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Crichton Castle photovoltaic system upgrading

Architectural system: 
Flat roof
Building use: 
BIPV costruction year: 
From 2013
BIPV meets history
© Historic Environment Scotland
Pathhead, Scotland, UK

This project involved the upgrading of solar PV units on the upper part of a 16th Century ruined castle in 2019, the original solar PV system was installed in 2005. The building is a ruin, but open to the public at ground floor level. It is part of the Historic Environment of Scotland (HES) estate.

Due to its isolated location, Crichton Castle is not connected to mains utilities. Despite this, source of warmth and light was needed for the on-site operators and visitors. Therefore, electrical power had to be generated on site. In this past, a petrol generator was used to supply this power but this is not ideal because the noise form the generator disturbs what is otherwise a tranquil and picturesque site. Also, the generator puts more carbon into the atmosphere than other sources of electricity and means that staff regularly had to handle flammable substances.

In 2005, an array of solar panels was installed on the roof of the castle. These were able to provide power for the lighting, card reader and fax machine, which meant that the generator was only required to supply the heating during cold weather, or as a backup when there is not enough sunlight striking the solar panels. This was a great benefit for the users, because it reduced both carbon footprint and the amount of money needed to spend on fuel – the sunlight is free, after all! The panels installed in 2005 converted 15% of the solar energy that hit them into usable power. Their produced power was not enough to supply the energy demand the new panels replaced ones first installed in 2005.

The new array is 5 square metres, monocrystalline, installed in 2019. Power generated 1800 W. The angle of the array is 25 degrees, orientation 220 degrees. The heating load in the custodians office is 2000 W, and lighting 330W. The array charges a battery bank which can give a normal usage time of 26 hours; this is more than adequate as the building is only open 6 hours per day.

The retrofit has proved to be reasonably simple to do, although crane access was needed to get the panels up. Existing power cabling was used, so no disruption inside the monument, and similar fixing points on the roof were used. The cables were surface mounted via existing routes within the ruin and were reused for the new units. The new batteries have given additional running time for the custodians in the event of low solar incidence.

Scheduled Monument Consent was required for this installation, but as it had no effect on the historic fabric that was granted back in 2005, and again for the new panels in 2019.

At present, the energy demand of the building is of about 2,330W. The heating for the site uses 2,000W, and the lighting uses 330W. The new batteries installed along with the new PV system can store 290Ah at 48V – that’s a total of 13.9kWh. This means that, if we were running all 2,330W of heating and lighting off the batteries without any input from the solar panels or petrol generator, they would be empty after 6 hours (note that in practice, we wouldn’t allow the batteries to drain completely). If the panels were producing their full 1,800W, you could run the whole site for over 26 hours before the lights went out! That is a significant improvement over the old system, and easily enough to cover the site’s opening hours.



HiberAtlas a, Retrieved October 2020, Datasheet.pdf

HiberAtlas b, Retrieved October 2020, Castle PV Additional Notes.pdf

Julia Morrison, Here Comes the Sun!, HES, Retrieved June 2021,

Kyocera, Retrieved October 2020,

Aesthetic integration

The panels were mounted on the roof of the castle. Due to the parapet of the ruin still being quite high, the panels could not be seen from the ground. Historic fabric was not affected by the installation that resulted unobtrusive and respectful to the aesthetic values of the monument.

Energy integration

Generated power is used for the building needs only as Crichton Castle is not connected to mains utilities. At present, the castle’s power consumption is dominated by heating and lighting. The card reader and fax machine are active for brief periods only, so they will be excluded from the following calculations.

The old panels generate a maximum of 1,000W when the sunlight is at its brightest. The less sunshine falls on them, the less power they will generate. By comparison, the new panels generate a maximum of 1,800W.

Technology integration

The panels were mounted on the roof of the castle, mechanically fastened to a modern flat roof.

Decision making

The power demand during operation times was modest, but not being met by the PV panels put up in 2005, and a generator was occasionally required. Upgrading was needed. The cabling required from the roof down to the ticket office was low power.

The new PV modules achieve a market-leading 22.2%. Combined with a slight increase in the total area of the array, we have been able to increase the power output to almost double what it was before.

As part of the upgrade project, we have also installed new batteries with a larger capacity. This means more power can be stored for longer, and the extra output from the new panels won’t be wasted.

Thanks to this extra power, we now have several options that we didn’t have before. We could:

  • Use the extra power to run the heating system, which would mean much less reliance on the petrol generator*. We are planning to make some changes to the heating system that will enable us to keep our staff warm without using so much energy; these would synergise well with the upgraded solar installation.
  • Keep the current lights on for longer without having to run the generator, even when it’s too dark to get any solar power.
  • Install additional lighting across the site to improve the visitor experience and bring more of the building to life.
  • Provide power to a computer or electrical cash register in the office.

Furthermore, the new panels will last much longer than the old ones. Even after 25 years, until 2044, the panels we have installed today should still be producing 87% of their nominal output.

Lesson learnt

At present, Crichton Castle is the only ancient monument in the Scottish HES estate that is fitted with solar panels. Since HES have made it an explicit goal to get more of its energy from renewables, Crichton Castle represents a vital proof-of-concept that will hopefully serve as a model for other sites, so that its carbon savings can be replicated elsewhere.

The old panels, which have been at Crichton Castle for 14 years, and the old batteries, which are around 4 years old, are still in good working order. HES is going to keep hold of them and, if possible, re-install them at another site. The roof space at Crichton Castle is very limited, and the lack of mains supply means that every kilowatt-hour we can squeeze out of the solar array is one we don’t have to get from the petrol generator. At other sites, with more roof space and pre-existing mains connections, this is less of a concern, so the old panels can still make a useful contribution.

We’ve also taken steps to minimise the amount of waste produced by the upgrade project. For example, we modified and re-used the old battery cabinet, and kept most of the existing electrical cables between the roof and the batteries. These items were still in perfectly good condition, so it would not make sense to throw them away now.



Project type: 
Building function: 
Integration system: 
Opaque flat roof


Module type: 
Standard modules
Solar technology: 
monocrystalline silicon solar cells modules
System capacity [kWp]: 
System size [m²]: 
Module size [mm]: 
Tilt [°]: 


Total cost [€]: 


KYOCERA Europe GmbH - Solar Technical Service Center
Fritz-Müller-Straße 27 73730 Esslingen, Germany
+49 (0)711 - 93 93 49 98 -


Pathhead, Scotland, UK

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