Circular reasoning (Rolfe's solar energy system)

[decrep]

I just set the inverter to protect 93% of the battery while the car is charging directly from the solar. Even if it tries it, it's not going to get very far.

I'm sure that will kill it dead.

 

[Rolfe]

Why wouldn't it? (I can't tell if you're being sarcastic or not.)

 

[decrep]

Earlier today I was trying to get my head around how your set up would affect ramping. So your comment cleared it up, I was just in confirmation mode.

 

[Rolfe]

Thanks. Right now I haven't set the battery to be protected. It's a cloudy morning with a breeze, and I want the car at 100% by five. It was sitting at 83% overnight, so probably doesn't need more than 10 kwh.

The solar was so weak that I was about to go out, unplug the Zappi and plug in the granny charger. Reasoning that the solar would support a granny charge without drastic draw on the battery. But suddenly the cloud cleared for a couple of minutes, the panels produced 7.5kw momentarily, and the Zappi sprang into life. It managed 1 kwh in 15 minutes.

The clouds are back and the Zappi has dialled back to the point where it's delivering less than the granny charger would, so I might still change it over. On the other hand the sky could clear any second. Welcome to Scotland.

 

[Rolfe]

I've got the approval for the G99, but apparently I now need an Export MPAN, whatever that is, to show to Octopus to get the export tariff. Maybe next week? But at least we're progressing.

Got the car fully charged on the granny lead in the end, during a period of quite thick cloud with only a couple of short sunny intervals, at the cost of bringing the home battery down to 67%. It has managed to struggle back to 75% and I'm going out, so it can do what it likes (or as much as the dishwasher will let it).

The Eddi is probably hungry too, because I had a nice hot shower and it hasn't had a bean from the system since, but it can take its time too. If I've managed to cover my driving this evening and tomorrow then despite the shocking weather it should all gradually right itself.

This is all pretty silly, given that I have a 7p/unit overnight tariff just sitting there, but I've developed a perverse determination not to give the car any mains electricity till the export tariff is up and running.

 

[GaryMG4]

This is all pretty silly, given that I have a 7p/unit overnight tariff just sitting there, but I've developed a perverse determination not to give the car any mains electricity till the export tariff is up and running.

I know what you mean, I've just got home and noticed I'm exporting 3.2kW, so I've plugged the car in on the granny and 15 minutes later instead of exporting around 800w and charging I'm now drawing 1.5kW despite having 5 hours at 8.5p overnight!

 

[Rolfe]

You've got better weather than me! Only three short peaks of generation over 3kw, hovered around 1-2 kw while I had the car on the granny lead, then it went down to under 1 kw and is currently excelling itself at 570 watts and falling. I need to take the raincoat.

 

[GaryMG4]

You've got better weather than me! Only three short peaks of generation over 3kw, hovered around 1-2 kw while I had the car on the granny lead, then it went down to under 1 kw and is currently excelling itself at 570 watts and falling. I need to take the raincoat.

We managed to generate a total of 22kWh yesterday so it was better than I thought.

 

[johnb80]

We managed to generate a total of 22kWh yesterday so it was better than I thought.

46.7 kWh here, the max weve done in terms of export. The system works best in bright sunlight but cooler temperatures, the panel performance drops off as they heat up, somewhere there i a sweetspot between light levels and temperature.

 

[Rolfe]

Yesterday? 13.04 kWh total. I'm surprised it was even that much. I managed to export none of it, getting it all into the battery and the car with a little bit of water heating in the evening after I'd gone out.

 

[Robf]

Will probably go back to using a Zappi and battery for my next house (I had a 1st generation previously). It is a great way to help the country balance the power systems and also do your bit for climate change. Taking power from the grid at night (for the car and running all the houshold appliances you can) allows the producers to keep the most efficient systems running (wind, tidal and the newer gas, its why its cheaper) and feeding back into the grid during the day enables them to keep the number of most expensive and polluting generators offline. Definately the way forward for the country.

 

[GaryMG4]

46.7 kWh here, the max weve done in terms of export. The system works best in bright sunlight but cooler temperatures, the panel performance drops off as they heat up, somewhere there i a sweetspot between light levels and temperature.

Yes cooler clear spring days seem to provide a more consistent output, although this is partly counterbalanced by less daylight hours. I've also noticed that the output ramps up a bit quicker in the spring, probably due to the orientation of our 4kW array.

 

[Coulomb]

I've also noticed that the output ramps up a bit quicker in the spring, probably due to the orientation of our 4kW array.

Could be.

But Spring tends to be better for solar production than autumn. The temperatures are about the same, but the days are longer in spring than in autumn. The days start getting longer about a third of the way through winter, at the winter solstice. The temperature changes lag the temperature changes by a month or so.

 

[Bam Bam]

30.35kWh for us yesterday. Anything over 30 is good, and we've never seen 40.

With the long days, even if they aren't fantastic, there a lot of daylight hours which adds up.

 

[Rolfe]

I checked back, and since I got the system the best day was 1st June, which generated 44.16 kwh. I feel quite proud that on that day the export (for which I would not have been paid) was 0.91 kwh! The car pretty much got the lot. It was more or less wall to wall sunshine, give or take a bit of cloud between 7.30 and 9 am, and it was only three weeks away from the solstice, so I would reckon that's close to the maximum potential of my system. I've seen 37-39 kwh on quite a few days too.

The worst day so far was 22nd May, which generated only 5.09 kwh. I dread to think what the weather was doing that day. I, fortunately, was in Sussex, as was the car, getting wind-turbine-produced electrons from a destination charger.

Today generated 15.7 kwh and exported only 3.1, by the time the water was re-heated after yesterday's shower (I turned the Eddi on to boost about eight, when I saw the battery was over 50%) and then the battery was recharged. So other than the car sitting at 23%, having driven a good 150 miles in 24 hours, all is stable.

The weather forecast is a bit mixed for the next few days. It will be interesting to see whether I get the car back to 100% before I get the export tariff sorted out. I'm probably going to do another 25 miles tomorrow, if the picture-framing job I left at the shop last week is ready now.

 

[GaryMG4]

We did slightly better yesterday, generated 23kWh (£5.29 thank you FiT), used the granny to put 12 in the car and purchased around 2kWh during the same period, where the house load/cloud cover exceeded the excess.

 

[Anon70]

I find all these discussions really interesting and potentially confusing for someone who is maybe interested in getting a solar and battery system installed. You have to be aware of each component and the different ways they can be configured (even more confusing than choosing an EV).

Found these recent YouTube videos interesting, one discussing difference in solar panel setup and the other comparing battery storage systems

 

[Rolfe]

I can see how it's confusing! I decided that rather than try to become an expert before carefully choosing my system then carefully selecting an installer, getting at least three quotes of course, I would simply get the guy who installed the system in my neighbours' (essentially identical) house to do mine too. After checking with him that he was happy with the job, of course!

So I'm learning on the job. I had no idea of how the various components interact before looking at my own system in operation, and it's fascinating watching them play this delicate game of pass the parcel with the available power. I didn't even realise that the components had to be balanced in terms of how many panels, how big a battery, what rating an inverter. But honestly, I far prefer this to having spent months reading up everything about it, watching innumerable YouTube videos, and getting hopelessly mired in indecision.

I was wrong about 44.16 kwh being my system's best ever. It did 44.92 kwh on 18th May, only three days after being installed. This was genuine wall-to-wall sunshine, helped by the battery not being fully charged till 11.30 allowing a bit of extra generation in the late morning. So I suppose with equally perfect conditions a month later it would be possible to exceed 45 kwh. But that must be about the ceiling.

Today, 20.52 kwh, mainly in the morning, with a small amount of generation still happening at 6.30, but it's raining and the battery is already having to step up with a few watts occasionally. The "bodge-up" work-round worked perfectly, as always.

The morning didn't look sunny but the cloud was thin and a fair bit of sunlight was getting through. Around 9.15 the battery had recharged enough for the Eddi to start heating, but that didn't last because about 9.35 there was enough surplus for the Zappi to take over (actually the water was still quite hot from the previous day's efforts). I had flipped the battery protection to 93% about nine o'clock.

Everything went swimmingly until about one o'clock when the cloud cover thickened dramatically and by 1.30 it was pouring with rain. The battery supported the Zappi until 2 pm, when it reached 93% and cut out. The remaining solar recharged the battery quite quickly (that's my reason for deciding on 93% as the cut-off - it's enough to support the Zappi when there's a reasonable amount of generation, but when the solar falls off it doesn't leave too big a hill to climb to get back into the game), and by 2.45 the Eddi was able to get back into operation.

The solar never recovered enough to restart the Zappi, but the generation that there was heated the water. It never quite got up to temperature, but it's fine as it is, and if I wanted the water hotter I could simply get the Eddi to run a 20-minute boost using the battery power. (Or I could use the kerosene boiler, but I wouldn't do that unless it was so cold I had to start the central heating, and it isn't.) I just turned the battery protection back to 4% so the house can have what it likes for the evening and night.

The Zappi put 13.34 kwh into the car (including losses), raising the SoC from 23% to 45% and adding 46 miles of range. Not bad for a day which was mostly horrible.

It seems to make sense to prioritise the Zappi over the Eddi if you want the car charged, because the Zappi needs a fair bit more solar in order to get up and running than the Eddi does, and the Eddi can always mop up any surplus during times when there isn't enough to power the Zappi. Also, if the water isn't hot enough it's easy enough to fix that from the battery or the central heating boiler.

So far so good. Still waiting to have it explained to me in what way I'm strangling my system and where there is any downside at all to this. (Confession. I did forget to turn the inverter setting back one evening, until after the battery had got to its set limit and the house was drawing a little from the grid. But it all happened after 11.30, so 7p/unit, and it had been going for less than an hour before I realised and remedied it. I couldn't even see that day as unusual as regards grid import - there's always a little, due to the pass-the-parcel games - and I worked out it cost me about a penny.)

 

[Bam Bam]

I find all these discussions really interesting and potentially confusing for someone who is maybe interested in getting a solar and battery system installed. You have to be aware of each component and the different ways they can be configured (even more confusing than choosing an EV).

I agree with Rolfe.

Get three quotes, you need to know enough to ask informed questions, but at the end of the day the system is going to work.

The main worry is that you get a system that the installer wants to sell rather than what works best for your own situation.

The G98/G99 threshold is the main barrier here - installers prefer G98 because there is much less paperwork (and application expense). That might mean people don't get as big a system as would be ideal.

That aside, a good MCS installer should set things up right for you.

 

[Rolfe]

That is probably the best piece of advice I got here on the forum. My installer initially quoted for 3.5 kw, but more than one person said no, you need more than that. Once I'd raised the issue he upped the inverter to 5 kw and I can totally see the difference. I'd have been unhappy with 3.5 kw. It has given him more paperwork and so on, but he has been very good about it.

So whoever it was gave me that advice, way back in the thread, many thanks.