Plug in solar, what do you think?

[ericmark]

total use 14kwh a day @ 27p = £3.78 per day with no investment.(£1397pa)

With solar and battery around £200 pa, so saving around £1100 pa, I can say that as I also use around the same amount of power per day and have 6 kW of solar, a 5 kW inverter and a 6.4 kWh battery, the cost of electric is 8.5p, off-peak, 32p peak, was 15p now 12p export. So my gains will reduce but not that much. But @JohnW2 is correct, I was also looking at maintaining the boiler during a power cut, so there are other factors.

So which is the better option, a third 3.2 kWh battery on the existing solar, or a 2 kWh battery independent which can also be used for a picnic for example?

I could add more panels to roof, or add panels to balcony, so it is better angled for winter sunlight, and will grab the morning sun better. And no installation cost either scaffold or electricians.

To have electric costs around £252 per year, even if you use zero kWh, just the standing charge. To go off grid is not really an option, so as it stands, I over the last 10 months have paid less than the standing charge. But this is not the question, the question is should all be allowed to export power into the grid, using a DIY set-up.

 

[JohnW2]

... total use 14kwh a day @ 27p = £3.78 per day with no investment.(£1397pa)
... Balcony solar - £2000 investment with £270 savings pa ( assuming average uk sunshine of 5 hours per day) so 7 years to break even.
... 14KW solar install is what 15k installed with a break even of 16 years.....

Quite so (and more!). As I recently wrote, when one is as old as eric and myself, the concept of even "being worse off for the next 7 years", let alone "being worse off for the next 16 years" is not very attractive and, I would personally say, verging on a pretty daft thing to even consdier

 

[plugwash]

There is also the question of what do you base your break-even calculations on.

1. Do you use todays electricity prices straight, or do you make some assumptions about how electricity prices will rise in the future?
2. Do you account for "cost of funds"? if so at what rate.
3. How do you account for the risk of failures of the solar equipment?

 

[JohnW2]

There is also the question of what do you base your break-even calculations on.
1. Do you use todays electricity prices straight, or do you make some assumptions about how electricity prices will rise ine the future?

One obviously ought to make some attempt to anticipate future price changes (rises!), which will somewhat reduce the 'break even' time

2. Do you account for "cost of funds"? if so at what rate.

Again, one might attempt to also take that into account, which would make the break even period even longer. Getting a useful return out of invested cash is not easy these days, so probably not much of an issue if one could be a 'cash buyer' of the kit - but, conersely, if one had to pay for the kit 'with credit', that could markedly increase the break-even ('worse off') time.

3. How do you account for the risk of failures of the solar equipment?

In terms of 'failures prior to break even', I suppose one should aim to only buy if the warranty is at least as long as the likely break-even period. However ....
.... 4. How soon after break-even (and end of warranty) is it likely to be before one has to 'start again' and render oneself 'worse off' for yet another X years, or whatever? (I suspect the answer is likely to be 'not long'!) !!

 

[ericmark]

There is also the question of what do you base your break-even calculations on.
1. Do you use todays electricity prices straight, or do you make some assumptions about how electricity prices will rise in the future?

One obviously ought to make some attempt to anticipate future price changes (rises!), which will somewhat reduce the 'break even' time

The drop in payment from 15p to 12p/kWh my not seem much, but it is a warning that in the future we may not be getting the same pay for export, the said due to general price drop in electric, but my peak is still around 32p/kWh

However for plug in, would not expect much export, unless adding to existing. If adding to existing then one will likely have the second MPAN number for export, but one is unlikely to get the second MPAN number for only balcony solar panels.

I have tried to work out what the 800 watt limit means? I would assume it means the unit can feed 800 watt into the socket outlet, so one may be able to run a heat pump drier from a different socket, but most heavy users would need to be plugged into the inverter direct.

I have on my meter tails current transformers which tell my inverter what to do. Also, the iboost+ for the immersion heater. Without those CTs, the inverter would simply not know what to do, in the video he talks about a CT to see results, (Shelly) but not any CT connected to the inverter. I know the iboost+ uses a wireless CT, but the inverter is hardwired.

So not sure how the inverter knows when to import and when to export?

 

[JohnD]

So not sure how the inverter knows when to import and when to export?

Perhaps I'm missing something.

I don't have a storage battery.

My inverter produces as much power as it can from the panels.

When my house is using more that the inverter produces, it is all used by the house.

When the inverter is producing more than the house uses, the excess is exported.

It all happens without any switching or decisions. By slight voltage difference.

 

[JohnW2]

Perhaps I'm missing something. ....

I also sometimes struggle to understand the thinking behind what eric writes about these matters ...

I don't have a storage battery. .... My inverter produces as much power as it can from the panels. ... When my house is using more that the inverter produces, it is all used by the house. ... When the inverter is producing more than the house uses, the excess is exported. .... It all happens without any switching or decisions. By slight voltage difference.

That's what I would have expected, and very probably the way that 'things are' (and have to be) for the vast majority of people with a PV installation.

I get the impression that what eric is talking about is that when there is an excess of generation (in excess of what the house needs to use), there is theoretically a 'choice' between exporting the excess and using it to charge his batteries (for subsequent consumption) - and , because of details of the (import and export) tariffs, one or other of those options might be financially beneficial at a given point in time.

However, I have no idea as to what extent one can exercise that theoretical choice, and even less idea as to whether there is any way it could be done 'automatically' (without constant human involvement).

 

[JohnD]

I suppose, if your tariff was time dependent, you could charge you batt with timer control.

I hear it is difficult to do that with an EV as they don't like being switched.

I would charge a battery for choice so I can use it at peak times.

 

[JohnW2]

I would charge a battery for choice so I can use it at peak times.

Maybe, but the financial arithmetic of that would presumably depend upon how much one could ('alternatively') export the excess electricity for 'in real time' (at the time in question), wouldn't it?