Neighbours in Norfolk have just had solar panels installed. What I don't understand is why they had 6 panels installed, rather than the 12 that there's room for on their roof?
Is there some reason for that?
The marginal cost of the 6 extra panels would be say £2k, given that the scaffolding is already up etc.
On a good day, they would produce say 20Kwh, worth £3 on the FIT. Say they produce £400-500 a year in revenue, that seems a good return on a £2000 investment.
Perhaps that is the limit of the extra weight the roof timbers can tolerate.
6 panels at 400Wp is 2.4kWp. 12 panels is 4.8kWp. Wholesale cost of a panel about £170 (no VAT if pro install), plus fitting hardware (same again, very roughly).
Some possibilities:
- shading, if the panels are going to be shaded by trees/chimneys/dormers/etc they may not generate as much as panels in the 'best' place
- inverter sizing (bigger costs more)
- optimiser cost (inverter has N inputs for strings. More panels means putting more in each string, which need [more] optimisers to compensate for shading)
- DNO approvals (if they need to go >16A per phase, they need G99 approval. The DNO can say no, but they can't for <16A per phase)
- self-consumption (don't buy more panels than power you can personally consume, if the FIT isn't paying enough)
- DIY install (no FIT on DIY, so no point in exporting)
- grid connection (4.8kWp is 20A. Seems unlikely that would be a problem)
- aesthetics / planning (eg easier to put on the back than front of a house in a conservation area etc)
- not having the spare cash
My instinct would be to install as many panels as you can, but it's possible the numbers don't stack up.
Theo
(I'm using the term FIT here for the smart export guarantee or whatever scheme is in place for when the panels are commissioned, as the old FIT scheme is long closed)
The FIT is gone for new installs, the SEG replaced it, between 1p and
24p/kWh
Solar panels are very light (thin glass and aluminium mostly). Roofs covered in tiles or slates are not (tonnes). It's unlikely the weight of the panels will make a difference, but it may be the structure underneath isn't amenable to mounting in some way.
More of a concern is wind loading, since they can act as sails. I suppose it's possible a roof with more panels could fail wind loading checks, but that seems somewhat unlikely for such a small number.
Theo
I hadn't factored in the fitting hardware, as I hadn't realised how expensive it is!
No shading
So, it sounds like I'm right to be a bit puzzled.
My 2 Eco-Worthy solar panels weigh 15kg
GB snipped-for-privacy@microsoft.invalid wrote
Most likely what cash they have available.
But it is far from clear how long that FIT rate will continue for and what matters is whether they have that £2000 available to invest.
The old FIT payments no longer exist for new installations. The payments for truly feeding back into the grid are now a lot less per unit than taking electricity from the grid. Depending on your supplier and the tariff you select the payment could be a low as 2p or 3p per unit.
alan_m snipped-for-privacy@admac.myzen.co.uk> wrote
Sure, I meant the term in the generic sense. I should have said that.
Maybe then, based on the poor FIT, the set of six panels is tied to a battery system with limited panel input connections or something. An emergency power source for a critical system. Six panels would not be an attempt to go "off-grid".
Paul
Using everything you generate yourself is probably the way to go. Heating water and charging a EV during the day is one way to use the solar output. A battery would enable you to use your solar generated electricity in the evening or in the morning before the sun is high enough in the sky, even yesterday solar produced next to nothing between
6pm and 6 am. Most of what solar produces is in the long summer days so no chance of going off grid during the shorter colder days.Have something to add? Share your thoughts — no account required.
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