Tuesday, 15 October 2013

Save the Merton Rule - Have Your Say

The Housing Standards Review Consultation closes in a week.  DCLG’s proposals will remove the Merton Rule, whereby Local Authorities can require developers to go beyond the Building Regulations on energy efficiency.  The Building Regulations themselves are not providing a pace of improvement to support renewable energy in new buildings and seem unlikely to do so for years to come.  We need to make our voices heard on this issue at DCLG.

Want to make a difference, but a bit short on time?  The solarblogger has helpfully done the hard work for you.

 Simply cut and paste the text below into an email and send it to:

Subject: Housing Standards Review Consultation

Dear Sirs

I wish to register my opposition to your plans to repeal the Planning and Energy Act 2008 before you have implemented Zero Carbon Homes.

Please carefully read the following three articles:

With kind regards,

Tuesday, 1 October 2013

Solar Energy Redeemed

The Last Piece Falls into Place for the Domestic RHI

A hot prospect? 
Image courtesy Viridian Solar
MCS recently unveiled its new calculation methodology for predicting the energy benefits of solar heating, and its great news for the industry. The announcement was eagerly awaited not least because it will be the way payments are calculated under the domestic Renewable Heat Incentive.

What's Changed?

The previous version was based upon the government's Standard Assessment Procedure (SAP), and so is the new version, but with some rather important changes:

1.  The Number of Occupants

Arguably the single biggest factor impacting the solar heating energy yield is the amount of hot water used, and in domestic properties this is almost entirely down to how many people live in the house.

The previous version of the calculation followed SAP, which was originally developed for new build where the number of people using hot water in the building is not normally known.  The SAP calculation predicts the occupancy from the floor area of the property, with an increasing number of occupants as the property size increases.

Because this SAP calculated occupancy peaks at around three people for homes that are not abnormally high, it is underscoring the potential for solar energy greatly for the many households with more people than this. If this were to have been used for the RHI payments it would incentivise a solar installation in a mansion with a retired couple living in it over a smaller house with a family of five living there.  

The new calculation requires the solar installer to enter the actual occupancy of the property at the time of the installation, taking into account any part time residents (for example children that visit regularly but who don't count the house as their primary residence).  Installations will be subject to random audit by OFGEM, discouraging potential cheating, but for RHI deeming purposes, it was also decided to limit the occupancy to six full time equivalent.

This change is broadly neutral for smaller households of one or two people, and increasingly positive as the number of occupants increases. The new calculation will significantly boost the energy yield for larger households, rewarding those solar installations that deliver the highest energy savings. 

2.  Electric Showers

The SAP calculation assumes a certain hot water use per person. In the previous (2009) version, the hot water use was based on an average for all homes in the UK including those with an electric shower.  Electric showers are fed with cold water so don't use water from the hot water cylinder and this has the effect of lowering the hot water use in the UK average.

By separating out homes without electric showers, in the 2012 version, hot water use is boosted by around 30 per cent and the benefits from solar heating further increased.

Incidentally, this welcome change should see some of the daft (predominantly new build) installations disappear where solar water heating has been installed alongside electric showers.

3.  Backup Heater Efficiency

The previous calculation worked out the solar heat input to the hot water cylinder and this was the figure presented to the customer.  The new calculation recognises that the customer is more interested in their saving on energy bills, and this is not the same thing.  Why?  Because the boiler that would have heated the water if the solar system wasn't there works with an efficiency, so in most cases the fuel energy bought  is higher than the energy input to the cylinder.

For example, a boiler operating with 80% efficiency would need to burn 1,250 kWh of gas to produce 1,000 kWh of heat. (1,000/0.8 =1,250)

It turns out that backup heaters have a summer and winter efficiency. Most are less efficient in summer than in winter - energy overheads from starting up are a larger proportion of energy delivered when you're only heating water and not heating the whole house too. Of course, most solar energy is delivered in summer when the back-up heater is least efficient.

The calculation takes this into account and a "solar efficiency" figure is used to calculate the energy saving as well as the renewable energy. The figure is expressed as an "additional fuel saving" so should be added to the deemed renewable heat to arrive at the total energy saving.

4.  Irradiation

Where the previous version used a single irradiation for the whole of the UK, the new version divides the country into 21 regions (see my earlier article on SAP 2012). The UK average remains the same, but some regions are lower than the average and some higher.

In addition, the irradiation is calculated for the absolute angle and orientation of the panel instead of using a look up table. 

5. Cylinder standing losses

A standing loss for the cylinder is added to the hot water demand increasing the total heat load that the solar system can contribute towards.

6. Other Minor Changes

The second order heat loss coefficient for the solar panel performance is taken into account.

Homes designated water efficient under Approved document G have their hot water demand reduced by 5%

Believe it or not, there are solar thermal panels out there with efficiency lower than the SAP default. A loophole where these could use the SAP default values has been closed.


The Effect of the Changes


Let's run a few examples through the previous and new calculations. To keep things simple, we'll use the same high quality solar thermal panel for each situation, as well as keeping the shading (none or very little) orientation (south) and pitch (30 degrees) the same for all options.  We’ll also locate the panels in Sheffield (which receives the UK average irradiation) and remove electric showers from the house.  We'll assume the house has a modern condensing gas boiler.

For the previous calculation, I have used a house size of 85 m2, an average sized town house with three bedrooms.  For the new calculation, a range of occupants between two and six is considered, with a panel area and cylinder size chosen appropriately.

The previous calculation ignores the actual number of people who live in the house and uses 2.7 residents in all cases, a figure derived from this floor area.  The results highlight the way that the previous calculation under-sold the benefits of solar in situations where more people live in the property.

In addition, the energy saving presented to the customer was the solar heat added to the cylinder, ignoring the efficiency of the boiler.  The new calculation takes the boiler efficiency into account. 

The new calculation gives energy savings between 50% higher and 142% higher than the old calculation.  The deemed renewable heat is calculated to be between 14% and 85% higher.

Many solar installers would have been disappointed by the tariff level of 19.2p set for solar heating under the forthcoming domestic Renewable Heat Incentive.  This improved calculation method provides just the boost that solar heating needs, and radically changes the economic attractiveness of solar heating within the domestic RHI.
The announcement of the RHI deeming calculation for solar heating is the final piece in the jigsaw.  Finally, solar installers can get out there and start presenting the financial benefits of the domestic RHI to potential customers.  In fact with a £600 upfront grant available for installations before the start of the scheme, there's every reason to install solar now.