Comparing Building Regulations for Energy - Scotland and England

 

Development of new homes in Glasgow by CCG Homes, Installation by Arc-Tech

New regulations have been published for Part L building regulations in England.

Let's take a quick look at how they compare to Scotland, where almost all new homes now come with solar panels.

The building regulations work by defining a specification for a 'Notional Dwelling' - read this article for more detail of how it works

In the table below I have shown a selection of the more significant requirements for each.  It is evident that not only do both Notional Houses include solar PV, but that the England requirement is much higher.

Housebuilders do not have to build the Notional House specification, but they must equal or exceed its performance.  The scope for reducing the solar provision by increasing the insulation performance of building elements such as walls, roofs and windows (collectively often referred to as fabric measures)  is limited in the new English regulations, which equal or exceed the fabric requirements in Scotland.

‘Notional Dwelling’ Summary Specification Selected Requirements
	Scotland 2015 (Gas Package)	England 2021
U Values in W/m2K
External Walls	0.17	0.18
Floors	0.15	0.13
Roofs	0.11	0.11
Doors	1.40	1.00
Windows	1.40	1.20
Air Permeability	7 m3/h.m2 at 50Pa	5 m3/h.m2 at 50Pa
Heating	Gas boiler 89% efficiency	Gas boiler 89.5% efficiency
Heat Emitter Type	Regular radiators	Low temperature heating 55°C flow
Heat Recovery	Instantaneous Waste Water 45% efficient	Instantaneous Waste Water 36% efficient
Solar PV in kWp	Smaller of (a) Total floor area (m2) x 0.01   (b) 0.3 x roof area based on 30 degree roof pitch x 0.12	40% of dwelling floor area/6.5
Example solar PV for 85m2 house with two floors	0.85kWp	2.6kWp

Solar By Others

How to Get What you Want and not Get What You're Given

Architects, developers and planning officers often go to exacting lengths to make absolutely sure that they get the look that they're aiming for in a building. For houses that can mean specifying the type of brick, the tile on the roof, and specific styles of windows and doors. Even soffits and guttering do not escape careful scrutiny, selection and specification.

Damn right, too! These materials have a huge impact on the overall appearance of the house and should be defined carefully to preserve the integrity of the design, and the quality and sale-ability of the finished product.

Which makes it all the more surprising to find in developers' design packages a great big rectangle drawn on the roof labelled "solar by others" or "solar by specialist installer".

Surely you know that once you hand over your beautiful, carefully considered design to a Quantity Surveyor, if your specification does not nail down the materials you're looking for, then the words "solar by others" might as well say: "solar - the cheapest you can find, no I honestly don't care what it looks like - yes, I know I was really fussy about the exact make and model of cavity closer, but really, just get what you want for the solar - it's not like anyone will notice it's there."

It doesn't all look this good.  Image credit: ARPower

Solar PV is becoming more and more common on roofs. Incentivised by Feed in Tariffs, more than 800,000 households have now chosen to install solar as a retrofit. Building regulations in Scotland have made solar the norm on new homes and planning conditions in many local authorities (including zero carbon homes in London) also mean new homes are more likely than ever to need solar.

With the coming shift towards electric transport - (the speed of which I predict will take policy makers and energy companies completely by surprise), economies of scale for battery manufacture will drive the availability of cost effective electricity storage, and make solar an even more compelling feature of a mainstream home.

What you Need to Know

The cheapest panels have silver frames, a white backing sheet and polycrystalline cells. Sticking them on a framing system above the roof covering is still (only a little) cheaper than going inline with the roof. If you don't specify what solar you want, this is what you're likely to get.

Here are the choices you face, starting with those that have the greatest impact on 'kerb appeal'.

1. Panel Layout

The number one impact on the overall look of the building is the layout of panels on the roof.  Early design engagement with solar specialists means that cluttered designs fitted around other roofing features can be avoided.  Higher power panels can be selected to achieve energy goals in the most aesthetically balanced way.  See also this guidance on panel design by the  Campaign to Protect Rural England.

2. Frame colour. 

Solar panel frames are most commonly either silver or black. Both have a protective anodised surface finish, but a silver (natural) colour avoids the dyeing process needed to make a black frame so is slightly cheaper.  In most (but not all) situations black frames are considered the most discreet and harmonious choice.


3. Mounting System. 

Panels can be mounted on metal racking above the tiles or slates or conventional roof covering, or they can be sunk into the roof covering (roof integrated), replacing the conventional roof covering and looking more like an intended part of the building design and less like a 'bolt-on'. Many systems use a 'top clamp' arrangement to hold down the panels to the framing, but some systems have hidden fixings, resulting in a less cluttered finish above the plane of the panels.

Roof integrated systems with visible clamps (top) and invisible fixings (bottom) 

4. Backsheet.

A white backing sheet means you can use ever-so-slightly lower power cells in your panel for the same overall panel output (the white sheet reflects light and keeps temperatures a little lower so the same cells perform better). When combined with mono crystalline cells (which are not quite square and have missing corners), a white backing sheet will produce a characteristic pattern of diamonds running up the panel in columns.

Monocrystalline cells (left) and polycrystalline cells (right) in combination with a white backsheet showing the characteristic diamond pattern of a monocrystalline panel

5. Cell Type. 

Polycrystalline cells are sometimes a similar price to mono crystalline cells, but in times of over-supply often seem to fall further and faster. Right now modules based on polycrystalline cells are around 10% lower in cost than those based on mono crystalline cells. In general poly cells will look a bit bluer than mono, and may have little more colour variation across and between panels , but modern cell production technologies can mean that nowadays they rarely show the crystalline pattern that used to be so characteristic of this type of panel.

(More information on the differences between polycrystalline and monocrystalline cells can be found in this blog).

6. Cell Interconnections. 

Some manufacturers hide the bus-bars (silver strips at the top and bottom edges of the panel that electrically connect the cells together, but obviously this also adds cost. Some panels have cells with rear face connections so there's no silver lines visible on the top face of the panel.

How About Just Asking For Roof Integrated Solar?

For sure there are some great looking roof integrated solar systems available. But specifying roof integrated can still result in a wide range of outcomes when you hand it over to the commercial team. This is particularly the case for roof integration systems that give freedom to use any old panel. 

I took the pictures below at the same site and they show two phases of the same development.  The specification called only for "in-roof solar", opening the door to the silver-framed installations in the lower image which meet the letter, if perhaps not the spirit, of the specification. 

Both are roof integrated solar

For something that has such a big impact on the way a building looks, surely it's time for designers to take control of the solar they get, rather than giving the commercial team carte-blanche to go with the cheapest option offered.  

Unfortunately there’s no substitute for carefully choosing and specifying the product you want, just like you do for other building materials.

In-roof Solar PV - Hot or Not?

Results from a study into heating effects on in-roof solar modules

In-roof solar PV may look great, but what's the trade off on energy performance?
Image: Viridian Solar and Elliott Brothers

Every solar professional knows it.  The power output from a crystalline silicon PV module reduces as it gets hotter.  PV systems installed in-roof suffer from lower ventilation rates on the shade side than modules installed on a rack above the roof covering and therefore produce less energy.

But how much less?  Is it a lot or a little?

How much of the heat is actually lost from the shade-side of a panel, compared to that from the sun-side?

I was recently in a meeting at the Solar Trade Association with a group of the top technical brains from the UK PV industry.  I asked the group to estimate the increase in annual energy yield by switching a crystalline silicon PV module from a sealed in-roof installation to an installation above roof.

The answers ranged from 1% to 14%. 

Conversations with other solar professionals have produced estimates as high as 25%.

Everyone knows it has an effect. But no one seems to know by how much.

Having a quantitative, evidence-based answer to this question is becoming more and more relevant in our industry.  As the solar market matures more and more customers for solar PV want the benefits of reduced energy bills but without compromise to the looks (and potentially re-sale value) of their properties.

In-roof systems offer an alternative that ticks the box on aesthetics for many people at a price they are willing to pay, but just how big is the trade-off on energy yield? 

Now researchers at Viridian Solar, collaborating with the Engineering Department at Cambridge University and Enphase Energy have produced an answer to this question.

The authors are aiming to publish the research in a peer-reviewed journal later this year, but a briefing document has been released summarising the experimental results.

 

Replacing Opinion with Evidence

 

The experiment is described in more detail here, but in simple terms it consisted of three steps:

 

• Build a test rig with PV modules installed in a range of situations representative of real life construction

• Understand the relationship between weather conditions and module operating temperature for each type of installation

• Use the experimentally derived temperature profiles to calculate the annual energy yield for each installation situation.

 

Test Rig

 

Clearline PV15 modules were installed in five different ways

1. Free standing on an open framework (rear fully open)

2. Above a pitched tiled roof on a metal framework (open gap between panel and tiles)

3. Integrated in a pitched tiled roof with cold-roof construction behind (batten-space ventilation)

4. Integrated in a pitched tiled roof with warm-roof construction behind (insulation between roof joists)

5. Integrated with a pitched shingle roof with plywood sarking board (module rear un-ventilated)

The images below show the roof build up for two of the pitched roof installations.

 

 

Temperature Rise

 

The graph below shows the temperature response of each of the installation types - the lines show the operating temperature above ambient as the light levels increase.  As expected, the temperature of a module with less ventilation to the shade side rise faster as light levels rise.

 

 

 

For example, at 1,000 W/m2 (a bright sunny day with sun directly onto the module) the rack-mounted module above the pitched roof was 10 degrees C warmer than the free standing module.  The integrated module in the cold roof is a further 9 degrees C warmer than the rack-mounted module.

 

Clearline PV modules have a power-temperature coefficient of -0.509 %/degree C, quite typical for a crystalline silicon module, so a reduction in temperature of 9 degrees would produce a power increase of 4.5%.

 

However it's not always sunny, and the sun isn't always directly onto the module.  In fact, in the UK irradiation levels higher than 1,000 W/m² are very much the exception and not the rule.  At lower levels of light, the temperature difference between different installation types is smaller.

 

Annual Energy

 

So, what's the answer?  What was the annual energy benefit for rack-mounted systems compared to the in-roof systems in the experiment?

 

The temperature characteristics were used with a climate file for Cambridge, UK and the power-temperature coefficient for the modules to calculate the annual energy yield for each installation.

 

It turns out that a rack-mounted module would yield 3% more energy than a roof-integrated module. 

 

 

 



 

 

 

 

 

Clearly, for some situations an extra 0.3% return on investment due to energy yield will matter, but for many domestic customers minimising the visual impact on their building will be more important. 

 

As an industry at least we now have facts to present to potential customers so that they can make an educated choice.

 

 

 

 

 

 

Wrong on Many Levels

The solarblogger is Concerned For You

While out and about near Cambridge, I passed a building site and snapped this photo. 

 

Discretion is my middle name

I guess I was planning to rant on my blog about one or all of the following (take your pick):

• The box-ticking mentality that results in house builders giving their customers a 0.5kWp solar photovoltaic system – something that no one would ever buy for their own home (see my earlier blog Specifying Solar for New Build Houses)

• How there’s really no excuse for these solar panels to be installed like an ugly roof-rack (see one of my most popular blog articles – The Best Looking Solar Panels You’ve Never Seen)

• Why the designers didn’t choose one of the many low-profile roof integrated solar options that would have been so very easy to do as a new roof was going on anyway.

It was only when I downloaded the photo and reviewed it on a larger screen, that I realised what I’d inadvertently caught.

Did you see that in the background?  If the guy working on the roof between the solar panels slips, they’re both coming down.

Can you see what it is yet?

I’m guessing what we’re looking at here is the result of having to install to a price. In new build, the panels are often fixed in place by the roofing contractor and you can’t complete the electrical installation until there’s mains power in the house (which normally means long after the scaffolding has gone). Repeat visits to site are costly, better to do it all in one trip than to make the electrical connections to the panels when the scaffold is up.  Must be really tempting to just nip up there on a ladder and get it done.

Is there a better way?  Well, one option is to roof-integrate the solar panels at the same time the roof covering is going on, pass the electrical connections from each panel through into the roof space and the whole system can be connected up from inside the building.

Perhaps you think I'm worrying unnecessarily for the welfare of my solar colleagues?  Is this 'elf and safety gone mad?  If the ladder was tied on, would that make it OK? Please post your thoughts in the comments box below...

Note Added: 22/07/2013

People have started to send me photos of their own - I have started an image set on Flickr here.  Please keep 'em coming!

Specifying Solar for New Build Houses

or how solar panels can be the 'pillow chocolate' of the house-building industry

Yes Please

I don' t know who it was that came up with the brainwave that the last thing you want before turning off the lights and going to sleep in a hotel is a chocolate, but they didn't share my dentist's views on oral hygiene.  Despite this the hospitality industry seems to have adopted a standardised procedure that involves a crack-team abseiling into your room while you're out at dinner and depositing unasked for confectionary on your pillow.  How do you know if you're in a top hotel?  The chocolate tastes the same, but the wrapping paper is branded with the hotel logo.

The solarblogger has recently returned from a walking holiday, involving a stay in a few hotels.  One of these stood head and shoulders above the others, and not least for their take on the complimentary chocolate. 

Upon checking into the room, we found a small basket of fruit and a dish of four selection box chocolates waiting for us. This hotel had actually given us a "free gift" we valued - something we might want to eat at a time of our choosing that afternoon or evening.   This is what marketing folk call a “moment of joy” a small touch that has an effect on the customer far beyond its cost.

I can confirm that they tasted as good as they looked.   (The solarblogger does the hard work so you don’t have to).

A Box is for Ticking

Building regulations and local planning requirements are putting energy performance of new homes in the spotlight.  At the same time, forward-thinking housing developers are catching on to the idea that their customers are keen to reduce ballooning energy bills and that solar panels are becoming an attractive feature that adds value to a property.

The question for a developer is whether they wish to delight their customers.

The trick, just like in the example of the chocolates, is giving your customer something that they actually want and value – something they might buy for themselves.

Some developers will struggle to leave behind a mind-set ingrained over many years.  It’s a mind-set that sees energy efficiency measures on homes as just another box to be ticked to meet regulations.  Forward thinking developers have escaped this trap and are seizing the opportunity to give their customer something of real value.

Yes Please
Read more about this development here

How to Delight your Customers with Solar

The average size of a PV system chosen by people retrofitting their homes is calculated by the Energy Saving Trust to be 3.5kWp, or around 14 panels.

A compliance-led developer will choose to install only the number of solar panels to just scrape over the bar required by regulation.  Solar PV installations of 1, 2 or 3 panels are not uncommon.  No sane person would spend their own money on installing such a small system, which might only deliver 200 kWh per year of energy savings, or 5% of electricity used in the average home.

Here’s my simple three-step plan for a solar system that adds value to a new-build property:

1.  Install at least 1.5kWp (10 sq m) of solar PV per house – a system of meaningful size that would give real value to the customer – delivering about 30% of average electricity use.

or

2.  Install a solar thermal system (3-4 sq m typically), to deliver 60%-70% of hot water used.  This will normally allow the property to meet regulations, and you’re giving the customer a system they might choose to buy for themselves.  Locate it so as to leave space on the roof for the householder to add a solar PV system later.

or

3.  Install a solar thermal system as standard, and sell customers buying off plan the option to complete their solar roof with additional PV panels.

Oh, and while you’re at it you might want to give some thought to the impact on the kerb-appeal of the property – see this article: “The Best Looking Solar Panels You’ve Never Seen”

The Domestic Renewable Heat Incentive for Solar

The Main Points

The best looking part of the consultation
Clearline Solar Panels

Today, the UK government launched a consultation on its proposals for the domestic stream of the Renewable Heat Incentive (RHI), slated for launch in summer 2013.  the solarblogger has read it all, so you don't have to.  Here is a quick summary of the contents of the consultation, more detailed analysis to follow. 

Timing

The consultation is launched on schedule, so we seem to be on track for a scheme launch in Summer 2013

Qualification

The system must be certified under the Microgeneration Certification Scheme (MCS)

Only systems smaller than 45kWth qualify.  This is unlikely to be relevant to solar (since 45kWth is 64 square metres of solar panel).

House must have a Green Deal assessment and to have completed all of the “green tick” measures that relate to thermal efficiency (those that are eligible for full financing through the Green Deal).  Measures must be installed before the RHI subsidy can be paid.

  

Tariff Payments

Tariffs are to be paid over seven years.

DECC have applied a value for money cap, based on the “marginal cost of renewable energy” – the subsidy levels supporting offshore wind.

Solar thermal tariffs would therefore be capped at 17.3p/kWh.year, but DECC are seeking evidence to support a tariff level higher than the cap, and want to look at other alternatives such as a partial upfront grant.

The energy is to be estimated by calculation (deemed) rather than measured by a heat meter, and MCS is the preferred route to develop a deeming methodology, with the calculation by the installer under MIS3001.

Legacy Systems

Systems installed since  15 July 2009 can apply for the RHI, subject to meeting all the qualification criteria.  If they have received a grant (such as RHPP), this would have to be re-paid.

 

New Build Housing

New build housing does not need to have a Green Deal Assessment. The consultation hints at a lower tariff rate due to lower installation costs in new build compared to retrofit.

Social Housing

DECC’s preferred current position is to exclude social housing, but the door seems to have been left open to include Registered Social Landlords on a different tariff.