Using landfill sites to generate power is a common approach to the management of greenhouse gases. But, as gas production declines while alternative use of such sites remains perhaps decades away, developers are considering extracting residual energy by installing renewables....
In February 2016, New Jersey-based utility company Public Service Electric and Gas Company (PSE&G) announced that its nearly 13 MW L&D Solar Farm project had started suppling power to the grid.
At face value the commissioning of another US utility-scale solar PV project may appear of limited note, but this installation is different – it is built upon a closed landfill site. One of the largest such projects in the country, it also marks a continuing trend that is seeing developers in the USA and elsewhere eke out residual commercial value from landfill sites through the production of energy.
Landfill sites, with huge volumes of organic material producing methane gas through decomposition, are already widely used as sources of energy. In many regions the management of such products of decomposition is mandated. Burning this gas in reciprocating engines to produce electrical energy not only resolves the issue of managing an extremely potent greenhouse gas, but also provides a revenue stream for site owners.
However, once capped, gas production from landfill follows a well-understood curve, gradually tailing off over a period of several decades or more as the organic fractions are consumed.
Now though, site owners are exploring further energy producing endeavours to add value to landfill sites that may not be suitable for other commercial uses.
Todd Hranicka, PSE&G’s Director of solar energy, explains the rationale: “In terms of benefits, from our perspective the primary benefit is that landfill solar provides a productive use to an otherwise unproductive piece of land.”
Building a case for landfill solar
The development of brownfield sites, such as former landfills, potentially offers a number of environmental and commercial advantages. But the re-development opportunities of such sites can be restricted by regulatory frameworks.
Hranicka explains: “Here in New Jersey you have very limited use to which you could do with a landfill or a brownfield in terms of building developments or homes or golf courses, so most of these sites just sit in an unproductive manner for decades. We’ve been able to provide productive use by adding solar to landfills.”
Indeed, the L&D project, comprised of 41,720 solar panels covering 53 acres of landfill spanning the New Jersey towns of Eastampton, Lumberton and Mount Holly, is the eighth to be built on a landfill or brownfield site by PSE&G, with a combined capacity of 45 MW.
These installations have been executed under the Solar 4 All initiative, a 125 MW programme that aims to develop urban and brownfield sites for large-scale, grid-connected solar projects. There are currently around 115 MW of projects in service. In this case Waste Management of New Jersey, Inc. owns the L&D Landfill and PSE&G owns and operates the solar farm.
A fourth landfill solar project is now under construction, with the full 125 MW of capacity under the programme projected to be installed by the end of the year, of which roughly a third are to be sited on landfill or other brownfield locations.
The Solar 4 All programme came on the heels of a number of key bills passed the New Jersey legislature, including a 2008 ruling that enables regulated utilities such as PSE&G to earn a rate of return on capital invested in renewable energy or energy efficiency developments. Operational revenues or savings are used to offset the cost of the programme under the terms of the state Board of Public Utilities (BPU).
Hranicka explains: “We earn a 10% rate of return. All the energy revenue, capacity revenue and S-RECs - solar renewable energy certificates - flows back to the rate payers.”
PSE&G put forward the proposed programme in 2009 and, with the plans accepted by the BPU, has invested more than US$500 million on Solar 4 All to date.
Nonetheless, while regulated utilities are guaranteed a rate of return on their investments, the commercial value of such developments is becoming increasingly recognised.
For instance, UK-based engineering consultancy firm Wardell Armstrong notes that project returns of 8-9% are possible for long term investors in utility-scale solar projects. In a white paper the company’s Regional Director Haydn Scholes argues that understandable criticism about the use of agricultural land for solar farms and preference for brownfield land is driving the use of sites such as landfills.
This is a point picked up by Geraint Rees, General Manager for Landfill at French giant SUEZ. Rees outlines the company’s landfill solar strategy: “Our focus right at the start of this was to try make good use of land that was in the process of being put back to countryside and knowing that it would take time to settle back and restore itself. Our view is: ‘What can we do in the interim period to put something on it which would be of benefit to purely pastureland?’”
In 2014 SUEZ forged an alliance with British Solar Renewables (BSR) to develop a number of landfills as solar power projects. BSR conducted an assessment of the SUEZ UK landfill estate to shortlist suitable sites and a planning application for the development of a site near London’s Heathrow airport was submitted in October 2015. “Regrettably this has now been refused by the local planning authority,” Rees says.
Rees argues that the long-term nature of landfill site restoration and the scale of such sites naturally lends itself to solar development: “We know that a landfill site doesn’t immediately become suitable for any arable agricultural use. It has to be done in staged manner and that takes many, many years.
“We put it back to creating additional energy source, over and above that which we have already been successful with in our landfill-gas generation projects.”
This is key point. Landfill sites already often come equipped with significant existing generation capacity infrastructure, notably a grid connection. As landfill gas production declines, additional power export capacity may become available. In addition, potentially the grid link could not only be optimised to support solar production during daylight hours, but also power production from gas during periods of darkness or low irradiation.
“One of the areas we are looking to benefit from in the future is the grid connection that we have as the supply into that grid connection is reduced. We will be looking at alternative ways of generating electricity at that facility to use up the spare capacity. So even if it is not today, because we are using all of our grid connections for landfill gas, as the gas depletes we might then be able to start switching over to solar,” Rees says.
However, while a suitable grid connection evidently has value, where such a connection is not available this can present a major stumbling block for landfill energy projects.
Say Rees: “In most cases we struggled because there was literally no capacity in the area with which we wanted to connect to the grid.”
Technical challenges
Although there are clear commercial benefits associated with ‘repowering’ landfill sites there are a number of technical issues which must be addressed in order to develop ground-mounted solar generation.
A major challenge is differential settlement which occurs as landfills age and which can be impacted by variations in depth, types of waste and the decomposition rate. Furthermore, former landfill sites are typically sealed with an engineered cap to prevent water penetration and the escape of landfill gas.
Rees explains: “One of the areas that you have to be very careful of when thinking of putting a solar farm on landfill is the way in which the solar panels are anchored to the ground. Bearing in mind that in most landfill sites, of course, these sites have waste contained in them. And they have a very scientifically designed and constructed cap to seal the sites off and to ensure management of the gas and water management.
The design that we have to do was different to that you would use on a virgin field. We had to design specific anchors that were not likely to impede or damage the containment of the cap that we had put on top of the landfill. And that was subject to considerable technical review.”
This is a point echoed by Hranicka. He notes that even the though the sites selected for development have been closed for decades – Kinsley Landfill, home to an 11.18 MW PSE&G solar project closed in 1987 for example - ballasted systems are used to support the solar panels “so the system rests on top of the landfill cap”.
And to ensure solar panel performance can be maintained German engineering, procurement and construction company Juwi, for example, has developed a design for landfill sites using a telescopic racking system that keeps panels in the correct orientation as the ground settles.
Indeed, geotechnical considerations have limited the use of such sites for wind power developments, although a number of proposals and projects featuring wind power at landfill sites have been put forward.
For instance, in 2010 a 3.2 MW wind energy project was completed at the Frey Farm landfill in Pennsylvania, USA, featuring two turbines. The $9.5 Million project supplies power to the nearby Turkey Hill Dairy.
Rees confirms that a company within GDS Suez group carried out a detailed survey of landfill sites to assess suitability for wind power. “Reluctantly, they reported back that none of them were suitable for wind project because of a number of issues.
“We were not looking ever to build a turbine on the landfill but on land perhaps for example where a weighbridge or site offices might have been there or what we call virgin land. We were unsuccessful in that project on that basis that, firstly, for many of our sites the footprint of the site is much taken up by land fill. And, secondly, proximity to properties and other infrastructure such as radars. The survey that we carried out proved that none of our sites were suitable for wind.”
Commercial challenges for solar landfills
While some sites are clearly well placed for additional generation capacity from solar, not all are suitable, as Hranicka explains: “There’s 1,000 landfills in New Jersey, we whittled that down to 400 in our electric service territory, we hired an environmental engineering firm by the name of Weston Solutions to create what we call the ‘Weston 45’, a list of 45 screening criteria which deems a site developable. We screened the 400 sites in our electric service territory and came up with 30 [suitable] sites and we're now in the process of building our fourth landfill project.”
Indeed, UK-based waste management firm Biffa has also considered installing solar on its landfill sites. However, Jeff Rhodes, Head of Environment and external affairs at Biffa explains that following a review “the conclusion from that was there was nothing that was attractive enough for us to take forward, we felt, at the present time, but it was something to keep under review.”
Biffa has had 1,000 solar panels installed at its Materials Recycling Facility in Edmonton, London, producing 250 kWp, but Rhodes highlights the different challenges associated with long-term site management when it comes to landfill sites rather than buildings. In particular he notes issues associated with sub-surface gas lines and potential contractual issues with the owner/operators of solar installations: “There can be complications putting it [solar] on landfill sites where you’ve got gas management infrastructure that you may need to re-lay at times If you’ve got somebody else’s solar panels sitting on top you’ve then got other contractual and practical issues to address”
Rees also emphasises the challenge of gas management at landfill sites: “All of our sites have got control points around and in the sites to monitor and control leachate and landfill gas. Whatever we did with any solar park we needed to ensure that we didn’t impede on that ability to do that so the design of where the panels were to be installed have to be designed around the priority of the environmental monitoring and environmental compliance.”
Rhodes outlines the business rational for Biffa: “Although, for us, the commercial case at present was not as compelling as some other business opportunities it is one of those things you keep reviewing, as it could prove more attractive in future”.
Certainly, there is scope for additional value from landfill solar, as Rees notes: “One area we have focused on recently is whether any of our generation schemes for solar could stand on their own two feet with direct supply to the industry, rather than suppling it through the national grid.”
“That could be a future area and is an area that is causing some interest. We are thinking if we were able to find an adjoining, adjacent user of energy then we could supply this directly to them and that might enable some projects that currently are unviable to become viable.”
Ultimately though, perhaps the biggest driver for the future of new renewable developments on closed landfill sites comes from wider environmental policy, as Hranicka notes: “As New Jersey’s largest and oldest utility, we see renewables as part of the future; and this is a way for us to support public policy and earn a rate of return for our shareholders; so it’s a win-win.”
David Appleyard is a freelance journalist
