Buildings account for around 40% of global carbon emissions. Solar cell technology integrated with the built environment offers an opportunity to make a significant difference to our future. Professor Trystan Watson gives a snapshot of our research on emerging non silicon photovoltaic solutions for tomorrow. Then Dr Richard Lewis leads us through the complexities and considerations of connecting photovoltaics to buildings. Watch it to find out more…
But what else did you want to know? Here are the questions asked by webinar attendees, answered by Trystan, Richard and Jo Clarke, our Design Manager and webinar host.
1. What would be the expected useful lifetime for a Building Integrated Photovoltaic (BIPV) panel?
Rich: So, for our building there are Tata panels, so they are warrantied for I think 40 years if I’m not mistaken. The photovoltaic (PV) panels carry a warranty of 25 years from the manufacturer.
Trystan: There’s a context in terms of emerging PV and how do you match the building. I think you have to plan to try and match the building guarantee. So even when we’re working on emerging PV, we have to think about 20 – 25 year lifetime targets. What’s interesting is that there are some few solar cells, for example, that were made in the 80s, that are still functioning and that have gone way beyond some of the incumbent technologies. So, what we have to do in the development stage is try and conform to the standards. To understand what the ISO standards are for being able to keep our solar cells stable within the right frame of encapsulation. And also trying to do some external weathering. So there’s lots of data that you can collect that’ll give you some confidence. And something like perovskite in the early stages was quite worrying about whether it would do it. Now we’ve moved on and we’ve done some of the technology developments, we are starting to see quite extensive tests and quite difficult tests being passed for perovskite cells and perovskite modules. So I think it’s looking quite promising. And just as a brief comment, there are other technology markets that you can access before you get to building integrated to sort of try the technology. Whether that’s Internet of Things (IOT), whether it’s aerospace or whether it’s some sort of canopy system that you can do where you can test it. So there are quite a few steps to get to that you need to explore to sort of give you confidence.
2. With the building integrated PV panels that we have on the roof of the active classroom what happens at the end of life, would it be a complete roof replacement?
Rich: The modular way that the roof is put together with the panels means that they can be replaced. And it’s not uncommon for a single roof panel to be replaced in a building due to mechanical damage or corrosion if it’s been scratched during installation and that’s only been noticed in a few years. So it’s very similar to the standard product replacement process. And with the PV, it’s interesting as Trystan has alluded to there, that even though the lifetime is guaranteed for a certain amount of time, the silicon panels, they are a solid state device and they have no moving parts so usually the only thing you really get is a degradation or reduction in the performance. So they will work, technically, for as long as the building will stand, unless it’s hundreds of years. But the only impact you’ll see is a loss of generation of 20% or so after 20 years.
Trystan: I think that’s actually a really good point that we don’t tend to talk about that much is that often when we’re talking about degradation, we’re not talking about a binary situation where it either works or doesn’t. I mean that’s bad – that’s a catastrophic failure. We’re often talking about a reduction in performance and that you’ve got to balance it with better use of technologies elsewhere within the building. So I think that’s a very valid point actually that we’re not always talking about catastrophic failure.
Jo: And I think this is a really important point when you come to look at the life cost. We had a life cycle cost analysis of our Active Classroom and that actually showed that over 60 year period, the PV roof would be entirely replaced I think it was three or four times during that time. Which of course will be very expensive and disruptive and not great from an embodied carbon point of view. But in reality, that wouldn’t actually be the case. It would continue to be working even if it was reduced capacity. So I think there’s more research needed in those areas definitely.
3. What are the efficiencies of the integrated PV compared to silicon panels?
Rich: So that depends on the type. As I mentioned, the rigid PV is effectively standard silicon monocrystalline or polycrystalline silicon in just a different form factor. So the actual efficiencies are very similar, the active area might be reduced slightly because of the framing requirements. But the actual cell efficiency is the same for CIGS, which is the semi rigid or flexible that we use on our buildings. Their efficiency is obviously lower than the monocrystalline, but they are comparable to other CIGS cells. So generally, the vast majority of them are comparable to their exact static solid framed equivalents.
Jo: And I think it can make a difference, you know with the CIGS that we’ve used on our classroom. You can cover the entire area, you don’t need walkways between them, you can walk on them all. So that that makes a difference as well, I think in terms of overall efficiency.
4. We have heard there are difficulties and challenges with BIPV roofs vs traditional panels, but what are the advantages of this approach vs use of traditional modules?
Jo: I can say from an architectural point of view it’s very nice to have PV integrated into the building.
Trystan: I can comment on the benefit of emerging PV such as perovskite. I think there’s a conversation to be had about whether you want to go head to head with an incumbent mega industry of silicon manufacture. If you do, you need to be competitive without a doubt on stability and lifetime and cost. There is of course the opportunity of augmenting the existing technology, and I think that’s something that we probably should make clear. The perovskite can be applied on top of the incumbent technology to make it better. So these are the concept of tandem solar cells. So there’s single junction and there’s multi junction. And the junctions can sometimes go up to 3 and sometimes 4 different junctions. We can take perovskite for example – you can do it with CIGS or other types of second generation solar cells, and you can make them a double layer structure. So we can take an incumbent industry which is finding it difficult to go up incrementally in terms of its performance and give them a genuine performance boost. So that is where perovskite will come into the market, I think. Initially, it will be making existing silicon solar cells better. From there, we might see the evolution of single junction perovskite solar cells.
5. Are they recyclable?
Jo: That’s interesting, especially when you’re integrating one technology into another fabric. I believe the BIPV product that we use on the classroom and office, the steel is completely recyclable so I’m not sure what happens with the thin film element of that. Do you know any more about that Rich?
Rich: So, the panel itself is bonded with an adhesive which can be removed, so that the panel can be reused effectively. Recycling is still something that’s being looked at for the nature of these panel CIGS and anything with a polymer sheet over the top of it because they’re not glass. And so that’s something that’s still in the process of and to be honest it’s a few years down the line before any would need to be recycled at that stage.
Trystan: For emerging PV, the answer is that it’s part of the research process. It’s absolutely not something that we’re delaying consideration about until we’re further forward. There are research groups in Swansea, for example, led by Matthew Davies looking at the sort of sustainability element, the recyclability element, the reuse and remanufacture of materials as well. So, even in the design process we think about critical raw materials, we think about the abundancy. We think about co-mining of materials with other materials – all of that cradle to grave process has come into consideration already. So we’re trying to avoid making any deal breaking mistakes that might mean that we get to a certain amount of production, and then we go no further. So we’re having those considerations already.
6. How do retrofit roof integrated systems like the GSE mounting system compare to BIPV and BAPV? Are there issues for connectors/strings as with BIPV?
Rich: So the GSE mounting system is the same as any other PV installation or electrical installation. The connectors are a design consideration for the electrical. So yes, in every installation the connectors need to be accessible unless they are certified to be maintenance free. So that is purely a manufacturer and vendor specific design criteria. And saving money on the connectors will mean potential headaches in the future in removing part of the roof of the string files, because of the connector.
7. How do you go about connecting printable PV? How did you go about making electrical connections for that?
Trystan: So these are conversations that are ongoing over the last couple of weeks. This is where the connectivity between the research team – in the early stages of lab device smearing silver contacts… to an engineering team that do not want that. They want a strict system of connections. So for example, we make modules that work of large area perovskites and we’ve got to develop the way in which we connect those modules up. And the questions that we’re asking is, do we borrow from the incumbent industry and learn from their ideas of being able to to add connectors. Or do we need to do more? For example, printing silver anywhere near perovskite is generally a bad idea. So, whereas you might screen print silver onto a silicon solar cell, you certainly can’t do that for for perovskite. So we have to think differently, both at the pre encapsulated module scale and the connections that come into it as well. Where do we locate them? So those conversations are ongoing and they’re starting to emerge now. It seems that it is going to be feasible for us to be able to produce some robust and rigid electrical connections to the modules. There’s no game changers there, but it’s a conversation going on at the moment.
If you have any further questions, please get in touch, we’d love to hear from you.