One of the criticisms of Solar PV, is that the power is generated mostly when you don’t necessarily require it all. The homeowner is probably not at home in the middle of the day to make best use of the peak power generated – so the majority is exported to the grid.
This is particularly relevant for south facing systems. These are often optimised to produce the maximum annual power output so to give the best return on investment. There is however, more to the savings from PV than just maximum power production and earnings from the FIT.
The standard model for calculating the payback time and savings from PV is based on the assumption that your self use will be 50% of what you generate. But what if you can directly use more of what you generate yourself?
A Solar PV system that is split over East / West roofs will provide a flatter power profile over a day. It will tend to wake up earlier in the day and carry on producing until later in the day than an equivalent sized South facing system. The peak production around noon will be less than it would be for an optimally South system, but you wont be exporting as much, if any, power. You have more chance to use what you are generating yourself.
Of course the raw annual output for an East / West system is reduced compared to a South facing system. But not by much.
For a 35 degree South facing roof in the SW of the UK with no shading, you would expect to see around 4100Kwh generated for a 4Kwp system (new MCS guide calculation). But a 4kw East West should generate in the region of 3448 Kwh.
Doing some quick numbers on the back of a Post It note – if you can self use around 63% of what you generate from an E/W PV system, then you are on a par with the returns from an equivalent sized South facing array.
Bearing in mind the better power production profile from an East West system compared to a South only, achieving 63% or more self use should be quite achievable.
Taking this to the next stage or further – there are systems available where panels can be placed on multiple aspects of roofs to make best use of any available sunlight. You are not necessarily fixed having a split over just 2 roofs. The split doesn’t even need to be 50/50. There is also some mileage – as crazy as it sounds – to install panels on a Northern aspect. Its surprising how much light is still available late on a summer evening when the sun has gone past West.
If you’d like to find out how much you can save, please try our solar pv calculator.
Keep a look out for our next News blog on breaking the 4kw “barrier”.
by Mark Smith