Choosing the right PV mount to maximize efficiency – A scientific approach

With the implementation of the target model in the Greek market, we see, as expected, a reduction in the wholesale price of electricity. Thus the careful planning of each project becomes necessary, not just in the implementation phase, but even from the calculation phase before a tender.

What we always aim for is minimizing the reduced cost of electricity, what we call L.C.O.E. (= Levelized Cost Of Energy). The L.C.O.E. is a measure of the present value of the cost for the production of the energy for the entire duration of its operation and is expressed in €/MWh.

The L.C.O.E. is a very useful tool to compare different implementation scenarios of a photovoltaic project. The lower the L.C.O.E., the more efficient and profitable our work.

In the present study we calculate the L.C.O.E. for different bases / methods of supporting the photovoltaic panels.

The calculation of L.C.O.E. is done by applying the formula:

where:

Ιt=Investment costs in year t (€)

Mt=Maintenance and overhead costs in year t (€)

Et= Energy production in year t (MWh)

r = discount rate (%)

n = project lifetime (years)

For those who are “intimidated” by mathematical formulas, the interpretation of the above is simple. The minimization of L.C.O.E., which is also our goal, is achieved in 3 ways:

1st) the minimization of construction costs

2nd) the minimization of operation / maintenance costs

3rd) the maximization of performance during the life of the project.

To achieve the above, it is no longer enough to buy some random materials and install them. The project must be properly planned before its execution and critical decisions, which we used to take for granted, must be made at this stage. As far as our part is concerned, i.e. the support of the panels, these decisions are:

• panel conventional or bifacial?
• if bifacial panels are chosen: simple fixed bases or special for bifacial panels? or perhaps trackers?

In an attempt to answer these questions we made a calculation of the L.C.O.E. for each of these cases, so that we can come to rational decisions based on numbers, not guesswork. “Because everyone can have their personal opinion, but they cannot have their personal numerical data.”

We decided to deal with 3 different alternative support cases, which we believe cover the whole range of possible options for Greece:

Case 1: conventional panels & simple supports

Case 2: bifacial panels & special support base for bifacial panels

Case 3: uniaxial trackers

At first we “ran” the calculations for a specific area in Greece (Terpsithea – Larissa) and assumed a 500kWp project using 440Wp monocrystalline panels and a 100kWp Huawei inverter. Lifetime of the project 20 years and with the following assumptions:

• the project is executed without bank borrowing but 100% with own funds
• Park cost: €275,000 Case 1

€282,000 Case 2

€320,000 Case 2

• Annual production (calculated by PVSYS program): 777.27 MWh for cycle 1 (simple base with simple panels)

Performance compared to Case 1:

+8% for case 2 and

+20% for case 3.

• Discount rate: 5%
• Annual maintenance cost: €2,000 + €1,000 per year for various expenses (accounting support, security services, electricity, internet…)
• sale price @60Euro / MWh
• In the park with the trackers, we suffer, within 20 years, 2 breakdowns costing €5,000 each and in these 2 months we also have a reduced performance by 20%.

Based on the above, and applying the mathematical formula of L.C.O.E. we get the following results:

SYSTEM SPECIFICATIONS € INVESTMENT L.C.O.E. €/MWh

Conventional panels & simple bases support 275.000 30.90

Bifacial panels & special base for bifacial panels 282.000 29.25

Trackers in a “small” project (500 kW) 320,000 30.00

The conclusions drawn from our simulation ‘run’ to calculate the L.C.O.E. is obvious:

• It is cost-effective to install bifacial panels and a special fixed base for bifacial panels (such as ELVAN’s BIF-2V with front clearance: 800 to 1200 mm), compared to simple panels and a contractual basis.
• The installation of trackers in “small” projects (eg 500kW) is not beneficial. If we consider:

a. increased maintenance,

b. unavoidable damages,

c. the consequent replacement of equipment

d. the loss of production during these failures

we see that the L.C.O.E. it is greater than that of the installation of bifacial panels and a special fixed base for bifacial panels.

• The installation of trackers starts to be “worth it” for larger projects (>5 MW), where it is justified by the size of the project to have permanent maintenance staff, a rudimentary stock of spare parts, etc.

ELVAN special bases for Bifacial panels have all the advantages of simple bases:

• robust construction
• CE certification
• easy and quick assembly
• adaptation to any type of terrain

while thanks to the front clearance of 800 mm to 1200 mm and the minimization of shadows at the rear:

• yield guaranteed +8% compared to conventional panels and base.

This is also the reason that since September 2020, when the product was released on the market, special bifacial bases have been delivered for tens of MW parks, while in the last two months their orders have now exceeded those of simple bases.

Here we should perhaps also refer to the so-called variable angle bases, which we did not include in our calculations for reasons that will be seen in the following analysis. Variable angle stands require the park owner to “manually” change the angle of the fixed base 4 times a year.

But the 7-8% increase in performance in this way is, for better or worse, not supported by the scientific data. Taking into account the latitude of Greece and the corresponding solar radiation, it follows that even with 6 changes per year, the yield increase does not exceed 3.6%. And if we take into account all the other factors that are there, we end up with a negative return in €.

The methodology used to reach the above conclusion was as follows:

For a specific area in Greece (Terpsithea – Larissa) we assumed a 550kWp project using 440Wp monocrystalline panels and a 100kWp Huawei inverter.

The panels are placed on a fixed base with a 2 portrait arrangement and a distance between the rows of 9 meters.

We calculated, with the PVSYS program, the incident radiation and the energy production for different installation angles of the panels, not taking into account the possible losses.

According to the above, the best performance per month is as follows:

January 40° 86.7kWh/m²

February 40° 109.5kWh/m²

March 35° 141.3kWh/m²

April 25° 166.0 kWh/m²

May 10° 197.9kWh/m²

June 10° 216.9kWh/m²

July 10° 228.1kWh/m²

August 20° 215.1kWh/m²

September 35° 173.4kWh/m²

October 40° 125.3kWh/m²

November 40° 94.4kWh/m²

December 40° 76.2kWh/m²

We thus see that by making 6 slope changes per year – assuming we had installed a variable slope base – we get a total of 1830.8 kWh/m² per year. Comparing this to the annual production of 1767 kWh/m² we get from a constant slope base at 25 degrees, we have an increased production of only 3.6%. The final energy efficiency in the network is similar: with the 6 different slopes we get a total of 885.27MWh, while with the fixed slope at 25 degrees we get 855.3 MWh.

This means 30 MWh more in the first year if we make 6 slope changes compared to making no changes at all.

30 MWh with a selling price @60Euro / MWh means a profit of €1800 (for the first year, because from then on this amount will be decreasing due to the drop in efficiency of the panels).

If we take into account: the labor required for 6 tilt changes per year (2 people for 2 days at €75 per day to change 32 tables), we have a cost of 2X2X6X75 = €1800, exactly as much as our profit.

If we also calculate the risk of cracking panels during the many changes, we are already in negative performance figures.

Another parameter that should be taken into account is that for a variable angle base the static calculation should be done for the maximum angle (40 degrees). This means that the distance between the piles should be reduced to 2.8 m. from 3.5 m. (for a 2Vx18 table).

So 32 tables with 4 extra stakes for the whole project, i.e. 128 extra stakes. This will burden the CAPEX of the project by approximately 1280 Euros more. So “coal is the treasure”.