SOLAR PV - Real world figures
Discussion
Does anyone have a real world set of numbers for the difference solar PV has made to their electricity usage?
The system that has been specced up for us is expected to generate 4060kw/h per annum. Our usage is c. 6500 kw/h per annum. What we don't use will be diverted to the immersion coils in the hot water cylinder (which is gas fired ordinarily). So I am assuming that we will use the full 4060kw, but some of that usage will replace gas rather than electricity.
What I'm wondering is how much of our 6500 could we generally expect to substitute with what has been generated by the PV? Apart from night time usage, I guess there will also be peaks in the day, or dull days, when we will still rely on the grid.
Roughly speaking I'm thinking half of our usage will be replaced with the PV.. and the other half will still come from grid. That seems to be the benchmark set by the industry, can anyone advise differently?
Cheers,
Klive
The system that has been specced up for us is expected to generate 4060kw/h per annum. Our usage is c. 6500 kw/h per annum. What we don't use will be diverted to the immersion coils in the hot water cylinder (which is gas fired ordinarily). So I am assuming that we will use the full 4060kw, but some of that usage will replace gas rather than electricity.
What I'm wondering is how much of our 6500 could we generally expect to substitute with what has been generated by the PV? Apart from night time usage, I guess there will also be peaks in the day, or dull days, when we will still rely on the grid.
Roughly speaking I'm thinking half of our usage will be replaced with the PV.. and the other half will still come from grid. That seems to be the benchmark set by the industry, can anyone advise differently?
Cheers,
Klive
Very difficult to say but I can offer some insight to my own situation.
We installed an immersun to store excess PV but also have solar hot water panels. Our hot water is 100% solar heated March-October. It looks like the immersun is going to take at least 4 years to pay for itself, probably as it doesn't get much chance to work through the summer. Your gas savings might make it more worthwhile.
Do not expect to generate much in the winter months (when you will probably have greater usage).
You will generate more than you can use in summer. Occupancy rates will be important when considering savings. I work from home so to my mind, the office runs on solar most of the year.
I have a swimming pool heated by ASHP. This is the real winner for me, as the pool is heated and filtered for free on sunny days.
I have a 5kw system and in the 2 years it has been operational I am about 10% under the predicted generation (and resultant FIT payment). Weather has been generally poor though, especially in summer.
My electricity DD is the same as when I moved in but I changed from oil central heating to a GSHP when I put the panels in. Presumably the solar panels are playing a significant role in my huge spike in electricity demand not actually costing me anything (summer savings negating winter increases).
We installed an immersun to store excess PV but also have solar hot water panels. Our hot water is 100% solar heated March-October. It looks like the immersun is going to take at least 4 years to pay for itself, probably as it doesn't get much chance to work through the summer. Your gas savings might make it more worthwhile.
Do not expect to generate much in the winter months (when you will probably have greater usage).
You will generate more than you can use in summer. Occupancy rates will be important when considering savings. I work from home so to my mind, the office runs on solar most of the year.
I have a swimming pool heated by ASHP. This is the real winner for me, as the pool is heated and filtered for free on sunny days.
I have a 5kw system and in the 2 years it has been operational I am about 10% under the predicted generation (and resultant FIT payment). Weather has been generally poor though, especially in summer.
My electricity DD is the same as when I moved in but I changed from oil central heating to a GSHP when I put the panels in. Presumably the solar panels are playing a significant role in my huge spike in electricity demand not actually costing me anything (summer savings negating winter increases).
Personal system here.
From memory we have 3.8kw on the roof and we average about £800-£1k payback a year.
We have oil and an Immersun Diverter and I would say for about 6 months of the year our hot water is heated by the solar electricity only.
We are about 6 years in now so we are on the 2nd best FIT ever available and literally today (just checked it, 19999.6w) we will have generated 20Kw in that time. So it should have paid for itself by the end of this / early next year.
V.
From memory we have 3.8kw on the roof and we average about £800-£1k payback a year.
We have oil and an Immersun Diverter and I would say for about 6 months of the year our hot water is heated by the solar electricity only.
We are about 6 years in now so we are on the 2nd best FIT ever available and literally today (just checked it, 19999.6w) we will have generated 20Kw in that time. So it should have paid for itself by the end of this / early next year.
V.
Should have mentioned, I have 5kw of panels but stepped down to just under 4kw in order to qualify for the best FIT available at the time. This means we are at max generation more frequently.
Apparently this should improve inverter life span as well (an important consideration when thinking about payback etc, as they are not expected to last as long as the system and cost >£1k).
Commissioned on 22/3/16, generated 9343 kWh so far. We are meant to be in one of the sunnier parts of the country but I would question that...
Apparently this should improve inverter life span as well (an important consideration when thinking about payback etc, as they are not expected to last as long as the system and cost >£1k).
Commissioned on 22/3/16, generated 9343 kWh so far. We are meant to be in one of the sunnier parts of the country but I would question that...
Hi chaps, thanks for the replies.
Interesting Pterdodrama that yours is 25% over specced but still falls 10% short of the forecast figure. I'm in a supposedly sunny part of the UK as well (South Devon) so have been given relatively high forecasts.
I'm leaning towards the conclusion that between winter months, times where our demand is over and above what the PV produces, evening use and dull summer days.. that actually the dent we make in our 6500kw/h might not be as substantial as I hoped. The payback very much depends on how much of our electricity usage we manage to replace with PV. Running the inevitable excess to the immersions is really a distant 2nd best (6500kw/h of electricity is worth somewhere approaching £900 whereas 6500 kw/h of gas is more like £200).
If I knew I would be in this house for 10 years it would be a no brainer..
Interesting Pterdodrama that yours is 25% over specced but still falls 10% short of the forecast figure. I'm in a supposedly sunny part of the UK as well (South Devon) so have been given relatively high forecasts.
I'm leaning towards the conclusion that between winter months, times where our demand is over and above what the PV produces, evening use and dull summer days.. that actually the dent we make in our 6500kw/h might not be as substantial as I hoped. The payback very much depends on how much of our electricity usage we manage to replace with PV. Running the inevitable excess to the immersions is really a distant 2nd best (6500kw/h of electricity is worth somewhere approaching £900 whereas 6500 kw/h of gas is more like £200).
If I knew I would be in this house for 10 years it would be a no brainer..
klivedrgar said:
Hi chaps, thanks for the replies.
Interesting Pterdodrama that yours is 25% over specced but still falls 10% short of the forecast figure. I'm in a supposedly sunny part of the UK as well (South Devon) so have been given relatively high forecasts.
I'm leaning towards the conclusion that between winter months, times where our demand is over and above what the PV produces, evening use and dull summer days.. that actually the dent we make in our 6500kw/h might not be as substantial as I hoped. The payback very much depends on how much of our electricity usage we manage to replace with PV. Running the inevitable excess to the immersions is really a distant 2nd best (6500kw/h of electricity is worth somewhere approaching £900 whereas 6500 kw/h of gas is more like £200).
If I knew I would be in this house for 10 years it would be a no brainer..
The forecast figure is for the 5kw system throttled down to 3.8kw (or thereabouts) as installed, so the 10% under is just weather related I think. Interesting Pterdodrama that yours is 25% over specced but still falls 10% short of the forecast figure. I'm in a supposedly sunny part of the UK as well (South Devon) so have been given relatively high forecasts.
I'm leaning towards the conclusion that between winter months, times where our demand is over and above what the PV produces, evening use and dull summer days.. that actually the dent we make in our 6500kw/h might not be as substantial as I hoped. The payback very much depends on how much of our electricity usage we manage to replace with PV. Running the inevitable excess to the immersions is really a distant 2nd best (6500kw/h of electricity is worth somewhere approaching £900 whereas 6500 kw/h of gas is more like £200).
If I knew I would be in this house for 10 years it would be a no brainer..
Presumably we would have been about 10% under forecast for whatever we had put in (planning went in for 10kw but Western Power wouldn't let us without a transformer upgrade, which they could do, for £14K).
Domestic solar seems to be in limbo now, FIT not making it worthwhile and battery tech not yet cheap enough to enable people to store/access better. If I didn't plan on staying put for 20 years and have a massive heat sink/pool I wouldn't have done it.
I had a 3.5KW solaredge system installed in 2014. Looking at the original quote using the standard MCS procedure I was to expect 2947 kilowatt hours per year. I have seen 3.7, 3.7 and 3.6MWh for the last three years respectively. I have added a monthly comparative breakdown for you above to give you an idea of what you can see throughout the year.
I run the immersion gizmo and it works well in summer but I have an old tank so have scheduled a gas top-up for the morning shower and the wife insists on running gas water for the evening also. In summer it works a treat, in winter not so much.
The forecast calculations in my original quote were based on a reduction of 33% in electricity. I would need some newer hardware to be able to calculate what that figure actually is but we do try and run dishwasher, washing machines when the system is generating.
I run the immersion gizmo and it works well in summer but I have an old tank so have scheduled a gas top-up for the morning shower and the wife insists on running gas water for the evening also. In summer it works a treat, in winter not so much.
The forecast calculations in my original quote were based on a reduction of 33% in electricity. I would need some newer hardware to be able to calculate what that figure actually is but we do try and run dishwasher, washing machines when the system is generating.
Edited by IIIRestorerIII on Friday 2nd February 14:38
We had 3.88kWp installed over 7 years ago on our house in Oxfordshire.
Our roof is south facing and unshaded.
Every month I record the generation, import and export units.
I had already installed Solar Thermal, so there was no point in driving an immersion to use up the excess - any excess is exported.
As you say; almost all of the generation is done when it isn't wanted. The tariff is the only viability. Ignoring our finances, as the rates and cost of installation have changed a lot in the last 7 years, here are the power figures for our generation and consumption.
Generation - There are huge differences between best and worst months, but each month I take a total of the previous 12 months to get a yearly average.
Our running past 12 month average has remained around 3800kWh per year.
I take the generation plus the import less the export to establish what has been used in the property. The savings due to having PV is Generation less export.
Looking at the past year our total usage was: 3098kWh
Our savings were: 1000kWh
I try to use stuff like the dishwasher and washing m/c during the day, but I'm not very diligent about it. I'd say our use pattern has hardly changed to maximise savings.
If you installed a solar powered water heater it would make the solar system more efficient. If you're a big user you may not have bigger savings unless you are using more during the generating day.
Our roof is south facing and unshaded.
Every month I record the generation, import and export units.
I had already installed Solar Thermal, so there was no point in driving an immersion to use up the excess - any excess is exported.
As you say; almost all of the generation is done when it isn't wanted. The tariff is the only viability. Ignoring our finances, as the rates and cost of installation have changed a lot in the last 7 years, here are the power figures for our generation and consumption.
Generation - There are huge differences between best and worst months, but each month I take a total of the previous 12 months to get a yearly average.
Our running past 12 month average has remained around 3800kWh per year.
I take the generation plus the import less the export to establish what has been used in the property. The savings due to having PV is Generation less export.
Looking at the past year our total usage was: 3098kWh
Our savings were: 1000kWh
I try to use stuff like the dishwasher and washing m/c during the day, but I'm not very diligent about it. I'd say our use pattern has hardly changed to maximise savings.
If you installed a solar powered water heater it would make the solar system more efficient. If you're a big user you may not have bigger savings unless you are using more during the generating day.
Electronics and hybrid cars being my thing I'm building a cheap battery bank using old hybrid car battery packs.
I have 4kw of (rented) solar on my roof and live on my own so use very little, so during the summer loads is wasted (exported)
I don't get paid for it the solar company do. But I can use as much as I can eat.
So I'm building a two stage excess solar diversion system.
1st stage divert excess to my battery bank until full. (My initial battery bank will be 6kwh)
2nd stage when battery full divert to immersion heater.
6kwh of nimh storage equates to 140 old Honda Insight generation 1 battery sticks. (The equivalent of 7 car's worth)
The storage will be easily scalable so i'll add more as I get more dying packs..
The normal issue with these sticks is higher IR or self discharge, rendering them unusable in the car but they normally all have at least 6ah of capacity left.
I'm also building my own diversion and solar control system..
https://www.youtube.com/edit?o=U&video_id=g4fO...
The build thread is here....
http://www.insightcentral.net/forums/honda-insight...
At night time or when no sun I will just swap to the battery powered 4kw inverter.
I have 4kw of (rented) solar on my roof and live on my own so use very little, so during the summer loads is wasted (exported)
I don't get paid for it the solar company do. But I can use as much as I can eat.
So I'm building a two stage excess solar diversion system.
1st stage divert excess to my battery bank until full. (My initial battery bank will be 6kwh)
2nd stage when battery full divert to immersion heater.
6kwh of nimh storage equates to 140 old Honda Insight generation 1 battery sticks. (The equivalent of 7 car's worth)
The storage will be easily scalable so i'll add more as I get more dying packs..
The normal issue with these sticks is higher IR or self discharge, rendering them unusable in the car but they normally all have at least 6ah of capacity left.
I'm also building my own diversion and solar control system..
https://www.youtube.com/edit?o=U&video_id=g4fO...
The build thread is here....
http://www.insightcentral.net/forums/honda-insight...
At night time or when no sun I will just swap to the battery powered 4kw inverter.
Edited by peterperkins on Tuesday 6th February 07:42
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