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The best technical articles of 2017

Written by our experts, our technical articles aim to deliver independent & valuable insights on challenges faced by wind & solar assets. We have gathered in this newsletter the best of our articles published in 2017. Stay tuned, more are to come in 2018. If you are interested in receiving our articles directly in your mail box, click here.

1. The five most common problems with solar panels

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Snow and solar photovoltaic panels

We often tend to think that solar panels need direct radiation from the sun to work efficiently. Yet, it is not necessarily the case. Indeed, electricity can still be produced as long as the sunlight, direct of reflected, reaches them in sufficient quantity/intensity. Cleaning the snow on panels is therefore crucial to maintain optimum production level.

Snowfall effects on solar production
We operate solar farms located in regions subject to snowfalls (north-west part of France). Through this experience, we have been able to notice the phenomenon described below.

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SDE+ Autumn 2017 – Candidacy results

Opened early October, SDE+ scheme opening hours are now closed. Minister of Economic Affairs and Climate has published candidacy results. Analysis by our experts in this article.

For this round of SDE+ 5,783 applications has been submitted for a total budget of € 9.9 billion, and are currently under careful review for technical, financial & economic feasibility. Indeed, budget commitment implies that only a budget of €6 billion is to be allocated, not all projects will be able to be granted with a subsidy, but the amount of applications, demonstrate the renewable sector’s dynamic & growth.

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Happy holidays!

2017 has been another great year for us, and we would like to thank you for the continued confidence you put in us over this past year and for all the wind & solar successes we have achieved together with you.

We are looking forward to continue along this path in  2018!

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Strike actions in the energy sector: impacts on wind & solar farms

Started earlier in November the strike movements called by several French grid operators (Enedis, RTE, EDF, GRDF) should continue in December and may have some consequences on wind & solar parks production.

Strikes actions are conducted on a national level and consist in decoupling the substation from the electrical network. This was for example the case in the Alpes de Haute Provence & Aube French départements on November 30th.
The main problem of such grid outage, apart from producers not being warned in advance, is their length. At Greensolver, some of the assets we operate remained disconnected for more than 8 hours. Moreover, it has to be noted that disconnections are usually abrupt and even after reconnection to the grid, some wind farm or solar park units were not able to restart, leading to unexpected repairs and expenses for asset owners. Production losses related to the substation decoupling are therefore increased.

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Wind farm: blade’s leading edges erosion

As its name suggests, the leading edge is the blade’s part which enters first in contact with the wind. Therefore, it is naturally the most vulnerable part towards environment’s stress.

Every wind turbine located in an environment that includes abrasive particles like rain, snow, hail, dust or insects is a lot more subject to erosion than a wind turbine located in a place where those factors are absent. Moreover, the turbine’s size has not stopped increasing. Yet, the bigger the rotor’s diameter, the faster the blade’s tip speed, which increases the damages on the blades.

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Solar PV: price & technology evolution

With the cost reduction battle carried out during the last 15 years (mainly due to the massive introduction of the Chinese solar products in the market), solar energy has now become a very competitive energy source. We estimate that prices have reduced by more than 90% over the last 15 years.

As one of the core parts of a PV project, the photovoltaic modules represent between 45 and 55% of the overall costs of a solar project. Likewise, the solar cells represent around 50 - 60% of the cost of the PV modules. Traditional crystalline cells are still the most efficient for solar technology (industrial efficiencies of around 20%). If we take a look to its price evolution, we’ll be able to see that it has drastically reduced: more than 90% in the last 15 years.

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SDE+ Autumn 2017 - Greensolver forecast

Since 2008 about 29,500 projects have been rewarded with subsidy allowing The Netherlands to develop its capacity in terms of renewable energy production. With the 2020 objectives getting closer, rounds of SDE+ have become larger and budget have been increased by 33% by the Government in order to reach the objectives – now reaching 12 billion euros to be allocated only for the year 2017.

Divided into two rounds which each have three phases, with a price per kWh increasing (from 0.090€/kWh to 0.125€/kWh), first round of 2017 subsidy have rewarded mainly solar PV (73%) & on-shore wind projects (20%), the rest (10%) being allocated to biomass, geothermal and hydro – largely rewarded in 2016 and previous years.

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Technical Management Contracts

As technical expert and manager of more than 860 MW of wind & solar assets, we would like to emphasize the importance of having a technical expert who will take away the burden of daily operation of your assets by managing both the technical and commercial sides. Indeed, managing an asset is a tedious work which requires to source all the competences internally, which you may not have.

When operating a wind or solar asset, our primary goal is to run efficiently the asset and to improve its performances. Hence, you’ll find below a resume of what should be mandatory included in your technical management contracts:

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Greensolver welcomes a new wind & solar construction project manager

Our Parisian office has recently welcome a new construction project manager on board, Guilaume Fauthoux.

Guillaume Fauthoux GreensolverAlong with our construction team, Guillaume will be in charge of supervising our wind and solar farm construction activities in Europe, including:

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Operating wind farm performance analysis

Technical management of a wind asset is a tedious work which requires not only to supervise the wind asset production, but also to analyze the turbine performances in order to detect if the turbine is under or over performing.

Data analysis is key when managing a wind asset. By transforming data into insight, into information, asset manager and owners are provided with a set of information useful to challenge the turbine manufacturer.

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Greensolver announces strategic partnership with Smart Blade

Partnership will focus on delivering exclusive products and services dedicated to blades.

GREENSOLVER, the independent technical expert for wind & solar assets, announced today a strategic partnership with innovative German company SMART BLADE GmbH. The partnership will provide the industry with services and products dedicated to wind farm production optimization.

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Serrations or the art of reducing wind farm noise

The noise of a wind turbine is estimated to reach about 55 decibels being at its foot (a car is estimated to be 80 decibels). Though acoustic is still one of the big challenge for the industry and a main risk for projects under development.

In some areas, due to the proximity with locals or their sensitivity, wind installations can be subjected to strong curtailment plans which aims to reduce the noise of the moving blades. Though those curtailment plan are necessary for closed landowners, it often leads to, significant production losses. Noise reduction, as a consequence, has become a main challenge for turbine manufacturers who are all investing in research & development. The latest development in the industry is now offered by most of the wind turbine manufacturers and is called “Serrations”. This barbaric name inherited from the Romans, is used to describe sawtooth add-ons installed on the trailing edge of each blade in order to decrease the sound made by the blade when moving.

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Why active filters are to be used in a wind energy asset?

We have often seen cases when an active filter had to be installed during operation of a wind farm. This article aims to demonstrate their purpose and benefits.

From high voltage centers, grid operators use a remote system to amend the tariff in energy meters. When a tariff signal is issued, each simple voltage imposed by the three-phase network is the superposition of the sinusoidal voltage V50 Hz and of a square alternating voltage V175 Hz.

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PID: causes and mitigations strategy

When PID effect can a be an underperformance root-cause of a solar farm

The performance of your solar park does not reach your expectations? Unexplainable power losses have been noticed? This can be due to a Potential Induced Degradation (PID). PID effects in a solar farm, can be responsible for losses up to 30% according to TÜV, one of the recommended testing organisation. As solar asset managers since 2008, we explore in this article PID effects, causes and solutions to mitigate its effects.

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How to ensure an optimum design of a solar park?

A successful solar project always starts with a good design. A good design ensures an optimum balance between the costs of the system and the anticipated output. However, a well-thought-out design also ensures lower maintenance costs. We regularly receive questions relating to the design of solar parks.  In this article, we use these questions to explain a number of choices and considerations that need to be made when designing a park.

Where do I start when designing a solar park?
To produce a good design, we must explore the extremes. Firstly, we establish what the maximum capacity that can be installed in a location is. Account is thereby only taken of the ‘physical’ restrictions of a location. These restrictions might, for example, be imposed by the permit granted (height restrictions, positioning direction, environmental constraints, etc.), landscaping to be created, minimum row distances for maintenance, ditches present, etc. Narrow row distances will mean that this variant leads to an array with a lot of internal shading (shadow from one row of panels on another row, called near shadow) and therefore relatively low production per panel. Set against this is the fact that the most kWh are produced in absolute terms. The filling factor for this positioning variant is typically at around 0.6 to 0.7, which means that 60-70% of the surface is used for panels.
 
At the other end of the spectrum, a positioning variant is calculated whereby the panels produce optimally. The row distance will thereby have to be greater in order to prevent inter-row shading. The production per panel is optimal, but fewer panels can be placed at the location and so the absolute quantity of kWh will be significantly lower. With this variant, the filling factor will be around 0.2 - 0.3.
 
When the extremes are known, the optimum positioning can be determined on the basis of number of iterations. What is optimal will depend heavily on the location's general fixed costs, such as the costs of using land, fees, network feed-in, etc. If fixed costs are high, more kWh will have to be generated in order to achieve the lowest cost price per kWh.
 
What is the best approach with regard to inverters?
The inverter is one of the more expensive and maintenance-sensitive components within a solar park. Since the solar panels will only produce at full capacity a few instances a year, the design will seek to install as few inverters as possible. This will raise the overload factor. The overload factor is the relationship between the capacity of the inverter (AC side) and the PV modules installed capacity (DC side). Undersizing the inverters can save costs on inverters. The consequence of this is that at times of peak production a small proportion of the production is lost (approx. 1-3%). Depending of the exact cost of the inverters and the location-specific energy production, the design can be further optimised in this way.
 
Another reason for undersizing inverters
The peak capacity of a solar panel (kWp) is the capacity that is achieved during the factory tests under Standard Test Conditions (STC). These test conditions (including an irradiance of 1,000 W/m2 (at vertical irradiation), a panel temperature of 25°C and an air mass of 1.5 spectrum) are not achieved in practice. For example, sunlight in the UK is virtually always less than 1,000 W/m2. A higher panel temperature results in a reduction in the yield. The panel temperature can easily be 20⁰-30⁰C higher (depending on the amount of irradiation, cooling by air flow and the external temperature). A panel temperature of 45⁰C can lead to loss of capacity of 8-9 %. A lower panel temperature has the opposite effect. We see overload factors between 20% and 40%. At a 20% overload factor in the UK, account must be taken of small loss of production during high irradiation. However, this does not outweigh the gain during lower radiation, since an undersized inverter is more heavily loaded and therefore has a higher efficiency.
 
Relationship between Design and Maintenance
Maintenance costs are deeply affected by two issues: 1) the choice of the material used, and 2) the design of the solar park. The fact that the choice of material affects the maintenance costs goes without saying (see our previous articles). The design must also take careful account of the maintenance of the operational park, such as the construction of maintenance roads, the accessibility of panels and the inverters, the layout of the site, the routing of cables, the choice of planting, the use of vegetation species, positioning of gates/fencing, distances to ditches, etc. The choices made here have a major impact on the number of maintenance hours required on site.
 
An oft overlooked area for optimising the park is the distance between panels. This is often set at around 2 metres in order to allow sufficient space for machinery to conduct maintenance. This distance between rows can often be reduced if the machines can manoeuvre under the high side of the panels on one side. With an array of 3 panels in portrait at an angle of 20°, the highest point will readily reach 2.4 metres, which offers around 0.5 metre of clearance for machinery. One or two rows of extra panels can then be installed on a large plot. It is therefore worth thinking carefully about the maintenance and taking account of it at the design stage.
 
Is it a good idea to use trackers?

We are often also asked about the benefit of solar trackers (single or multi-axis). In the UK, solar panels perform optimally at an angle of 37°-41°⁰ and an azimuth of 0⁰ (due south). If the panels are not 100% oriented to the south, but deviate by say 5°, that leads to reduced performance. That effect can be prevented by turning the panels with the sun and therefore keeping them continuously optimally aimed at the sun. Tracking the sun can, in theory, result in approximately 25% more production in the UK without taking account any additional losses (such as shadow). However, trackers significantly increase the system costs and lead to higher maintenance costs due to more parts in motion.
 
The installed capacity is also reduced by the space required for the tracker tables. Account must be taken of 10-12% higher purchase costs and 3-4% higher operational costs. In practice, in the UK, where the climate has a lot of diffuse light (diffuse light normally represents between 30 to 50% of the global light in the UK), we have not yet seen any examples whereby the benefit of using trackers outweighs the higher costs.
 
East-West: a worthwhile alternative design?
An east-west orientation means that the panels are not oriented to the south, but to the east and west. The panels are at a shallower angle (8⁰-15⁰). A solar panel with a due south orientation has a typical energy yield with a sharp peak around noon. There is little or no energy yield in the morning and evening. An east-west orientation, on the other hand, has a less sharp peak around noon but more yield in the morning and the evening, which also has consequences for the number of inverters and the overload factor.
 
The shallow angle of the panels means that there is less shadow cast between the panels themselves. The installed capacity (kWp/m2) is therefore higher (filling factors of 0.9 are possible) in a park with an east-west orientation. Depending on the PPA and the development of the electricity price, this could be lucrative over the coming years in view of the fact that the electricity price is higher on average in the morning and evening than around noon. The more solar power is installed, the more interesting this will become. Particularly in the regions in the UK with relevant high solar irradiation and projects with high general costs, we recommend that an east-west orientation should also be carefully costed.

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Welcoming a new Asset Manager for the United Kingdom

UK Greensolver office welcomes Stephen Horry as Asset Manager for wind & solar assets in the United Kingdom.

Stephen Horry

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Greensolver supports Innergex with wind assets acquisition

Greensolver provided expert feedback on 119.5 MW of French wind assets.

Greensolver, the independent technical expert for wind & solar assets, was selected by Canadian renewable energy producer Innergex to provide due diligence advisory work on one of the largest under-construction portfolio in France.

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Greensolver to deliver HSE expertise to ib vogt in the Netherlands

Greensolver to advise ib vogt on HSE on 9.3 MWp Geldermalsen project.

Greensolver, the independent technical expert for wind & solar assets, has been selected by German solar EPC and expert, ib vogt to advise their team on Health & Safety topics.

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Greensolver Index now available for solar assets

Asset manager Greensolver launches new version of its benchmarking tool allowing performance comparison of solar parks.

Greensolver, the independent technical expert for wind and solar assets, has announced that its unique performance benchmarking tool, Greensolver Index, is now available for European solar assets.

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