design, architect, plans, solar, layout

Don’t just tessellate it – design it!

Designing high quality solar systems isn’t as easy as you’d think.

Architects and Solar Design

When architects design a new build or renovation project they are often asked, or required by law, to have some solar PV capacity there. The architect will typically set aside some roof-space for solar panels, or even do their own panel layout on the roof. In many building projects this is what actually ends up being installed, which can lead to some problems, as we will show you below! We believe it is important to draw on the experience of a specialist solar PV company at the solar design stage to avoid problems further down the line.

Now this isn’t meant to be a put down of architects – far from it, they do a phenomenal job, and are expected to have a deep understanding of a huge range of products. However, good solar design isn’t just a question of layout. It interfaces with a whole host of skills including:
• structural engineering (weight, wind-loading, mounting structure),
• electrical engineering (inverter specification, wiring run)
• cost optimisation (designing a system to provide a cost effective solutions for the client)
• aesthetics ( we think a solar PV arrays should be part of the overall building design and philosophy, not an add-on)
• buildability (we consider the ease of build, including logistics and H&S requirements)
• and the most important one – shading.

This is the sort of holistic design approach we take, so here’s our guide to the common design mistakes we see (and correct) in our work.

Solar Design Issues

1. Laying panels flat on the roof. The most common mistake I see on a roof plan is the perfect tessellation of solar panels laid flat against a flat roof space. This is understandable – if you are laying out panels on a pitched roof this is very much the pattern you will see. However, on a flat roof the panels need to be mounted on a pitched frame so dirt and debris can wash away. This means rows of panels need to be spaced apart so that each row isn’t shaded by the one in front. That, in turn, means a lower capacity of PV than the specifier was expecting.

2. Different modules are different sizes. Although the majority of modules on the market are 1.6m x 1m, not all of them are. We often see systems initially specified using assumptions about module size, or with modules of non-standard dimensions. Have you ever seen a square panel? We have to lay out again with a product that can actually be purchased and installed.

3. Mansafe systems getting in the way. Ironically, mansafe systems are often included in the design to allow for the future maintenance of solar PV, yet are placed bisecting the roof in ways which prevent panel installation.

4. Energy performance requirements. For new builds, the building will be designed to meet an overall carbon footprint under BREEAM, and the solar PV is an important and helpful contributor here. We are often asked to design systems to give a certain kWh solar output per year, or install a certain capacity on the roof. However, sometimes this just isn’t possible or sensible, even using design tweaks such as incorporating high-efficiency panels. Then the main contractor is going to face a choice – rearrange other elements of the roof or building fabric to compensate for the lower than expected contribution from the solar of performance elsewhere…or they can just go ahead and install something we have advised them won’t work.

5. Shading. Simply tessellating panels into available roofspace doesn’t address the 3-D effects of shade, from other roof plant or the wider environment. Shade is particularly problematic for solar PV as shade on one module can detrimentally affect the performance of a whole string of modules. Below is a photo of a PV system (not one of ours!) from a school we recently inspected on behalf of a local council. Can you spot the problem?

shaded, solar panels, design

The system was so badly shaded, the solar PV inverter error log suggested the remedy is to ‘check whether the modules are covered with snow’. So here is a system that meets design specifications, but in practice, just doesn’t work. No client wants that.

6. Electrical design. Inverters can only accept some combinations of panels as their input, and this is an aspect of solar design not considered by non-solar professionals. So although you may be able to fit 37 panels on the roof, electrically this will be a lot simpler if you lose one panel. The 36 panel system will be a lot easier to deal with from an electrical design perspective. And it will probably look neater too.

7. Mounting Systems. Some mounting systems have requirements for the roof that they are sitting on.  For example, a lightweight roof material may not be suitable to be used in conjunction with a certain mounting systems.  Our experience shows what products work well in combination.  For example, we know that the Sika SolaRoof system is an integrated combination of Sika Sarnafil membrane roof and solar mounting system that comes with a fully integrated 20-year warranty covering all components.  The client benefits of this are huge, but it is unlikely that an architect would know this.

8. Timescale problems. As the solar specialist we normally see the roof plans a matter of days before the tender is due, and our experience shows that roofing contractors and M&E consultants are usually in the same position. Where there is an issue with the solar PV layout this timescale creates problems. Do we quote for what is asked forand deal with any issues later, or flag up the issue now and potentially delay the entire build?

Great Solar Design

To avoid this, what we want to encourage is greater collaboration between the Architect and the solar PV specialist. It’s our opinion that the best solution is to involve a solar PV contractor at the design stage, or at least get some input if you are unsure. At Joju Solar we design systems to suit the environment and site specific requirements. If you would like support with the solar PV element of your project please contact
If a solar PV contractor is not involved please remember the following when working with flat roofs:
• Panels need to be mounted on a frame to secure them to the roof, and to pitch them at an angle to improve yield. Typically the angle will be 10-15°.
• Allow spacing between the rows of modules so that the row in front doesn’t cast a shadow on the row behind.
• Shading from on-roof obstacles should be avoided wherever possible. Shading will reduce the output of multiple panels, even if only one panel is obstructed.
• Check panel dimensions before adding them to drawing.
• All the panels should face in the same direction.
• Panels are usually orientated in landscape on a flat roof.
• Panels need to be located a minimum of 1m from the edge of the roof in most cases.
• If using a ballasted system, these work better (require less ballast) when they are in larger blocks. Try not to split the array in to tiny sub-sections.
• Solar panels have no moving parts and require minimal maintenance. These rarely need attention and can be cleaned with a telescopic window cleaning device.

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