One of the great benefits of a green roof is the ability to cool a building by reducing the rooftop temperature. This is achieved by the fact that plants can only heat to a temperature of 25 degrees and unlike bitumen or other roofing materials it doesn’t hold this heat overnight combined with the cooling mechanism of evaporative loss.

Solar panels are not able to control their temperature and with this they could be increasing the urban heat island effect whilst hindering their own performance. Solar panels work by converting the DC current generated by the panel into AC current that can be used to power appliances.

Heat has a massive effect on PV modules. Testing is done at 25 degrees Celsius and every degree above this can cause power output to drop by .5% per degree dependant on the semiconductor.

What is a little less understood is the fact that heat can also have an impact on the inverter used to change the DC current to AC current. This process itself generates heat as well as the ambient temperate having an effect. Invertors can start to derate after 40 degrees Celsius.

It is very hard to generate specific data on how much a green roof can enhance the performance of solar panels however what is clear is solar panels operate more efficiently at lower temperatures and green roofs are a fantastic way of facilitating this whilst bringing all the many other benefits along for the ride!

What is the urban heat island effect?

areas due to human activity. This temperature difference is usually much more noticeable at night as the building materials such as concrete and bitumen hold onto the heat absorbed throughout the day. UHI can also have an impact on growing seasons, decrease the air quality by producing more pollutants and decrease the water quality.

Heat island on other surface.

Bergdahl et al. 1997 [5] showed that a sunny day could heat streets and pavers to 27-50°C (50-90°F) hotter than the ambient air temperatures. Shaded or wet areas didn’t however deviate too much from the ambient temperature.

Urban heat island mitigation – what are the options?

In order to reduce heat islands surfaces need to have a high ‘albedo’. Simply put albedo is another word for reflectivity and indicated how much sunlight a surface absorbs and warms or reflects keeping a very neutral temperature.

Example – fresh snow has the ability to reflect 95% of incoming radiation meaning a high albedo of .95 whereas water only has a 10% reflection generating a low .10 albedo. The earth reflects roughly 30% of sunlight therefore giving the earth an albedo rating of .30. See https://climate.ncsu.edu/edu/Albedo for more information.

Generally speaking dark surfaces absorb more sunlight and therefore heat with lighter surfaces having the opposite effect. This means that one option to mitigate the effects would be to increase the use of lighter surfaces in urban environments however it isn’t quite that straight forward due to trying to determine where that reflection is actually going.

How do green roofs mitigate the urban heat island effect?

Good news…there is a solution to combat UHIE! Green roofs are a key element in combatting the rising temperatures of urban areas.

Green vegetation being darker you’d think this is bad option however the albedo is still relitavely high. Berardi et al. report albedo values of 0.7-0.85 for living roofs, which is significantly higher than the 0.1-0.2 measured for gravel, tar, or bitumen roofs.

By replacing a traditional roof with a green roof you will gain thermal benefits and reduce the urban heat island effect.

Green roof on bus shelter Utrecht  – Source: ClearChannel  / Barbra Verbij

Green roofs can be an important factor for improving the living environment especially in sparse city centres and urban areas where greenery is lacking.  These areas are often left devoid of a flourishing wildlife.

Although green roofs are becoming more commonplace in cities, it is still a challenge to add more greenery where space is limited. A potentially clever use of space can be achieved through greening bus shelters and even bike stores.  A wonderful example of this is the Dutch city of Utrecht,  since June 2019 more than 300 bus shelters featured a sedum roof.

The Sedum plants that are used on green roofs are ideal for various weather conditions. The plants store water in their leaves, allowing them to survive well during long periods of drought. This is why a Sedum roof is a product that requires little maintenance.

Green roofs provide space for the development of biodiversity. They offer hiding and breeding places for birds, bees, butterflies and other insects. Adding a green roof to a bus shelter is a simple concept one which has evoked attention and positivity worldwide, as international media reported “bus stops” have been transformed to “bee stops”

Around the world it is widely recognised that people want to contribute to a healthy living environment, residentials and town planners alike are left enthusiastic about contributing towards a greener world.

Did you know?

Worldwide there are around 20,000 bee species.  Most of these bees are known as solitary bees.  There are only 250 Bumble bee species, & 9 Honeybee species. 

In Britain we have around 270 species of bees, just under 250 of these species are solitary.

There are 3 types of Bees, The Bumble Bee, The Honeybee & The Solitary Bee.  Each bee type has distinctive characteristics and unique properties.

Honey bees

Honeybees live in colonies between 20,000 to 60,000 bees per colony, which consists mostly of female worker bees.  These bees work throughout their entire life, which is approximately 6 weeks.  The male honeybee otherwise known as drones are larger than the female worker bees, they have no stinger and do no work, their one and only job is to mate.  In every colony there is 1 queen bee she lives for approximately 5 years and lays up to 2,500 eggs per day.

Honeybees can fly as fast as 15 miles per hour and they will fly for up to 6 miles in order to find a good source of nectar, Once back at the hive they perform a dance known as a waggle dance by showing the position of the flower in relation to the sun and hive by doing this they are communicating to the other bees where the nectar source is.

The honeybee is the only insect that produces food eaten by man. One single bee will make approximately 1/12 of a teaspoon of honey in its lifetime.

Honey is the only food that includes all the substances necessary to sustain life, including enzymes vitamins, minerals, and water; and it is also the only food that contains “pinocembrin”, an antioxidant associated with improved brain functioning.

Bumblebees

Bumble bees are important pollinators of wild flowering plants and crops. They do not depend on any one flower type, although some plants do rely on bumble bees to achieve pollination. The loss of bumble bees would have big ecological impacts due to their role as pollinators.

Bumble bees live in smaller groups than honeybees, A bumblebee colony can contain up to 150 individual bees, which is small compared to honeybees. they don’t tend to swarm, and will not die if they use their sting, unlike honeybees.

There are 24 species of bumble bee in the UK, bumblebees are peaceful and non-aggressive and will only attack if they feel threatened, if you stay calm, they will fly away.  Only the worker bees and the Queen have a sting.

Bumblebees are hugely important, they are on the decline especially in Europe, North America and Asia, with around one third of human food requiring bee pollination

this decline could have a catastrophic impact on other wildlife and our crops which depend on bumblebees for pollination.

Protecting the Bumblebee is genuinely something that everyone can play a major part, a great and easy way for everyone to help bumblebees is to plant wildflowers in gardens or in plant-pots for window ledges.

Solitary Bees

 Solitary bees are fantastic pollinators they are the unsung heroes of our pollinator world, although they are easily overlooked, they are known to pollinate plants more efficiently than honeybees.  The solitary bee doesn’t have a pollen basket for carrying pollen so each time they visit a flower they will lose far more pollen than social bees, for example a single red mason bee is equivalent to 120 worker honeybees in the pollination it provides.

Solitary bees don’t live in colonies instead they can nest in holes in wood, in hollow stalks, tunnels in the ground, or even snail shells.

The Solitary Bee varies considerably in size and appearance and where they choose to nest. Unlike honeybees, where nest building and maintaining is a task shared by the whole colony most species of solitary bees and in the case of some species, a nest is built by a single female.

Roughly 70% of solitary bees are called mining bees and nest in underground burrows. Bees that nest in houses are called cavity nesting bees.

Solitary bees do not have a Queen, they do not produce honey they are non-aggressive and do not swarm

How to make better bee environments

All bees are vitally important to humanity & the environment, in fact, one third of our global food supply is pollinated by bees. 

Bees keep plants and crops alive. Without bees, humans wouldn’t have very much to eat. … If bees do not have enough to eat, we won’t have enough to eat

It is easy to create a bee friendly habitat, here are a few easy ways to get inspired, we can all to play a part in bee conservation.

Installing a water fountain is not only a great feature, Honeybees can’t get enough amounts of water from drinking nectar alone and need to find additional sources they will really thank you.

Planting colourful flowers, a few bee friendly flowers include Crocus, hyacinth, borage, calendula, and wild lilac. And bees will feast on, cosmos, echinacea, snapdragons foxglove, and hosta in the summer, try and aim to make sure something is blooming each season.

Herbs are a wonderful way to attract bees and other pollinating insects. Herbs are easy to grow adding great flavor to food whilst attracting a little bit of nature to your windowsill, back yard or garden.

Create a bio-diverse wildflower haven, just a small area will add huge value, consider ready established wildflower turf, as a quick simple and effective way to bring wildflowers into the garden.

Sow bee friendly perennial flower seed mixes for beautiful flower displays.

Green roofs are starting to becoming a more regular feature in our towns and cities.  They enhance bio-diversity in so many ways and are starting to grow in popularity and demand in the garden, think bike sheds, log stores, garden sheds home studios and summer houses you can create an interesting feature and talking point whilst playing a vital part in creating a home and food source for bees & many other pollinating insects.

Add colour smell & visual interest to your back yard or balcony with the use of Planters you can create a wonderful haven of wildflowers, flowers and herbs.

Create insect houses into your garden with a bee hotel, fix bee boxes in a south-facing spot but not in direct sunlight. Also make sure the entrance points downwards so that rain doesn’t get in.  Leave a little bare ground. Most species of bees are solitary, and some 70 percent of them dig a nest in the ground to raise their young—something they can’t do if mulch is in the way. They need loose, crumbly and exposed soil or sandy banks.

Bees are vitally important,  protect our bees never ever kill bees, if you find a nest contact the experts, they will remove them safely from your site.