Pressurised system:

The vast majority of Solar Thermal systems installed in Ireland are of the pressurised variety. The solar circuit is completely filled with a heat-transfer fluid, which is then pressurised to increase its boiling point. A circulating pump drives this fluid around the solar circuit, transferring heat from the solar collector to a storage tank. An expansion vessel is fitted to damp out changes in fluid volume caused by thermal expansion throughout the day, maintaining a steady system pressure.

Safety is provided in the form of a blow-off valve on the pump station, which, in the event of a system over pressurisation, will allow some of the heat-transfer fluid to escape to a catch tank.

Click here to view a detailed schematic of that type of system.

The Problems of Pressurisation:

Pressurisation of the solar circuit comes with its own drawbacks. The most notable drawback is Stagnation. The collector is always filled with fluid, even when the system is not actively circulating.

If the system settles into stagnation on a hot day, continued heat production in the collector will raise the temperature of the heat transfer fluid to the point where it begins to boil.

This has the potential to cause the system pressure to increase, ultimately causing the system blow-off valve to activate and dump solar fluid, leading to a loss in pressure when the system cools. Sustained high temperatures can also damage system components, while accelerating wear and tear.

Stagnation mitigation solutions such a heat dump do not entirely eliminate the risk. If the heat dump has not been correctly sized to match the power output of the solar collector then the system still has the potential to overheat. If the system should lose electrical power, there will be no pump to drive the circulation of the fluid, allowing the system to stagnate anyway.

Drainback system:

A drainback solar system consists of a circulating pump, solar panels, a drainback vessel, a controller and some form of thermal store. Nothing else is required.

Drainback functions on the same basic principal as a conventional pressurised system. A circulating pump pushes water up to a solar collector on the roof, where it absorbs heat from the collector, then carries it back down to the hot water store.

The difference between drainback, and pressurised solar systems is that, when the circulating pump shuts off, heat-transfer fluid is allowed to drain under gravity from the solar panels down into a dedicated drainback storage vessel. The solar circuit is unpressurised.

This drainback vessel is mounted such that the fill level is somewhere above the level of the circulating pump, ensuring the pump never runs dry and that no air can enter the circuit. A good gravity flow is also required between the solar panels and the drainback vessel to ensure they properly drain.

Click here to view a detailed schematic of that type of system.

No overheat protection or anti-freeze is required.

The chief advantage of Drainback solar is that, when the circulating pump is not operating, the collector is dry. In summer, there is no fluid in the collector to boil. In winter, there is nothing in the collector to freeze. Thus, the system cannot enter stagnation and cannot freeze solid.

The requirement for a heat-dump and anti-freeze is eliminated, simplifying the installation. There is no longer a need for holiday recooling functions and frost-protection modes within the solar controller. The system is also passively safe – should the pump lose power, all fluid will drain from the collector to the drainback vessel as normal.

The lack of pressure minimises the potential for leaks. Pipe corrosion and seal degradation due to acidic antifreeze is eliminated, improving system reliability and robustness.

Drainback Solar is a simplified, safe, robust and reliable solution.

Currently, Greentherm are the only company in Ireland offering Drainback solar thermal systems. Geentherm systems are based around Veridian ‘Clearline’ solar panels. These are one of the few flat-plate panels that are specifically designed for the Irish climate. All Clearline panels and flashing come a BBA agreement cert, verifyingtheir suitability for use as a roofing material.

For more information on Viridian solar panels Click Here

Short answer: Yes. Solar Panels work in Ireland.

It’s that simple. There’s no catch. From April to September, Ireland receives more than enough sunshine to enable a well-designed and well-sized solar thermal system to meet your domestic hot water needs. It might not seem like it when you look out the window, but the statistics bear it out. Ireland receives between 910 and 1100 kWh of energy per meter squared, per annum from the sun, with the majority of this falling during the summer months.

What can Solar Panels really achieve in Ireland?

A well designed Solar thermal system can supply up to 60% of your annual domestic hot water needs. This energy replaces either your boiler, or an electric immersion heater. Over the winter months, Solar Panels give a lower output – but are still capable of providing some pre-heating to your hot water. The effect in winter then is similar to boiling a half-boiled kettle.

Can I heat my home with Solar Panels?

The energy output from your solar panels is at its lowest, when demand from your heating system is at its highest. For normal houses, it’s a challenge. It’s not impossible, but it may be impractical.  For passive houses, or houses that are highly airtight or insulated, it may be doable. What we can do is highly dependent on the home design and is something that needs to be discussed with us in detail.  We will advise you on what’s possible with your home and what the costs will be.

What about Stagnation?

Stagnation is a problem for Solar Panels in Ireland. Greentherm however, offer Viridian Clearline Drainback Solar Panels.  Drainback Solar systems eliminate the potential for stagnation damage by leaving the panels dry when the circulating pump is not operating. For conventional pressurised systems, a dedicated heat-dump radiator controlled by a motorised valve can be fitted.

Do I need to replace my existing hot water cylinder?

It’s up to yourself. If your cylinder already includes a solar coil as standard then it can be connected straight up. Furthermore, if your cylinder is still reasonably new and fully insulated, but doesn’t have a solar coil – or if you would simply prefer to do without the hassle of dismantling the hot-press, draining a cylinder, then refitting, we do have another option. The Viridian Pod offers an alternative that allows you to retain your existing hot water cylinder and hot-press, while still achieving an acceptable system performance. However, if your cylinder is of an older, uninsulated type, then it may be better to replace it with a 316L Stainless Cylinder which will be more efficient.

I have a heat pump/Biomass Boiler/Stove/Gas Boiler, can I install Solar.

Of course! The exact method we use however will depend on your exact system and setup. Our expertise will ensure that your Solar Panels complement the existing energy sources in your home, allowing them all to work at their best potential and efficiency to achieve the best out of your energy sources.

Why Should I go with Greentherm?

First and foremost, we at Greentherm are an Engineering company. This means that – while our competitors will sell you a one-size-fits-none product – Greentherm offer genuine solutions. We work to understand the needs and expectations of our customers, then build an integrated solution for them that meets their expectations and budget. It means we can back all our work with hard figures and show our customers how we arrived at those figures.

Contact Us for more information on Solar Panels in Ireland

Stagnation is a common problem faced by Solar Panels in Ireland.

Often, stagnation is a symptom of poor system design, or cost-cutting by an installer.

Stagnation occurs when the solar cylinder is up to its set temperature, but heat is still being collected in the solar panels. This can happen on especially sunny days, or on days when the homeowner is away on holiday and there has been no hot water drawn off from the cylinder. Once the solar cylinder is up to working temperature, the solar pump shuts down and circulation within the system is prevented. As the solar panel is still producing heat and cannot be shut off, it will heat up to the point where the solar fluid will begin to boil. Depending on the set pressure, most pressurised solar thermal systems will begin to boil at 130°C.

Steam temperatures of 180°C or more in a stagnating vacuum tube solar panel are not unheard of.

Effects of Stagnation on Solar Panels.

First and foremost, extreme temperatures accelerate wear and tear on the system. While most solar panels are rated for stagnation on paper, continuous extreme-temperature heating and cooling will stress fittings and accelerate the breakdown of any sealants. Boiling solar fluid can damage system components if it is allowed to move from the collector down to the pumpstation or tank. We’ve seen cases of pumpstation impellers being outright melted by overheated solar fluid, and expansion vessel membranes being ruptured.

When the fluid in the panel boils to steam, it expands massively, causing a pressure spike inside the sealed solar system which further stresses overheated fittings. Pressure can get high enough to open the system’s pressure relief valve, dumping solar fluid into a catch tank, and causing a loss of system pressure when the solar panel cools and boiled fluid condenses. The loss of pressure only accelerates the boiling process and makes the system more likely to blow-off in the future.

Stagnation also has the effect of accelerating the decay of solar antifreeze. Boiled propylene glycol antifreeze not only loses its effectiveness rapidly, it begins to turn acidic. Acidic antifreeze will attack system components accelerating corrosion and reducing the lifespan of your solar system. Furthermore, antifreeze that has lost its effectiveness may allow the system to freeze solid in winter, bursting pipes and fittings, leading to an expensive suprise when everything melts again.

Clear Fresh Glycol, Aged Glycol, and burnt Glycol degraded by Stagnation.

How do I prevent Stagnation on my solar panels?

There are techniques to mitigate stagnation. Some installers will undersize a system slightly, fitting a smaller solar panel or larger solar cyclinder. This ensures that the system will only stagnate in unusual circumstances. The downside of this, is that the system will require supplimentary heating more often, which has the effect of increasing your energy bills.

An alternative is to fit a heat dump to the system. A heat-dump is a secondary radiator sized to match the solar panel’s rated heat output, with a diverter valve that switches flow to the radiator automatically when the cylinder is up to temperature. It’s a good solution, but it’s also an expensive one. A heat-dump fitted to a solar system can represent an additional cost of €400-€500 on an installation.

For this reason, most installers outright ignore stagnation as a problem. By the time it begins to affect the homeowner, the system has left its statutory warranty. A solar thermal system will be a part of your home for decades to come.

The bottom line is, excessive stagnation will cost you money. Either on installation, or several years down the line due to accelerated wear and tear.

The Alternative Solution: Drainback Solar Panels from Greenthem

Drain back Solar Panels offer a much better solution. Greentherm are the national agents in Ireland for the full Viridian Clearline range of flat panel drain back solar panels.

With a Drain back solar thermal system, fluid is only present in the collector when the circulating pump is active. At all other times, fluid is allowed to flow back to a storage vessel under gravity flow, leaving the panel dry. Therefore, there is no fluid left in the panel to boil and turn to steam.

Because of this a drainback solar system does not require a heat-dump or an expansion vessel. Because the panels remain entirely dry when the system is shut down, it is safe to leave them idle over the summer. Furthermore, in Winter, because the panels remain dry, the risk of freezing is minimised. Antifreeze isn’t even required.

Clearly then, Drain back solar thermal represents the ultimate solution to stagnation questions. It’s more cost-effective to install than a heat-dump system. The system is longer lived, and more robust, and can be sized to give a higher output.

Contact us now, for sales inquiries, or more information on Drainback Solar Panels.

Solar, Simplified with the Viridian Pod:

One of the costliest and most time-consuming jobs in any solar thermal retrofit, is fitting a new solar cylinder. The old cylinder must first be removed and disposed of, with central heating and hot-water systems being disconnected, before a new cylinder is fitted, then plumbed into place. Not to mention the lost space in the Hot Press which is consumed by a large hot water tank.

The Viridian Pod is a game-changing new approach that simplifies installation work, saving you time and effort. And saving the Hot Press.

Why Pod?

The Pod acts as a preheating buffer tank, supplying the existing domestic hot water cylinder in the home. Therefore:

• Plug and Play Technology
  Compatible with both Drainback and Pressurised Solar Panels. Pump station and controller integrated into one package. No unnecessary wiring. No time consuming plumbing work. It just Works.
• Discrete space saving design
  Horizontal design. Can be fitted into any attic or crawlspace. Can be located directly beneath the panels for maximum installation convenience.

• Fewer connections required. Robustness built in.
  No need to disassemble and rebuild the existing plumbing system to fit a new solar cylinder. Reduced potential for leaks requiring repairs and costly call backs, saving time.

• Compatible with any heating system.
  Preheated water can be supplied either to an existing domestic hot water cylinder or to a combi-boiler, simplifying system design. Custom designed systems are not required.
• Greentherm Recommends Viridian Clearline Solar Panels.
  Greentherm recommends matching Viridian Clearline Solar Panels with your Pod, for maximum compatibility and ease of installation.

• Special Introductory offer.
  Call now, at 01 5314781 to avail of introductory pricing on full system kits, and individual Pod systems.

Existing Cylinder

Combi-Boiler

The Viridian Pod saves you Time.

• Time designing.
• Time installing.
• Time commissioning.
• Time on maintenance and repair.

Contact us now for sales and technical inquiries.