Sunamp for UFH

[SteamyTea]

6 minutes ago, Ed Davies said:

I've started some code

Is it going to be Python?

[SteamyTea]

Right, after struggling with a new scaffold tower for 3 hours, and finding out that I do need the extension to get to my top windows, I decided to do a simpler thing and chart the relationship between successive rain free days and solar power.

As @Ed Davies mentioned.  There is less power in winter than summer, so this possibly skews the data.

Normally I would segment the year into weeks to get a clearer picture, but as there is no guarantee that Sunday really is sunny, or Monday for that matter, this cannot be done.

So what I have done is to count the incidents that the sun is delivering power into 100W.m^-2 bins.  So 0 Up to 100, 100 up to 200 etc.

Then plot the percentage count for 1, 2 and 3 extra days that are rain free.  I have chosen rain as a key indicator as you can have cloud without rain, but you cannot have rain without cloud.

The percentage count is of all the valid datapoints between 20/01/2010 and 16/09/2014.  So about 4 and half years worth.

Basically, my interpretation is that the more rain free days you get (and I get no more than 4 in a row), the more solar power you get.  This may not translate directly to solar energy.

 

[ragg987]

1 hour ago, Ed Davies said:

I've started some code to look at @SteamyTea's data. Will do more on that and similar for @ragg987's later.

Will be interested in any analysis you can provide. I once tried to do this and even loaded the data into a PowerBI "big data" tool to see if there were any interesting correlations in the data apart from the obvious. All it proved is that I am no data analyst and have no idea of how the toolset work !

[Ed Davies]

I'm no data analyst, either, and a bit scared of statistics, one of those areas where a little knowledge can be a dangerous thing so I just plot graphs and if something's not obvious from those I leave it to others.

 

Yes, it's a Python program. Standard Python3 (no non-standard libraries needed) but it does need the gnuplot program installed. That'll be easily available in the Linux repositories and simple enough to install on a Mac or Windows I imagine. The program reads the .csv files, either the one from Steamy's .zip file or the appropriate tab exported (via Save As in LibreOffice) from Ragg987's spreadsheet. It takes a --steamy or --ragg command-line switch to choose which data source to use.  Try --help for how to produce PNG (or SVG) output instead of just displaying gnuplot windows.

 

To get round partial correlation for the time of year I normalised the solar energy amounts by dividing by the average for days from ten days before the first day to ten days after the second day in each pair. If there were fewer than 15 days of data available in that period the pair was ignored. So the point at (1, 1) represents an average day for the time of year followed by another such average day.

 

To be honest, I'm a bit disappointed as it all seems a bit inconclusive. There's not much obvious pattern in the results. Maybe Ragg987's data shows that an unusually bright day is not likely to be followed by another such day but there are few enough of those that it's not really conclusive. Still, a negative result is still a result.

 

Mildly interesting: Steamy's data doesn't much go below 0.2 times the average whereas Ragg987's is close to zero quite often. I'd assume that's because the inverter doesn't bother to turn on until there's sufficient solar radiation to at least cover its own power consumption plus enough for a small about of actual generation whereas a solar energy monitor would sum all the light in the day, however low level.

solar-correlation.py.txt

[SteamyTea]

Quite interesting as @ragg987 is pretty central in the England landmass, and has a large plain to the west.

I am quite the opposite, surrounded by sea and a large ridge that splits West Cornwall quite nicely between North and South. Perranporth is on the North side.

When I get home I shall have a look at the proportion of sunny and rainy days. From that it should be able to get an idea of standard error.

If the error is close to the standard deviation, then we can say there is no correlation.

I may normalise my data to see if it makes it clearer.

Bugger that work gets in the way, it ruins free thinking.

Edited September 13, 2019 by SteamyTea

[ragg987]

Most of that went above my pay grade.

4 hours ago, Ed Davies said:

so I just plot graphs and if something's not obvious from those I leave it to others

Damn, I've been outed,  that was my approach, the "others" being you! Except my plots are limited by my skills in Excel.

[Jeremy Harris]

On 12/09/2019 at 08:24, JSHarris said:

 

 

Just a very dull day, first one for ages where we've exported nothing at all.  We generated around 5.5 kWh in total, so some went to heat hot water, but not a lot, as the house tends to use around 300W or so.

 

 

And, by way of contrast, today we've generated 32.8 kWh, and we're still generating ~150 W.  Just goes to show how variable PV generation can be from day to day.

[SteamyTea]

3 hours ago, JSHarris said:

And, by way of contrast, today we've generated 32.8 kWh, and we're still generating ~150 W.  Just goes to show how variable PV generation can be from day to day

Quite fun to look at days with similar hours of daylight.  Then look at the temperatures and outputs.

[SteamyTea]

Right, I stayed up late (for me) and got up as normal, and looked at this problem a bit more.

If we are trying to see what sort of difference there is between days and if a sunny day can 'influence' the next day, then the answer down here in Cornwall, is no.

Only 21.5% of the time are the conditions matched (by my criteria, the no rain days), which is close to my earlier statement that tomorrows weather will be within 20% of today's.  Not really.

The average difference in solar power is 5.2%.

There are 42.5% days that are sunnier than the day before, and 57.5% when it is not as sunny.

I normalised the data to reduce the influence of seasons.

 

18 hours ago, Ed Davies said:

Still, a negative result is still a result.

Interesting that we ended up in the same place, eventhough we used different methods. I would call that a good result.

 

Because of the rough difference of 40% (more sunny) to 60% (less sunny), this may be why we remember a few good sunny days in a row, they are not normal. The absence of normal.

 

In the past, I looked at the influence of wind direction, I seem to remember that was a better indicator of solar power, and temperature.

 

Edited September 14, 2019 by SteamyTea

[ragg987]

That makes sense.

 

Looking at it another way, if there was a positive correlation then, over time, it would get sunnier and sunnier until we were all blinded. Sunshine

 

Or is that what global warming is all about?

[SteamyTea]

54 minutes ago, ragg987 said:

Or is that what global warming is all about?

Don't tell Trump, he will blame it all on the Rising Sun.

 

 

[Ed Davies]

1 hour ago, ragg987 said:

Looking at it another way, if there was a positive correlation then, over time, it would get sunnier and sunnier until we were all blinded.

 

No, that's not what a positive correlation means. There's clearly a positive correlation on a minute-by-minute basis: if it's sunny now it's more likely than not to be sunny a minute later and vice-versa. It could change dramatically in that minute but for most minutes it doesn't; even in England the weather's not that random. Still, it's equally likely to be a tiny bit more sunny or a tiny bit less sunny; just because it's equally likely to be a bit less sunny doesn't mean there isn't a positive correlation.

 

12 hours or 6 months out there will be a negative correlation in the sense that if all you know is that it's sunny somewhere (you don't know where or at what time of day) and somebody asked you to bet on whether it'll be more sunny or less sunny in 12 hour's time or 6 month's time you'd be better off betting it'll be less sunny. OK,  if it's just past dawn on a long summer day then it'll be more likely to be sunnier in 12 hour's time but taking the solar radiation time series overall there will be a negative correlation at 12-hour intervals.

Edited September 14, 2019 by Ed Davies

[ragg987]

8 minutes ago, Ed Davies said:

Still, it's equally likely to be a tiny bit more sunny or a tiny bit less sunny; just because it's equally likely to be a bit less sunny doesn't mean there isn't a positive correlation.

Yes you are right. I read it as getting sunnier.

[SteamyTea]

23 minutes ago, ragg987 said:

I read it as getting sunnier.

Sunnier is an odd term, especially in the UK.

We can mean sunnier compared to yesterday, sunnier because the sun is high in the sky, or not cloudy.

When looking at power generation, we could mean just longer hours of daylight, or very powerful daylight.

Why we use terms like radiation, irradiance, insolation, but much easier to stick to power and energy, as that is really what we are interested in. 

[scottishjohn]

as we are a maritime climate whilst it will get wamrer it cold mean more rain as more evaporation over the atlantic means more cluds +rain 

 but ambient temp will be higher --not that it may be less rain

all depends on where the jet stream goes 

Edited September 14, 2019 by scottishjohn

[SteamyTea]

12 minutes ago, scottishjohn said:

as we are a maritime climate whilst it will get wamrer it cold mean more rain as more evaporation over the atlantic means more cluds +rain 

I am hoping that it pushed north, may get a decent August then.

 

[ProDave]

 

36 minutes ago, scottishjohn said:

as we are a maritime climate whilst it will get wamrer it cold mean more rain as more evaporation over the atlantic means more cluds +rain 

 but ambient temp will be higher --not that it may be less rain

all depends on where the jet stream goes 

I wish the jet stream would bugger off somewhere else.  I was supposed to be sailing today

 

[SteamyTea]

This is the wind for Newquay.

 

[Sandybay]

Hi,

Had never heard of a Sunamp before, watched a YouTube video, looks very good, I am hoping to build a well insulated ICF next year,was planning an air source heat pump to run under floor and hot water system, would a Sunamp do the same job and do away with hot water storage tank?  I would like to fit solar panels, but would  Sunamp cost more to run in the winter than asap? 

Would appreciate any advice, 

Thanks Alexander. 

[Jeremy Harris]

13 minutes ago, Sandybay said:

Hi,

Had never heard of a Sunamp before, watched a YouTube video, looks very good, I am hoping to build a well insulated ICF next year,was planning an air source heat pump to run under floor and hot water system, would a Sunamp do the same job and do away with hot water storage tank?  I would like to fit solar panels, but would  Sunamp cost more to run in the winter than asap? 

Would appreciate any advice, 

Thanks Alexander. 

 

The Sunamp is just a heat storage device, so it needs a heat source of some kind.  An ASHP is a challenging way to heat one, as ASHPs don't normally perform well at the high charge temperature a Sunamp needs (~65°C).  A Sunamp is a very efficient thermal store, though, much more so than a tank of water, and more compact for a given heat storage capacity.

 

We use a Sunamp heated with its own internal electric heating element to provide our hot water.  It works well, and can be charged up either from off-peak electricity or from excess generation from our solar panels.  The running cost for getting hot water this way is pretty low, as more than two thirds of the year the Sunamp is heated for free and the rest of the time it's heated with electricity at a bit over 8p/kWh.

 

You can heat a Sunamp from boiler (gas or oil only, I believe), too.

 

We have a small ASHP but use that really just for heating and cooling the ground floor of the house.

[Sandybay]

Hi, 

Thanks for the reply, so I see the Sunamp needs a heat input, but has its own element of sorts which a solar panel or mains  electricity would run?

I wonder  how it's running costs would compare to an ASHP? 

[SteamyTea]

8 minutes ago, Sandybay said:

I wonder  how it's running costs would compare to an ASHP? 

The SunAmp does not loose too much energy when it is charged, so the running costs are just a little less than parity i.e 1 kWh in, 1 kWh out.

An ASHP runs above parity, usually somewhere between 2.5 and 4.  So 1 kWh in, about 3 kWh out.

The limiting factors of an ASHP is that they tend to get the high coefficient of performance at lower output temperatures.  So limiting the output temperature to 40°C improves the CoP.

This means that a larger storage cylinder is needed, a larger cylinder can mean larger losses, but good insulation will counteract this.

Edited September 14, 2019 by SteamyTea

[Jeremy Harris]

13 minutes ago, Sandybay said:

Hi, 

Thanks for the reply, so I see the Sunamp needs a heat input, but has its own element of sorts which a solar panel or mains  electricity would run?

I wonder  how it's running costs would compare to an ASHP? 

 

 

The basic Sunamp is just a thermal store, like a hot water cylinder, that can be heated by either a boiler or their version of an immersion heater, depending on the model.  The version we have has the internal immersion heater, so is just like a water-filled thermal store with an immersion heater, but is smaller for a given heat capacity and more efficient, as the heat losses are a lot lower.

 

Heating water using a Sunamp with an electric heating element is very slightly cheaper than heating a water filled thermal store with an electric heating element, because of the lower losses.

 

An ASHP is a whole different matter, as the inability of most ASHPs to produce really hot water (about 50°C is as high as most will go) means that the hot water storage capacity needs to be greater (as there will be much less cold water mixing to get to a comfortable temperature for use).  This makes any comparison between the two pretty challenging.  Very roughly, a 9 kWh (10 kWh max) capacity Sunamp is about the same as a 210 litre hot water cylinder that's set to work at about 65°C.  Because a hot water cylinder running from an ASHP will be running a bit cooler, it needs to be larger in capacity to give the same amount of hot water, probably aroun 250 to 300 litres.

 

An ASHP providing hot water at about 50°C may run with a COP of about 2.5, so every kWh of hot water will use about 0.4 kWh of electricity, plus a bit for tank loss, so maybe 0.5 kWh of electricity.  However, you cannot run an ASHP with excess generation from solar panels, so you don't have the advantage of getting a fair bit of free hot water for a fair bit of the year.

[SteamyTea]

7 minutes ago, JSHarris said:

However, you cannot run an ASHP with excess generation from solar panels

PV can contribute to the running of the ASHP if timed right.

What it cannot do is quickly switch on and off.

[Jeremy Harris]

Just now, SteamyTea said:

PV can contribute to the running of the ASHP if timed right.

What it cannot do is quickly switch on and off.

 

 

True, and the real issue is that the ASHP varies the amount of power it draws pretty much all the time, and that cannot be synchronised to times when the PV system is generating an excess.

 

It's dead easy to get an immersion heater, or other resistance heater, to just absorb any amount of excess PV generation, up to it's maximum rating.  Makes resistance heating a great deal easier to interface with a solar system.