Renewable energy to save money? Sorry It doesn't work.

[rxe]

4Q said:

I seem to have killed this thread with my facts and figures

Not really. The really important assumption in those sheets is that you use 50% of the power, and export 50%.

The challenge is that it is effing hard to use 50% of your generated power during daylight hours in the summer (when you get most of the power) and you’ll struggle to do anything on the power generated during the winter.

If you have electric immersion DHW, then it can work. If you’re (say) replacing gas, then it is not as cost effective.

If you live at home all day (unemployed, retired etc), then you can optimise your summer power consumption. If you go out to work, it is harder.

And it assumes zero failure in the system. Hands up whose fly by night solar installer is still in business 5 years later - oh, that’ll be none of them. The warranties aren’t worth a jot.

[NMNeil]

rxe said:

And it assumes zero failure in the system. Hands up whose fly by night solar installer is still in business 5 years later - oh, that’ll be none of them. The warranties aren’t worth a jot.

That was my concern, and why I built my own with redundancies.
I have two identical charge controller/inverters, and if one quits, the house will happily run on just one, but i have to tell the wife not to run too many high power appliances at the same time or it will trip and shut down. The Batteries are in four parallel banks each with it's own BMS. Each bank has a capacity of 9.6KwH, and each bank can be disconnected if there's a problem, still leaving me with more than enough storage until I can fix the problematic bank.

[rxe]

NMNeil said:

That was my concern, and why I built my own with redundancies.
I have two identical charge controller/inverters, and if one quits, the house will happily run on just one, but i have to tell the wife not to run too many high power appliances at the same time or it will trip and shut down. The Batteries are in four parallel banks each with it's own BMS. Each bank has a capacity of 9.6KwH, and each bank can be disconnected if there's a problem, still leaving me with more than enough storage until I can fix the problematic bank.

I’m thinking more of the cost of replacing inverters etc when they fail.

[4Q]

rxe said:

Not really. The really important assumption in those sheets is that you use 50% of the power, and export 50%.

The challenge is that it is effing hard to use 50% of your generated power during daylight hours in the summer (when you get most of the power) and you’ll struggle to do anything on the power generated during the winter.

If you have electric immersion DHW, then it can work. If you’re (say) replacing gas, then it is not as cost effective.

If you live at home all day (unemployed, retired etc), then you can optimise your summer power consumption. If you go out to work, it is harder.

And it assumes zero failure in the system. Hands up whose fly by night solar installer is still in business 5 years later - oh, that’ll be none of them. The warranties aren’t worth a jot.

I did two PV spreadsheets, one with 40% self-consumption and one with 50%. I also offered everyone the spreadsheet to put their own figures in!

[4Q]

Evanivitch said:

Hard to see what you've varied between each. It doesn't appear to be a best, medium and worst case scenario model, which ultimately gives the best representation of the variables and risk over the period.

I put median figures in and offered the spreadsheet to everyone to put their own numbers in. You didn’t take me up on the offer.

[NMNeil]

rxe said:

I’m thinking more of the cost of replacing inverters etc when they fail.

Under $700 if I need to replace mine, but they still have some of the factory 2 year warranty to go. And even if it does fail you can buy a new control board direct from the factor in Taiwan if you can't fix it yourself.
https://watts247.com/product/pip-3048lv-mk/

[Traffic]

rxe said:

The challenge is that it is effing hard to use 50% of your generated power during daylight hours in the summer (when you get most of the power) and you’ll struggle to do anything on the power generated during the winter.

I manage to use most of my solar energy up in the winter running my air heatpump and dishwasher, laundry etc. Just on Friday 32% (19Kwh) of my energy came from solar, the rest from the grid 39Kwh. As I have mentioned earlier, if you know it is going to be sunny pre programme dishwasher, laundry etc.

Edited by Traffic on Monday 21st February 06:08

[Jambo85]

Traffic said:

rxe said:

The challenge is that it is effing hard to use 50% of your generated power during daylight hours in the summer (when you get most of the power) and you’ll struggle to do anything on the power generated during the winter.

I manage to use most of my solar energy up in the winter running my air heatpump and dishwasher, laundry etc. Just on Friday 32% (19Kwh) of my energy came from solar, the rest from the grid 39Kwh. As I have mentioned earlier, if you know it is going to be sunny pre programme dishwasher, laundry etc.

Edited by Traffic on Monday 21st February 06:08

It’s still winter though isn’t it…. You must have a fair size of array to be getting 19 kWh in February too?

[Traffic]

Jambo85 said:

It’s still winter though isn’t it…. You must have a fair size of array to be getting 19 kWh in February too?

My best day this month has been 32Kwh on the 11th of Feb. So far this month I have harvested 272Kwh. 90Kwh we sold to the grid (35%) a the rest we have used (165Kwh) ourselves.

My system has a top effect of 21Kw per hour which is a little bit bigger than the regular ones around here, but not exactly massive.

[Evanivitch]

Traffic said:

My system has a top effect of 21Kw per hour which is a little bit bigger than the regular ones around here, but not exactly massive.

The average UK domestic solar array is 4kW. If yours is 21kW then yes, it's relatively massive in domestic solar terms.

[Traffic]

UK systems seem very small then compared to what I see around here in southern Sweden.

[PushedDover]

Traffic said:

UK systems seem very small then compared to what I see around here in southern Sweden.

LOL / Love it.

Armchair experts be : "Oh. my presumption was incorrect"

[monkfish1]

Evanivitch said:

Traffic said:

My system has a top effect of 21Kw per hour which is a little bit bigger than the regular ones around here, but not exactly massive.

The average UK domestic solar array is 4kW. If yours is 21kW then yes, it's relatively massive in domestic solar terms.

Indeed. In an average UK domestic setting, a 21KW array isnt going to happen.

Having enough roof facing the right way.

Edited by monkfish1 on Monday 21st February 09:08

[Traffic]

monkfish1 said:

Indeed. In an average UK domestic setting, a 21KW array isnt going to happen.

Why not? obviously not possible on really small houses, but mine is not exactly big. The length of my roof is 8 Metres long and has 3 dormer windows in it on the south elevation.

[Evanivitch]

Traffic said:

monkfish1 said:

Indeed. In an average UK domestic setting, a 21KW array isnt going to happen.

Why not? obviously not possible on really small houses, but mine is not exactly big. The length of my roof is 8 Metres long and has 3 dormer windows in it on the south elevation.

I have a 4 bedroom detached property. So above average sized for most the country. I'd fit about 7kW at a push. That's from quotations and with some modifications and using high efficiency panels.

[Traffic]

Evanivitch said:

I have a 4 bedroom detached property. So above average sized for most the country. I'd fit about 7kW at a push. That's from quotations and with some modifications and using high efficiency panels.

Mine is same bedrooms, technically 3.

Have you looked at panels on both elevations?

[Evanivitch]

Traffic said:

Evanivitch said:

I have a 4 bedroom detached property. So above average sized for most the country. I'd fit about 7kW at a push. That's from quotations and with some modifications and using high efficiency panels.

Mine is same bedrooms, technically 3.

Have you looked at panels on both elevations?

North and South?

[Traffic]

Evanivitch said:

North and South?

Is it directly facing S?

We did SW/NE elevations. Rear module get's morning sun in the winter and the front module gets afternoon sun. In the summer the same but the sun goes almost overhead for good portions of the day.

[Jambo85]

PushedDover said:

Traffic said:

UK systems seem very small then compared to what I see around here in southern Sweden.

LOL / Love it.

Armchair experts be : "Oh. my presumption was incorrect"

"Presumably" that is aimed at me. My presumption that his solar array was bigger than a typical UK one was proven entirely correct, by a factor of at least 5x. The presumption that he was in the UK was wrong but entirely reasonable on the basis that this is a UK dominated forum AND traffic's profile says he is in the UK!

To further explain my post to the hard of thinking, I was addressing the part of rxe's post which stated that it's hard to use 50% of the power that PV systems generate in the height of summer. That's clearly all the more true with a 21 kW array. And yes he's getting a meaningful amount of power in winter, but only by having an array 5x the typical UK size, requiring roughly 5x the investment and 5x the area. Not typical, and it is useful to others to point this out.

Edited by Jambo85 on Monday 21st February 09:48

[Evanivitch]

Traffic said:

Evanivitch said:

North and South?

Is it directly facing S?

We did SW/NE elevations. Rear module get's morning sun in the winter and the front module gets afternoon sun. In the summer the same but the sun goes almost overhead for good portions of the day.

Unless the Sun over the south of Sweden is drastically different to the Sun over Scotland, I find it quite hard to believe that the sun is "almost overhead" and that you're generation is peaking at 21kW unless you have something approaching a 30kW installed capacity.