Solar PV – Frequently Asked Questions and Answers

silverwhistle

zeupater wrote: »

as soon as you start factoring in the storage requirement to supply standard appliances such as a fridge, freezer..
Z

On the basis that every little helps, as the days are getting longer I plan to put my freezer on a time switch so it mainly draws power during the day. On my model I think contents remain frozen for over 24 hours (some models have considerable longer autonomy) without power and I fill spare spaces with bottles of frozen saline solution.

Robwiz

In reply to zeupater:

Yes, of course it's serious.

I don't want to take this FAQ off topic by getting into a discussion about my heating system. I shared what I have learnt about my own heating system as an example to show that heating DHW indirectly with gas may not always be cheaper. However, I will provide some more details so that you can appreciate the context.

I have been working since last summer on reducing our household energy consumption and am currently on track to save £2500 per annum. I have been taking daily meter readings (gas, elec and solar PV) since last October and tracking gas usage against heat degree days.

The DHW has never been left 'always on' – my figures come from running the system set on 'hot water only' using a Hive controller to ensure it was on for precisely one hour. Incidentally the Hive reduced gas consumption for heating by about 10% through closer temperature control compared to the old Honeywell electro-mechanical stat.

The towel rails are 1.8m tall by 0.4m wide and 1.1m tall by 0.5m wide respectively. The boiler is a Potterton Suprima 100 (78% efficient/50% efficient heating water – according to the SEDBUK database). The total length of the pipe run (vertical plus horizontal) between the boiler and the cylinder is approx. 21m.

When the boiler starts up, the system initially draws heat from the warmer stored water because the circulating water will be at room temperature (typically 16º when the boiler starts in the morning) and the tank could be at 40ºC or higher.

zeupater

Robwiz wrote: »

Yes, of course it's serious.

I don't want to take this FAQ off topic by getting into a discussion about my heating system. I shared what I have learnt about my own heating system as an example to show that heating DHW with gas may not always be cheaper. However, I will provide some more details so that you can appreciate the context.

I have been working since last summer on reducing our household energy consumption and am currently on track to save £2500 per annum. I have been taking daily meter readings (gas, elec and solar PV) since last October and tracking gas usage against heat degree days.

The DHW has never been left 'always on' – my figures come from running the system set on 'hot water only' using a Hive controller (which incidentally reduced gas consumption for heating by about 10% through better temperature control).

The towel rails are 1.8m tall by 0.4m wide and 1.1m tall by 0.5m wide respectively. The boiler is a Potterton Suprima 100 (78% efficient/50% efficient heating water – according to the SEDBUK database). The total distance between the boiler and the cylinder is approx. 21m.

When the boiler starts up, the system initially draws heat from the warmer stored water because the circulating water will be at room temperature (typically 16º when the boiler starts in the morning) and the tank could be at 40ºC or higher.

Hi

I appreciate what you are saying, but there must be something wrong, either with the calculation, the way you're using the system, or the system itself.

With a 6kWh demand and 44kWh input the total system efficiency is 13.6% .... we had a much older boiler with a 5kWh/day pilot light, a 30metre primary pipe run (feed+return) of 28mm copper tube (of which ~8metres is inside a loft, but insulated) and a similar daily usage and used well below 20kWh/day of gas, usually somewhere around 16-17kWh on average, so our comparative total system efficiency would be well over double @35% (6/17), and if it had spark ignition instead of a large pilot light the efficiency would have been closer to 50% (6/(17-5)).

For heating DHW the control system makes little difference, you provide heat and the cylinder warms up ... the large towel rail looks similar in size to one we have (1100x600mm), which is rated at 400W at deltaT50 (that would mean a boiler output temperature of ~70C), so twice that for an hour is only 800Wh ... the water cooling effect on startup doesn't really matter that much in the calculation, all it's doing is adding to the boiler heating input and initially increasing the heating circuit faster, which is made up for by the boiler later in the cycle, there's really nothing you can do about it with a cylinder system.

There are definite issues with running a gas DHW system with the cylinder temperature being set high and the boiler output low as this simply creates a situation where the heating period is extended and the primary pipe circuit and, in your case, radiators would be bleeding more heat than necessary.

Using 44kWh/day of gas just to provide DHW is ridiculously high and should be classified as being atypical to the extreme. I really do think that there is an issue here which needs looking at, so if you would like to open a separate thread you'll find that there will be some who could provide useful input ...

HTH
Z

Martyn1981

Robwiz wrote: »

I don't want to take this FAQ off topic by getting into a discussion about my heating system.

Appreciate the point, but just thought you might be interested in this thread that started today on the Navitron forum. Although primarily comparing leccy to oil, the OP does start of comparing about 7kWh of leccy to about 30kWh of oil.

Can anyone explain why My hotwater is using so much oil

So a thread (as suggested by Z) may be interesting, whilst keeping an eye on how the Navitron thread evolves.

Mart.

tinbum1

I've had a problem with two 3 phase meters, Landis&Gyr (also Ampy) 5219 and an Itron ACE3000-520. The problem is that export is always treated as zero when it comes to incrementing the meter. So if your exporting say 10kW in total on two of the phases but importing 3kW on the other it is increasing the meter by 3kw when it shouldn't be increasing at all. Another example, export of 2kW in total on 2 phases and 3kW import on the other should see the meter increasing by 1kW (3-2) not the 3kW that it was.
These meters are configurable but they aren't being configured correctly for PV. I believe many, probably 1000's of people are affected by the same problem but aren't aware. Yes their bills will have come down when PV was installed but probably not by as much as they should have.
My two suppliers both said they had never heard of this before and it was only because I was absolutely insistent with them and told them they were wrong about my meter calculating my usage correctly that something has and is being done about it.

EricMears

A friend of mine has recently paid £6k for a 1.75 kWp system and been persuaded to take out a Barclays Bank personal loan to pay for it. I was looking in the FAQ section to see if it gives contact details for any 'industry watchdog' which might be able to review the quotation he was given.


His quotation was (correctly, indeed slightly conservatively) suggesting that such a system in Ashford, Kent should generate 1700kWh/year (given his details the PVGIS page says 1800) and earn FIT payments of £245(gen) + £40(exp) (again fairly plausible) but that he can also expect "electric + other savings" of £450/year. Given that using 100% of his generation costed at 15p/kWh (rather more than I pay !) would only produce a saving of £256/year that rather smacks of mis-selling ! There are several other 'arithmetical errors' (fraudulent claims ?) in his quotation which anyone interested can read at :-
http://www.khormaksarschool.org.uk/KAS/ExtractFromNsurvey.jpg

Fruit_and_Nut_Case

EricMears wrote: »

A friend of mine has recently paid £6k for a 1.75 kWp system...

The double glazing cowboys have new hats. :eek:

zeupater

EricMears wrote: »

A friend of mine has recently paid £6k for a 1.75 kWp system and been persuaded to take out a Barclays Bank personal loan to pay for it ....

Hi Eric

What's the cancellation period on the order ? .... if it's credit there must be 'cooling off' (plus doorstep selling & REAL etc) ... with quotation being 21/11 I'd guess that it's only in the preliminary stages (deposit paid ? - credit card ?), so I'd be looking at the possibility of cancelling, stepping back and doing a little more research ... taking this approach would likely result in the current quotation being halved without much resistance ...

HTH
Z

EricMears

zeupater wrote: »

Hi Eric

What's the cancellation period on the order ? .... if it's credit there must be 'cooling off' (plus doorstep selling & REAL etc) ... with quotation being 21/11 I'd guess that it's only in the preliminary stages (deposit paid ? - credit card ?), so I'd be looking at the possibility of cancelling, stepping back and doing a little more research ... taking this approach would likely result in the current quotation being halved without much resistance ...

HTH
Z

Installed yesterday !


& BTW I didn't find out about it until after it was working.

zeupater

EricMears wrote: »

Installed yesterday !

& BTW I didn't find out about it until after it was working.

... was the date on the survey/quote wrong ?? ... looked like it was last Friday when I looked .... If it was last Friday and Barclays finance was involved, I'd be really surprised if the FCA wouldn't be interested in piling up a tonne of bricks and starting to winch them up above someone's proverbial head ...

Z