East/West facing roof - any point in solar panels

Filikin

Hi, in an attempt to cut down on a €2,800 annual energy bill, I am in the process of putting in an oil condensing boiler and I was thinking about also putting in solar panels. Since €720 of this is just for an electric shower, my thought is to get a cheaper way to heat the water. so the condensing boiler will be on during the summer just to heat water - hence the idea of solar panels. But my roof faces East/West - does this rule out solar panels?

ccsolar

Hi Filikin
You can still fit the solar panels on your roof, you would be fitting half of your solar collector on the east side of the roof to catch the morning sun and the second solar collector would be fitted on the west side for the afternoon sun.
In the morning the east facing solar panel would heat the water, and the west facing solar panel would work in the afternoon.

What angle is the pitch on your roof as this also has to be considered?

CC

Filikin

the roof is very shallow - I would guess 25 to 30 deg

heinbloed

At this angle you won't get much to cover the DHW consumption. Have you thought about fascade mounted ST collectors on the south side - if possible?

It can be technically done as proposed (East-West at 25-30 degrees), however, but the initial investment plus maintenance can hardly be justified. Neither in monetarian nor ecological units.

ccsolar

Hi Filikin
As Heinbloed has pointed out, you could also mount the solar panels on the gable end of your house.

CC

Hi, I am in the same position as you. A recent self-build show I went to had thermodynamic panels on show. they are more expensive but they are the better option for me to get DHW.

I cant remeber the name of the company but I remeber the panels. I'll PM you the name of them, yo9u can google some suppliers

saibhne

Hi Filikin,
East West systems are very common and work quite well. Your roof pitch of 25 - 30 degrees isn't optimum but is ok. You will be losing 5 - 10% efficiency from optimum according to CIBSE. However this can be factored in to the design of the system and compensated for easily.

One thing to note is that East West systems are a little more costly than standard south facing systems as you require more panels and some extra equipment. Increasing the size of the array can sometimes be covered by the Greener Homes grant from SEAI so this does not have to be a big cost factor.

I'd recommend getting a site survey done before making your mind up as there are always options. Site surveys are usally free.. PM me if you need assistance with this.

Davegalway wrote: »

Hi, I am in the same position as you. A recent self-build show I went to had thermodynamic panels on show. they are more expensive but they are the better option for me to get DHW.

I cant remeber the name of the company but I remeber the panels. I'll PM you the name of them, yo9u can google some suppliers

Be wary of these panels, check out the threads below. They are basically a heat pump installed on your roof.

http://www.boards.ie/vbulletin/showthread.php?t=2055699634

http://www.boards.ie/vbulletin/showthread.php?t=2055918952

Filikin

thanks, yes I had noted the cost of running the heat pump. I saw the panels at the SEI show and wasn't impressed.

PeteHeat

Hi,

When looking at summer use it can be best value to fit the panel on the west side as we have the sun for the long summer evenings so you can collect heat from about 1 pm to 9.30 pm depending on your location.

It is also possible to fit the system in two stages, do west facing first then fit the east facing at a later stage.

A lot depends on the amount of hot water you use in your home, number of people, size of cylinder etc.

The low angle can be increased using a good mounting bracket however the average improvement would be around 10%.

.

soldsold

Assuming due east/ west roof with a 35 degree pitch and no shadowing on the roof (house is in offaly), any estimate as to the effectiveness during spring/ late autumn of a 6m2 vacuum panel solar system with 3m2 on each side of the roof?

Thanks for any opinions/ wild guesses as to what part of the year my solar heating season would start and finish...

S

saibhne

soldsold wrote: »

Assuming due east/ west roof with a 35 degree pitch and no shadowing on the roof (house is in offaly), any estimate as to the effectiveness during spring/ late autumn of a 6m2 vacuum panel solar system with 3m2 on each side of the roof?

Thanks for any opinions/ wild guesses as to what part of the year my solar heating season would start and finish...

S

Hi Sold,
Would need to know your water usage (the size of your cylinder anway) to come up with a reasonable estimate. If it was me I would size this system with a smallish cylinder - 150L approx looking to get 50% - 60% of your hot water energy requirement for the year. The bulk of this contribution will be in Summer.

S.

Mothman

PeteHeat wrote: »

Hi,

When looking at summer use it can be best value to fit the panel on the west side as we have the sun for the long summer evenings so you can collect heat from about 1 pm to 9.30 pm depending on your location.

I'm curious with the focus on west side first. In my experience of recording sunshine, there is more sunshine in morning and arguably makes up for the higher ambient temperature during the afternoon. We get more cloud in afternoon because of convection which is what produces showers

Here are the sunshine hours ignoring the hour either side of midday at my location.
Year, am, pm hours
2006 603, 538
2007 568, 539
2008 513, 469
2009 537, 513

Mothman

saibhne wrote: »

Hi Sold,
Would need to know your water usage (the size of your cylinder anway) to come up with a reasonable estimate. If it was me I would size this system with a smallish cylinder - 150L approx looking to get 50% - 60% of your hot water energy requirement for the year. The bulk of this contribution will be in Summer.

S.

Why would you size the cylinder so small, at least what I consider small.
When I was researching panels for my house (in the 90s) most systems had about 150l tank as standard. One system had 300l tank and I went for this. It means I have hot water in top half of tank, but always have bottom half for the panels to work on. I wouldn't have had the smae flexibility with a small tank.

soldsold

Just married a year so only the two of us so two showers a day, but who knows down the line, I'd like to size for 5 if possible

saibhne

Mothman wrote: »

Why would you size the cylinder so small, at least what I consider small.
When I was researching panels for my house (in the 90s) most systems had about 150l tank as standard. One system had 300l tank and I went for this. It means I have hot water in top half of tank, but always have bottom half for the panels to work on. I wouldn't have had the smae flexibility with a small tank.

The 150L cylinder size is only relative to the size of the array that is being installed as this is the only information to go on. This 3m2 East-West configuration typically gives 50 - 60 % of the annual energy requirement to heat the 150L cylinder to useable (45 degrees or so) temperatures.

If more water is required in the household and a bigger cylinder needed then the 3m2 on each roof East -West array would be too small to to provide the 50% and would likely result in the requirement for heat from another (probably fossil fuel) heat source most of the time.

Oversizing the cylinder beyond the needs of the household is commonly done however I'm not a fan of the practice as it increases cost, raw material use and water usage. My preference is to size the cylinder according to the requirements of the people in the household.

Filikin

Just had a quote for one panel on the East side of the roof. €4,300 (inc vat) with a 300l cylinder.

saibhne

soldsold wrote: »

Just married a year so only the two of us so two showers a day, but who knows down the line, I'd like to size for 5 if possible

HI Sold,

If you're looking at sizing for 5 people I would recommend a 250L-300L cylinder but the 3m2 array on the roof will spend most of the year acting as a preheat source requiring top -up from another heat source. It's not ideal but if 3m2 on each roof is all you can fit in then it's better than nothing IMO. 4- 6m2 of flat plate panel on each roof should give you the 50% + energy yield I mentioned above. I should say here that I'm assuming these are 3 m2 of flat plate panels - if you're talking evacuated tubes then it may be adequate..

PM me if you would like me to run through a few simulations of different systems for you.

Cheers,

S.

saibhne

Mothman wrote: »

I'm curious with the focus on west side first. In my experience of recording sunshine, there is more sunshine in morning and arguably makes up for the higher ambient temperature during the afternoon. We get more cloud in afternoon because of convection which is what produces showers

Here are the sunshine hours ignoring the hour either side of midday at my location.
Year, am, pm hours
2006 603, 538
2007 568, 539
2008 513, 469
2009 537, 513

That is brilliant! I have been looking for info like this for ages. Can you tell me if the radiation figures are horizontal or are they pitched at an angle?

I had heard that we experience more cloud in the early afternoon alright from your experience does this dissipate later in the afternoon?

Mothman

saibhne wrote: »

That is brilliant! I have been looking for info like this for ages. Can you tell me if the radiation figures are horizontal or are they pitched at an angle?

I had heard that we experience more cloud in the early afternoon alright from your experience does this dissipate later in the afternoon?

This is not radiation figures, but straight sunshine. Sun out record, sun in not recording.
campbell stokes recorder.
I forgot to mention that I excluded Jan, Feb, Nov & Dec from the above hour figures.
I'll have to look at the sunshine data to see about less cloud late on, but the sun is weaker at this stage

and I've just realised the PM is from yourself
I'll reply to that sometime

quentingargan

Great info here. There are two reasons for favouring west over east, but they may well be discounted by the sunshine.

1) The ambient temperature is higher in the afternoon, therefore flatplate panels will be more effective. This wouldn't apply to tubes
2) Most hot water use is at night, so hot water from a west panel is stored for a shorter time with less heat loss.

With heat pipe type vacuum tube systems, going east west doesn't require a second pump. With flatplates or direct flow systems, you do need to prevent pumping hot water through a cold panel. That's also a factor. Q

Doctor_L

We have east west panels on our dormer home. The east panels stay active until about 3pm in the summer. The west panels start to get the sun around 12.00 p.m until late in the evening. So from 12 - 3 all 4 panels are often active.


The east panels are utilised more than the west as they tend to heat the water from a lower temp in the morning. Very happy with the setup the only real extra cost is the fact that it uses 2 pumping stations so it needs a bit more space in the hotpress for the pumping stations unit.

PaleRider

The energy you use for the shower does appear to be very excessive, if say for two people. It would be no harm to try and reduce your needs, costs nothing. Are you a BB. The New Boiler is a good step. Have you installed separate zones, ie DHW / Heating. The solar panels may be installed on the wall.

quentingargan

PaleRider wrote: »

The solar panels may be installed on the wall.

It is generally reckoned that panels mounted vertically on a south-facing wall are less efficient than the same panels mounted on a west-facing roof. They are also more vulnerable to breakage, and you would require planning permission to do this.

I have also seen panels bracketed out on a south facing wall, but to be honest, the losses on a west facing roof are about 20% - 30%, depending on pitch, and it is cheaper to just put in an extra few tubes in most cases.

But you're right about reducing demand. That bit is definitely free, (but less fun!)

Filikin

thanks for all the advice.
I have given up on the solar panels for the moment, installed a condensing boiler (measured at 97.6% efficiency) and a hot water tank with the integrated insulation. Now in the process of installing the shower to use the water from the tank.
(The shower usage was for four people, five for the summer now that college is closed)
Eamon

soldsold

The last couple of days have changed my mind on east-west vs south facing solar panels. My south facing roof is slightly shaded by two gables, but this morning the snow on the south side had totally melted by early morning, and the East and West didn't melt all day.

Also the south facing roof is much lower so easier access for replacing vacuum flasks down the line.

So my conclusion has to be to put the solar panels on the south facing roof, even though its slightly shaded...?

quentingargan

soldsold wrote: »

The last couple of days have changed my mind on east-west vs south facing solar panels. My south facing roof is slightly shaded by two gables, but this morning the snow on the south side had totally melted by early morning, and the East and West didn't melt all day.

Also the south facing roof is much lower so easier access for replacing vacuum flasks down the line.

So my conclusion has to be to put the solar panels on the south facing roof, even though its slightly shaded...?

You're right to want ease of access, but the key point is that putting panels on east or west roofs will lose 20% to 30% of the output of a solar panel, depending on the roof slope. If your south roof is shaded for less than 25% of the time, it makes more sense.

Your argument about the winter sun melting snow may be the source of a useful epiphany, but may not be entirely relevant. In winter time, the sun is much lower in the sky, and gives very little heat in the morning and evening on east and west sides. It isn't quite so useless in the summer.

soldsold

Thanks for the reply Quentin.

Because my place will be airtight and very well insulated (10-12 inches of different types of insulation all around with minimal cold bridging, triple glazed 0.7 u value windows), I'm more concerned with extending the heating season than getting performance in summer, so I'm installing 6m2 of vacuum flasks.

Do you still think south facing is best? South is also the front of the house and It looks good now but a load of vacuum flasks will take from the look of the house.

quentingargan

soldsold wrote: »

Because my place will be airtight and very well insulated (10-12 inches of different types of insulation all around with minimal cold bridging, triple glazed 0.7 u value windows), I'm more concerned with extending the heating season than getting performance in summer, so I'm installing 6m2 of vacuum flasks.

Do you still think south facing is best? South is also the front of the house and It looks good now but a load of vacuum flasks will take from the look of the house.

If you want to extend the season, again, because of the lower sun in spring and autumn morning/evening, you would be better off on the south. If you pm me your geographical location, roof pitch of each roof, and an email address, I can email you back a simulation of each option (I can't post it here as an attachment because the software puts company logos on the pdf).

My guess is that you will see the east/west output more dramatically changed in spring and autumn - exactly the effect you don't want.

Over the years since we built out house, we have become less concerned about aesthetics, and more concerned about practicalities. We have a sod roof and went to a lot of trouble putting the panels in the wrong place in order not to spoil our elegant roof line, but we moved them later. But that's all a matter of taste - if there was only one correct answer, there would only be one type of panel in the world

I would go for one of the flask systems that comes with black frames and manifold rather than the shiny stainless stuff. I think in the long run, solar panels are going to become part of the vernacular in architecture, and will become less conspicuous as that happens.:)

soldsold

Thanks Quentin, PM on the way.

Steve