carbon limited

Communal wind turbines are currently of no use when trying to achieve Zero Carbon status for Stamp Duty Exemption. Here’s why…

There are 3 criteria that need to be satisfied in order to issue a Stamp Duty Exemption certificate for Zero Carbon Homes:

1. The Heat Loss Parameter to be less than 0.8

2. The DER to be less than 0

3. The net CO2 emissions, including cooking and appliances to be less than 0.

Now, this all seems fairly straightforward except for no.2, where there are some hidden complications. Namely, where a near/on-site wind turbine, connected via a private wire network, provides power to more than one dwelling within a development, the output from the turbine can not be entered into SAP 2005 for consideration in the DER calculation. It can be entered into box ZC6 in the Stamp Duty Relief calculator, but not SAP.

Therefore, it is unlikely that the DER is ever going to be less than zero except where there are other ‘on-building’ renewables, ie PV. For example, we currently have an 8 dwelling housing scheme, with communal biomass heating and 3no. 20KWp on site, private wire turbines. The dwellings achieve (theoretically) an HLP < 0.8 and net emisisons < 0, but without the turbines in SAP, the DER averages say 6.2 compared to a TER of 24.5kgCO2/m2.yr. With the turbine output included proportionally in SAP, the DER is -22.00KgCO2/m2.yr

What is particularly frustrating, is that the power output of a communal PV array or biomass CHP system can be averaged by floor area across each of the dwellings, but not from an on-site turbine, if it is not on the building.

So at this juncture, I would suggest that any ‘zero-carbon’ housing development that relies on on-site, additional, private wire wind, will not be able to achieve Stamp Duty relief. I guess that a biomass CHP scheme would still comply, as the CHP power output would be included in SAP.

Interestingly, I have heard it stated that the reason for excluding communal wind from SAP is that it is not possible to determine the proportions for power used on site and exported. However, SAP assumes that all PV or CHP power is used on site, so why not for wind. Granted that this is not representative of reality, but why oh why are we adopting different scenario assumptions for different technologies? You could indeed argue that a greater proportion of wind power is likely to be used on site compared to PV in domestic situations (where the array is sized to achieve Code Level 6) as dwellings are largely unoccupied during the day and will have a minimal base load whilst wind continues to generate during the evening and at night.

As far as I can see, the turbine is allowable under the BRE Code for Sustainable Homes ENE 1 & 7 calculators, but this is supposed to be in sync with Stamp Duty Relief. I am not sure whats going on exactly, other than sheer disjointed thinking.