Solar PV - electricity bill reduction

[Shell820810]

So we all know that Solar PV will reduce our electricity bill.  But how does this work in practice? 

I know we put our readings in for the FIT etc, and that's separate.  And that the electric company will assume we export 50% and we will get 4-5p a unit for this.  But how do we receive discount for the power we use when the solar PV is generating?

My little girl mustve turned the immersion heater on a few weeks ago  . We ran up about 1500 units on the meter, but this was over a sunny period, where the solar PV was working well.  Has the solar PV saved us from say 2000 - 2500 units going on the meter, or do you have to provide a reading from the solar PV at the end of the year and get a refund etc?

 

[Ferdinand]

Usage reduction is automatic when the panels are generating.

As I understand it the solar panels generate a slightly higher voltage than the grid, so when they are generating power it flows from there before drawing on the grid. 

If there is an excess after you have used some, that then flows into the grid due to the higher voltage.

That can probably be illustrated using Prof Heinz Wolff, bathtubs on piles of bricks with connecting pipes and jugs of water to use pressure as an analogue for voltage, your ever-loving partner, and a bicycle pump. But you risk a Great Crested Newt infestation of your bathtubs.

Ferdinand

 

Edited May 26, 2016 by Ferdinand
Added Heinz Wolff and a bicycle pump

[DeeJunFan]

Yeah, it think it works that when the PV is generating then you use it and your meter doesn't count it.

So you may have had any extra few thousand units on the meter.

[Jeremy Harris]

If you look at your meter, then (assuming it's a new one) then it will indicate clearly when you're not using any power from the grid, but are exporting.  Usually the red LED stays on solidly, indicating reverse current flow, rather than flashing for each Wh used.  The digital display may well alternate between the energy reading and a message that indicates that current is flowing back to the grid.

Whenever the meter has a solid red light or other reverse flow indication then the PV system is powering everything in the house with enough left over to export some to the grid.

[Declan52]

When sse are looking a reading I have to put in both of my import and export readings from the main meter. I think it was around September that Nie asked for my total export amount and was at the end of March where they wanted my total generated amount. 

I worked out how my pv was saving me money by looking at my yearly figures. I think my total bill for the year was near £600. I got £55 back from exporting and hope to get near enough £650 back from the generating tariff. So all in by having pv I was £100 up. If I hadn't had pv then my bill would have been £1250 as I would have had to buy in the units i generated. That's not taking into account how much I saved by using pv to heat my water.

Well worth having in my view.

[ProDave]

Different meters behave in different ways.  Ours (A Siemens merter) does acruallt flash the red lamp when it is exporting power, but I have checked and although the red led flashes it doesn't count up any units.

For best self use of self generated power, make sure you use all the big appliances like dishwasher, washing maching and tumble dryer as nerar as you can to the middle of the day, and one applionce at a time (easier to arrange if you are not out art work, but you can set them on timers)

[jack]

30 minutes ago, ProDave said:

For best self use of self generated power, make sure you use all the big appliances like dishwasher, washing maching and tumble dryer as nerar as you can to the middle of the day, and one applionce at a time (easier to arrange if you are not out art work, but you can set them on timers)

My wife's a wonderful woman, brilliant mother, etc, but I just can't her interested in this.  I've tried pointing out that there's a reason we got the 8.5kW array, but it just isn't on her radar.

I have about as much chance of getting anyone but me to turn off lights in the house. It's a standing joke (me being the only one who doesn't think it's funny) that when I get home from work in winter, sometimes literally every single light in the house is on!  I was talked out of occupancy sensors but am now committed to retrofitting them throughout the house in due course.

Edited May 26, 2016 by jack
typo :-(

[Ferdinand]

44 minutes ago, Declan52 said:

When sse are looking a reading I have to put in both of my import and export readings from the main meter. I think it was around September that Nie asked for my total export amount and was at the end of March where they wanted my total generated amount. 

I worked out how my pv was saving me money by looking at my yearly figures. I think my total bill for the year was near £600. I got £55 back from exporting and hope to get near enough £650 back from the generating tariff. So all in by having pv I was £100 up. If I hadn't had pv then my bill would have been £1250 as I would have had to buy in the units i generated. That's not taking into account how much I saved by using pv to heat my water.

Well worth having in my view.

To me that looks like £650 up - £1250 that you would have paid minus £600 that you had to pay.

My (10kw mainly east-facing) array has generated around 1500 kwh since mid-Jan, before the relevant shading 2 large trees were removed by my neighbour. I hope to get 6000-6500 kwh for the year, but we'll see.

At my FIT of (iirc) 10.9p/kwh, that will be around £650 plus the electicity saved plus the export, perhaps very approximately £1100-1200 in toto. Perfectly acceptable even in financial terms for a 12k investment.

Ferdinand

[Declan52]

I didn't count that as that's what you use to cover your initial investment. 

I was slightly under 3800 units for a 4kw system at a fit rate of 16.4p so am well glad that I installed it.

[Stones]

I've concluded that to make it worthwhile, it has to have a payback of 15 years or less, otherwise, I would rather just buy in my energy and keep the capital invested elsewhere (I have the luxury of being surrounded by renewable generation so don't feel any pressure on this front).  

On the question of how much of a reduction you get with PV fitted, friends of ours report a consistent 20 -25% annual reduction in their import, which corresponded to our own reduction.  My parents, saw a near 50% reduction but only because they had a very electricity hungry hot-tub.

The house we are currently renting has a 5kW wind turbine.  Given the near constant wind up here you would expect near zero electricity bills.  We are seeing a 50 - 60% reduction in our import.

[Ferdinand]

Piccie for comment.

 

[ToughButterCup]

On 5/26/2016 at 13:20, jack said:

I have about as much chance of getting anyone but me to turn off lights in the house. It's a standing joke (me being the only one who doesn't think it's funny) that when I get home from work in winter, sometimes literally every single light in the house is on! 

Dads all over the world do this job. 

[SteamyTea]

On 26/05/2016 at 14:41, Stones said:

The house we are currently renting has a 5kW wind turbine.  Given the near constant wind up here you would expect near zero electricity bills.  We are seeing a 50 - 60% reduction in our import.

This highlights the difference between Power and Energy.

If you draw power that is greater than the wind turbine is producing, then it tops up from the grid (an import), regardless of how much energy the turbine produces over a year.

You also need a high windspeed to get close to the maximum generation capacity of a turbine.  You may well find that the load factor is quite low.

 

[Nickfromwales]

On 26 May 2016 at 14:41, Stones said:

(I have the luxury of being surrounded by renewable generation so don't feel any pressure on this front).  

 

If you're surrounded by micro generation, have you checked your local grid voltage at the supply head? 

You might find that peak output will tip you over the acceptable voltage margin and shut the inverter down ( due to all the neighbouring systems going flat out too ). 

If that were the case then you'd have to do the maths as to how much export you're going to be doing, and maybe that would sway you to an off grid system just to offset your own consumption with reduced capital expenditure. 

[Stones]

1 hour ago, SteamyTea said:

This highlights the difference between Power and Energy.

If you draw power that is greater than the wind turbine is producing, then it tops up from the grid (an import), regardless of how much energy the turbine produces over a year.

You also need a high windspeed to get close to the maximum generation capacity of a turbine.  You may well find that the load factor is quite low.

 

Indeed, and very much highlights the problem with renewable energy.  Orkney generates over 100% equivalent of its consumption (and that doesn't include what's generated by the 100's of <50 kW turbines dotted about the place.  Overall, Orkney is 60% renewable, the rest either imported via a restricted interconnect with the Scottish mainland, or by an small oil fired power station in Kirkwall.

32 minutes ago, Nickfromwales said:

If your surrounded by micro generation, have you checked your local grid voltage at the supply head? 

You might find that peak output will tip you over the acceptable voltage margin and shut the inverter down ( due to all the neighbouring systems going flat out too ). 

If that were the case then you'd have to do the maths as to how much export your going to be doing, and maybe that would sway you to an off grid system just to offset your own consumption with reduced capital expenditure. 

Where we are building there is very little renewable (be it solar or wind), but overall in Orkney there is.  My comments were more directed to the notion that as a 'green' requirement, there isn't really a lot of point as Orkney is already way over 100% equivalent in terms of renewable generation.  The decision for me is purely a cost based one.

[Nickfromwales]

[jack]

On 5/28/2016 at 17:28, recoveringacademic said:

Dads all over the world do this job. 

Yep, and I remember various fathers doing it when I was growing up and wondering what their problem was!