Solar PV – Frequently Asked Questions and Answers

EricMears

matt691944 wrote: »

I was thinking of buying these panels from the USA and mounting 18 of them on a flat room (I assume this should read 'roof' ?) of my 3 bedroom house.

If you were thinking of buying & installing the panels yourself, you probably won't be able to benefit from the Feed-In Tariff scheme. One of it's conditions is that panels have to be fitted by a registered installer and it would be unusual for one of them to work on a labour-only basis.

Not sure that you would need PP to fit panels on a flat roof if they were also flat and not more than a few inches above the existing roof surface but you would of course need PP to mount them on a framework angled toward the sun. If PP for frames is refused, you might consider horizontal panels and looking at the pvgis site should give you some idea of how much you'd lose by doing that.

matt691944

do you think its just as good to have the flat, or is there big benefits to mounting them? I guess I'm asking is it worth the cost to mount them?

but also was just looking at maybe a 6kw system might as well produce as much as i can, and it doesn't seem a huge jump from form a 4kw system to a 6kw just a couple of grand

EricMears

matt691944 wrote: »

do you think its just as good to have the flat, or is there big benefits to mounting them? I guess I'm asking is it worth the cost to mount them?

It's certainly better to have them angled at 30deg (to face directly into Sun on Summer Solstice day), better still to have a variable angle (so you can crank it up to 70deg in Dec/Jan) but lying flat still generates a lot (and would reduce installation costs). Only way to work out best approach would be to input your position to the pvgis calculator webpage (http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php# ) and input the two different slopes. Gut feeling is that it would be worth fitting the framework but otoh FIT rates (IF you'd qualify) have dropped a lot so that if there's a large cost involved in fitting frames the ROI without them might be almost as good as with. And of course if planners say no frames your decision is easy.


Have just run the sums for Sheffield (it's widely used as 'typical').


Panels at optimum slope (they say 39deg) would produce 916kWh/kWp/year; at zero slope that drops to 774 (= 15.5% reduction). Hence (but strictly only for Sheffield) if cost of installing frames would increase total cost by more than 15% it wouldn't be worth bothering.

matt691944

ok so definitely frames for me then ! i will call me council see how much they'd like to tax me for planning

zeupater

EricMears wrote: »

It's certainly better to have them angled at 30deg (to face directly into Sun on Summer Solstice day), better still to have a variable angle (so you can crank it up to 70deg in Dec/Jan) but lying flat still generates a lot (and would reduce installation costs) ....

Hi

Problem is that they'll get dirty very quickly and as rain will not run off effectively they'll need a lot of cleaning. I saw some (late 40's ?) flat roof houses with (angled) panels a couple of days ago and they looked pretty good.

HTH
Z

matt691944

whats (late 40's ?)........year of the build

zeupater

matt691944 wrote: »

whats (late 40's ?)........year of the build

Hi

Yes, the flat-roof properties in question were built as part of the post (second world) war scramble to expand the national housing stock and would have been built either in the late (19)40s or early (19)50s. With the number of flat-roof properties which had panels mounted on angled supports, which looked to be protruding well over 200mm from the roof (ie not permitted development), their local authority mustn't have an issue with granting permission - probably be a good idea to ring your LA and have a chat or simply talk to a local installer and check the position with them ...

HTH
Z

Ainsley1

Great thread that I have just read.
I note the Recc cooling off period of 14 days (mentioned above )can be circumvented only if the consumer gives written agreement to that effect. However, and perhaps this answers one earlier query, if the installation need to be removed then the consumer could be liable for the removal cost. Also there is a different start date should finance be required. From their top tips:-

• Remember if you sign an order form or contract with a sales rep in your home you have the right to cancel the contract from when you signed it up to 14 days from the date the goods are delivered to you.
• If you want the installation to start during the 14-day ‘cancellation period’ you must give your express written consent; if you later cancel the contract you will have to pay for any work completed.
• Even if you do not sign an order form or contract with a sales rep in your home you still have the right to cancel the contract within 14 days from when you signed the contract; make sure you don’t give up this right by signing a waiver.
• If you are being offered finance by the company you’re contracting with remember you have 14 days from the date you receive the documentation from the finance provider to cancel the agreement without penalty.

NacNac

Hello,
The original post is 3 years old now. I am wondering what the latest news are on benefits of PV for those who got them installed for over 4 years now.

I am currently considering them before the FIT comes to an end.

I am actually wondering the following and could not find much about it.
My roof is large enough to fit 16 panels. I was therefore recommended to have 16 panels at 250W which gives the maximum power (4kW) I can have.
However, the panels will only reach 4kW only during a small % of the year. I am therefore trying to understand what is the drawback of having 300W or even 350W (but let's base my example on 300W). The price of the panels will be more expensive but my research so far does not show it will be 20% more expensive while a 300W will produce 20% more electricity. I have a limit not to exceed which is 4kW, As a consequence I must have a switch to prevent feeding the grid with more than 4kW. The question is, does the extra 20% electricity produced during the year where the maximum output is less than 4kW compensate the loss of not feeding the grid when the output is above 4kW. Also mean that I should be reaching 4kW more often with 300W panels

I have attached a diagram to illustrate what I mean.





What do you think of the logic ? Is that worth it

Thanks a lot
Best regards

EricMears

NacNac wrote: »

Hello,
The original post is 3 years old now. I am wondering what the latest news are on benefits of PV for those who got them installed for over 4 years now.

I am currently considering them before the FIT comes to an end.

I am actually wondering the following and could not find much about it.
My roof is large enough to fit 16 panels. I was therefore recommended to have 16 panels at 250W which gives the maximum power (4kW) I can have.
However, the panels will only reach 4kW only during a small % of the year. I am therefore trying to understand what is the drawback of having 300W or even 350W (but let's base my example on 300W). The price of the panels will be more expensive but my research so far does not show it will be 20% more expensive while a 300W will produce 20% more electricity. I have a limit not to exceed which is 4kW, As a consequence I must have a switch to prevent feeding the grid with more than 4kW. The question is, does the extra 20% electricity produced during the year where the maximum output is less than 4kW compensate the loss of not feeding the grid when the output is above 4kW. Also mean that I should be reaching 4kW more often with 300W panels

I have attached a diagram to illustrate what I mean.




What do you think of the logic ? Is that worth it

Thanks a lot
Best regards

The original post was indeed 3 years ago - but it wasn't really intended as a discussion topic - just a quick reference page. It would really have been better to start a new topic.

My 16x250Wp panels are now 4 years old and I'm really happy with the savings in household use they've helped me to make. Also very happy that FIT receipts are now more than 50% of capital cost with over 20 years of the contract still to run.

Re your proposed large system, by far the best way would be to ask your DNO for permission to install 6kWp. They might agree in which case your problem is solved instantly. If they refuse, then you might have to settle for 3.68kW which apparently everyone is allowed without special permission (though some exceptions have been reported) which is just a bit less than 4kW although a 'capped inverter' will solve problem easily.

The capped inverter would probably also work with much larger systems but I agree, it does seem wasteful.

But apart from that, I don't think DNOs accept any other scheme for limiting output (else something like an Immersun trying to heat a swimming pool would be ideal).

There is another way of getting permission for even larger systems which is to ask for a 3phase supply to your property (assuming you haven't already got one) as the 'permission automatically granted' limit is actually 3.68 kW per phase

HTH