Solar PV performance review

[H F]

Our solar PV array has been up for four months and I thought it was a good time to have a look at their performance providing an unbiased report, based on real life experiences, illustrating power output on overcast, rainy and sunny days.

 

 

 

More info is available here about our array: https://myhomefarm.co.uk/solar-pv-and-inverter-review

 

Would be very interested to hear comments and how our array compares to yours.

[H F]

As always, looking forward to hearing your comments @JSHarris.

Edited August 3, 2019 by Home Farm
@ added.

[SteamyTea]

Interesting that EON said that undersizing inverters was an industry practice.

It is not unusual to undersize an inverter as this often gives better performance at lower light levels.  It all depends on the performance curve of the inverter.

It will be hard to tell if you are taking a performance hit during the winter months.

Also worth noting that PV production is also affected greatly by hours of daylight and not just intensity.  A little for a long time can give the same yield as a lot for a short time.

Temperature can also have an affect, this is why systems can often give better daily performance in March/May and September/October.  Though that does depend on the azimuth and module angles.

You also did not mention the 16A/phase limit that most people have, or how you got special permission to have a larger system.  Did EON sort all that out for you?

[H F]

Thanks SteamyTea - I read about the temperature factor last night and was astounded to see they perform better when it's cooler. 

 

Excellent points about the larger system - that was a pain in the ass. EON did sort it out all. Follow up video scheduled for this week.

[Ferdinand]

To ask an eco-awkward question, why are you using a tumble dryer on warm sunny summer days?

 

Washing line? Or a number of Buildhub bears use traditional Pulley Maid things, which have made a big comeback. I cannot go for one of those as my parent says it reminds her of eating tea in a damp steam filled kitchen when she was 8 or 9.

 

 

Rather jealous of of the amount of electricity you get. I get less than that and my array is 10kWp, albeit mainly East facing.

 

Ferdinand

 

Edited August 3, 2019 by Ferdinand

[PeterW]

1 hour ago, Ferdinand said:

Or a number of Buildhub bears use traditional Pulley Maid things, which have made a big comeback.

 

Fitted one of these recently and surprising how quick it drys stuff. With MVHR too, I’m going to be interested to see how it performs. 

 

https://www.lakeland.co.uk/24576/Dry%3ASoon-Wall-Mounted-Heated-Airer

 

Plus point is that it folds up to the wall so you can mount above a work surface in a utility space. 

[Ferdinand]

Yep. It’s all about the humidity and removing it.

 

My cousin swears by one of these, even though it is a relatively low spec house.

[Ed Davies]

The standard practice of having a smaller power capacity inverter than the panels' nominal output makes complete sense. It's a matter of spending money where it'll give the most benefit. There will only be a few dozen hours in the year when the panels are producing within 10% or so of their nominal output. Spending money on a bigger inverter to harvest that extra doesn't make sense compared with spending it on a few more panels which will be producing extra power all year round.

 

Bear in mind that the marginal benefit of the extra power on those days where it's produced will be small if a) you're self consuming when you're not likely to have much use for it or b) you're feeding into a variable-price grid on days when electricity prices are likely to be low. Only if you're feeding into the grid at a fixed (and significant) price (e.g., on the old FiT scheme) would the extra production actually benefit you, but that's history.

[H F]

On 03/08/2019 at 17:27, Ferdinand said:

To ask an eco-awkward question, why are you using a tumble dryer on warm sunny summer days?

 

Washing line? Or a number of Buildhub bears use traditional Pulley Maid things, which have made a big comeback. I cannot go for one of those as my parent says it reminds her of eating tea in a damp steam filled kitchen when she was 8 or 9.

 

My wife tumble dries all our towels, duvets, pillows, etc. as if we leave them outside to dry they get crunchy and crispy. All clothes are line dried. 

[H F]

On 03/08/2019 at 17:27, Ferdinand said:

I get less than that and my array is 10kWp, albeit mainly East facing.

 

Interesting. I’m kicking myself for not installing four more panels on our west facing roof to get light in the late afternoon. We were lucky to have a large south facing roof so took advantage of that.

 

do you have batteries?

[ProDave]

1 hour ago, Home Farm said:

 

My wife tumble dries all our towels, duvets, pillows, etc. as if we leave them outside to dry they get crunchy and crispy. All clothes are line dried. 

Yes the TD is know as the towel fluffer here.  That is it's sole purpose.

[Ferdinand]

3 hours ago, Home Farm said:

 

Interesting. I’m kicking myself for not installing four more panels on our west facing roof to get light in the late afternoon. We were lucky to have a large south facing roof so took advantage of that.

 

do you have batteries?

 

No. Not currently viable - even at optimal prices. Jeremy is in a far better position to use batteries and benefit from them, so I will not be looking at it seriously until after he has done the hard work ?. 

 

I also do not have his dodgy power supply. Civilisation starts in the Midlands.

 

For me, viability is one of the keys guiding sustainability. I recall some very stupid green campaigners demanding that 40p per unit solar pv subsidies be maintained "to support solar", when in reality the same amount of money could support twice as much eco-benefit by halving the subsidy as technology has improved. All it would have achieved would be more 100m fortunes held by rent-a-roof solar types. But then many green politicos always were spectacularly gormless imo.

 

(I should point out that there are also many whirring away in the eco-engine room, doing brilliant stuff.)

 

I cannot use an electric car yet, which would be part of the benefit, as I need to tow a couple of tons from time to time. No electric cars are serious tow-wagons yet in sensible price-ranges.

 

Next step would be to build a car-port on the S side and move some of my panels to there, and then perhaps an ASHP when the current boiler dies. Currently accessibility has the priority.

 

Edited August 10, 2019 by Ferdinand

[Jeremy Harris]

Yes, I'm going to fit batteries shortly, but they don't make economic sense, yet.  Part of the reason I'm fitting them is to give a backup supply, as we get a fair few power cuts here (just waiting for the power to go now, the wind's enough to take a cable or two down again).

[joe90]

2 minutes ago, JSHarris said:

as we get a fair few power cuts here

 

Ha, was digging with the JCB yesterday afternoon in an area where I knew my incoming cable was and bingo everything went off, I knew the cable was about a meter deep and I was only taking top soil off so knew I was nowhere near it but I still got flak. It came back on shortly afterwards and heard on the news about the cuts (but was worried fir a bit ?).

[SteamyTea]

15 minutes ago, joe90 said:

It came back on shortly afterwards and heard on the news about the cuts (but was worried fir a bit

You knocked out the traffic lights in Truro, which is 50 miles from you.

And they blamed it on a windfarm and a gas plant, now we know the truth.  Shall we call it the 3C event.

[Pete]

14 hours ago, Home Farm said:

 

My wife tumble dries all our towels, duvets, pillows, etc. as if we leave them outside to dry they get crunchy and crispy. All clothes are line dried. 

I like my towels dried outside so they are rough!

[H F]

4 minutes ago, Pete said:

I like my towels dried outside so they are rough!

 

That's hard core - you can exfoliate while you dry off.

[H F]

21 hours ago, JSHarris said:

Yes, I'm going to fit batteries shortly, but they don't make economic sense, yet.  Part of the reason I'm fitting them is to give a backup supply, as we get a fair few power cuts here (just waiting for the power to go now, the wind's enough to take a cable or two down again).

 

Which batteries have you opted for? 

[Jeremy Harris]

52 minutes ago, Home Farm said:

 

Which batteries have you opted for? 

 

Probably the Pylontech battery packs and the Luxpower inverter, as it's an expandable system.

[scottishjohn]

so how much £ of mains electricity can these things hold --assume 9.6kw  4 stack system ?

probably looking at it wrong --but at 15p per kw  thats  = £1.44 of electricity ?

£3k =seems a lot to invest to save the occasional use of  it?

correct my thinking please

 you could  buy a good stand generator for that ,if its power cuts thats the problem 

Edited August 11, 2019 by scottishjohn

[ProDave]

15 minutes ago, scottishjohn said:

so how much £ of mains electricity can these things hold --assume 9.6kw  4 stack system ?

probably looking at it wrong --but at 15p per kw  thats  = £1.44 of electricity ?

£3k =seems a lot to invest to save the occasional use of  it?

correct my thinking please

 you could  buy a good stand generator for that ,if its power cuts thats the problem 

That is the sum I keep doing. But remember if it could store and self use £1.44 worth every day, then that's £525 per year.  Of course it won't store much in the winter when PV generation is low.

 

With my 4Kw PV system, I have so far since January only exported 97Kwh so that's just £14.35 worth of electricity gone to "waste"

 

Lets take a guess and assume I am going to export £25 worth per year, then any battery storage system to recover that has to be damned cheap.  So at the moment, beyond some silly low power hobby thing, it is a non starter for me.

 

However if you have more than 4Kw of PV then you will very likely be exporting a very much higher percentage of what you generate and the numbers might start to be viable.

 

About a third of my "self usage" is heating hot water with the immersion heater.  It is arguable that I could make "better" use of that if I stored it and used it for something better at a different time, and just let the ASHP heat the hot water for less pence per KWh of hot water.

 

In my case most of my export is the middle of the day when PV generation exceeds what the immersion heater can take, so typically at a rate of 600W.  To ensure I could get my self usage up to 100%, any battery system would have to be capable of using 600W for probably 3 hours of the day, so a modest 2KWh of battery storage should enable me to hit 100% usage. But the number of days it would be needed to do that ensure it would never pay for itself.

[Jeremy Harris]

As I previously mentioned, the pure economics don't yet stack up.  We currently export more than 50% of the power we generate, and I can recover some of that (although not much in summer) for later use.  The plan is to try to get the house to be off-grid, in effect, during the summer and for it to be as close to 100% running on off-peak E7 in the winter.   The payback time is pretty much the useful life of the battery packs, but the advantage of having a reliable back up power supply if there are power cuts swings it for us.  I've been looking at getting a reliable generator that could deliver around 2.5 kW or so, but can offset the cost of a decent generator against the cost of the batter system, in effect.

[SteamyTea]

I am watching paint dry (literally), so have just read (skimmed) a paper about embodied energy to make Lithium Ion batteries.

The materials takes 391 Wh to deliver 1Wh

The processing takes 763 Wh to deliver 1Wh

Total is 1154 Wh/Wh.

https://www.sciencedirect.com/science/article/pii/S2212827119301015

So as soon as you have 'used' the battery 1200 times, you should be into energy negative.

The interesting thing is that the vast majority of the energy is in the processing, this will only come down in the future, and, so say the old worn out meme, if that energy comes from a low CO_2e source, it does not matter too much environmentally.

[scottishjohn]

6 hours ago, SteamyTea said:

I am watching paint dry (literally), so have just read (skimmed) a paper about embodied energy to make Lithium Ion batteries.

The materials takes 391 Wh to deliver 1Wh

The processing takes 763 Wh to deliver 1Wh

Total is 1154 Wh/Wh.

https://www.sciencedirect.com/science/article/pii/S2212827119301015

So as soon as you have 'used' the battery 1200 times, you should be into energy negative.

The interesting thing is that the vast majority of the energy is in the processing, this will only come down in the future, and, so say the old worn out meme, if that energy comes from a low CO_2e source, it does not matter too much environmentally.

my thoughts have always been that untill we get orbital manufacturing plants --where energy from sun is much better and being able manufacture in a near vacum --then we will not get these technolgies at cheap enough price /carbon offset 

[SteamyTea]

28 minutes ago, scottishjohn said:

orbital manufacturing plants

What planet you from. One with very low gravity.