Sunny Thoughts

PV After the Feed in Tariff - FiT RIP!


Now the Feed in Tariff is dwindling away, its significance in the decision to install a solar system is reducing, soon to become totally irrelevant. No longer will we be looking for a financial vehicle for money to give a return on investment on money, we will be looking for value for money and energy in return for our investment. The current payment of between 3p/kWhr and 4p/kWhr, pales into insignificance when compared with the electricity purchase price, which could be as high as 16pkWhr. The payment for exporting energy is around 5p/kWhr and increasing, so this is becoming more valuable than the FiT. The payments and savings are now for actually exporting energy plus saving you importing your own required energy.

With this principle in mind we now need a re-appraisal of the design of the system. When we were targeting the maximum Feed in Tariff payment the perfect roof was a south facing 30º pitch which gave the maximum annual generation. Now and in the future it represents a better saving to have energy generated when you want it, so it could be better to look at other orientations and other angles dismissed under the “old thinking”.

Take for instance a business working from 8.00am to 6.00pm, it makes no sense to have a south facing only system which gives a gradual energy increase peaking at midday, and tailing off in the afternoon. What would be better is to have a system with east and west facing panels at a low angle which will give generation earlier in the morning and later in the afternoon, and much flatter whole day generation profile. This is good for all the summer months.

A problem with this installation is whilst it will be good for spring, summer and autumn, in the depths of winter the sun rises in the south east, is low in the sky at midday, and sets in the south west. Whilst the system will still generate with the sun at this low angle what ideally is needed for the winter months is panels facing due south and set at a steeper 50º pitch – although at this angle in the height of the summer these will miss eight hours of ealry morning and late afternoon sunshine! – nothing is ever straight forward! – but every cloud has a silver lining, what is convenient here is that this angle is the typical pitch of a Cotswold roof.

Something that can influence the solar panel layout is if storage batteries are to be installed. Here if a large PV output is installed, good for additional energy, the issue will be recharging the batteries in the shorter daytime hours in the winter, so some south facing panels preferably at a steep pitch would be an advantage. Having an electric vehicle to charge may also influence the design layout.

The likelihood is that more than enough energy will be generated at midday in the summer because the demand may be lower anyway. Typically in a domestic situation the midday loads may only be the fridge/freezer and standby loads from electronic equipment, so the old FiT ideal south facing 30º is far from ideal now.

What all this illustrates is a need to consider the energy requirements when designing a solar system. In a typical situation the roof might already exist, so there is little design flexibility but with the knowledge of the sunpath and the energy requirements, the most appropriate design can be arrived at, and the building owner can understand the issues and what compromises need to be considered. All buildings will benefit from solar energy, the system just needs to be designed to maximise the output at the times there is a demand,  - alternatively using batteries, the generation can be stored until required.

Considering the bigger picture the electricity supply network operators will have less problems with solar systems that are targeting the demand and giving a flatter generation profile over more daylight hours, not giving them a large generation peak from every system in the district at midday! – which they then have to deal with. Storage will further help them by buffering both the generation peaks and the demand peaks.

To sum up we will discuss with the building owner to establish what is required and then propose a system that best fits the site and the budget. In these days with the decline in the FiT payment typical system sizes are 4 to 8kW peak with export limitation to meet the Network Operators maximum allowance. The default permitted export limit is 3.68kW/phase and permission has to be obtained to exceed this.