Circular reasoning (Rolfe's solar energy system)

[Rolfe]

Well, here's the plan. The daytime settings worked perfectly. From 7 am to 5.30 pm the battery was set to export to 80% (that's arbitrary, it just has to be higher than the amount of charge I expect to pick up in that time. That directed all the solar (above the house load) to export, until clipping started, when the excess was directed to the house battery. Today that brought the battery up to 56%, which is plenty and to spare. When clipping ended the battery stopped charging and export of the solar continued, and the battery kept the charge it had gained. Didn't have to change anything, it all worked perfectly.

At 5.30 pm (when the solar can no longer meet the house load) the export setting ends and the battery then powers the house through till 11.30 pm. Anything left over can be exported for profit just before 11.30. So far so good.

However, what happened during the night, during the time when the battery would normally be charging, was a load of random fluctuations that weren't terribly helpful, and I still ended up importing a little peak-rate power. So now I think what I need to do is export down to say 12% or maybe 15% in the late evening, rather than exporting everything. Then if I keep that export limit throughout the night, that should preserve that amount of charge to run the house 5.30 am till sunrise.

If this works then it's close to being set and forget, any time there's a nice day. Nice days being so infrequent sometimes that I'd better write it all down so I don't forget.

 

[Rolfe]

I would guess that is down to your inverter's settings. It is common for an inverter to have a minimum SOC% specified below which the battery power will only be used for powering the inverter and not for powering the house. IME those default values are typically in the 10% to 20% range.

Hence, you may need to have more SOC in the battery before it can be used to power the house.

It usually powers the house down to 5%, so it still doesn't quite compute. Also, there are times when the battery % seems to increase with no clue where that came from, so it's a mystery. Anyway, I'll set it only to export to 15% this evening and hold that until 5.30 am, when there should be plenty to power the house for an hour and a half. It will be interesting to see how much it takes. Then the switch to exporting to 80% at 7 am will let it charge on the excess above the clipping, rinse and repeat.

 

[johnb80]

I could probably do it with the Zappi if I fiddled with the settings, but the granny charger is easier for that job. The Eddi is another possibility but to be honest I heat that for 7p/unit just before the end of the off-peak tariff every night and it usually does me for the day,

"
16.2 Device Limit
Sets the maximum current that the zappi will draw (including when boosting and FAST mode). This is useful if the supply current is limited, for instance, if zappi is connected on a 16A circuit instead of a 32A."

 

[Rolfe]

OK thanks.

 

[Rolfe]

Well, this worked rather well.

I was away from home, and left the system set up, knowing that a sunny day was forecast. I had exported the battery before 11.30 the evening before. Then the battery was set to charge from midnight and export (down to 15%) from 3.15, finishing at 5.30 am. That gave it enough time to do that cycle before the off-peak period ended. Partly that cycle is to gouge a few more pennies from the system, but it also has the side-effect of meaning that the battery is low for a shorter period than it might otherwise be, in case of a power cut. (I don't have my EPS yet but I'm getting one.)

The battery actually ended up at 14% at 5.20 am, after which the house drew on the grid for ten minutes until the end of the off-peak tariff. It then drew on the battery, because its export period had ended. However it had only dropped by 1% by the time the solar started to take over the house load. I had set the battery to start exporting down to 90% from 7 am (about when the solar takes over, I note there was just a tiny hint of the battery starting to charge from the solar before that happened.) That stops the battery taking any solar below the export limit, but it then takes the solar after that, eliminating the clipping.

It did that from 9.50, and between then and 3.10 pm, when the clipping stopped, it charged up from 13% to 75%. Not bad. That would appear to be 4.5 kWh (maybe, I'm getting some very strange readings on the GivEnergy app). The solar went on exporting and running the house, and was still running the house at 7 pm when I returned home. I cancelled the battery export at that point, because obviously when I got in and started switching things on the battery would be needed to cover the increased house load. (It was close to being needed anyway.)

And that's that. I'll probably export whatever is left of that 4.5 kWh at the end of the evening, then start again. However, as the car will be on charge, I'll cancel the home battery cycling, as the export from that would just get gobbled up by the car. I also need to turn the Eddi back on to get hot water in the morning. I had it off while I was away, and have just let the central heating heat it a bit this evening.

Solar generation appears to have been 49.3 kWh for the day, but as the GivEnergy app and web site is giving some very peculiar readings I'm not sure how much was directly exported.

 

[Bam Bam]

Well, this worked rather well.

Glad to hear it.

I'm getting some very strange readings on the GivEnergy app

Solar generation appears to have been 49.3 kwh for the day, but as the GivEnergy app and web site is giving some very peculiar readings I'm not sure how much was directly exported.

I also had bizarre readings today that did not make any sense.

It said we had put 20kWh into the battery (but it is a 9.5), and that we had somehow bought over £5 of electricity without having the car plugged in and also that it was pretty much our best ever day for solar even though it is only April.

 

[Rolfe]

Mine thinks that in the half-hour period from 1 pm, I exported 23.19 kWh solar to the grid. It also thinks that in the half-hour from 7.30 am I put 9.49 kWh solar into the battery. (The solar is only just covering the house load at 7 am.) It thinks the total generation for the day was 63.58 kWh, which is impossible. Nevertheless the daily tally along the top reports that total was 49.3 kWh, which is plausible. Hopefully they'll sort it out at some point.

 

[Rolfe]

Now I have discovered how to harvest the generation that would otherwise be clipped, I'm wondering what percentage of summer days are worth leaving this setup on for. It might be possible to make it all of them, if I figure out the best percentage for the battery to be at in the morning.

The perfect day is as shown above, no clouds and a perfect arc of generation. That was Thursday, and it added 62% to the battery. More is presumably possible as we get closer to the solstice.

The following day had exactly the same weather forecast, but a very different outcome. The sky was never clear, with a haze of light cloud for the entire day.

The result was relatively little clipping, and the battery only harvested 18% charge. The snag was that, expecting the day to be the same as the previous day, I had exported the battery right down to 15% in anticipation, and in fact it dropped to only 11% after sunrise for no readily apparent reason. The result was that I had only 29% in there to do me through the evening. (Obviously I could have let the battery have some of the solar in the afternoon rather than exporting it, but I decided just to leave the settings as they were and see what happened.) This was sufficient, I ended up on 9%, but if I had intended to do a lot of cooking it wouldn't have been enough. I decided that I needed to leave more in the battery at the beginning of the day to allow for this eventuality.

So to Saturday, which had some cloud forecast anyway. I set the battery to retain 30% in the morning, and there was 28% in there by the time the solar took over. The forecast was right this time, very sunny in the morning but getting cloudier in the afternoon.

The cloud started to come over about 10.30 however the clipping was only intermittent until about 1.30, after which there was so much cloud that the panels didn't exceed the export threshhold at all. Nevertheless the battery picked up 32% which would have been enough for most purposes. (As it happens I was out anyway.)

Today was forecast to be a lot more cloudy, so I increased the battery percentage for morning to 40%. In fact, though, it was again quite bright. There were clouds, but in between them the panels did very well, and the battery picked up 36%.

There was an interesting effect here, which I think must be down to temperature. The panels hit 7.5 kw during most of the sunny intervals, and the highest peak was just over 8 kw. The day was quite a lot cooler, so that's probably the explanation.

Now I know how to do it, I can choose the amount of charge to leave in the battery at the start of the day, and at 40%, even if there was no clipping and so no free charge to be had, I'd still have enough for the evening even if I was cooking. (And this will get better as the daylight length increases.)

Tomorrow looks likely to be like that, with heavy cloud forecast throughout the relevant period, but rather than simply revert to the settings I was using in winter I might leave 50% in the battery and see what happens, if there is in fact anything to be had.

It's a judgement call, but if say 65% charge is the most I might harvest on a sunny summer day, then if the forecast is good I should maybe start on 30%, 40% for so-so days and 50% for horrible days. It's taken some time to figure all this out, but now I have the set-up in the inverter it really only needs a decision in the evening of whether to leave the setting at 40%, or increase it for a bad forecast or decrease it for a really good forecast.

The clipping was bugging me a bit, so I'm pleased to have figured out a way round it. It can still be set and forget if I want to, because having 40% in the battery in the morning, in the summer when the solar will at least be able to run the house right through to the evening, should actually cover most eventualities.

 

[Archev]

Now I have discovered how to harvest the generation that would otherwise be clipped, I'm wondering what percentage of summer days are worth leaving this setup on for. It might be possible to make it all of them, if I figure out the best percentage for the battery to be at in the morning.

The perfect day is as shown above, no clouds and a perfect arc of generation. That was Thursday, and it added 62% to the battery. More is presumably possible as we get closer to the solstice.

View attachment 36113

The following day had exactly the same weather forecast, but a very different outcome. The sky was never clear, with a haze of light cloud for the entire day.

View attachment 36114

The result was relatively little clipping, and the battery only harvested 18% charge. The snag was that, expecting the day to be the same as the previous day, I had exported the battery right down to 15% in anticipation, and in fact it dropped to only 11% after sunrise for no readily apparent reason. The result was that I had only 29% in there to do me through the evening. (Obviously I could have let the battery have some of the solar in the afternoon rather than exporting it, but I decided just to leave the settings as they were and see what happened.) This was sufficient, I ended up on 9%, but if I had intended to do a lot of cooking it wouldn't have been enough. I decided that I needed to leave more in the battery at the beginning of the day to allow for this eventuality.

So to Saturday, which had some cloud forecast anyway. I set the battery to retain 30% in the morning, and there was 28% in there by the time the solar took over. The forecast was right this time, very sunny in the morning but getting cloudier in the afternoon.

View attachment 36115

The cloud started to come over about 10.30 however the clipping was only intermittent until about 1.30, after which there was so much cloud that the panels didn't exceed the export threshhold at all. Nevertheless the battery picked up 32% which would have been enough for most purposes. (As it happens I was out anyway.)

Today was forecast to be a lot more cloudy, so I increased the battery percentage for morning to 40%. In fact, though, it was again quite bright. There were clouds, but in between them the panels did very well, and the battery picked up 36%.

View attachment 36116

There was an interesting effect here, which I think must be down to temperature. The panels hit 7.5 kw during most of the sunny intervals, and the highest peak was just over 8 kw. The day was quite a lot cooler, so that's probably the explanation.

Now I know how to do it, I can choose the amount of charge to leave in the battery at the start of the day, and at 40%, even if there was no clipping and so no free charge to be had, I'd still have enough for the evening even if I was cooking. (And this will get better as the daylight length increases.)

Tomorrow looks likely to be like that, with heavy cloud forecast throughout the relevant period, but rather than simply revert to the settings I was using in winter I might leave 50% in the battery and see what happens, if there is in fact anything to be had.

It's a judgement call, but if say 65% charge is the most I might harvest on a sunny summer day, then if the forecast is good I should maybe start on 30%, 40% for so-so days and 50% for horrible days. It's taken some time to figure all this out, but now I have the set-up in the inverter it really only needs a decision in the evening of whether to leave the setting at 40%, or increase it for a bad forecast or decrease it for a really good forecast.

The clipping was bugging me a bit, so I'm pleased to have figured out a way round it. It can still be set and forget if I want to, because having 40% in the battery in the morning, in the summer when the solar will at least be able to run the house right through to the evening, should actually cover most eventualities.

On a much much smaller scale I’m playing around with my Vtoman power station and solar panels in preparation for staying away this year. I’ve nearly got the car sorted with a bed platform folding out from the boot. The power station gathers a fair bit of sunshine from the panels so I’ve used much less mains power for cooking etc in the house. So camp trips ought to be comfortable and not relying on burning gas for cooking although I’ll take it as a backup. I’m hoping to be able to carry that and the charging cable plus granny in the frunk.
I’ve got a frame to fit under the boot area to carry the spare wheel easily.
I might be tempted to investigate some garden panels and a house battery at a later stage.
I’m enjoying the solar stories and the battery banter on here and I’ve really been enjoying my sunshine porridge cooked on the induction hob.

 

[Rolfe]

Damn, did something silly. I cooked during the time when the battery was set only to export to 80% (this is what stops it from charging from the solar below the clipping threshhold), and as a result the house drew from the grid (peak-price) rather than the battery. Not quite so set-and-forget then. I won't make that mistake again.

Archie, we need photos of the new setup with the Berlingo.

 

[Everest]

@Rolfe It is great what you are doing. It seems you are having to make assumptions about the weather in advance. I'm wondering if it is possible to have a configuration where you will can limit export in the day so that you will always end up with the required SOC% at (say) 6pm to see you through the evening without using peak electricity?

 

[Rolfe]

@Rolfe It is great what you are doing. It seems you are having to make assumptions about the weather in advance. I'm wondering if it is possible to have a configuration where you will can limit export in the day so that you will always end up with the required SOC% at (say) 6pm to see you through the evening without using peak electricity?

I can do that easily without limiting export. My problem is that I should have switched the battery to allowing discharge before starting to cook. At that point in the evening the remaining solar was enough to power the house base load, but as soon as the cooker went on it had to draw from the grid, as the battery wasn't playing. Earlier in the day when I boiled the kettle there was no problem because there was enough solar to power that. The answer is probably to set the battery to start discharging early enough so that this doesn't happen.

 

[Rolfe]

I moved the Berlingo discussion to its own thread, here.

Thread 'Archev's adventures in the Berlingo'

Sunday at 8:21 PM

Mod: This is a new thread created out of a derail, describing @Archev's project to modify his Berlingo EV van to sleep in overnight.

Work still in progress but this is the sleep platform unfolded from the boot area, bridging the nearside folded rear seats and supported on the folded front seat. The latter part slides out of the centre section.
I think I’ll pay a visit to ikea tomorrow to check out cushions/ mattress toppers for the sleep mat. I have an air bed but I want to investigate what else might be available.

• Archev
• Replies: 32
• Forum: General Chat Forum

• 
• 

I also deleted a few posts that were made redundant by the move.

 

[Rolfe]

I tried the business with harvesting the clipped solar today, and it did work, but it possibly wasn't worth the hassle. The weather was poor, but there was a period from 10.30 to noon when the sun came out from between the clouds and managed to put 9% into the battery.

Although I set the battery to hold on to 50%, it actually settled at 56%, then went up to 65% from that bit of sunshine. The hassle is, on a generally dull day, remembering to allow the house access to the battery if I want to boil a kettle or something. On a sunny day it's fine because it just uses the solar, but if it's really dull then it will grab peak-rate mains juice if the solar isn't enough and it can't get battery.

In the end I switched off the export setting just before six because the solar was about matching the house load, although it did brighten up again after that leading to the battery charging a little rather than that power being exported. Negligible anyway.

I also got a little nervous in the morning when it was still very dull just before nine, and switched off the export, but in fact that proved to be unnecessary as the house didn't need any mains power and when I saw the battery was starting to charge I switched it back on again.

It's a hassle for only 9%, so I think it's only worth doing when reasonable sun is forecast. Tomorrow and Wednesday look terrible so I'll revert to the winter set-up.