thinking about getting solar panals

hi all,

I am currently building a house in the cork area and i am looking to install solar tubes. I was wondering if people could please pm me with details of companies that ye have used and were very happy with. I am looking to the entire system including the hot water tank, which is preferable glass lined or stainless steel.

Thanks

PM's sent.

In a heat pipe system, there is no transfer of liquid between the tube and the rest of the solar thermal system. The water/antifreeze mix circulates through the the system (cylinder coil/pump/pipework) and through the solar manifold on the roof. The heat pipes fit into sealed pockets in the manifold to transfer heat from the evacuated tubes to the water/antifreeze mix and onto the hot water cylinder. This is often known as a 'dry' connection.

In the direct flow systems, the water/antifreeze mix flows to the manifold where each tube is individually connected to two separate pipes, a flow and a return. The water/antifreeze mix flows down through a U pipe in each tube, heating as it's going, back up to the manifold and continues on to the cylinder. Call this a wet connection.

To me, the dry connection (heat pipe) system has a number of advantages over the wet connection (direct flow/U pipe):

1. More reliable as there are less connections to fail. In an example of a 20-tube panel, the dry system has only 2 plumbing connections to make (and potentially leak), 1 in and 1 out. On a 20 tube wet system, there are 42 connections, 1 in and 1 out plus 2 connections per tube. Each connection is a potential weak point or source of leakage.
2. Easier to install: With a dry system, the manifold and frame are usually assembled on the ground, installed on the roof, filled and pressure tested before any tubes are added. This makes it easier to manage on a roof and also safer to work on in my opinion. There's also the added benefit of being able to work on this type of system on the hottest days without having to worry about getting burnt or the system overheating before the installation is complete. The panels for the direct system are usually supplied pre-assembled making them more like flat plates when it comes to installation.
3. More robust: There is always a possibility of damage. If a wet system is damaged and a single U pipe fractured, then the water/antifreeze mix will leak out and the system will not work at all until fully repaired. If it is left in this state for a period of time, there is a chance that more damage could be done by repeated overheating of the panel due to the lack of any fluid in the manifold. As the dry system has no direct connection with the water/antifreeze mix, breaking a heat pipe tube should not cause the system to leak and drain itself onto your roof. The system will continue to operate but just lacking the input from that broken tube.
4. Easier to maintain and repair: To replace a single damaged tube on a dry system is a quick and simple job. Remove offending tube from manifold, replace with new one. With the direct system, the entire system must be drained down (if it hasn't already leaked), the tube disconnected from the flow and return pipes in the manifold, new tube connected and entire system flushed, vented and repressurised.

Of course there has to be an advantage of a direct system and that is often performance. Depending on the brands of direct and heat pipe, direct systems may give a slightly higher performance and quicker reaction time to short spells of sunshine.

There is also the possibility that you are talking about an indirect vs. direct system but I'm not going there at the moment other than to say avoid a direct system!

BoozyBabe wrote: »

But, my thoughts on that is it'd take an awful lot of immersion heated baths or showers before the solar would begin to pay for itself!

I checked this myself before ruling out a solar hot water installation and came up with a back of the envelope calculation that compared with heating water by electricity, in my family of 2 adults & 3 young children, it would take about 25 years for a solar system to pay for itself (and this is after allowing for the SEI grant). Compared with hot water from a wood pellet boiler, payback was more like 35 to 40 years - and this on a system with a design life of 20 years.

My calculations are confirmed by this article on the Sustainability Ireland website: http://www.sustainability.ie/solararticle.pdf

In Ireland it currently costs €5-8000 to have a domestic solar heating system installed. This seems extraordinarily bad value for money. At current oil prices and typically boiler efficiencies, it will cost under €400 per annum to provide domestic hot water for a family of four. Of this, the solar fraction (the proportion of total hot water provided by the solar heating system) may be as
little as 15-20%. In such cases, the value of the solar hot water may be no more than €60 per annum. A detailed assessment of solar water heating by Seamus Hoyne on behalf of the Tipperary Institute estimated the payback on a solar thermal system as 40 years! (see www.ilsu.ie/documents/SemRE/SHSolar.pdf)

I know there are environmental reasons for considering solar hot water, but there are other renewable energy sources, such as wood, and from an economic standpoint, solar hot water makes no sense at all. You should make sure that you have looked at every other way of improving your home's energy efficiency before putting money into a solar system.

quentingargan wrote: »

labour costs are on the way down, and I reckon you should be able to get a modest system installed for about €4K

You could also buy an awful lot of insulation for four grand and the cheapest, most environmentally friendly energy is the energy you don't use as a result of having proper insulation. I stand by my opinion that unless one has an unlimited budget, a solar hot water system is the very last thing to go on the energy efficiency shopping list. I take the point you made in another thread that its easier to justify in a new build, when some system has to go in anyway and you're only looking at the marginal cost of adding the solar components. On the other hand, there's no grant for that . . . .

quentingargan wrote: »

Your system will be displacing your most expensive hot water. In the winter time, your central heating heats the water on its way to the radiator at a cost of between 4c and 7c per KwHr depending on boiler efficiency. During the summer, when the heating is off, your hot water is probalby costing you twice that. So although your solar fraction is about 60%, this is displacing virtually all of your more expensive summer fraction. I reckon the savings are about €300 to €350 a year for most houses.

Can you clarify your assumptions for annual domestic hot water energy use and calculations for solar energy savings? This Canadian Greenpeace website, using figures it says are originally sourced from the OECD reckons that on average, domestic hot water uses 3,200 kWh annually using electricity, or 3,800 kWh using oil. I don't imagine we use substantially more or less hot water than the Canadians, but I could be wrong . . .

http://www.greenpeace.org/international/campaigns/climate-change/take_action/your-energy

It would cost about €600 p.a. for 3,200 kWh of standard tariff electricity or about €315 if using night rate electricity. (If you used night rate, you could also save money by running appliances like washing machines, dishwashers and tumble dryers at night.) If I use your assumptions above to guesstimate an average cost per kWh of 10.5c for oil, the 3,800 kWh would cost about €400. I find it very hard to believe one could make savings anywhere near €350 on those sorts of costs.

[CJH: tks for comments re SHW in dish/clothes washers. it helps in prompting the current move re using a higher volume solar water tank and storing more water at a lower temperature and then using an inline booster, such as a combi boiler, to heat the water to the required temperature when needed. The solar panels will work better as the delta t between input and output water will be greater for longer periods of the day. The heat loss from the SHW tank will also be less. For existing systems who want to link the SHW into dish/clothes there are thermosatic mixer valves available ]

In relation to thermosyphon solar systems, they are supposed to be more efficient so I wonder why we don't see them here: is it the absence of a pressurized water system like in most other countries. From a planning perspective, are they too ugly?

Thanks

Gizmo:

As CJHaughey has pointed out, in general it can't. Yet every analysis I've seen of energy savings from solar hot water assumes it can. This would cause me even greater doubt as to the likely real life payback period for solar HW.

What CJH has pointed out is that most machines only take cold water, that does not mean that u cant feed them with warm water from the SHW.
I have never seen a cost benefit for shw including the dish/clothes issue: can u post a link please.

Thank you for the reply and the link.

You have pointed out a number of issues which can be resolved so I will leave it at that. Thank you for 'flushing them out' so to speak:

Those who can derive benefit from your post will, those who cant, well....

I missed the dw/wm detail in the presentation: which in summary is based on a requirement of 180L/day of water at 60 degrees at a solar fraction of 30 % with a 200l tank.

I have to hand the book from which the vast amount of the material that the author has used.
He has, IMO, over simplified the calculations and has perhaps erred somewhat. However that is for another day.

For anyone interested in a detailed, easily understood discussion of the methodology, see isbn 978 1 84407 125 8 This is what the link above is heavily based on.
--

The other thing I meant to point out is your reference to water wastage which is good.

In Europe there is a move to modularizing the water using components of houses around a central store which greatly reduces the water wastage.

quentingargan wrote: »

The calculations on that slide show are over-simplified. For example the assumption is made that the hot water from the solar panel is replacing €124 worth of heating oil. If you use an oil boiler during the summer, just to heat a hot water cylinder, I doubt if the efficiency will be anywhere near 60%. You are heating a boiler, flue, pipes etc., just to heat 120L of water in a hotpress.

In the summer, because the boiler is so inefficient, many households use electric instead.

In order to be as costly as electricity, even taking into account the price cut announced yesterday, the boiler would have to be down to 33% efficiency. Also, the energy taken to heat water in summer will be less, as the cold water feed will be at a much higher temperature than in winter. This will surely offset the reduced boiler efficiency or higher cost of water heating with electricity to a significant extent. For example, in summer I turn down the power on my Triton electric shower to less than half that needed in winter, because the cold water feed is that much warmer.

quentingargan wrote: »

Secondly, about half the cost of a solar installation is replacing the cylinder - usully an old copper one with the lagging jacket hanging off it. This isn't comparing like with like.

You're right, it's not! :) You'd only need a €2,000 hot water cylinder if you were installing a solar HW system. A new standard copper cylinder with factory installed spray on insulation would only cost about €500 including fitting. A new lagging jacket would be about €25 and cost nothing to fit . . .

quentingargan wrote: »

I've had solar for years, and we fill the washing machine with a hose from the hot tap. It reduces the electricity required to wash the clothes by about 60%.

We are talking about the cost effectiveness of retrofitting solar HW in an existing house. I, like everyone else I know and I'm sure like 99.9% of the readers of this thread, have my dishwasher and clothes washer permanently plumbed in, so even if I wanted to, I couldn't do this. It's fair to say that for almost all existing houses, if they have a dishwasher, it is unfeasible to replace any of the ca. 20% of domestic HW used for dishwashing and clothes washing with solar and attempting to do so will actually waste energy. This is exactly why these machines are nowadays almost all supplied with cold water only inlets.

quentingargan wrote: »

The cost of an install around me is down to about €4,000. Knock of €1k for the grant, and you are well below the €5K suggested in that link.

If I'm not mistaken, the suggestion on that slide show is that you will get 2.6 sq m of tubes for your €5K. That would be a lot closer to 4 Sq m on systems I see quoted.

He was pricing for 4m2 and in fairness, the SEI website suggests that prices would be in the range €800 to €1,300 per sq mtr. So, both your prices are in the SEI's ballpark.

quentingargan wrote: »

I have to laugh at people promising a five year payback, but solar panels are not a 40 year payback. A good installation will save the householder about €300 per year, and if they system is €4k less a grant, you are into a 10 year payback time. That's twice bank interest at todays rate.

OK, from figures on this thread and elsewhere, I understand the average annual energy use for domestic hot water is 3,500 to 4,000kWh. If I understood you correctly, at best, one could expect to replace 60% of this with solar. If one excludes dishwashing and clothes washing, this is more like 50%, or 1,750 to 2,000kWh. It seems to me the only way one could achieve savings close to the €300 to €350 you suggest would be if all water heating all year round was done using standard rate electricity, which is the most costly way possible. If, for example, one used night rate electricity, savings would be less than €180 p.a., or a 17 year payback. And this assumes a good, well installed system with optimal operating conditions bought for a relatively low price.

There are also grants for a wide range of other energy efficiency measures, such as wood pellet boilers, ground and air source heat pumps, heating control systems, insulation, etc, etc.