Solar Energy Data .

[mtpipe]

I`ve been collecting data from our solar panels over the duration of 10 years. These are the Evacuated tubes, on a 38 degree south facing roof line, comprising 32 tubes, (Schott), or 16 tubes x 2 panels. This set up heats our water for bathing.
These figures are hours of sunlight activating the controller, so they are based on the average amount of hours worked for each month , (all based over 10 years) starting with January. Figures in hours per month.
Jan:42.5, Feb:75, Mar:150, Ap:211, May:230, J:243, Jl:260, Aug:229, Sep:180, Oc:111.5, Nov:56.6, Dec 35.4 Since living at this house, family of 3, average consumption, (ie no olympic sized baths etc) we used to use around 1200 litres of heating oil per year, this was before putting in the solar panels. Since installing the panels and linking it in with the hot water tank we dropped the consumption of oil per year to between 350 to 400litres . A huge saving.
Incidentaly the cost of all the solar equipment all those years ago was £1500. That was the 2 panels,controller,pipework,pump,sensors, bladder and flow gauge. I hate to think how much it would cost now. Installation was nil as a plumber mate and me did that bit. Its not difficult, just took me months to get my head round its benefits.
In my next thread in due course, I will let you know of my rainwater havesting savings.
I hope you have found this of interest , Mike.

 

[efficiencyman]

Well interested Mike, thanks for the post. I did a similar install on my house 24 years ago, I only paid £1700 all in (including extra storage cylinder), paid for itself about 4 times over I reckon. 20 Thermomax evacuated tubes are still performing well, ( now that all 4 offspring have flown the nest, we have loads of DHW ) when there`s a few hours of sun. We can take longer showers for free most of the year, common sense if you ask me ! With energy prices rising year on year, may be more systems will be hybrid in the future, common sense ! NO question.
PS fitted a 15 Kw Heat Pump 15 months ago think the pay back will take a little longer !

 

[Jimbob]

Did the exact same. We're on oil and got the kit for £1500, so easily pays back. Can't compare fuel costs as haven't lived here long enough to know but there is definitely a saving and some days in summer the boiler doesn't even fire.

 

[Worcester]

Would be about 5k today for a 30 tube system with new unvented cylinder ... (got another one to do next week, and another in 2 weeks time..) - Our customers qualify for the DRHI payments though, so they get it back

You're monthly proportions are almost spot on what we would predict, here's the comparison:

Month	Yours	PVGIS Prediction
Jan	2.33%	2.04%
Feb	4.11%	3.71%
Mar	8.22%	7.87%
Ap	11.57%	11.96%
May	12.61%	14.69%
Jun	13.32%	14.94%
Jul	14.25%	14.57%
Aug	12.55%	11.96%
Sep	9.87%	8.74%
Oc	6.11%	5.29%
Nov	3.10%	2.57%
Dec	1.94%	1.65%
Total	100.00%	100.00%

Not knowing your collector size and aperture, I can't tell you what we would predict in kWh though

 

[chris watkins]

What cylinders did you install guys ? trying to remember how long twin coils (un-venteds) have been around for or were they all pre-heats ?
How have you got the auxiliary heating times set up for ?

thanks CW

 

[Jimbob]

I used the gledhill solar cylinder - 250ltr. But I don't worry about the boiler timing so much because the solar coil has a dedicated volume which is often big enough.

 

[Worcester]

I used the gledhill solar cylinder - 250ltr. But I don't worry about the boiler timing so much because the solar coil has a dedicated volume which is often big enough.

Even with a 'dedicated volume' boiler timing and settings are critical to get the best use out of the available solar power, else it just heats up it's 'dedicated volume' and then goes to waste, as the boiler effectively overides it, as it may not even get the chance to preheat the water before the boiler jumps in. (p.s. my degree included 3 years of study of thermodynamics..)

As you said "some days in summer the boiler doesn't even fire", - ours NEVER fires up for hot water between May and September

 

[Jimbob]

How would you suggest controlling it? We have a big family so cylinder is never satisfied so can't see how it would make much difference in our case

 

[Worcester]

It aint simple, as you need to be monitoring the temperature of the cylinder in more than one place, and have variable temperature settings at various times of the day on the DHW clyinder for the boiler to work to - effectively you need to control the DHW like any zone in the house, matching demand with supplies, so you need to know your usage profile and then match the supplies (solar / boiler) to that, hence why integrated control systems cost a bob or two. It should really be one control system not two.

 

[chris watkins]

It aint simple, as you need to be monitoring the temperature of the cylinder in more than one place, and have variable temperature settings at various times of the day on the DHW clyinder for the boiler to work to - effectively you need to control the DHW like any zone in the house, matching demand with supplies, so you need to know your usage profile and then match the supplies (solar / boiler) to that, hence why integrated control systems cost a bob or two. It should really be one control system not two.

What / whose integrated controls do you use?
Isn't it just as simple as not turning the auxiliary heat source on until the sun goes down? (or at least at the end of the day)

 

[mtpipe]

The Solar controller has 3 sensors. One on the outlet of the solar panels, (the hottest part of the tube once its been heated by the sun), two in the HWT, top and bottom. These 3 sensors "talk "to each other via Deltasol 2 controller,, and there are peramiters to set , so that when the panel sensor is 10 degrees hotter than one of the tank sensors, (sorry cant remember which one),the circulating pump clicks in delivering the heated glycol to heat the coil, thus the water in the tank. Then at the end of the day when say the glycol water is at say 72 degrees c and the tank is reading 5 degrees less, the pump will shut off.
Its very important to get these perameters correct and set up or you can end up with extracting heat out of the HWC back into the panels. Mike

 

[Jimbob]

I think Worcester is talking about a control system similar to what I fit with biomass. Probes that monitor the cylinders stratification and calculates its 'charge'. But never seen this as a stand alone unit, and it's never going to be worth it.

On solar thermal system I install, I just speak to the customer on what they want from it. Some want to squeeze every last drop from it but then there's the risk of delayed hot water or none if conditions aren't great. I prefer to leave it doing its thing with the delta t controller and it's dedicated volume in the cylinder.

 

[Worcester]

Yep the problem is squeezing the maximum out of the solar, and still ensuring the client has water when they need it.

We do Solar Thermal, Air and Ground Source Heat Pumps, Biomass, Solar PV, and also renewables / oil / lpg in hybrid systems, so are used to putting comprehensive control systems in place, and stratified buffer tanks are common in our installations, - usually with 3 (or more) temperature probes to monitor 'charge' of the tank, we have yet to find a client that isn't prepared to pay for that extra bit of control sophistication, however as I've said before we have yet to be even asked to quote for anything on a semi detached property, that's the nature of our clients.

The Deltasols are good units (we fit them - got one going in to my mum's place next week), and if you go up the price scale a bit (BS plus and above), they can also provide controllers with boiler interlock, stratified charging etc, though frequently installed Germany, I have yet to come across many UK installers that understand the benefits / reasons for specifying them, let alone install them. -

Me, I just like to squeeze every once of free / renewable energy out of a system hence getting the maximum efficiency out of a system before resorting to carbon based fuels.

An example of 'standard practice' that we find.. called in to out local plumbers merchant the other day and since biomass boiler in garage and household c/h pump and zone valves in the (unheated) utiltity, I needed insulation for the pipework to cope to meet the Part L requirements, yet they said the had NEVER been asked for insulation by thickness, and so never stocked anything thicker than 19mm...., so I then asked for the insulation values of the material they supplied, no idea.. Yet B&Q round the corner stocked 25mm (15 &22) and have the insulation / heat loss value displayed, apparently they've only ever been asked for it by pipe diameter.....

 

[mtpipe]

Renewable energy is brilliant, BUT, generally the installers, and self installers, (anoraks like me),understand that you have to work with the system. By that I mean, that there is no good running a very large hot bath at around 1 pm, (whilst the solar is doing its bit to heat up the mass of hot water,) only to expect there to be a nice quantity of hot water later on in the day, generally it just wont happen, this is generally when the disappointment sets in.
To ask `Joe Customer ` to alter a habit of a lifetime, may be a hard one but thats how it is.
So if you have had a sunny day, have the bath in the evening/early morning.
I guess that some installers have heard of this , and I guess it applies to rain water harvesting in a different way; if we have had a drought, there wont be much water in the tank!

 

[Worcester]

Renewable energy is brilliant, BUT, generally the installers, and self installers, (anoraks like me),understand that you have to work with the system. By that I mean, that there is no good running a very large hot bath at around 1 pm, (whilst the solar is doing its bit to heat up the mass of hot water,) only to expect there to be a nice quantity of hot water later on in the day, generally it just wont happen, this is generally when the disappointment sets in.
To ask `Joe Customer ` to alter a habit of a lifetime, may be a hard one but thats how it is.
So if you have had a sunny day, have the bath in the evening/early morning.
I guess that some installers have heard of this , and I guess it applies to rain water harvesting in a different way; if we have had a drought, there wont be much water in the tank!

We ALWAYS explain to our customers how it works / the benefits they'll get, and the impact it will have as well as the limitations / drawbacks. Those that listen buy from us... Those that don't go for the sweetest salesman..