Deleted

ABrass

Calculating kWh and working out what proportion you'll use is the way everyone does it. You get those from PVGIS and you pick a realistic % to work out what you're likely to use based on others experience and lifestyle factors like if you work from home or not. That typically comes out at 30% without a battery and 50% with a battery, higher for small systems, lower for larger.

It is really confusing me here, you seem to think you'll be using every kWh you generate from your 1 kWh array. They'll typically generate around 1,000kWh a year, which would be a saving of £330. For a saving of £290 you'd need to use 88% of your possible power generation, which is really ambitious.

ABrass

As to diminishing returns, yes that's so obvious it's not worth digging into. You start to see it when you generate as much as you use in a year. EG. We use around 7,000kWh a year and our sweet spot is around 8kW of panels. After that it may or may not make sense to buy more.

For low users like you that's a small system. For higher users it's a larger system. This is all well known.

ABrass

Most people export to the grid, which makes the diminishment less significant. Most systems are also significantly cheaper to add additional panels than the first ones, so you get better value for the additional kW. It normally works out that you get more benefit from a larger one than a small one.

With SEG of 15p/kWh if you pay £1.50 a Watt then they'll pay for themselves after 10 years, then continue to pay you for another 15 or so. If you use any of the power that's a bonus.

ABrass

Deleted_User said:

ABrass said:

Most people export to the grid, which makes the diminishment less significant. Most systems are also significantly cheaper to add additional panels than the first ones, so you get better value for the additional kW. It normally works out that you get more benefit from a larger one than a small one.

Not relevant to me, but absolutely that's a factor that will impact return on investment.

Which is why you're such a niche case. Your experiences aren't relevant to most people. It is interesting theoretically but so is basket weaving.

ABrass

Most people with PV do not have batteries, most people with batteries don't have battery 'backups'.

Most people with PV sell back to the grid.

When going off grid the common theme is to accept wastage and oversized systems to allow for sufficient power over the winter months because they don't have the backup of a grid connection.

Solarchaser

There are alot more people on here have batteries than did 3 years ago certainly, but still the amount with batteries is very small in comparison with the amount of users.

silverwhistle

I think I am getting diminishing returns the more time I spend looking at this thread..

zeupater

Hi scarter

From the 'outside' it looks like you're struggling to understand that the people you're conversing with are simply trying to be helpful and pointing out that what you've described and how you're describing it is open to misinterpretation and confusion because your understanding is different to the way that most of the the rest of the world sees it.

Power is an instantaneous measure ... for example if you use an electric oven it consumes electricity at (say) 3kW for an amount of time to heat before a thermostat cuts the power supply to the heating element for a while ... it's the thermostat's control of power through switching that maintains the oven temperature.

Somewhere within the house there's normally an electric meter which continually measures the amount of instantaneous Power (kW) over various measured time intervals, which is known as Energy and normally measured in kWh .... the metered Energy you've consumed over time is what you pay for through your billing account with your supplier .... when you pay the bill it is based on a cost per unit (say 30p), the unit being referred to is normally kWh.

To add to the confusion, the solar PV panels you have been talking about have a nominal Power performance rating based on 1000W/sqm of illumination of synthetic sunlight at a standardised temperature. This Power rating is rarely achieved under normal operation, therefore it is referred to a 'peak' and normally referenced as kWp.

Note that a nominal 2kWp PV array generating 1kW of Power for 30minutes would produce 0.5kWh (500Wh) of Energy .... that's what (almost) everyone here understands, that's what industry understands & that's what's universally taught in schools & universities.

The confusion being caused is due to the context used ... effectively "2kW of panels is producing 1kW thus making 0.5kW" makes little immediate sense to anyone following, particularly if the elements are referenced separately, whereas "2kWp producing 1kW for 0.5hours thus making 0.5kWh" would have a much better chance.

HTH - Z

70sbudgie

To get more 'bang for your buck' have you considered how the orientation of the PV panels affects the seasonal performance? For example, my E-W panels give me longer duration of usuable generation for the summer 6 months, with a lower peak which would be wasted (or in my case exported). Now well into my second year of PV ownership, I have started looking in more detail at other aspects - for example, how much shorter my generating days are now, because the sun doesn't really get far enough from south (either E or W). So if I were going to add extra panels to improve my winter generation, I would look at a south facing panels and mount them closer to vertical. I wouldn't necessarily expect this to add much to my summer generation, but it would improve the winter generation. And consequently, I believe it would be the opposite of a diminishing return on my investment.

Edit to add: this is the principle behind the architectural feature of big eaves - they provide shade from the high sun in the summer, but let in more low winter sun.

70sbudgie

Deleted_User said:

70sbudgie said:

To get more 'bang for your buck' have you considered how the orientation of the PV panels affects the seasonal performance? For example, my E-W panels give me longer duration of usuable generation for the summer 6 months, with a lower peak which would be wasted (or in my case exported). Now well into my second year of PV ownership, I have started looking in more detail at other aspects - for example, how much shorter my generating days are now, because the sun doesn't really get far enough from south (either E or W). So if I were going to add extra panels to improve my winter generation, I would look at a south facing panels and mount them closer to vertical. I wouldn't necessarily expect this to add much to my summer generation, but it would improve the winter generation. And consequently, I believe it would be the opposite of a diminishing return on my investment.

Edit to add: this is the principle behind the architectural feature of big eaves - they provide shade from the high sun in the summer, but let in more low winter sun.

We've done our best with this, but it's a bit of a trade of with appearances and performance. 

We have two 700w arrays each feeding into a different generator. They get sun all day long, but face SSW. I can't remember the angle off-hand, but I think 10 degrees or so (so not far off flat). This is mainly for appearances. At the time our thinking was that it would allow the very early morning sun to hit the panels a bit sooner. We also figured that when the sun hardly shows it's face in winter there wasn't a lot of point going overboard to optimize for it. But we haven't done the actual calculations to prove that theory. 

We also have additional panels feeding in via the mains adaptor - half are SSE, half are SSW - angle about 45 degrees or so - they're mounted on the walls of the house and I don't remember the exact angle. 

So we've bits and bobs in various places that each do better at certain times of year/day. Changing angles isn't completely out of the question, but it'd need to make a big difference to make it worth doing. But good idea to add this to my spreadsheet and 'what if' scenarios. 

I'd be interested what information your spreadsheet gives. It was unseasonably warm on a recent sunny day and I was surprised that my panels didn't manage a higher peak. After a short period standing in the garden staring at them and surrounding shadows, I decided that it must have been due to the angle of incidence. Not very scientific, I appreciate.