Category Archives: Living in the House

Solar PV Export Tariff Options

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When the solar panels on the House were commissioned in 2017, the UK’s Feed-In-Tariff (FIT) arrangement was still available so currently (2024-25 pricing) that system generates payments based on:

  • 5.87p per kWh of Generation, as reported by the dedicated generation meter
  • 7.14 p per kWh of Export, based on 50% of generation being treated as “deemed export”

When the new solar panels on the Outbuildings get commissioned later in 2025, those will not be eligible for any sort of FIT payments – but they will be able to generate revenue based on the actual exported energy, as reported by the SMETS2 Smart Meter.

Since the Smart Meter won’t be able to distinguish an export originating from the ‘new’ solar panels from one originating from the ‘old’ ones, it’s not possible to continue on the 50% “deemed export” basis for the older installation; the whole site needs to be switched to a tariff which makes payments based on actual, measured export.

The question then is whether it’s worth swapping over now, or waiting until the new panels are commissioned in about 6 months time – which depends on:

  • The relative rates per kWh for a metered-export tariff versus the deemed-export tariff
  • Whether the site is actually exporting (more than) 50% of generation or not

The electricity supplier is currently Octopus Energy, and the import tariff is Intelligent Octopus Go, which is very good for overnight EV charging. Octopus offer quite a wide range of export tariffs. The ‘best’ ones being:

  • Octopus Outgoing, which pays a flat rate of 15p per kWh exported
    • This is generally the best option for sites with no battery
  • Octopus Outgoing Agile, which pays a variable rate based on half-hourly electricity prices
    • This is generally preferred when there is a battery which can store a significant proportion of the solar PV generation during the middle of the day then export that in the early evening, when export prices are often (but not always) higher than 15p

On the face of it, 15p per kWh is significantly better than 7.14p per kWh, and spring-into-summer is generally very good for solar generation so a greater proportion of generated power is likely to be exported – which implies it would be beneficial to switch sooner rather than later, as long as Octopus Outgoing is compatible with Intelligent Octopus Go.

Electric Roller Blinds for More-Than-4m-Wide Sliding Doors

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One thing I didn’t pay enough attention to when planning for the electric window blinds was the width of the sliding glass doors. Some of these are more than 4m wide, which is problematic because:

  • A more-than-4m-long roller tube would need to be quite a large diameter to be stiff and strong enough
  • Very few blind fabrics are available more than 4m wide – and they’re expensive

Therefore, it’s generally better to use two narrower blinds instead of one very wide blind. The small gap between them is mostly blocked by the sliding door frame.

The issue then is that I only specified that a single 230V KNX relay be wired to each door location – and it’s not possible to simply connect two 230V blind motors ‘in parallel’ to one relay channel. The reason is nicely explained in this text from Schalk Steuerungstechnik GmbH:

Roller shutters or louver blind motors with mechanical limit-switches must as a rule not be electrically connected directly in parallel, because due to the different motor running times the limit-switches of some motors may be reached while other motors are still running. The motors that are already switched off would then receive inductive voltage at the counter-winding from the motors that are still running, which can lead to destruction of the limit-switches.

There are two main options to overcome this issue:

  • Using blind motors with ‘electronic’ (rather than ‘mechanical’) limit switches, since these don’t suffer from the same limitation
    • This was the approach adopted for the wide sliding door in one of the bedrooms and it has mostly been successful – though the limit settings on one of the motors do tend to ‘creep’ over time and periodically need re-setting
  • Multiple motors can be isolated from each other using relays, installed adjacent to the blinds, that block the induced voltage from a still-running motor from damaging an already-stopped motor

Various companies manufacture suitable relays but the products from Schalk Steuerungstechnik GmbH seem pretty good. In particular, their MGR U2 which can take the output from one KNX relay (or a pushbutton or whatever) and drive two blind motors. Variants are available for 1, 2, or 4 motors and for DIN-rail or ‘flush’ mounting (in a regular back-box, behind a blank cover plate). These do not require an additional permanent live supply and are very competitively priced.

Schalk MGR U2 flush-mounting relay for 2 roller blinds