Off-grid systems eligible for feed-in tariffs

It is possible for a solar power system that is not connected to the national grid to be eligible for feed-in tariff payments.

The system will have to be installed by an MCS-accredited installer, and will have to use MCS-accredited solar panels. It has to meet a number of requirements in terms of the configuration and installation of the system.

The scheme is extremely badly designed for off-grid systems. One requirement of the scheme is that the amount of energy generated must be metered with an approved meter. There is no approved meter for DC battery-based systems however. So in practice you have to invert the DC power from the battery bank to 240V AC, and measure the energy actually used from the battery bank with an approved AC kWh meter.

The fact that you are then measuring energy used creates an incentive to use as much power as possible - even if it is going to waste. Typically, you might run an immersion heater as a dump load to get rid of excess power when the batteries are full. Even if you have no need for the heat generated by the immersion heater, you get paid up to 41.3p per kWh that is used, so you are better off using as much power as possible.

We don't like encouraging customers to waste energy, and we'd much rather the government hadn't been quite so daft in setting up this bizarre loophole, but it exists so you may as well make use of it!

If you have an off-grid property and would like us to come up with a suitable system for you we would be delighted to do so, please get in touch.

Feed-in tariffs and Energy Performance Certificates

The information on this page is now out of date - from 15 January 2016 the rules have changed

Energy efficiency requirements for feed-in tariffs – two options

The EPC performance requirements for feed-in tariff eligibility have not been challenged in recent court decisions, and will apply whether or not the Supreme Court rejects or accepts the Government's appeal. These new domestic energy efficiency requirements will come into force from 1st April 2012.

Where a domestic property does not meet these energy efficiency requirements, the Solar PV installation may receive the lower tariff. The UK Government is consulting on two alternative proposals (taken from the EST website). As of 1 April 2012:

  • that the owner or occupier should bring the property up to an Energy Performance Certificate (EPC) rating of level C or above; or

  • that the owner or occupier of a building should undertake all the measures that are identified on an EPC as potentially eligible for Green Deal finance, with no additional finance required.

Depending on which of these options are decided upon, this may mean that the building doesn't necessarily need to have an EPC rating of level C or above. In the second case, the householder only needs to undertake any measures possible under the Green Deal, which is the Government's planned scheme for energy efficiency improvements that are paid for through savings in energy bills.

One year to make the necessary improvements

As a transitional arrangement, installations with an eligibility date between 1 April 2012 and 31 March 2013 would have 12 months from the eligibility date to install any energy efficiency measures that are necessary to comply with the energy efficiency requirement. During this period, installations would receive the applicable standard tariff rate. If, at the end of the 12 month period, the relevant energy efficiency measures had not been installed, the tariff would automatically be reduced to the lower tariff of 9p/kWh for the remainder of the eligibility period.

EPC rating level C – is that high?

A building is given an energy performance rating of C when it achieves a score of 69-80 using the Standard Assessment Procedure. To get an idea of what this means, most houses in the UK have a rating of D or E. Most newly-built, gas-heated houses are rated C. If you are living in an old house that hasn't had many energy efficiency improvements, it is likely that this has an EPC rating of D or below.

What next, after 1 April?

Householders will require an energy assessment of their homes, either to prove that they have an EPC rating of level C or above, or to see what measures they are required to take before being eligible for the feed in tariff. As well as being a requirement for the FITs, solar PV is also one of the measures eligible for Green Deal financing.

There is a three-step process to assessing energy efficiency improvements under the Green Deal:

  1. Is the proposed measure eligible for Green Deal finance?

  2. Is it suitable for the property?

  3. Does it meet the “Golden Rule” requirement?

According to the Golden Rule, energy efficiency improvements must pay for themselves – without the need for any additional funding by the householder. Instead, the funding is provided by a registered Green Deal Provider, because over their lifetime the measures should, at the very least, pay off their up-front cost in the form of savings on energy bills.

The following table gives the measures eligible for Green Deal finance.


Heating, ventilation and

air conditioning

Condensing boilers

Heating controls

Under-floor heating

Heat recovery systems

Mechanical ventilation (non-domestic)

Flue gas recovery devices

Building fabric

Cavity wall insulation

Loft insulation

Flat roof insulation

Internal wall insulation

External wall insulation

Draught proofing

Floor insulation

Heating system insulation (cylinder, pipes)

Energy efficient glazing and doors


Lighting fittings

Lighting controls

Water heating

Innovative hot water systems

Water efficient taps and showers


Ground and air source heat pumps

Solar thermal

Solar PV

Biomass boilers


I've heard of voltage optimsers - what are they?

Voltage optimisers reduce the mains supply to the house from 230V to around 220V. In some situations this can reduce the power used by appliances – saving you money on your electricity bill.

A number of trials have tested different appliances on reduced voltages – with differing results.

Old fashioned light bulbs will use less power at a lower voltage, but they will also be dimmer! A better way of saving energy would be to switch to efficient LEDs. Other simple electrics used for heating - such as kettles and electric hobs - will also use less power, but will also become less hot – meaning you would need to leave the appliance on for longer to generate the same amount of heat.

Other appliances such as TV screens and computers will respond differently to different voltage levels. But most research suggests that there will be minimal (if any) savings.

The biggest savings are likely to be made from appliances with motors – but these can vary greatly depending on the efficiency of the motor and the about of load applied.

Most domestic properties will benefit very little from a voltage optimiser. Bigger savings are likely to be made on commercial buildings.

These are not to be confused with MPPT voltage optimisers used for minimising shading on solar panels!

Can you install panels on my type of roof?

The answer is almost certainly yes - but some are easier than others! Most houses have either pan tiles, clay tiles or slate roofs. It is also possible to install panels on flat roofs such as extensions and garages, with the panels either laid flat or pitched towards the sun. Commercial buildings often have corrugated fibre cement roofs or sheet metal roofs. We have solutions for all of these common roofing materials. Just let us know what type of roof you have and we can find the best solution. If your roof really is unsuitable - they can always be ground mounted. The only common roofing material that would cause problems is thatch!

Can I install a system larger than 4kW on my house?

The information on this page is now out of date - from 15 January 2016 some of the rules have changed

It is possible to install a system larger than 4kW on a domestic house. However, if you exceed the 4kW mark you get paid a slightly lower rate for every unit generated. In practice, it is probably only worth going over 4kW if 6kW or more can be installed on your roof. This would require a roof of approximately 4m x 12m. If you have a large detached house or a bungalow you may well have enough space for a system larger than 4kW - in which case a larger system would certainly be worth considering!

However, the 4kW mark is slightly daft anyway - and has caused confusion throughout the industry. When connecting a Small Scale Electricity Generator (ie - solar panels or a wind turbine) to the national grid, the installation is required to meet legislation set our by the Distribution Network Operator. Through out the UK, most domestic installations under 4kW are installed under G83 rules - G83 rules state that a system must not exceed 16A per phase. On most houses this will be 3.68kW (230V x 16A) - which is less than 4kW! To get around this, inverters limit the AC output of the system to 16A - in practice a 4kW system would rarely exceed 16A per phase as conditions are rarely ideal! Current limiting is most likely to happen on a cool sunny spring day - click HERE to find out why.  If you wanted to exceed 16A, the inverter needs to comply with G59 rules. If you have a three phase supply it is possible to install just over 11kW on G83 - so probably best to make use of the 10kW Feed in Tariff band. Having said that, it is quite easy to get G59 permission to install a system larger then 16A per phase.

If this is giving you a headache there is no need to worry - we deal with this on a regular basis and handle everything for you.