A roundup of the new MCS solar thermal standards

Brand spanking new MCS standards for solar thermal products and installers have just been released. Here's a round up of the important changes they bring to our industry. 

Inclusion of air collectors

The MCS 004 product standard has been modified to be inclusive of solar thermal collectors that heat air instead of water/glycol. 

Energy calculation 

The energy calculation has been thoroughly updated to better reflect the benefits of solar heating and improve accuracy:

  • Regional irradiation data replaces a single figure for whole of UK
  • Collector performance takes account of second order heat loss coefficient
  • Hot water use based on number of occupants not floor area
  • Hot water use takes electric showers into account
  • Cylinder standing loss is added to heat load
  • Efficiency of back up heater is taken into account

The changes to the energy calculation are discussed in greater detail in an article on my blog, but the outcome of the changes is very positive for the deemed solar energy, especially for larger households. In some situations the solar energy saving is more than doubled. This is now of greater importance because it will be the deeming method for the domestic RHI payments calculation.

The energy calculation has been implemented in an easy to use spreadsheet for installers. This approach ensures consistency, and provides a clear audit path. 

Pipe Insulation

The EST solar thermal monitoring trial found evidence of exceptionally high heat losses from solar hot water cylinders in some of the properties assessed. The response of the solar industry has been to beef up the requirements in MIS 3001, so that all pipes connecting to hot water storage are insulated, not just the solar pipes. 

The new standard also helpfully clarifies the required pipe insulation thickness for the solar pipes, eliminating a grey area where pre-insulated solar pipes didn’t previously seem to meet the standard. 

Heat Export

A clause aimed at preventing the loss of fossil-fuel derived heat (for example as a collector freeze prevention measure) has been clarified to allow export of solar-derived heat for this purpose. 

Wind Loading

The requirement on the installer to ensure that the solar panels and fixings are adequate for the wind loading that they will endure has been made clear. It was always there, through the Building regulations, but is now spelt out in clear terms in MIS 3001. MCS 012 is signposted as a means of demonstrating compliance, but other ways are possible. The key take home here is that it's down to the installer to check the wind loading at the location, taking into account the roof type, building height and altitude. The installer must then ensure the products they are fixing are of sufficient strength, taking into account these wind loads. Just because a product is sold in the UK doesn't mean that it is suitable for use everywhere, or indeed anywhere! I have seen products on sale in the UK that require 38mm thick battens. I sincerely doubt any UK installer of this product has ever stripped off the whole roof and replaced the 25mm battens before installing this product. 

I have written a more detailed briefing on wind loading here.  

Fire resistance

Similarly, building regulations have always (in theory) required solar installers to comply with rules around the external spread of flame on roofs. Roof integrated solar kits must be tested, and the fire classification declared. The installer should then follow restrictions on the location on the roof and roof area put over to integrated solar collectors or modules for products that do not achieve an A rating. 

Again, a more detailed briefing on fire regulations for in-roof solar panels can be found here


MIS 3001 introduces similar restrictions on weatherproofing as the recent MCS PV guide. 

Drilling through slates and tiles is strictly forbidden. 

Installers must use in-roof systems that have been tested and proven to not impair the weather tightness of the roof.  Using products accredited to MCS 012 is one way to demonstrate this.

Installation Checklist

A more rigorous checklist for solar installers to follow has been created.

Industry has a grace period to 1 January 2014 before adoption is mandatory, however I am expecting installers to want to use the new energy calculator from day one so customers can benefit from a higher deemed energy for the Renewable Heat Incentive.