HOW TO CHOOSE BETWEEN SOLAR, HYBRID OR GRID-CONNECTED STREET LIGHTS

When planning a new lighting project, one of the new most important decisions is how the lighting will be powered.

Should the project use completely solar, a hybrid solar-grid system, or grid-connected streetlights?

At SolarVision Lighting Technologies (SVLT), we work with councils, developers, highways teams, commercial organisations and private estates across the UK. Although there are some key factors which can determine what the power source should be in circumstances, most of the time the customer has the choice. The correct power source depends on the required lighting performance, the site conditions, the available infrastructure and the acceptable level of operational risk.

The decision should not begin with the column style or the wattage of the light head. It should begin with the lighting requirement.

Lighting Design

The first step is to find out if you need a formal lighting design. This would include a contour design and a calculation report. These designs are necessary whenever going through planning.

If you do not need planning for your project, then a ‘concept’ design is sufficient which is usually the case when the columns are 4 metres or shorter and on private land. A concept design is more of a decorative illustration to what you can expect once the lights are installed. If you don’t need a formal design or need to go through planning, you then have full reign to make your own decisions about the options below.

Before choosing the power source, a designer must establish what the scheme needs to achieve.

Road and public-realm lighting schemes are normally designed using specific BS or BS EN (British Standard European Norm) standards, alongside the relevant local authority specification. These standards help determine the appropriate lighting class and the required photometric performance.

In general:

P classes relate to pedestrian routes, public spaces and subsidiary roads.

M classes relate primarily to motorised traffic routes.

C classes apply to conflict areas where different road users interact.

The lighting class may set requirements for average illuminance, uniformity, glare control and lux levels. Wattage and lumens alone do not prove that a scheme will provide suitable lighting. The optical distribution, mounting height, column spacing and surrounding environment must also be considered.

Once the required lighting performance has been established, the designer can calculate the electrical demand and determine whether solar, hybrid or grid power is appropriate.

Off-Grid Solar Street Lighting

An off-grid solar streetlight operates completely independent and is self-sufficient.

During daylight hours, the photovoltaic cells generate electricity. This energy is managed by the controller and stored within the battery. During nighttime, the battery supplies the LED’s according to its programmed lighting profile.

A properly designed solar streetlight should therefore be considered as a complete energy system consisting of:

·      Photovoltaic’s

·      Battery

·      LED optics

·      Controller

·      Lighting programme

·      Structural lighting column

Solar street lighting is often the strongest option where there is no convenient grid connection. It avoids trenching, underground electrical cabling, feeder pillars, landlord metres and ongoing electricity consumption. This can significantly reduce disruption on pathways, parks, private roads, car parks and new developments.

Solar yield

The available solar energy changes according to location, season, panel orientation, surrounding buildings, vegetation and shading.

Attention must be paid to winter, when nights are longer and the available solar generation is lower.

A solar lighting design must be based on the site’s worst operating conditions, rather than its best summer performance.

Battery capacity and autonomy

Battery capacity is normally stated in watt-hours. The usable capacity must be sufficient to power the light while maintaining an appropriate reserve for consecutive low-yield days.

Autonomy should be assessed using the battery’s usable energy, not simply the headline battery capacity, and should consider the battery ageing and the programmed lighting profile.

SolarVision’s ASTRAL, for example, combines vertical SOLARWRAP® photovoltaic technology, LiFePO4 battery storage, intelligent controls and programmable lighting operation. The product can be configured as a completely off-grid solar system where grid infrastructure is unavailable or uneconomical. This product is the most comparable solution to a standard grid streetlight.

Solar Is Generally Best When:

·      No practical electricity connection is available

·      Trenching would be disruptive or expensive

·      The site has suitable daylight exposure

·      The lighting demand can be supported through winter

·      The client wants to eliminate ongoing grid electricity consumption

·      Fast installation and minimal ground disturbance are priorities

·      The site is privately owned

Option 2: Hybrid Solar Street Lighting

Hybrid street lighting combines solar generation and battery storage with a grid connection.

The solar system remains the primary energy source. When the available solar energy or battery state of charge falls below the programmed operating level, the controller can call upon the grid supply to maintain the required lighting performance. Once sufficient stored solar energy is available, the system returns to solar operation.

This provides the environmental and energy benefits of solar while retaining the security of a mains connection.

It is important to understand that hybrid does not simply mean that the light uses 50% solar and 50% grid electricity. The actual proportion will depend on:

·      The solar yield at the location

·      The lighting profile

·      Battery capacity

·      LED power

·      Weather conditions

·      Controller programming

·      The threshold at which mains assistance is activated

A well-designed hybrid system should maximise solar utilisation while using the grid only when required.

For a HYBRID ASTRAL, you can expect to achieve 70% solar power 30% grid across the whole year. This is based on a HYBRID ASTRAL performance being set to a highways output. If your project demanded less than a highways output of luminosity, then you can expect to have more of the year powered by solar.  

When Hybrid Becomes the Stronger Option

Hybrid lighting is particularly useful where the required lighting class or operating profile uses a higher energy demand.

This can include:

·      Adopted roads and footways

·      Higher-output luminaires

·      Areas requiring consistent full-night operation

·      Locations where dimming lighting is not acceptable

·      Sites with some winter shading

·      Projects where mains supply already exists

Hybrid Is Generally Best When:

·      A grid connection is available

·      The client wants to reduce grid energy consumption

·      Lighting performance cannot be reduced during poor weather

·      The site has a demanding lighting class

·      The lighting authority requires additional operational resilience

·      Existing grid-connected columns are being replaced or retrofitted

Hybrid can be a sensible middle ground for those that want to introduce renewable technology without depending entirely on grid energy.

It is now important to mention that no highways department in the UK warrants the use of any semi/fully renewable powered light on public highways. This is due to the unreliable aspects of stormy/heavy overcast weather for prolonged periods of time which can effect a lights performance. Therefore, potentially causing a danger to pedestrians or vehicles. Except a Hybrid configuration would eliminate that risk and we are pushing for this outdated guidance to be revised based on our hybrid controller which does not compromise luminosity or safety.

Option 3: Grid-Connected Street Lighting

Grid-connected street lighting remains appropriate for many applications.

The luminaire is powered through an underground electrical connection, usually using a metered or unmetered supply arrangement. It does not require renewable generation or battery storage to provide normal operation.

The principal advantage is access to a predictable energy supply. This makes grid-connected lighting suitable for locations with high or continuous electrical demand.

However, the column and light head are only part of the overall project cost. A new grid-connected installation will most likely require:

·      Trenching and excavation

·      Ducting and underground cables

·      Electrical jointing

·      Feeder pillars or distribution equipment

·      Network or private supply connections

·      Protective devices and isolation

·      Surface reinstatement

·      Electrical testing and certification

·      Ongoing electricity charges

These infrastructure requirements can make grid-connected lighting significantly more expensive and disruptive where no existing supply is present in the long term.

Grid-Connected Lighting Is Generally Best When:

·      Suitable electrical infrastructure already exists

·      The route carries high volumes of fast-moving traffic

·      The scheme requires a high and continuous electrical load

·      Solar exposure is severely restricted

·      Columns are positioned beneath dense tree cover or between tall buildings

·      Battery storage is unsuitable for the operational requirement

·      The adopting authority specifically requires a conventional system

Grid-connected lighting should not automatically be treated as the default. Its complete infrastructure, energy and maintenance costs should be assessed alongside the alternatives.

Questions Before Making a Decision

1. Is a lighting design required? If so, what lighting class must be achieved?

The required illuminance, uniformity, lux levels, and glare control should be established before choosing the power.

2. Is there an existing grid connection?

The economics change considerably when usable ducts, cables and supply points already exist. Where there is no infrastructure, solar can remove a significant amount of civil and electrical work.

3. Does the light need to operate at full output all night?

Adaptive dimming, part-night profiles and motion detection can reduce energy consumption, but they must remain appropriate for the area’s use and lighting class.

4. What level of resilience is required?

A council highway, private driveway and occasional-use footpath do not necessarily have the same operational risk. The consequences of reduced output or temporary failure should form part of the assessment.

5. What is the whole-life cost?

The comparison should include more than the initial column price. Consider:

·      Groundworks

·      Electrical connections

·      Battery replacement

·      Electricity consumption

·      Inspection and maintenance

·      Surface reinstatement

·      Remote monitoring

·      Future infrastructure repairs

Comparing only the purchase price of the lighting column rarely provides an accurate financial picture.

Conclusion

The right solution is not always completely solar, and it is not always grid connected.

For a remote pathway, public open space, private estate or commercial car park without electrical infrastructure, a correctly specified off-grid solar system will provide the most practical and cost-effective answer.

For an adopted footway or more demanding public-realm project, hybrid lighting may offer the ideal balance between renewable generation and guaranteed performance.

For major traffic routes, heavily shaded locations or sites with substantial existing infrastructure, grid-connected lighting remains the appropriate choice.

Sources:

https://knowledge.bsigroup.com/products/road-lighting-performance-requirements-1

https://theilp.org.uk/training-development/short-courses/british-standard-for-lighting.html

https://joint-research-centre.ec.europa.eu/photovoltaic-geographical-information-system-pvgis_en

https://landingpage.bsigroup.com/LandingPage/Undated?UPI=000000000000789885

At SolarVision Lighting Technologies, we assess the lighting requirement, site conditions, energy balance and infrastructure before recommending a system. Our objective is not simply to install a solar product. It is to design a reliable street lighting solution that is suitable for the location, and long-term requirements of the client.

Need help choosing between solar and hybrid street lighting?

Send our team your site plan, project specification or required lighting class, and we can review the most appropriate solution for your project.

Call SolarVision Lighting Technologies on 01923 726150.