Assessing the Feasibility of Integrated PV and Wind Farms

Introduction

Wind farms by the nature of wind resource provide power intermittently and unpredictably both on a moment by moment basis and across the days, weeks and months of the year. This unpredictability can cause technical problems for the electricity grid through power quality fluctuations. It also results in an inability for the developer to fully exploit the revenue opportunities of the fixed grid connection associated with each individual wind farm.

Wind farms by the nature of wind resource provide power intermittently and unpredictably both on a moment by moment basis and across the days, weeks and months of the year. This unpredictability can cause technical problems for the electricity grid through power quality fluctuations. It also results in an inability for the developer to fully exploit the revenue opportunities of the fixed grid connection associated with each individual wind farm.

Diagram of wind farm with own grid connection

There is an expectation in the UK that at a general level when it is more windy, it is less sunny. Therefore, it would seem to be a good opportunity to explore the possibility of filling the physical and generation gap with PV panels. New grid connections are expensive and time consuming to obtain. So if a PV park is added in to an existing wind farm, it would be possible to eliminate this expense in order to make the financial proposition more attractive.

WInitial scoping of the concept identified the following questions as those which should be answered in order to make an overall assessment of the feasibility of adding a PV park to an existing wind farm:

• What is the magnitude and extent of shading from the turbines on the PV panel output and how could this potentially restrict the placement of panels?
• How are wind and solar resources really correlated in the UK and how does this impact the ability of a combined park to fill in the generation gap?
• What are the expected outputs from a theoretical wind farm and solar park at the same UK location and how do their magnitude and timings correlate? What is the ratio of PV nominal to Wind nominal generation capacity which gives the most effective contribution to the generation gap?
• What are the costs and potential revenues achievable from a PV park at a wind farm location? Does this model add up to achieve financial feasibility for the project?

By answering these specific questions, the project aimed to discover the possibilities of utilising the physical space between turbines and how to effectively fill the power generation gap using PV panels in order to demonstrate the feasibility of integrated PV and Wind farms.

Click on the Shading, Climate, Output or Finance tabs above for full details of the investigations carried out to answer these questions.

First of all the group determined the database of any relevant scientific and industrial information by performing overall research around the project. For each specific sections Research has been done separately as well.

The second step of our methodology once we’d got the valuable information was to set up assumptions and justifications for our investigations. Since we’re not dealing with an actual case and rather with a concept, each section required many assumptions and justifications for them. Details are in the individual sections.

Further work was to determine success criteria for our investigations, which is to simply choose the important values that might describe feasibility of the given concept.

Once we knew what we were looking for, we had to establish boundaries for our further work and then finally proceed with analysis and calculations, done by software or self-made.

At the end we focused on interpreting the results of our investigations and drew final conclusions for each section and the whole project.

Project Methodology Overview

Overall, project investigation revealed that adding PV to an existing Wind farm isn’t an effective way to fill the power generation gap. It is however possible to effectively utilise the physical space between the turbines with PV panels.

The project didn’t reveal any major technical barriers to prevent the installation of PV panels into an existing wind farm – it simply uncovered that it isn’t the most effective way of addressing the problem of wind power variability and current economic factors make it financially unattractive.

Read on for more specific feasibility conclusions in the sections below.

Shading

The analysis has proven that even for a tough scenario there is still plenty of space to install PV panels without significant losses. This works very well especially when the land belongs to a developer and so the cost related to losses are lesser than cost of leasing the land at most of the spots. Northern summer shadows are the ones responsible for major losses; fortunately summer shadows are way shorter, so most of the area is unshaded during summer. Winter shadows despite their length won’t really affect yearly output first of all due to lack of sunny days in winter and secondly due to smaller amount of time the sun might provide energy. All in all for a real case the results would be even more promising. Complexity of wind turbine model simulation in the software forced us to use a conservative model; also spacing of the turbines was at its minimum. More detailed please look up the shading section.

Full details of how this conclusion was reached can be found in the Shading main tab.

Climate

The key element of this project was getting a healthy data to work with. It was easy to get "Velocity Exceedence Curve" for locations around the UK which is widely used in the business. Unfortunately this data was useless for our project, since what we needed to see was the correlation between the hourly power outputs of a wind turbine and a PV panel in a certain location. The problem with obtaining this data is, it needs real time on-site wind speed measurements for a long period of time and then sensitive calculations to create an average to create this data. It is a hard work that takes long time which results with it being really expensive. We had extremely hard time to obtain this for free with no chance. In the end we used Strathclyde own ESP-r software to obtain the data we needed for 11 different locations in the UK. The problem with doing this was, conditions were always ideal, so wind turbine was generating max power output for most of the time. In real life, most of the wind farms perform less then their predicted outputs. In the end we realized that a project like this would be more successful if it was applied to an existing underachieving wind farm which has a real time power output data at hand.

Full details of how this conclusion was reached can be found in the Climate main tab.

Output

Due to the positive feedback between the general pattern of the wind and solar resource in the UK according to the data available for use in this project, the addition of PV panels at an existing wind farm location isn’t the most effective way to fill the power generation gap.

Whilst small quantities of PV panels can create a small improvement in grid capacity utilisation, this is insufficient to offset the financial investment required. Adding increasing quantities of PV panels, whilst improving the PV contribution, very rapidly increases the proportion of this additional resource which is wasted. Since one driver for introducing PV was the desire to improve and smooth out energy quality characteristics, introducing over capacity generation with the control systems complexities this brings would seem illogical in the extreme.

Full details of how this conclusion was reached can be found in the Output main tab.

Finance

In order to announce this project feasible, it has to be economically viable and profitable. This is translated to IRR=10%. The results from the financial analysis demonstrated the opposite. Unlikely the major advantage of utilising the same land and grid connection is not adding noticable value to the project's economics. The three most influential factors regarding the IRR are the level of subsidy, the cost of the technology and the efficiency of the technology regarding the annual output.

Even when a best case scenario is occurring, the economics of the solar farm do not indicate the stakeholders to invest into that concept(PV/Wind). This is mostly caused by the recent reform of the solar market.

Although the particular project is mostly never responding to the expectations of the stakeholders, other alternatives might by the case for reversing the undesirable outcome, such as another location, small sized solar schemes etc.

Full details of how this conclusion was reached can be found in the Finance main tab.

There were a lot of details which were scoped out of the project at the early stages in order to concentrate on the fundamental questions of feasibility. However, together with outstanding issues identified through the course of the project, they do offer significant opportunities to more comprehensively understand and improve the feasibility of combined Wind and PV generation for the future.

Energy management

1. Control systems to manage preferential energy spillage for dual technology generation system
2. Financial modelling to determine whether it is more cost effective to spill excess wind or PV generation
3. Introducing energy storage in order to capture excess generation and feed it back into the grid to smooth out variability. Technology selection, energy flow modelling, control system selection and modelling and financial modelling could all be investigated

At the beginning of the project, there was concern with the management of the spill of excess energy. There are three main aspects which could be explored further:

Real data case study

The climate data which was available for this project was limited to long term measured data extracted from ESP-r. Data locations were typically airports and low lying areas where wind farms would not normally be situated. The MET Office carry a more extensive data set including locations which would be much more representative. However, this was not available for use for this project. Gaining access to this data could provide a much clearer picture of detailed matching and energy yields. Even more relevant information would be forthcoming if it were possible to access actual wind turbine output data, matched with irradiance data from the same site in order to further validate the model, the results and conclusions drawn from access to a relatively limited dataset.

Environmental impact and planning

The consent regimes for planning of new Wind Farms and new PV Parks currently have quite different criteria and guidelines applied to them. Whilst Wind Farms occupy a large physical area of land, the turbines themselves occupy only a very small proportion of the space. In practise, once operational, this means that the majority of the land space is still available for continued use for farming or recreation/amenity. In contrast, PV panels are much closer to the ground and themselves occupy the majority of land on which they are situated. By their nature, PV parks are designed to capture as much of the incoming solar irradiance as they possibly can. In combination, this makes the continued use of the land for anything other than extensive sheep grazing impractical. Adding large quantities of PV panels to an existing wind farm would therefore introduce potential land use conflict and significantly influence the desirability of such a scheme to both the landowner and the planning authorities. Assessing the environmental and practical aspects in further detail would provide further insight.

Cost and energy price tracking

Cost of PV panels and inverters formed the most significant portion of investment costs for the combined project. Income was at the mercy of energy prices which are uncertain at the time of writing due to the recent introduction of CFD pricing. There is likely to be an interconnection between technology costs and the subsidy offered to developers for PV electricity production. Tracking and understanding these trends could give further insight into the financial viability of potential future combined generation sites.