Circular reasoning (Rolfe's solar energy system)

Full sun today, so this will tell u a few things.
It's only 2PM here now and already there is a very big difference, we hit max inverter capacity at 11Am. so the A/C is on now warming us up.
House battery hit 100% at 10:30 after running the house all night with a bit of A/C thrown in.

Will be interesting to see when the tree shadows cut in. I'll post a graph of today's production this evening.
 
Here's an interesting thing, The aircon is consuming just under 4kW. There's a very flat consumption line at 4.8kW, but when the aircon cycles off, and there's mainly export, the inverter output drops and goes a bit wobbly.
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The spikes are the kettle going on for our cuppas
 
So the sun is very low and the battery has taken over, so here's the phone app's view of our solar production.
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Must admit to being a bit confused by this, I'm used to using the water heater app.
That is showing this.
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That's starting to make sense, "to grid power", means export.
Because of the way it's hooked up, battery is at the front of the line. The water current clip, doesn't see power to or from the battery. So the early morning above, where it shows no solar is the battery charging. Like wise in the evening power shown from the solar is actually from the battery. Blue is the water heater, and orangey brown is mainly the A/C.

But both show the strange drop in inverter o/p when it goes to mainly export.
And the messy drop off after 1530 when the tree shade intervenes.
 
The water current clip, doesn't see power to or from the battery.
Good the system is working well. Re the water heater, it's a pity that most of these commercial systems don't communicate with each other and therefore without complex customisation, you can't heat water until the battery is charged.
 
But you NEVER get the money 'back'. Stop treating like a lump sum investment - where you DO get the money back. The money saved each year is about the return on a good private investment fund, but at least at the end of that you get back the capital on top.
Yes, no, maybe....
My own experience;
Nine odd years ago we bought property which had recently installed a 4kW array (cost previous owners £5.5-6k) , which puts it on the mid level FiT scheme, about 23p per kWh generated. Over that time it has generated 36,000kWh which has paid me around £7000. Initially I took little interest in them other than sending in readings and collecting the money, which at the time covered our electricity cost. Since getting an EV (and smart meter) I have tried to use more of the free solar, achieving over 50% in April and May.
IF I had paid for the installation I would consider that I had already had my capital back and perhaps a paltry £1500 in interest and going forward the payments and reduced paid for electricity are the results of 'my investment'.
Regarding a good private investment fund, I doubt that £6k would be enough to buy into a good one and however good they are they are subject to risks. Over he same period I had a stocks and shares ISA, after about 4 years that £6k was worth about £8.5k, Covid happened then Ukraine and half of the growth was wiped out, unfortunate if I needed the capital at that point. It has taken until now to get back to that position, so investments are always a gamble if you will need the money back.
 
But you NEVER get the money 'back'. Stop treating like a lump sum investment - where you DO get the money back. The money saved each year is about the return on a good private investment fund, but at least at the end of that you get back the capital on top.
You could apply this logic to lots of companies, which don't have an infinite lifespan. Particularly fossil fuel companies. Once they have exhausted the well there is nothing left. Plus any company could go bust at any time.

The difference is that a private equity fund will invest in lots of these companies, some will grow, others will decline and overall you hope that the fund will gradually shift towards the profitable ones.

Essentially, I think it is the same sort of thing, except you have one investment rather than a portfolio, so it follows its own "investment - payback - profit - demise" track rather than evening out across many such tracks to last (hopefully) forever.

For solar panels you still own the panels even when they have paid back the up front cost. That profit can be put towards other investments, just like an investment fund would. They will degrade over time but will likely still be producing in 40 years.

Sure, panels don't last forever, and inverters will need to be replaced, but that doesn't make them a bad investment.

And when you add ever higher carbon taxes on to electricity prices (plus an ever increasing price for gas as it runs out) then I think that PV electricity will continue to be valuable.

Especially if you offset your carbon emissions, because producing clean energy is essentially reducing gas burning so I count it as a kind of carbon offset and buy fewer as a result.
 
Good the system is working well. Re the water heater, it's a pity that most of these commercial systems don't communicate with each other and therefore without complex customisation, you can't heat water until the battery is charged.
Probably my fault, I think we could have gone with the company that installed the water heater, then it could have all been integrated. I don't think it will be a big issue though, we don't use a lot of hot water, and it's a big storage tank. It also will use grid power if the temp gets too low.
 
We seem to be revisiting my dilemma at the very start of the thread. Do I buy the system, or do I just go on using the money to pay for electricity? I can see the merits of the latter argument, and frankly life's too short to be doing all these sums. I decided to go for it in part because I wanted the new toy to play with. Expensive toy to be sure, but one that will at the very least contribute to its own upkeep. And then, once I've bought it, what's the point in keeping meticulous accounts? I can't go back and unbuy it if I don't like the answers.

I have perhaps an idiosyncratic way of looking at it. I had provisionally earmarked about £30,000 from my savings to buy a new car when the Golf had to be replaced. Now look what I spent the money on.

MG4 SE SR £26,950
Solar system including Zappi £13,700
Total £40,650

But then I got £4,000 for the superannuated Golf, so really £36,650 net expenditure.

So for only £6,650 more than I was provisionally intending to spend on just a car, I have a car I like just as much as the Golf if not more, plus free fuel for it and free electricity for the house. I'm largely funding the road trip fuel from the solar excess payments, through my Electroverse card. No more petrol bills and no more electricity bills.

You can always pick this apart if you want to and accuse me of being delusional, but I don't think these "investments" have to make money overall to be satisfying and worthwhile.
 
PS. Anyone who is proposing to pour their solar directly into the car rather than exporting it and charging the car overnight on cheap rate may be assumed to be Australian to a fairly high degree of confidence even before you look at their profile.
 
After all your head scratching Rolfe, I couldn't be bothered and just went with what my most trusted sparky sold us.
It's possibly not optimum, but I'm getting too old to agonise over details

We've just had dinner with a delightful 97 year old, she asked me how the car was going and how much it cost to run. Then she asked me how much we'd saved on petrol, a very rough exercise in mental arithmetic came up with $1,000, over the last 15 months.
 
I did what you did. My next door neighbours, identical (mirror-image) house, had installed solar the previous year and also run EVs. I simply asked my neighbour - who is an engineer - if he was happy with his installation and if so, please give me the installer's contact details. Yes I have the odd little niggle about things I might have done slightly differently, but I would have spent all summer educating myself about it and still maybe not learned as much as simply operating my system has taught me. I thought, Nick has done the research, why have a dog next door and bark yourself?

The savings bond the money was taken out of managed about 5% last year. I think in financial terms the solar is doing OK and I definitely notice the absence of an electricity direct debit (OK I have one but it's for £1) and regular petrol fill-ups from my current account.
 
After all your head scratching Rolfe, I couldn't be bothered and just went with what my most trusted sparky sold us.
It's possibly not optimum, but I'm getting too old to agonise over details

We've just had dinner with a delightful 97 year old, she asked me how the car was going and how much it cost to run. Then she asked me how much we'd saved on petrol, a very rough exercise in mental arithmetic came up with $1,000, over the last 15 months.
You know it, you expect it but seeing it in black and white ? WOW. I might not wait the 47 years for the nuclear fusion version of the Berlingo to appear
 
Getting back to the performance of my own system, I have refined it so that I can easily harvest anything that would have been clipped by the 5 kw export cap, as I was describing earlier. The settings, once set up, are easy to control.

The battery charges at the cheap rate overnight, having exported whatever is left just before 11.30. it stays on charge till 5.30 so that the house uses mains electricity until the end of the cheap rate. I then have an export setting from 6.30 till 8.30, which is long enough to get the battery right back down to about 20% if desired. This is late enough that the house will be running on solar by the time the export has finished, so there's no risk of importing peak-rate power. I take a minute in the evening to set the export limit depending on the weather forecast. If it's wall to wall sunshine, particularly if it's not that warm, I could go down to 20% - it's possible to pick up 80% on a really favourable day, usually in April or May. I usually go for somewhere between 30% and 50%. The idea is to leave enough room in the battery for the possible extra generation, but at the same time to have enough there to run the house and cook in the evening if the solar doesn't live up to expectations. If the forecast is terrible I just turn off the export setting for that day.

After 8.30 the export limit is changed to 100%, to keep the battery from charging from the solar during the peak generation time unless the 5 kw export limit is exceeded. If it's a sunny day I don't need to worry about anything, but if it's cloudy at the time I want to boil the kettle I have to remember to switch the export off temporarily or it will draw a bit of mains power. If it's really dark with rain clouds and I have the central heating and the hi-fi on so the house base load is high, it's possible for it to draw mains power at that time too, but frankly if the weather is that bad it's best just to switch off the export and forget the entire thing.

I have the export set to finish at 7.30 which is about when the solar stops supporting the house, but I often switch it off earlier if I'm wanting to cook. All that happens is that the solar goes into the battery to be exported later, so I suppose a 10% loss which ain't much on a small amount anyway.

The next place I need to do something is mid evening, decide when to set the export to start so it finishes as soon as possible after 11.30. I've got quite good at this. I tend to set that and decide where I want to export to the following day at the same time, so not much fiddling.

Is it worth it? I reckon I made about £15 in May this way, on top of £100 regular export - it was a very good month for solar. Less in other months. If it wasn't worth it I don't have to do it, it's just so damn satisfying to grab that extra bit of generation that would otherwise be capped by the G99 export limit.

I always said I didn't want to be fiddling with it, just set and forget. I'm still fiddling a year later. But "set and forget" exists and I could do that if I didn't want to fiddle. Just lose a small percentage of my returns.

Here is a day where I only exported to 50%, expecting poor weather, and I got the battery right up to 100% before the clipping stopped. (The left hand side of that graph is what happens when I forget to set the evening export until way too late - export went on till about 12.30 am. The right hand side shows it finishing at 11.30 pm because I remembered.)

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Here is a day when I expected it to be good so exported to 30%, but due to a fairly extensive cover of high light cloud the generation didn't often exceed 5 kw. It was still a nice day, but this game needs at least periods of clear blue sky.

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I'm noticing a much more marked effect of temperature than I had imagined, and I might even start a separate thread on that.
 
PS. Anyone who is proposing to pour their solar directly into the car rather than exporting it and charging the car overnight on cheap rate may be assumed to be Australian to a fairly high degree of confidence even before you look at their profile.

Not quite... I'm definitely not Australian 🙃 But have fully powered my EV directly from excess solar since I got it nearly 6 months ago :cool:
 
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