THINK SOLAR: Roofs that generate electricity coming alive with possibilities
Technology / 8 November 2019, 2:30pm / Professor Louis C H Fourie
JOHANNESBURG - The sun burns 637million tons of hydrogen atoms into 632million tons of helium and thus creates 38460septillion watts (3.846 x 1026W) of energy per second, which equates to roughly 1386 watts per square metre (W/m²) in the upper atmosphere of Earth or 1000 W/m² at sea level on a clear day.
This is still about 10000 times more than the whole of earth needs at the moment and could over time eliminate the need to burn environmentally-unfriendly resources and as a result decrease carbon dioxide (CO2) emission levels.
As I have illustrated in Business Report over the past few weeks, this realisation is one of the reasons why the solar photovoltaic market has been expanding exponentially. Costs of silicon solar cells have declined considerably in the past few years, making solar photovoltaic systems easily accessible to many house or building owners.
However, one of the biggest complaints against solar is that solar panels installed at a house or building do not look aesthetically or visually appealing. But the ever-innovative Elon Musk and his company Tesla may have solved the problem of aesthetics by totally changing the visual appearance while at the same time providing a reliable source of solar electricity.
The Tesla Solar Roof, consisting of integrated solar glass shingles, is a building-integrated photovoltaic (BIPV) product that integrates the functionality of solar panels and roof shingles, currently available in Tuscan, slate, textured and smooth glass tiles.
Although solar roof tiles and other solar modules integrated into buildings have been on the market for some time, the concept of an entire solar roof is new. The full roof coverage approach involves a solution where photovoltaics do not represent just an addition to an existing roof surface, but instead it is integrated into the structure of the house for aesthetic, constructive and electrical purposes.
The Tesla solar system could both convert and store solar energy throughout the day and then make it available when needed such as during the night. To store the solar energy the Tesla Solar Roof incorporated an embedded Powerwall battery system.
A major benefit of the Tesla Solar Roof is the durability of the tiles and shingles made from quartz and therefore virtually unbreakable. According to Tesla the glass tiles are harder and more stable than traditional clay tiles. They have a class 3 hail rating and class F wind rating. It carries a 25-yearwarranty, which is in line with traditional roof warranties.
The Tesla Solar Roof was originally announced to the world in October 2016, but due to some design issues production was initiated only in 2018. The rollout was, however, very limited while Tesla was working on version 3 of the design.
The price of Tesla Solar Roof Tiles decreased by 40percent from version 2 to version 3 (now known as the Solar Glass Roof) due to optimisation and faster installation. Tesla installation took double the time than the installation of a normal tile roof, which usually takes about five to seven days depending on the size of the roof.
The new Solar Glass Roof (version 3) has been simplified with fewer parts and sub-assemblies to get the installation, according to Tesla, down to as little as one day, thus bringing down the installation costs significantly. Version 3 is apparently not only simpler and faster to install, but more intuitive than previous versions. The new roof tiles are also much larger in size and more power dense, which will in the words of Musk “make roofs come alive” to gather energy.
But Tesla is not the only company to launch a solar roof product. Several companies have been designing versatile solar tiles and rooftop technologies, intending to integrate them seamlessly into the construction of homes and other buildings.
In South Africa there are several suppliers of solar roof products. One supplier, using a German manufactured product, claims that its photovoltaic roof will pay for itself in less than 10 years depending on the size of the roof and the energy demand of the particular household.
In addition to supplying electricity, these weatherproof photovoltaic roof tiles also insulate the house against cold and heat from above. It can also provide heat for daily hot water and any other heating needs during the winter since the entire roof area is used as a large thermal collector. The heat energy is extracted from under the tiles and is then utilised for domestic hot water and household heating. This process has the additional benefit of improving the cooling of the solar cells contained within the tiles, which increases their efficiency and results in an increase in electricity generation.
Using the usable fraction of the sunlight spectrum one South African solar roof supplier claims to generate an output of up to 212 Wp/m² or 93 kW/* per day for a 100m² roof. These roofs also have long life spans of 80 years or more and therefore carry warranties up to 40 years.
However, the solar roof market is a difficult market and the US leader of a few years ago, Dow Chemical, gave up in 2016 after installing about a 1000 units. The brand resurfaced a few years later as part of RGS Energy with a much-improved efficiency. However, the board of RGS recently decided to abandon the solar roof business since it was losing too much money.
Perhaps one of the biggest problems currently is the cost of solar roofs. A 9.45kW Tesla Solar Glass Roof of 173m² will typically cost about R566500 for the roof, another R157000 for the Powerwall and R126000 for roof and site repairs. This amounts to a total of R849500 at the current exchange rate. Obstructions and complex roof designs may even increase the installation costs.
The cost per square metre of a Tesla Solar Glass Roof is thus still significantly higher than a standard roof with traditional solar panels installed, mainly due to the high acquisition costs, but also due to a relatively low efficiency ratio and a slow return on investment over 10 years or more. The lower efficiency ratio is according to Tesla due to the accommodation of aesthetics and also depends on the colour used.
In light of the high cost and slow return on investment it only makes financial sense to consider a solar roof for new houses or if a roof needs to be replaced in less than five years. Otherwise a standard solar panel set-up is much more cost-effective.
Musk is, however, a firm believer that residential solar roofs will not only power household activities, but eventually can make money for the owners.
According to him, solar roofs will in the near future cost less than traditional roofing materials. However, a major difference in some other countries like the US is the significant tax credits that make solar solutions much more attractive. But, in South Africa, at least one company claims that its solar roof solution costs less than a normal roof.
Overall solar roof tiles are still expensive, but if it is compared with the cost of a new premium roof plus the cost of a solar array, it may become competitive and is certainly much more aesthetically pleasing than a roof with solar panels. The continuous progress with regard to improved solar efficiencies will also make the return on investment time much shorter.
But if aesthetics is not a consideration at all, it would be much more cost-effective to currently stay with traditional silicon panels. Traditional silicon panels have become quite cheap, and the price is continuously dropping. According to Jenny Chase, the head of solar analysis at BloombergNEF in Zurich, Switzerland, it is “one of the cheapest sources of electricity.”
The solar industry keeps moving forward at an amazing pace. In future it will probably be rare for roofs not to gather energy. And it will be very affordable, aesthetic and cost less than a normal roof.