over the remaining 10 years will increase by approximately 26%, and the increase or decrease generation of the current FIT price will be slightly negative, while the increase generation of the new FIT price will be approximately 26%. In case of the current FIT price is 40 yen/kWh and the new FIT price is 10 yen/kWh,

the income from electricity sales increased by approximately 2.21 million yen, or 6.3%.

Renovation proposal A-2:

• Panels were replaced with 240pcs. high output panels (monocrystalline 415watt: 1722mm x 1134mm x 30mm) and the mounting structures were modified.
• Total panel output increased from 72,000 watts to 99,600 watts.
• Panel degradation: first year 2.0%, annual degradation (after 2nd year) 0.55%.
• Replaced with PV inverters, capable of high DC/AC ratio (4.95 kW, 97% conversion efficiency, 4 input circuits, 2 MPPT circuits).
• Continued capacity at current FIT price: 72,000 ÷ 99,600 = 72.29%
• Capacity at new FIT price: 27,600 ÷ 99,600 = 27.71%.
• Additional costs: single-phase 4.95 kW PV inverters (10 units), related equipment, and replacement costs + monocrystalline 415watt panels (240 pcs.), replacement costs + mounting structure modification costs + wiring work, etc.

Table 4. Renovation proposal A-2 (Average, 49 locations in Japan):

The simulation results showed that the amount of electricity generated over the remaining 10 years increased by approximately 40%. On the other hand, the increase generation of the current FIT price was approximately 1.6%, and the increase generation of the new FIT price was approximately 39%, with most of the increase coming from the new FIT price. In case of the current FIT price is 40 yen/kWh and the new FIT price is 10 yen/kWh,

the income from electricity sales increased by approximately 3.41 million yen, or 11.4%.

From the renovation proposals A-1 and A-2, the improvement in power generation by replacing the panels is seen to have a significant effect. It will be necessary to consider the cost-effectiveness of new panel procurement costs.

Renovation proposal A-3:

• Replaced with a PV inverter, capable of high DC/AC ratio (4.95kW, 97% conversion efficiency, 4 input circuits, 2 MPPT circuits)
• Utilizing existing panels and racks while also adding panels (1720mm x 1134mm x 30mm) and mounting structures
• Existing 250wp panels: 12 in series x 4 inputs x 6 PCS (250watt x 288 panels, 72,000 watts)
• Additional 415wp panels: 12 in-series x 2 inputs x 4 PCS (415watt x 96 panels, 39,840 watts)
• Total panel output increased from 72,000 watts to 111,840 watts.
• Panel degradation (additional panels): the first year 2.0%, annual degradation (after 2nd year) 0.55%.
• Continued capacity at current FIT price: 72,000 ÷ 111,840 = 64.38%.
• Capacity at new FIT price: 39,840 ÷ 111,840 = 35.62%.
• Additional costs: single-phase 4.95 kW PV inverters (10 units), related equipment, and replacement costs + additional monocrystalline 415watt panels (96 pcs.) + mounting structures for additional panels (for 96 panels) + wiring and installation work, etc.

Table 5. Renovation proposal A-3 (Average, 49 locations in Japan):

The simulation results show that the amount of electricity generated over the remaining 10 years will increase by approximately 45%. On the other hand, the increase or decrease of the generation of the current FIT price decreased by approximately 6%, while the increase or decrease of the generation of the new FIT price increased by approximately 51%, showing a marked decrease in the current FIT price. In case of the current FIT price is 40 yen/kWh and the new FIT price is 10 yen/kWh,

the income from electricity sales increased by approximately 2.00 million yen, or 6.7%.

As the additional panel capacity increases, the peak shaving kWh based on the rated capacity of the PV inverter also increases, resulting in a decrease, and in some cases a negative impact, on the amount of the current FIT price applied. The results of the estimation suggest that it would be a good idea to renovate the PV power plant with the main purpose of eliminating the negative factors caused by panel and PV inverter failures and shadowing effects.

The results (model PV plant data, A-1, A-2 and A-3 in 49 locations in Japan) of this simulation (Excel format) can be downloaded here.

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In the next issue, we will estimate and evaluate the comparative evaluation of panel replacement/addition and PV inverter replacement for three-phase low-voltage PV power plants.