Discussion
It is. 3.13kW in and 15kW out according to the specs, which also matches my experimental results too, broadly.
But an 18' diameter above ground pool is about 20 tonnes of water. It heats up at half a degree an hour
So from 20C to 30C takes way over 232kWh and somewhere approaching 20 hours to heat up (accounting for losses) and then needs something near a 50% duty cycle to maintain that temperature.
It is what it is. A godsend during the pandemic summers and during the very hot days we had.
But you can see the difference it makes. In June 2021, I kept it warm through much of June. (Graph is average daily usage during the period)
In 2022, I heated it up only when a playdate or party was organised. You can see the massive reductions on both gas & electricity already, before we have solar installed - just by getting in to habits of turning things off when we don't want them, turning the thermostat down. using hive TRVs to heat individual rooms rather than the whole hose, having the hot water on a bit less (we still never run out) and so forth.
I'm not OCD about it all, but when were were predicting an 18K fuel bill, this prompts action! I'm not some gentrified landower, we just live in a town in a decent size 4 bed detached that's 110 years old and doesn't insulate well. Which is probably the situation many others here have found themselves in. And even if prices stayed at the current september levels (which my friends in the industry reckon is probably where it'll stabilise eventually, but it's all guesswork isn't it)
Anyway, just gotta be patient now until the solar stuff is all installed, just in time for winter and no sun light.
But an 18' diameter above ground pool is about 20 tonnes of water. It heats up at half a degree an hour
So from 20C to 30C takes way over 232kWh and somewhere approaching 20 hours to heat up (accounting for losses) and then needs something near a 50% duty cycle to maintain that temperature.
It is what it is. A godsend during the pandemic summers and during the very hot days we had.
But you can see the difference it makes. In June 2021, I kept it warm through much of June. (Graph is average daily usage during the period)
In 2022, I heated it up only when a playdate or party was organised. You can see the massive reductions on both gas & electricity already, before we have solar installed - just by getting in to habits of turning things off when we don't want them, turning the thermostat down. using hive TRVs to heat individual rooms rather than the whole hose, having the hot water on a bit less (we still never run out) and so forth.
I'm not OCD about it all, but when were were predicting an 18K fuel bill, this prompts action! I'm not some gentrified landower, we just live in a town in a decent size 4 bed detached that's 110 years old and doesn't insulate well. Which is probably the situation many others here have found themselves in. And even if prices stayed at the current september levels (which my friends in the industry reckon is probably where it'll stabilise eventually, but it's all guesswork isn't it)
Anyway, just gotta be patient now until the solar stuff is all installed, just in time for winter and no sun light.
Edited by Arnold Cunningham on Saturday 17th September 17:31
Yes, of course. Seems to help. The main loss of heat on a pool is by evaporation, so keeping it covered is part 1. Part 2 is that the solar covers also help heat it when in sunshine. 20 tonnes of water is what it is though. But you can see the huge difference in electricity consumption on the chart - that's just by our change in behaviour. 3 degrees cooler on the pool and only heating it when a play date was arranged.
Anyway, the poles are gettng a bit rusty now (3rd season up), so I suspect it'll be OK for next summer and then we'll probably dispose of it and review the options after that - whether to replace or get some lawn space back. Partially depends on how successfull we are at solar energy production, I guess.
Anyway, the poles are gettng a bit rusty now (3rd season up), so I suspect it'll be OK for next summer and then we'll probably dispose of it and review the options after that - whether to replace or get some lawn space back. Partially depends on how successfull we are at solar energy production, I guess.
I’m really interested in getting solar panels now, not just to save money long term but also to stick two fingers up to Putin and the Petro-oligarchs!
With 2 teens and a lot of washing machine use our consumption is about 14 kWh per day. We have a south facing sloped roof perfect for a 4-6 kw array with no shade at all in it.
There’s also a garage roof with the same again although this is in shade in the morning.
I’m not the best at doing the calculations but am I in the ball park that if we got a 6kw system and had 4-5 hours of bright daylight then that would make 4 x 6 = 24 kWh of electricity which allowing for some losses and with say a 11 kWh battery would allow us to go completely solar for electricity. How much of the year is this likely to be the case? Have I got the maths right?
If we added a second array on the garage and another battery potentially we could also charge an EV does that sound realistic?
Thanks for any wisdom!
With 2 teens and a lot of washing machine use our consumption is about 14 kWh per day. We have a south facing sloped roof perfect for a 4-6 kw array with no shade at all in it.
There’s also a garage roof with the same again although this is in shade in the morning.
I’m not the best at doing the calculations but am I in the ball park that if we got a 6kw system and had 4-5 hours of bright daylight then that would make 4 x 6 = 24 kWh of electricity which allowing for some losses and with say a 11 kWh battery would allow us to go completely solar for electricity. How much of the year is this likely to be the case? Have I got the maths right?
If we added a second array on the garage and another battery potentially we could also charge an EV does that sound realistic?
Thanks for any wisdom!
Arnold Cunningham said:
Eloit & Gaz. Agreed.
I'm trying to ensure the systems is robust - so if the cheap overnight tariff is not possible, it doesn't undermine the usefulness of the system
On a rolling 12 month basis we use an average ot 16kwh per day (including the kids pool, which I only keep calling out since it its an energy hog, and also optional - so if anyone else uses any of my sums to look at their own setup, the numbers are not unfairly biased. I mean, I'm looking back at the middle of june 2021 use and we burnt an average of 115kWh per day. Those days are long gone - hence I'm using rolling 12 months).
So I'm pretty much ignoring feed in tariffs and also want to make sure that during the summer period, if there's a cloudy day we have enough to carry us through withouth consuming much from grid. And during the winter, we have enough battery capacity to ensure that all solar production can be stored for us to use. but with enough grid charging going on during any off peak periods to make sure that gives us enough capacity if solar is doing nothing that day.
The givenergy gen 2 inverter handles 3.6kW of charging - so 3.6kw x 4 tells me we can consume up to 14.4 kWh from the grid in a 4 hour period.
So I'd like to make sure that we can charge the battery up enough to give us 24 hours of battery power with no solar, and then if we get to the next charging window, if the battery is still over the daily average, we consume 0 from the grid. Even factoring in my 2022 heating strategy for the pool, I think it should be possible to stay virtually off grid for 6 months of the year. I would love that. Lots to think about.
It needs a fair bit of data to work out whether it's cost effective to add more battery.I'm trying to ensure the systems is robust - so if the cheap overnight tariff is not possible, it doesn't undermine the usefulness of the system
On a rolling 12 month basis we use an average ot 16kwh per day (including the kids pool, which I only keep calling out since it its an energy hog, and also optional - so if anyone else uses any of my sums to look at their own setup, the numbers are not unfairly biased. I mean, I'm looking back at the middle of june 2021 use and we burnt an average of 115kWh per day. Those days are long gone - hence I'm using rolling 12 months).
So I'm pretty much ignoring feed in tariffs and also want to make sure that during the summer period, if there's a cloudy day we have enough to carry us through withouth consuming much from grid. And during the winter, we have enough battery capacity to ensure that all solar production can be stored for us to use. but with enough grid charging going on during any off peak periods to make sure that gives us enough capacity if solar is doing nothing that day.
The givenergy gen 2 inverter handles 3.6kW of charging - so 3.6kw x 4 tells me we can consume up to 14.4 kWh from the grid in a 4 hour period.
So I'd like to make sure that we can charge the battery up enough to give us 24 hours of battery power with no solar, and then if we get to the next charging window, if the battery is still over the daily average, we consume 0 from the grid. Even factoring in my 2022 heating strategy for the pool, I think it should be possible to stay virtually off grid for 6 months of the year. I would love that. Lots to think about.
If you have enough battery for evening and overnight, that will get used on every sunny day.
To make use of twice as much battery requires a day or more of good sun before each dull day when you'd benefit.
Just eyeballing the daily yield graphs suggests doubling the size of the battery might only increase the number of 'grid free' days by 20 or 25%.
Tobermory said:
I’m really interested in getting solar panels now, not just to save money long term but also to stick two fingers up to Putin and the Petro-oligarchs!
With 2 teens and a lot of washing machine use our consumption is about 14 kWh per day. We have a south facing sloped roof perfect for a 4-6 kw array with no shade at all in it.
There’s also a garage roof with the same again although this is in shade in the morning.
I’m not the best at doing the calculations but am I in the ball park that if we got a 6kw system and had 4-5 hours of bright daylight then that would make 4 x 6 = 24 kWh of electricity which allowing for some losses and with say a 11 kWh battery would allow us to go completely solar for electricity. How much of the year is this likely to be the case? Have I got the maths right?
If we added a second array on the garage and another battery potentially we could also charge an EV does that sound realistic?
Thanks for any wisdom!
I have a 6Kw solar array and even with the New Mexico climate of brilliant sunshine, I never see anything close to 6Kw, 4.5Kw maybe.With 2 teens and a lot of washing machine use our consumption is about 14 kWh per day. We have a south facing sloped roof perfect for a 4-6 kw array with no shade at all in it.
There’s also a garage roof with the same again although this is in shade in the morning.
I’m not the best at doing the calculations but am I in the ball park that if we got a 6kw system and had 4-5 hours of bright daylight then that would make 4 x 6 = 24 kWh of electricity which allowing for some losses and with say a 11 kWh battery would allow us to go completely solar for electricity. How much of the year is this likely to be the case? Have I got the maths right?
If we added a second array on the garage and another battery potentially we could also charge an EV does that sound realistic?
Thanks for any wisdom!
Just from personal experience most mornings my battery bank (38KWh) is at around 70% capacity, by around midday the bank is fully charged and the house runs directly from the panels unless we put on a heavy load, when it pulls on the batteries for a short time, but they are normally fully charged by the time the sun goes down.
We have the normal electrical loads of TV, washer/dryer (gas for the dryer), microwave, induction cooker, water well pump and two mini-split A/C heatpumps.
Been off grid for over a year and it all now just seems normal and we forget we're on solar power
Thank you, I doubt I’d need anything like as big a battery in the UK! But with a 6kw system and British levels of sunlight it sounds like I should be able to produce most of my electric needs via solar at least. I’ll get in touch with an installer to get a specific calculation for my location.
Even if a 6kw system produces 3kw for 5 hours, that should just about cover it and I imagine an 11kwh battery would cover our nighttime needs.
Thank you
Even if a 6kw system produces 3kw for 5 hours, that should just about cover it and I imagine an 11kwh battery would cover our nighttime needs.
Thank you
Edited by anonymous-user on Monday 19th September 20:04
V-spec said:
38kwh of batteries? Wow. Big house?
We do have the occasional overcast day so 38kwh gives us about 3 days of battery supply if there's no solar input.Each of my four battery banks are like this, but using 200amp cells, so each battery bank is around 10kwh and physically a lot smaller.
https://www.youtube.com/watch?v=atYZ4RtUJhU
Tobermory said:
... would allow us to go completely solar for electricity.!
... Apart from the late autumn, all winter, early spring. Any grey winter days generate pretty much nothing. Just bear that in mind. Have a think about how many sunny winter days we actually get. And when we do, the sun is very low.I am involved in vehicle solar systems and I have already started receiving the annual wave of "something is up with my solar" emails, where the customers are expecting summer performance from autumn sun,. We are mid September and the difference is big already.
Griffith4ever said:
... Apart from the late autumn, all winter, early spring. Any grey winter days generate pretty much nothing. Just bear that in mind. Have a think about how many sunny winter days we actually get. And when we do, the sun is very low.
I am involved in vehicle solar systems and I have already started receiving the annual wave of "something is up with my solar" emails, where the customers are expecting summer performance from autumn sun,. We are mid September and the difference is big already.
No you've got that all wrong the cooler tempertaure makes the panels much more efficient................ I am involved in vehicle solar systems and I have already started receiving the annual wave of "something is up with my solar" emails, where the customers are expecting summer performance from autumn sun,. We are mid September and the difference is big already.
dmsims said:
Griffith4ever said:
... Apart from the late autumn, all winter, early spring. Any grey winter days generate pretty much nothing. Just bear that in mind. Have a think about how many sunny winter days we actually get. And when we do, the sun is very low.
I am involved in vehicle solar systems and I have already started receiving the annual wave of "something is up with my solar" emails, where the customers are expecting summer performance from autumn sun,. We are mid September and the difference is big already.
No you've got that all wrong the cooler tempertaure makes the panels much more efficient................ I am involved in vehicle solar systems and I have already started receiving the annual wave of "something is up with my solar" emails, where the customers are expecting summer performance from autumn sun,. We are mid September and the difference is big already.
dmsims said:
No you've got that all wrong the cooler tempertaure makes the panels much more efficient................
It's quite interesting how the 'power curve' differs as we go through the seasons. Last month, full sun at midday and 36c, I was seeing 12kw off a 16kw system. Yesterday at midday, 17c and some shading- 14.5kw...There do seem to be quite a few people posting who don't understand the variation during the year. Clearly generation will differ based on area and positioning of the solar. For my array, the following production is expected:
Jan 3%
Feb 5%
Mar 9%
Apr 11%
May 12%
Jun 13%
Jul 14%
Aug 11%
Sep 9%
Oct 6%
Nov 4%
Dec 3%
So someone with a 4kw system near me could generate (at say 75%) 3,000 kwh per annum. But 70% of the energy is produced between April and September and a relatively small 90 kwh during December. Obviously the numbers can vary significantly over the year.
MaxFromage said:
dmsims said:
No you've got that all wrong the cooler tempertaure makes the panels much more efficient................
It's quite interesting how the 'power curve' differs as we go through the seasons. Last month, full sun at midday and 36c, I was seeing 12kw off a 16kw system. Yesterday at midday, 17c and some shading- 14.5kw...There do seem to be quite a few people posting who don't understand the variation during the year. Clearly generation will differ based on area and positioning of the solar. For my array, the following production is expected:
Jan 3%
Feb 5%
Mar 9%
Apr 11%
May 12%
Jun 13%
Jul 14%
Aug 11%
Sep 9%
Oct 6%
Nov 4%
Dec 3%
So someone with a 4kw system near me could generate (at say 75%) 3,000 kwh per annum. But 70% of the energy is produced between April and September and a relatively small 90 kwh during December. Obviously the numbers can vary significantly over the year.
So for a 6kw system between October and March I could expect to generate 24% x 3,000 x 1.5 = 450 kWh
that's 7kWh per day, or around a third of what we use for the same period.
In Summer it would generate around 20kWh per day, more than the approx 15kW/day we use in the Summer
5kWh would give around 20 miles of EV range, my annual average mileage (8,000 miles pa) is 22, so that would nearly cover all my EV miles in Summer. Or it could be used to power the immersion heater and reduce our gas usage.
In summer there would be an excess that we could use to het water with an immersion heater or charge an EV.
Doesn't sound too bad to me. Adding a second 6kw system on the garage would get us nearer (but not up to) being grid free for the whole year but at the expense of having to export units in the Summer for quite a low rate judging by today's deals (unless we can use the extra up on charging an EV during the day, which we probably could.)
So it seems that for me at least a 6kW system (+ 11kWh battery) might make some sense?
Even if there are not massive savings, I'm inclined to go for it just to reduce our carbon footprint and reliance on overseas energy imports.
Tobermory said:
Thanks, that's really helpful. The calcs are complex to be sure.
So for a 6kw system between October and March I could expect to generate 24% x 3,000 x 1.5 = 450 kWh
that's 7kWh per day, or around a third of what we use for the same period.
In Summer it would generate around 20kWh per day, more than the approx 15kW/day we use in the Summer
5kWh would give around 20 miles of EV range, my annual average mileage (8,000 miles pa) is 22, so that would nearly cover all my EV miles in Summer. Or it could be used to power the immersion heater and reduce our gas usage.
.
On average yes. But the average never happens over an entire month. There will be days when little is generated, and days when the generation is 3x the average. So you have to consider that in your calculations and also work out the best size array (and battery) to utilise the energy generated (or not).So for a 6kw system between October and March I could expect to generate 24% x 3,000 x 1.5 = 450 kWh
that's 7kWh per day, or around a third of what we use for the same period.
In Summer it would generate around 20kWh per day, more than the approx 15kW/day we use in the Summer
5kWh would give around 20 miles of EV range, my annual average mileage (8,000 miles pa) is 22, so that would nearly cover all my EV miles in Summer. Or it could be used to power the immersion heater and reduce our gas usage.
.
Tobermory's post above is a good example of the dangers of looking at 'averages'.
Your 'average' yield in February might be equivalent to about an hour of sun. I.e. 4kWh from a 4kW system.
But you might get a few days in a row which only yield half an hour.
No credible amount of panels and batteries is going to keep you off-grid reliably in February.
Even in July, it's a mistake to think too much about the average day's sun meeting your average needs including your average car charging.
You will have varying generation and varying demand.
The demand tends to be higher when generation is lower!
Your car use might average 25 miles a day or whatever, but how many days do you do few miles and how many days do you do more than 50 miles?
Averages are only really any use when you put together the yields and demands of lots of households.
That's why the grid is extremely valuable.
A battery of course is a good tool for averaging across short time spans.
But diminishing returns set in if you try to average beyond 'one day at a time'.
Without a battery, you can't even think about your average yield in an hour timeslot, it's up and down as clouds go by, so subject to the vagaries of metering you don't average imports and exports.
As a very rough guide, consider that whatever the average daily yield is for a calendar month, about ten days in that month will be less than half that.
And those are the days when the tumble dryer is earning its keep!
Your 'average' yield in February might be equivalent to about an hour of sun. I.e. 4kWh from a 4kW system.
But you might get a few days in a row which only yield half an hour.
No credible amount of panels and batteries is going to keep you off-grid reliably in February.
Even in July, it's a mistake to think too much about the average day's sun meeting your average needs including your average car charging.
You will have varying generation and varying demand.
The demand tends to be higher when generation is lower!
Your car use might average 25 miles a day or whatever, but how many days do you do few miles and how many days do you do more than 50 miles?
Averages are only really any use when you put together the yields and demands of lots of households.
That's why the grid is extremely valuable.
A battery of course is a good tool for averaging across short time spans.
But diminishing returns set in if you try to average beyond 'one day at a time'.
Without a battery, you can't even think about your average yield in an hour timeslot, it's up and down as clouds go by, so subject to the vagaries of metering you don't average imports and exports.
As a very rough guide, consider that whatever the average daily yield is for a calendar month, about ten days in that month will be less than half that.
And those are the days when the tumble dryer is earning its keep!
AW10 said:
Excellent informative post!
I pulled out some data from my old 4kWp system collected over 10 years:
You can see the variability from the best months to the worst months and how a month that is "good" one year can be carp another year.
Good info. It's approx a factor of 4/5 from best to worst averages. I pulled out some data from my old 4kWp system collected over 10 years:
You can see the variability from the best months to the worst months and how a month that is "good" one year can be carp another year.
It is an interesting challenge and there is a logic to having a bigger array and battery that can help smooth out the lumps and bumps, coupled with things like your EV has a battery too and typically a range that can do the commute for a week easily - so you can spread the charging up over a week (each night) say.
Does the EC link take into account cloud etc.? I'm assuming a 10kW panel on a roof will give 50kWh a day in summer, but only 5kWh a day in winter (and that being variable perhaps).
Some posts suggest you get nothing usable in winter, but it still seems a useful amount to me if the array is big enough (5kW would be half my current daily elec demand).
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