Solar PV - Viability - Economics?

[bungeejumper]

How long is the expected lifetime of the system? Would seem to be a relevant factor in these calculations?

It's not something I have much personal knowledge of - we live in a rural conservation area where putting up solar panels would get us hung, drawn and quartered - but would you own the installation under the plan that you've quoted, or would that be a "rent-a-roof" arrangement where the solar company continues to have rights over your property after you sell it?

BJ

[bungeejumper]

If it is 10 or 20 years or anything in between. It is a poor return, it seems. I think generally, 20 years is the lifetime used. The scenario here is for owned PV systems.

Ha, I think you can do better than that. So can I - my ISA is up 167% in 17 years. But fully appreciate that the green aspects of EV are an attractive (though different) subject for many people.

Just for clarification, I'm not really such a solar nimby as all that. Our five-mile radius already has the highest concentration of solar farms in the whole of the UK. Our nearest one made the national headlines in 2016 by installing five pairs of filthy diesel backup generators for the days when the sun don't shine. So forgive me if I look rather closely at the quality of the claims that are sometimes made.

BJ

[dspp]

1. Did you add: FIT + deemed export + avoided consumption ?

2. What lifetime did you use ?

3. What panel degradation rate did you use ?

4. Did you allow for any maintenance ?

5. Did you risk your NG divis in any way ?

Re the above:
- Actual PV lifetimes are beginning to look better than most assumptions. Likewise for degradation. Getting 25 years and only 5% degradation is beginning to look fairly reasonable.
- Allowing for inverters at 10 year intervals is sensible. On my SolarEdge panels I have had one DC-DC fail in 5 years from 12 panels, so far. Done under warranty. None failed on my GF's 12 panels in same span.
- Investing in NG carries risks. That is worth taking into account. How big are they ?
- It is not just about the money.
- My roof gets a lot less wear and tear, my gutters are clean & clear, and that moss is a goner. Unanticipated benefits.
- Putting them in conservation areas and on listed buildings can be done, with care. I am in a conservation area, done with one informal appeal against initial ruling. My GF is a listed (gr 2) building, also done with no appeal.

regards, dspp

[Rover110]

One thing that concerns me is if there is any impact on maintenance requirements.

I seem to remember reading one report that had, in its small print, the fact that the PV panels were washed every couple of years. Presumably there's a build-up of crud that rain isn't sufficient to wash off.

And then what about if the roof needs repairs / replacement during the lifetime of the PV panels? I guess it's relatively easy to take them off and on, but it must add to the cost. And what if any panels are found not to work afterwards?

My mum is a keen advocate of solar panels. But in the 10 years since hers were fitted, she has had to have a new controller for the PV panels and a new hot water tank and pump for the solar-water-heating.

- Rover

[richlist]

Well surely the new water tank and pump replacement won't have much to do with the solar hot water system ?

[Rover110]

Well surely the new water tank and pump replacement won't have much to do with the solar hot water system ?

In this particular case, I think they might.
As the only other heat source for the water is an electric immersion heater in the tank, the only job for the pump is to circulate "water"* from the tank to the roof hot-water panels.
And it was claimed the tank (which was newly fitted when the solar-water-heating was installed) only needed replacing because it had got too hot from the solar heating.

* I assume it's a closed loop, with this "water" containing necessary antifreeze, rust-inhibitors.

- Rover

[richlist]

My solar panel hot water system operates totally differently.

My panels heat the hot water through the immersion heater. Once temperature of the thermostat is reached solar power to the immersion heater is directed elsewhere. The water in my system doesn't get pumped up to the roof it stays in the tank until one turns on a hot tap.

[dspp]

Some of you need to pay attention to the title of this thread. It is about solar PV (= PhotoVoltaic) panels. The ones that make electricity. The clue is in the name. Some of you are clearly quite confused.

Solar thermal panels are an entirely different thing with lots of plumbing and icky things that leak.

(PV panels can make hot water but just the normal way by sticking spare electricity into the immersion heater using a diverter system, such as I have.)

It makes a difference to the economics.

regards, dspp

[xeny]

(PV panels can make hot water but just the normal way by sticking spare electricity into the immersion heater using a diverter system, such as I have.)

When you say "diverter system", I'm presuming you mean a device that tracks output from the panels vs other household demand so any excess can be used to dump energy into a hot water tank? Do you have a link to the product, that sounds very useful.

[dspp]

(PV panels can make hot water but just the normal way by sticking spare electricity into the immersion heater using a diverter system, such as I have.)

When you say "diverter system", I'm presuming you mean a device that tracks output from the panels vs other household demand so any excess can be used to dump energy into a hot water tank? Do you have a link to the product, that sounds very useful.

Yes. Ordinarily there is a clip-on clamp meter between the consumer unit (fuse box in old speak) and the utility supply fuse. This radios to the diverter to say when/if the electricity is flowing ('spilling') out to the grid, and if the hot water tank (or other load) is needy then it switches it on to try and mop up the spilled electricity. Basically it is trying to store electricity as heat (or cold, or in a battery) for later usage.

Two popular models include the Marlec iBoost, or the Immersun. Personally I have an iBoost but I am slightly biased as I used to compete against Marlec and so know them well.

For immersion tank use you need a dual coil tank if I remember correctly. Anyway that's another reason to retain immersion tanks when thinking through your plumbing options. The diverter I have can switch two devices and I have mine wired so that I can also run a fan heater if I wish, though note that switched device must be pretty basic as all you can do is switch supply on or off. That limits what can be switched from this (second) generation of devices.

regards, dspp

[richlist]

Yes that's exactly the system i have installed.

People i know who have new boilers that eliminate a hot water storage tank often ask me if it's possible to have a hot water tank installed with that type of boiler....Anyone know ?