Circular reasoning (Rolfe's solar energy system)

[Rolfe]

Good to know that, bigger picture, its doing its job!

It's doing its job just fine. I'm just disappointed that it can't be as hands-off as I wanted, as regards this battery export operation. In fact, if there were a setting that said, discharge battery to end at a certain time (as opposed to start at a certain time) it would be absolutely fine. Maybe that is possible, and perhaps it's that I should be trying to track down.

Tonight is so different from last night. Although it was quite bright in the morning, the weather became overcast and rainy in the afternoon. (Just as well I didn't export any battery, really.) The battery dropped below 100% before four, and it's now at 97%. That's a full hour and a half earlier than yesterday. Although yesterday's discharge over-ran the target by 21 minutes, today's might actually fall short, and I need to be ready to pause it if necessary.

I can calculate when to start the export so as to hit (say) 11.30-11.35 on any given evening. I just don't care to spend every evening doing that. Maybe there's some way to write a script to do it, but I have no idea at all where to begin. Maybe someone else has already done it.

It's so horrible I can scarcely believe I am packing for a weekend away camping in the car, chosen because the weather forecast is spectacularly good for the next few days. Well, the system can look after itself and earn me some money while I'm away.

 

[johnb80]

Not all inverters are grid tied.

Well of course but I would guess 99% are grid tied and in the context of the discussion taking place it was reasonable to accept ALL inverters were operated in this way.

I research mainly the group of inverters that Voltronic Power call "off-grid" inverters. These can and usually are connected to the grid, and are not supposed to export power to the grid, but occasionally do briefly when large loads come off.

Either you or I have misread the manual / spec, off grid inverters dont export, they take energy in from various sources (including grid) and provide power out.

The inverters powering my house at present are totally not capable of exporting at all.

That would seem to be an odd situation.

They do synchronise to the grid

Why if theyre not grid tied?

, and connect their DC-AC converter to the grid, but only for drawing power from the grid, in order to charge the battery from utility/generator.

In which case, it would not be the 'converter' running in reverse, it would be a straight forward battery charger.

The DC→AC converter in this case operates in reverse, becoming a DC→AC unity power factor rectifier. At such times, the loads are powered entirely from AC-in, and solar power is used only to charge the battery.

I don't know what inverter you have, are you suggesting the house supply physically disconnects from the inverter and connects to the grid and vice versa during battery charging?

The Victron GX inverter that I have is capable of running like this and has seperate outputs if grid tied operation isn't needed. The problem in this mode is the brief interruption in power while it changes over.

 

[JackRussell]

About 9 minutes in on this YouTube video it shows how you can pause the battery charging or discharging easily from the the App

 

[Bam Bam]

About 9 minutes in on this YouTube video it shows how you can pause the battery charging or discharging easily from the the App

They've removed that button in the recent version of the app.

I found it wasn't reliable - often you didn't get a response when changing the setting.

 

[Gadget Geek]

They've removed that button in the recent version of the app.

I found it wasn't reliable - often you didn't get a response when changing the setting.

Which is the crux of Rolfe's problem. If that function was available, she could set and forget.

 

[Bam Bam]

I haven't watched it, but saw this video from EV Puzzle and thought of Rolfe!



There is also a recent video from speak to the geek about this, so check out his work as well. He may be lurking around here somewhere as he is now an MG4 owner!

 

[Gadget Geek]

Andy EVM has posted his thoughts on export tariffs.

 

[Rolfe]

That was more or less what I was thinking. Mine's fixed till next August anyway, of course. I hope it goes on being beneficial to export the solar because despite what I was saying, it's an awful lot less hassle.

The system as I have set it up has been running OK for the last two weeks without needing intervention, and every day my export has been a little more than my total generation, so I can't complain.

 

[Gadget Geek]

I certainly can't complain . . . I got my FIT payment yesterday. (Sorry to rub it in)

 

[Rolfe]

That's OK, I know that ship sailed some time ago!

 

[GaryMG4]

I certainly can't complain . . . I got my FIT payment yesterday. (Sorry to rub it in)

I normally would have had mine by now too, but they rejected the reading as out of tolerance so are doing a manual check. Waiting for around £350 to turn up!

 

[Rolfe]

Wow, how long a period does that cover?

 

[Gadget Geek]

I normally would have had mine by now too, but they rejected the reading as out of tolerance so are doing a manual check. Waiting for around £350 to turn up!

They questioned mine as well this time, so I sent them a photo of the meter reading. They have questioned it a couple of times in the past.

Wow, how long a period does that cover?

3 months. Mine was £480. A better return on the investment than you will get from a savings account.

 

[Rolfe]

For sure!

 

[GaryMG4]

Wow, how long a period does that cover?

The 1st June to 31st August quarter, we are on the middle rate, about 23p/kWh.

They questioned mine as well this time, so I sent them a photo of the meter reading. They have questioned it a couple of times in the past.

They have just changed the reporting dates so I suspect the automated checker just got confused, I'll call them on Monday and sort it out then.

 

[Exdro]

It goes like this.

1. I really should get a home charger.
2. If I get a home charger, I need a variable electricity tariff.
3. A variable electricity tariff will make my daytime usage more expensive.
4. The answer is to get a home battery and fill it with cheap electricity overnight.
5. Look at your roof, if you have a home battery it would be criminal not to install solar.
6. That will be £13,700 altogether.
7. But I could buy a hell of a lot of electricity for that. Um.
8. But I really should get a home charger.

How do you get out of this loop?

Buy a home charger BUT avoid EO like the plague. Most useless unhelpful company I’ve ever dealt with and their products fail with no repair possible. Guarantee doesn’t cover it. Avoid.

I showed my roof earlier, here it is again. The supplier recommends six panels on the garage and twelve on the main roof.

View attachment 25750

It's always seemed to me to be a bit of a sin not to put solar panels on that.

Simplistically, I look at the current recommendation for my monthly electricity DD, which is £146. Not actually a huge amount in the grand scheme of things. (I'm actually paying a bit less at the moment but the Scottish Power app is recommending an increase, possibly it's realised I'm consuming a bit more than I was.)

The entire quote (including solar panels, battery and Zappi) is £13,710. If I divide the quote by the monthly DD, then that makes 7 years 10 months worth of monthly payments. Obviously not accounting for inflation or lost interest and so on. My supplier is estimating 6-7 years of payback time. This suggests that over the year I'm not simply paying nothing for my electricity, I'm making a little bit.

I appreciate this is highly simplistic, but is this actually possible? And yet people who have the systems seem to be quite satisfied with the return they're getting, on the whole. And my electricity consumption is on the high side of average, so that should actually be advantageous.

The way I worked it out in a simple manner using easy figures. System costing £15k gives about £1.5k electricity per year. Where else can I invest £15k at 10% tax free index linked to cost of electricity? Only downside being that you can’t withdraw a your investment. I have 10 panels, 5kWh battery storage, currently only able to charge on granny charger because EO charger is obsolete and is currently in the process of County Court proceedings.

 

[Gadget Geek]

The way I worked it out in a simple manner using easy figures. System costing £15k gives about £1.5k electricity per year. Where else can I invest £15k at 10% tax free index linked to cost of electricity? Only downside being that you can’t withdraw a your investment. I have 10 panels, 5kWh battery storage, currently only able to charge on granny charger because EO charger is obsolete and is currently in the process of County Court proceedings.

Exactly how I looked at it. Why would I want to withdraw money making me that much interest? With the FIT, the panels were paid for in 4 years and it's been profit ever since.

 

[John T]

We paid a bit under £1k for our 7kW charger having had to pay to have an additional new meter box installed and our PV meter moved in to it, along with the charger's fuse board. The charger gives us 5 hours off-peak at 8.5p a unit. Assuming 4 miles per kWh 1000 miles would cost £21.25, cheaper than the 65p per unit at a Shell station £141.25 per 1000 miles. We expect to be doing around 5000 miles in a year, saving £706 on the Shell cost.
The off-peak tariff applies to anything we have running in the early hours, washing machine, dishwasher and heat pump. In summer we have to choose between 8.5p and possible free PV energy for each wash cycle!

 

[johnb80]

We paid a bit under £1k for our 7kw charger having had to pay to have an additional new meter box installed and our PV meter moved in to it, slong with the charger's fuse board. The charger gives us 5 hours off-peak at 8.5p a unit. Assuming 4 miles per kw 1000 miles would cost £21.25, cheaper than the 65p per unit at a Shell station £141.25 per 1000 miles. We expect to be doing around 5000 miles in a year, saving £706 on the Shell cost.
The off-peak tariff applies to anything we have running in the early hours, washing machine, dishwasher and heat pump. In summer we have to choose between 8.5p and possible free PV energy for each wash cycle!

Change to Tomato Energy and save even more, your 1000 miles on TE would only cost £12.50 nearly half price! In the same way you get all of your house supplied at the same rate, the daily standing charge is only 43p and the peak rate 23p but with 2 x 2 hour slots at 13.37p.

 

[Bam Bam]

Change to Tomato Energy and save even more, your 1000 miles on TE would only cost £12.50 nearly half price! In the same way you get all of your house supplied at the same rate, the daily standing charge is only 43p and the peak rate 23p but with 2 x 2 hour slots at 13.37p.

For how long are they fixing/guaranteeing these prices?

I guess maybe we will get back to the days when you changed provider all the time as new tariffs came available.

More complicated though when you've got credit built up.