Two million watts of Oregon electric solar farm power now coming online
Story by Aubra Salt - The Oregon Herald
|Oregon’s community solar program||Neighborhood Power and Mana Monitoring|
Three of the projects, online now, are the first projects commissioned in Oregon's state-mandated community solar program.
Those who have committed to renewable energy goals include WorldMark by Wyndham, Daimler Trucks, Portland Waterfront Park vacation club resort and Clackamas County. Currently, a small number of subscriptions are still available for small businesses that have energy loads less than 30 kW. This includes restaurants, law offices, gas stations, car washes and low-income residential customers.
"We believe everyone deserves the opportunity to benefit from renewable energy but also recognize not every home, building, or housing situation allows for the purchase and installation of solar PV," said Benjamin S. Collinwood, vice president of sales at Neighborhood Power. "Community solar projects like this help contribute to a healthier environment for the entire community, and Mana Monitoring helps us ensure our solar farms reach peak performance and generate the expected returns we can pass on to subscribers."
Operating under the Oregon Community Solar Program, the project allows qualified low-income customers to purchase energy from local renewable resources that will deliver advantages of renewable energy credits and reduced electricity bills. Subscribers should save an average of 7 to 25% on annual electricity costs.
Neighborhood Power is urging the Mana Monitoring Platform to track, report and manage each farm's production in a centralized area that should allow good performance. Mana Monitoring specializes in managing solar PV and renewable energy sites into a single course that should provide efficient monitoring and automated reporting.
Photovoltaic power stations
Photovoltaic power station, also known as a solar park, solar farm, or solar power plant is a large-scale photovoltaic system designed for the supply of merchant power into the electricity grid. They are differentiated from most building-mounted and other decentralised solar power applications because they supply power at the utility level, rather than to a local user or users. The generic expression utility-scale solar is sometimes used to describe this type of project. The solar power source is via photovoltaic modules that convert light directly to electricity. However, this differs from, and should not be confused with concentrated solar power, the other large-scale solar generation technology, which uses heat to drive a variety of conventional generator systems. Both approaches have their own advantages and disadvantages, but to date, for a variety of reasons, photovoltaic technology has seen much wider use in the field. As of 2019, concentrator systems represented about 3% of utility-scale solar power capacity.
In some countries, the nameplate capacity of a photovoltaic power stations is rated in megawatt-peak , which refers to the solar array's theoretical maximum DC power output. In other countries, the manufacturer gives the surface and the efficiency. However, Canada, Japan, Spain and the United States often specify using the converted lower nominal power output in MWAC, a measure directly comparable to other forms of power generation. A third and less common rating is the megavolt-amperes . Most solar parks are developed at a scale of at least 1 MWp. As of 2018, the world's largest operating photovoltaic power stations surpass 1 gigawatt. As at the end of 2019, about 9,000 plants with a combined capacity of over 220 GWAC were solar farms larger than 4 MWAC .
Most of the existing large-scale photovoltaic power stations are owned and operated by independent power producers, but the involvement of community- and utility-owned projects is increasing. To date, almost all have been supported at least in part by regulatory incentives such as feed-in tariffs or tax credits, but as levelized costs have fallen significantly in the last decade and grid parity has been reached in an increasing number of markets, it may not be long before external incentives cease to exist.
Serpa Solar Park built in Portugal in 2006 The first 1 MWp solar park was built by Arco Solar at Lugo near Hesperia, California at the end of 1982, followed in 1984 by a 5.2 MWp installation in Carrizo Plain. Both have since been decommissioned, though Carrizo Plain is the site for several large plants now being constructed or planned. The next stage followed the 2004 revisions to the feed-in tariffs in Germany when a substantial volume of solar parks were constructed.
Several hundred installations over 1 MWp have been since installed in Germany, of which more than 50 are over 10 MWp. With its introduction of feed-in tariffs in 2008, Spain became briefly the largest market, with some 60 solar parks over 10 MW, but these incentives have since been withdrawn. The USA, China India, France, Canada, Australia, and Italy, among others, have also become major markets as shown on the list of photovoltaic power stations.
The largest sites under construction have capacities of hundreds of MWp and some more than 1 GWp.
Siting and land use
Mosaic distribution of the photovoltaic power plants in the landscape of Southeast Germany The land area required for a desired power output, varies depending on the location, and on the efficiency of the solar modules, the slope of the site and the type of mounting used. Fixed tilt solar arrays using typical modules of about 15% efficiency on horizontal sites, need about 1 hectare/MW in the tropics and this figure rises to over 2 hectares in northern Europe.
Because of the longer shadow the array casts when tilted at a steeper angle, this area is typically about 10% higher for an adjustable tilt array or a single axis tracker, and 20% higher for a 2-axis tracker, though these figures will vary depending on the latitude and topography.
The best locations for solar parks in terms of land use are held to be brown field sites, or where there is no other valuable land use. Even in cultivated areas, a significant proportion of the site of a solar farm can also be devoted to other productive uses, such as crop growing or biodiversity.
Agrivoltaics Agrivoltaics is co-developing the same area of land for both solar photovoltaic power as well as for conventional agriculture. A recent study found that the value of solar generated electricity coupled to shade-tolerant crop production created an over 30% increase in economic value from farms deploying agrivoltaic systems instead of conventional agriculture.
Co-location In some cases several different solar power stations, with separate owners and contractors, are developed on adjacent sites. This can offer the advantage of the projects sharing the cost and risks of project infrastructure such as grid connections and planning approval. Solar farms can also be co-located with wind farms.
Sometimes the title 'solar park' is used to describe a set of individual solar power stations, which share sites or infrastructure, and 'cluster' is used where several plants are located nearby without any shared resources. Some examples of solar parks are the Charanka Solar Park, where there are 17 different generation projects; Neuhardenberg, with eleven plants, and the Golmud solar park with total reported capacity over 500MW. An extreme example is calling all of the solar farms in the Gujarat state of India a single solar park, the Gujarat Solar Park.
Technology Most Solar parks are ground mounted PV systems, also known as free-field solar power plants. They can either be fixed tilt or use a single axis or dual axis solar tracker. While tracking improves the overall performance, it also increases the system's installation and maintenance cost. A solar inverter converts the array's power output from DC to AC, and connection to the utility grid is made through a high voltage, three phase step up transformer of typically 10 kV and above.
Solar array arrangements The solar arrays are the subsystems which convert incoming light into electrical energy. They comprise a multitude of solar modules, mounted on support structures and interconnected to deliver a power output to electronic power conditioning subsystems.
A minority of utility-scale solar parks are configured on buildings and so use building-mounted solar arrays. The majority are free-field systems using ground-mounted structures, usually of one of the following types:
Fixed arrays Many projects use mounting structures where the solar modules are mounted at a fixed inclination calculated to provide the optimum annual output profile. The modules are normally oriented towards the Equator, at a tilt angle slightly less than the latitude of the site. In some cases, depending on local climatic, topographical or electricity pricing regimes, different tilt angles can be used, or the arrays might be offset from the normal east–west axis to favour morning or evening output.
A variant on this design is the use of arrays, whose tilt angle can be adjusted twice or four times annually to optimise seasonal output. They also require more land area to reduce internal shading at the steeper winter tilt angle. Because the increased output is typically only a few percent, it seldom justifies the increased cost and complexity of this design.
Dual axis trackers
Bellpuig Solar Park near Lerida, Spain uses pole-mounted 2-axis trackers To maximise the intensity of incoming direct radiation, solar panels should be orientated normal to the sun's rays. To achieve this, arrays can be designed using two-axis trackers, capable of tracking the sun in its daily orbit across the sky, and as its elevation changes throughout the year.
These arrays need to be spaced out to reduce inter-shading as the sun moves and the array orientations change, so need more land area. They also require more complex mechanisms to maintain the array surface at the required angle. The increased output can be of the order of 30% in locations with high levels of direct radiation, but the increase is lower in temperate climates or those with more significant diffuse radiation, due to overcast conditions. For this reason, dual axis trackers are most commonly used in subtropical regions, and were first deployed at utility scale at the Lugo plant.
Single axis trackers A third approach achieves some of the output benefits of tracking, with a lesser penalty in terms of land area, capital and operating cost. This involves tracking the sun in one dimension – in its daily journey across the sky – but not adjusting for the seasons. The angle of the axis is normally horizontal, though some, such as the solar park at Nellis Air Force Base, which has a 20° tilt, incline the axis towards the equator in a north–south orientation – effectively a hybrid between tracking and fixed tilt.
Single axis tracking systems are aligned along axes roughly north–south. Some use linkages between rows so that the same actuator can adjust the angle of several rows at once.
Power conversion Solar panels produce direct current electricity, so solar parks need conversion equipment to convert this to alternating current , which is the form transmitted by the electricity grid. This conversion is done by inverters. To maximise their efficiency, solar power plants also incorporate maximum power point trackers , either within the inverters or as separate units. These devices keep each solar array string close to its peak power point.
There are two primary alternatives for configuring this conversion equipment; centralized and string inverters, although in some cases individual, or micro-inverters are used. Single inverters allows optimizing the output of each panel, and multiple inverters increases the reliability by limiting the loss of output when an inverter fails.
Waldpolenz Solar Park is divided into blocks, each with a centralised inverter These units have relatively high capacity, typically of the order between 1 MW up to 7 MW for newer units , so they condition the output of a substantial block of solar arrays, up to perhaps 2 hectares in area. Solar parks using centralized inverters are often configured in discrete rectangular blocks, with the related inverter in one corner, or the centre of the block.
String inverters String inverters are substantially lower in capacity than central inverters, of the order of 10 kW up to 250 KW for newer models , and condition the output of a single array string. This is normally a whole, or part of, a row of solar arrays within the overall plant. String inverters can enhance the efficiency of solar parks, where different parts of the array are experiencing different levels of insolation, for example where arranged at different orientations, or closely packed to minimise site area.
Transformers The system inverters typically provide power output at voltages of the order of 480 VAC up to 800 VAC. Electricity grids operate at much higher voltages of the order of tens or hundreds of thousands of volts, so transformers are incorporated to deliver the required output to the grid. Due to the long lead time, the Long Island Solar Farm chose to keep a spare transformer onsite, as transformer failure would have kept the solar farm offline for a long period. Transformers typically have a life of 25 to 75 years, and normally do not require replacement during the life of a photovoltaic power station.
System performance Main article: photovoltaic system performance
Power station in Glynn County, Georgia The performance of a solar park is a function of the climatic conditions, the equipment used and the system configuration. The primary energy input is the global light irradiance in the plane of the solar arrays, and this in turn is a combination of the direct and the diffuse radiation. In some regions, soiling, i.e. the accumulation of dust or organic material on the solar panels that servers to block incident light, is a significant loss factor.
A key determinant of the output of the system is the conversion efficiency of the solar modules, which will depend in particular on the type of solar cell used.
There will be losses between the DC output of the solar modules and the AC power delivered to the grid, due to a wide range of factors such as light absorption losses, mismatch, cable voltage drop, conversion efficiencies, and other parasitic losses. A parameter called the 'performance ratio' has been developed to evaluate the total value of these losses. The performance ratio gives a measure of the output AC power delivered as a proportion of the total DC power which the solar modules should be able to deliver under the ambient climatic conditions. In modern solar parks the performance ratio should typically be in excess of 80%.
System degradation Early photovoltaic systems output decreased as much as 10%/year, but as of 2010 the median degradation rate was 0.5%/year, with modules made after 2000 having a significantly lower degradation rate, so that a system would lose only 12% of its output performance in 25 years. A system using modules which degrade 4%/year will lose 64% of its output during the same period. Many panel makers offer a performance guarantee, typically 90% in ten years and 80% over 25 years. The output of all panels is typically warranted at plus or minus 3% during the first year of operation.
The business of developing solar parks
Westmill Solar Park is the world's largest community-owned solar power station Solar power plants are developed to deliver merchant electricity into the grid as an alternative to other renewable, fossil or nuclear generating stations.
The plant owner is an electricity generator. Most solar power plants today are owned by independent power producers , though some are held by investor- or community-owned utilities.
Some of these power producers develop their own portfolio of power plants, but most solar parks are initially designed and constructed by specialist project developers. Typically the developer will plan the project, obtain planning and connection consents, and arrange financing for the capital required. The actual construction work is normally contracted to one or more EPC contractors.
Major milestones in the development of a new photovoltaic power plant are planning consent, grid connection approval, financial close, construction, connection and commissioning. At each stage in the process, the developer will be able to update estimates of the anticipated performance and costs of the plant and the financial returns it should be able to deliver.
Planning approval Photovoltaic power stations occupy at least one hectare for each megawatt of rated output, so require a substantial land area; which is subject to planning approval. The chances of obtaining consent, and the related time, cost and conditions, varying from jurisdiction to jurisdiction and location to location. Many planning approvals will also apply conditions on the treatment of the site after the station has been decommissioned in the future. A professional health, safety and environment assessment is usually undertaken during the design of a PV power station in order to ensure the facility is designed and planned in accordance with all HSE regulations.
Grid connection The availability, locality and capacity of the connection to the grid is a major consideration in planning a new solar park, and can be a significant contributor to the cost.
Most stations are sited within a few kilometres of a suitable grid connection point. This network needs to be capable of absorbing the output of the solar park when operating at its maximum capacity. The project developer will normally have to absorb the cost of providing power lines to this point and making the connection; in addition often to any costs associated with upgrading the grid, so it can accommodate the output from the plant.
Operation and maintenance Once the solar park has been commissioned, the owner usually enters into a contract with a suitable counterparty to undertake operation and maintenance . In many cases this may be fulfilled by the original EPC contractor.
Solar plants' reliable solid-state systems require minimal maintenance, compared to rotating machinery for example. A major aspect of the O&M contract will be continuous monitoring of the performance of the plant and all of its primary subsystems, which is normally undertaken remotely. This enables performance to be compared with the anticipated output under the climatic conditions actually experienced. It also provides data to enable the scheduling of both rectification and preventive maintenance. A small number of large solar farms use a separate inverter or maximizer for each solar panel, which provide individual performance data that can be monitored. For other solar farms, thermal imaging is a tool that is used to identify non-performing panels for replacement.
Power delivery A solar park's income derives from the sales of electricity to the grid, and so its output is metered in real-time with readings of its energy output provided, typically on a half-hourly basis, for balancing and settlement within the electricity market.
Income is affected by the reliability of equipment within the plant and also by the availability of the grid network to which it is exporting. Some connection contracts allow the transmission system operator to constrain the output of a solar park, for example at times of low demand or high availability of other generators. Some countries make statutory provision for priority access to the grid for renewable generators, such as that under the European Renewable Energy Directive.
Economics and finance In recent years, PV technology has improved its electricity generating efficiency, reduced the installation cost per watt as well as its energy payback time . It had reached grid parity in at least 19 different markets by 2014, and in most parts of the world subsequently to become a viable source of mainstream power.
As solar power costs reached grid parity, PV systems were able to offer power competitively in the energy market. The subsidies and incentives, which were needed to stimulate the early market as detailed below, were progressively replaced by auctions and competitive tendering and leading to further price reductions.