What is SolaRoad?

SolaRoad is a new concept for the generation of sustainable energy. Here, the road surface also acts as a solar panel. The generated electrical energy can be used for various applications, such as road lighting and traffic systems. Households may benefit from it as well. In time, electric cars might possibly be able to make use of the energy. The energy will then actually be generated at the place where it is needed: this is a big step towards an energy-neutral mobility system.

Who is developing SolaRoad?

The idea for SolaRoad was born at TNO. The Province of Noord-Holland, Ooms Civiel and Imtech have joined to develop SolaRoad. Together they form a consortium.

What is a solar cycle path?

A solar cycle path is an application of SolaRoad in a cycle path. In other words, it is a cycle path that absorbs solar energy and converts it into electrical energy.

Is it possible to cycle on glass?

The SolaRoad cycle path will be safe, comfortable and sustainable. We realize this with several technical solutions:

Skid resistant road surface
The surface of the SolaRoad cycle path consists of a layer safety glass with a skid resistant coating on it. The coating ensures that the road users have sufficient grip and are able to safely drive and walk on it. In the laboratory the skid resistance of the road surface is being tested. The skid resistance may not be lower than that of a normal cycle path, not even in the long run.

Strong road surface
Special attention is paid to the strength of the road surface. The tempered glass in the top layer and the solar cells underneath are applied in such a way that they can withstand everyday use. Not only cyclists must be able to ride on it, but for example service vehicles as well. In addition, shock loads of falling objects should be taken into account. Influences from the environment (heat, cold, salt, …) must not cause any problems. These aspects are being examined in the laboratory using various mechanical and thermal tests.

Comfortable road surface
SolaRoad consists of prefabricated elements, which are placed end to end to form a cycle path. In order to achieve a good riding comfort for the cyclists, the elements are interconnected to one another. This link ensures that no height differences can arise at the transitions between the elements. The road construction is designed to avoid damage from in the soil underneath, or from expansion and contraction due to temperature changes.

Why would you include solar cells in the road and not next to it or on rooftops?

It is not either-or, but both-and. The total electricity consumption in the Netherlands lays around 110,000 GWh and increases annually by about 3% (according to CBS Netherlands). This means that if all suitable roofs in the Netherlands would be equipped with solar panels, they could only supply approximately 25% of the Dutch electricity demand. In order to reach a larger share of solar energy, a larger surface area of solar panels is required and therefore alternative types of solar cell applications than only rooftops must be found. In this regard, roads are an interesting option. The approximately 140,000 km of roads in the Netherlands cover a total area of about 400-500 km2, which is significantly larger than the total (suitable) roof surface area. With the integration of solar cells in road infrastructure, a great potential has come into existence, creating a complementary market for solar panels.

Why is the pilot a cycle path (and not a highway)?

A cycle path is more practical as a pilot site (than for example a highway) for various reasons. A cycle path is less heavily loaded, because the means of transport that use it are lighter. It is also easier on a cycle path to make any possible adjustments and to implement improvements. This way, we can learn and develop faster. In addition, a cycle path is a typically Dutch product.

Why has the location in Krommenie been chosen?

The pilot location in Krommenie meets several important criteria. It is a separate cycle path with free space on both sides. This is important in order to be able to make measurements next to and around the cycle path easily and to make any possible adjustments or improvements. In addition, the cycle path is located conveniently with respect to the sun. The path is intensively used, so that the influence of the use can properly be monitored. Also, the location is easily accessible by both car and train, the cycle path is under the control of the Province Noord-Holland and the current asphalt surface is to be replaced soon. Finally, we prefer working with an enthusiastic and progressive community that is engaged in renewable energy. This is how we ended up in Zaanstad. These arguments together make the selected cycle path in Krommenie a suitable location.

Why isn’t SolaRoad applied over the full width of the bicycle road?

We aim at maximum efficiency in the process of learning and improving, using a combination of (lab) experiments, pilot testing and further development. This helps us to make the time to market as short as possible. In June we made the final decisions on the pilot-design. At that stage, we chose to use apply SolaRoad on only one lane of the bicycle road in Krommenie. This allows us to execute the planned research and monitoring programme in full, while saving costs in the pilot. The extra money can be deployed for further development.
Moreover, the other lane on the bicycle road will be used for specific R&D to improve the transparent top layer. In a number of test sections in this lane, dedicated measurements will be carried out to evaluate various solutions for the top layer e.g. on pollution and wear. Loads and exposure are almost identical to the adjacent SolaRoad-lane. The test sections can easily be replaced, to support accelerated optimization of the top layer.


How will the generated energy be used?

During the pilot, the generated electrical energy will be supplied to the electricity grid, just like most solar panels on rooftops. It is expected that the pilot cycle path of approximately 100 m will generate as much electricity as is used by 2-3 average households annually. When SolaRoad is going to be applied extensively, straightforward supply to the electricity grid will not be an optimal solution anymore. For example, smart ICT applications that help to distribute the energy production at peak times (lots of sun) and dip times (night) as efficiently as possible are needed then. This issue will be addressed in the pilot study as well.

How can the solar cells be protected against use (load and shock), environment (heat and cold) and vandalism?

The solar cells are located between two sheets of tempered glass in a concrete housing. The results of the mechanical and thermal tests of the prototype show that the elements are able to withstand everyday use very well. The glass surface can also resist large impact loads. Damage caused by vandalism, however, can never be ruled out. We use safety glass. When this type of glass breaks, it will break in the form of a lot of small pieces. There will be no dangerous shards. Moreover, the glass remains in its place due to the coating on the surface and the frame. Thus, even when the glass is broken, it can still be safely walked and cycled on, until repair can take place.

How strong is the glass?

We use tempered glass that is particularly strong and that is mounted in a concrete housing. The strength of the glass in the housing is being mechanically tested in different ways. For example, extreme traffic loads are simulated in a bench press, pressing different tyre types on the surface with great force. Also, we drop steel balls and bags with marbles of different sizes and from different heights on the SolaRoad surface, in order to test the resistance to impact loads. This is based on internationally recognized standards. In this way, we test whether the glass is safe for use in practice.

Do shards occur if the road breaks?

No, we make use of safety glass. When this type of glass breaks, it will break in the form of a lot of small pieces. There will be no dangerous shards. Moreover, the glass remains in its place due to the coating on the surface and the frame. Thus, even when the glass is broken, it can still be safely walked and cycled on, until repair can take place.

Will SolaRoad break due to tree roots that may grow under the road?

The current version of SolaRoad has been tested in the laboratory on structural strength. A specific ‘tree root test’ was not possible, but the concrete elements are designed and produced in such a way that they will not break very easily. To prevent height differences at the transitions of the elements, we pay special attention to the way in which they are interconnected. When dealing with factors from the (natural) environment, we make full use of existing knowledge and experience with prefabricated slabs.

Is it possible to use existing solar cells or do they have to be adapted? If so, what are the costs?

Technically, there is no need for special solar cells. In the pilot, we make use of standard silicon solar cells. Of course, the solar cell, the translucent surface and the other components must be adjusted to one another. We develop the SolaRoad concept in such a way that in time we can integrate other types of solar cells, for example thin-film solar cells. A decisive factor for the choice of the best solar cell technology is the economical assessment of costs versus benefit (revenues).


How do you deal with generating, using and storing energy/electricity? How do you deal with peak and dip demand?

SolaRoad is an example of decentralized energy generation (in contrast to central generation in large power stations). We will develop ICT solutions to optimally distribute the energy from SolaRoad amongst applications, for example along the road (lighting, charging of electric bicycles) or to the energy grid. ICT systems help to smartly switch between roadside applications. The difference between the moment of generation and use is not unique for SolaRoad, but it plays a role with all forms of solar and wind energy. SolaRoad can therefore make use of techniques that already exist or that are being developed in parallel.

What happens when there is a traffic jam on SolaRoad?

Traffic jams mean a heavier traffic load and lots of shade on the underlying road surface. The traffic load is not a problem. The shadows during a traffic jam will cause the energy yield to hold up locally for a short amount of time. However, for most of the roads the amount of time that traffic jams occur is so short that we do not expect significant yield losses. On road sections where a lot of traffic jams occur, application of SolaRoad paving is less suitable. The exact influence of shading by road users is part of the pilot study.


Is SolaRoad safe for cyclists and motorists? Does SolaRoad meet all requirements with respect to (traffic) safety?

The main design requirement that is imposed on SolaRoad is that it meets the requirements regarding safety that apply to regular pavement.

What is the effect of a translucent cover layer on the vehicle/the user? How do we experience a road of glass?

The coating on the road surface looks very similar to a regular road. As a result of the large light transmittance, the underlying solar cells will probably be slightly visible. It is expected that the road surface will lead to a positive and safe experience for road users, posing no obstacles for normal use. During the pilot this will be further investigated.

Do users suffer from reflection?

The starting point for the SolaRoad design is that no more discomfort due to reflections may occur than with regular road surfaces. This is an important factor in the development of the top layer. In the laboratory, extended optical examinations are carried out, in which reflection is measured as well. During the pilot this aspect will also be monitored.

Is it possible for cyclists/users to get a current surge from the road?

No, the electrical components are shielded very well. Moreover, the voltage per element is low.

Costs and revenues

 What was the 3.5 million euro’s used for?
The €3.5 mln was invested by the various partners in the research and development process, which has so far taken five years. The test route in Krommenie represents just a small part of this. We consciously opted for an initial pilot  involving a short length of cycle path and yielding only a small amount of energy (enough to power around three households). This is enough to generate a wealth of practical information while keeping pilot costs down so that we can allocate a larger part of the available funds to developing SolaRoad into a marketable product.     

What are the costs per squared metre? How do these costs compare to ordinary roads and cycle paths?

In the current development stage it is too early to make reliable statements about this. The starting point for the development is that the balance of costs and benefits of the life span is positive, compared to existing road surfaces. SolaRoad is being developed by a tripartite consortium of partners, in which industry, knowledge institutes and government join forces in order to innovate. The intention is that the product will soon become available on the open market and that an appropriate and healthy business model will be developed.

Is it economically feasible?

The techno-economic feasibility study indicates that it is possible to achieve a return of investment within a life span of 20 years. A side note here is that the production, management and maintenance of this new type of road are yet to be optimized. Eventually, we are aiming for a payback period of 15 years or less.

Does SolaRoad have additional maintenance costs? How much?

In the development of SolaRoad the starting point is that SolaRoad meets the same requirements as regular pavement types. In current studies, we assume regular maintenance regimes. According to expectations, an optimization can still be made, in which the maintenance of the technical systems will be integrated.

Can pollution of the road surface reduce the yield of SolaRoad?

Pollution will certainly affect the amount of light that falls through the top layer. By making the top layer dirt repellent and by putting the road under a sufficient slope, we make sure that the effects of pollution as small as possible. The exact degree of pollution is not clear yet. Currently, we are performing experiments on this topic. The profits are expected to be lower than solar panels on rooftops. What the yield will be exactly is one of the research questions in the pilot.

Even the most optimistic scenarios foresee in 2030 not more than 10% share of electric vehicles. What is the use of such a road then?

SolaRoad provides solar electricity, which can be used for vehicles that drive across/over it, but also for other energy users, such as street lighting, households, etc. The success of the transition to electric vehicles is therefore not a prerequisite for SolaRoad. In contrast, a large-scale application of SolaRoad may work as an enabler or incentive for electric mobility: together they may have a greater chance of success than separately.


The first results are known. What does the development process look like and what is still needed for this?

For SolaRoad we are continuously developing knowledge and products in the field of engineering, material choice, energy distribution and (social) business model. Also the boundary conditions that are set from user perspective (safety, comfort) are further investigated. The next step in this process is the realization of a first practical application of SolaRoad in the form of a cycle path. Krommenie is going to be the first worldwide. Here, a 100-meter cycle path will be built in 2014, which will generate electricity using built-in solar cells. Knowledge and product development will be linked to the realization of this practice test.

Will SolaRoad be applied in highways as well? What should be done in order to do this?

The next steps in the development and scaling up of SolaRoad will be (pilot) applications provided in smaller motorways (for example municipal roads) and in specific applications such as bus lines. Whether application onto highways will be possible in the future, cannot be assessed yet. For the potential of SolaRoad, application in highways is not necessary: of the 140,000 km of roads in the Netherlands approximately 90% consists of municipal roads. Highways cover only 5% of the road surface.

Why is it important for TNO to be involved in SolaRoad?

TNO focuses on innovations to increase the sustainability of energy supply and infrastructure. The R&D-organization has responded to this with technologies that make fossil fuel extraction and use more efficient and cleaner and combines this with renewable energy sources. TNO develops knowledge and encourages innovations, in cooperation with companies and governments. A good example is SolaRoad, a road that generates electricity: sustainable and profitable.

Which parties will be involved as well?

We are always open to parties wishing to contribute to SolaRoad with specific expertise or (financial) resources.

How can you get involved as a business, institution or government?

Anyone interested in participating in SolaRoad should contact Gerrit Jan Valk from TNO (Gerritjan.Valk@tno.nl, +31 (0)6 53 54 80 30).

What is the position of the consortium compared to Solar Roadways from the U.S.A.?

The SolaRoad consortium uses an approach that is comparable to that of Solar Roadways. The developments are at a similar stage: the stage of the prototype. There are differences too, for example in the technical details. Solar Roadways aims at the integration of many different features, which include making texts (STOP, SLOW DOWN) by means of LEDs in the road and the signalling of crossing pedestrians. We have chosen to focus entirely on the generation of electricity and only afterwards to consider the integration of other functions. This way, we are working as fast as possible towards a well-functioning and practically applicable solution.

What is the difference with heat extraction from asphalt (www.wegvandetoekomst.nl)?

For heat extraction from roads commercially viable solutions exist. Road Energy Systems is a product of Ooms Civiel (partner in the consortium), consisting of water filled pipes that run through an asphalt road. The sun heats the road surface, the temperature of the water in the pipes increases, and the hot water is pumped out of the road. SolaRoad generates electricity using solar cells in a translucent road surface. The advantage of electricity is that it can be transported more easily and that it can be used for more purposes. In the future, both systems may possibly be combined.