What sort of savings can I expect from a solar hot water system?
This is a hard one to answer as each household uses hot water differently. All that can be ever claimed is that on average, over a year you can expect solar to provide 70% – 75% of your hot water. Having said that, we have had customers who have been (falsely) accused by power companies of tampering with their power meters because their electricity consumption was so low. When doing your sums, you need to be aware that a typical New Zealand household uses about 3,500 – 4,000 kWh/year of water heating.
Is there really a big difference between different brands of solar panel?
From a solar collection efficiency point of view there is not a lot of difference between the panels of reputable manufacturers. You need to be looking at other things such as longevity, street appeal, on-going maintenance costs, equipment price, ease of installation, cost of installation and warranty before you start looking too hard at performance.
But you do need to make sure you are comparing like collector areas with like collector areas. At the end of the day, the amount of effective collection area you have is what really matters. Take a look at the Consumers’ Instutute article on solar hot water heating, also available at EECA, to see the actual performance ratings of different panels. Check also how the panels perform overnight- not for collection, but for losses and for protection.
…so, why buy Thermocell?
We like to think that the street apeal of our panels is second to none (indeed, trying to find photographs of our in-roof panels that look like panels and not just skylights is very hard); we don’t compromise on performance; it doesn’t get simpler (or cheaper) to install our panels, and there is no maintenance requirement.
The losses our system incurs from overnight cooling- which detracts from overall performance in cooler areas- is particularily low. A panel containing a lot of water or working fluid will take a lot more energy to warm up than a more agile system, such as ours which holds just a few litres of water.
Our own microprocessor controller and display forms the heart of our frost protection systems. Without boasting, the protection our controller provides is as good as it gets.
And we did mention that word “reputable”- we have been building and installing our solar panels for over thirty years now and we like to think we deserve our solid reputation.
Why is a pumped system better than a thermosyphon system?
Firstly, a pumped system is more efficient than a thermosyphon system for the same collector area. More importantly for New Zealand conditions, a pumped system allows for true flexibility in building layout- there are no restrictions on the solar panel and hot water cylinder configuration so that the hot water cylinder can be placed for optimum useage and the solar panels for best performance. Thermosyphon hot water cylinders are normally located on the roof and the roof structure may need to be strengthened to accommodate it (under the BIA, hot water storage greater than 300 litres needs a structural report).
What happens in winter?
In the South Island, solar panels will generally not produce a high output water temperature in winter. They will however still provide a significant contribution to your hot water heating when you consider that the cold water inlet temperature will be less than 10°C. Having said that, we have had a Christchurch customer who found that his hot water cylinder element had been accidently switched off in October, but hadn’t noticed any shortage of hot water until June the next year.
Is the Thermocell solar system frost-proof?
Yes! The standard Thermocell system is good for areas that experience mild frosts. The Thermocell controller incorporates two panel sensors, one of which is a dedicated frost detectector. Either sensor will trigger the frost protection pump routine. Where prolonged, heavy frosts are experienced we recommend a glycol circuit which can safely withstand any amount of frost. The heatpipe operation of Thermocell panels means that only a small amount of warming water needs to be circulated, unlike conventional solar panels.
Why don’t Thermocell panels have selective coatings?
Selective coatings provide improved performance under low light and low ambient temperature conditions, such as to be found in Europe and North America. Most solar collection in New Zealand is under (comparatively) strong light and relatively high ambient temperatures. Our research indicates that the extra effort rquired to add a selective coating to our absorbers is not currently warranted.
Do Thermocell panels corrode?
No! The steel collectors do not come into contact with the circulating water. The panels are phosphate treated and are not exposed to the weather. The glazing arrangement prevents rain ingress. We have had panels installed in the Cook Islands alongside several of our competitors for many years now and we are advised that ours are the only panels that have not rusted. The cases are available in galvanised or power coated.
What is the life of a Thermocell solar system?
We design and test each panel so that it will be as good in 20 years time as the day it leaves the factory. Having said that, panels that were installed in the early 1980’s are still working just fine.
Can Thermocell panels be used in a thermosyphon system?
No. The serpentine water-way we use is not suitable for thermosyphon operation.
Can Thermocell panels be used in mains or high pressure water systems?
Yes! Thermocell panels have a unique serpentine waterway which can withstand mains pressure and then some… mains pressure systems operate with a 50 metre head and our panels can withstand in excess of 150 metres of head.
Will I run out of hot water?
You are less likely to run out of hot water with a Thermocell solar hot water system than you are with a conventional (i.e. non-solar heated) hot water cylinder. The hot water cylinder and controller designs mean that there is always a reservoir of hot water waiting to be drawn off in the hot water cylinder. Should there have been insufficient sunshine to heat the water to a useable temperature, the electrical heating arrangement will automatically “top up” the temperature.
Are all solar hot water cylinders the same?
You want to make sure that your hot water cylinder is designed for New Zealand conditions. A hot water cylinder optimised for much warmer Australian conditions will have a much higher overnight heat loss than an A-Grade Watermark hot water cylinder designed for our cooler climate. This is especially true if you are going to sit your hot water cylinder on your roof, or in your roof space.
Do I lose performance by going to a glycol loop system?
Sadly, yes… any liquid/metal/liquid interface introduces thermal resistance. As going to a glycol loop will cost you between 5-10% of your annual performance, this can be offset by an increase in installed panel area and in warmer climates you don’t need a glycol system.
Is glycol safe?
While we don’t recommend drinking it, propylene glycol is safe for humans. Indeed, some years ago a number of European wine manufacturers used to add it to their wine to provide extra flavour. We use glycol loop systems only for New Zealand’s coldest regions and when we tasted it, we thought it rather pleasant! Ethylene glycol as used in automobiles is toxic and should not be used.
Can I run underfloor heating from my solar system?
But why?! There is a very good reason why it is cold in winter and it is directly linked the the amount of sunshine you get (or rather, don’t get) then. Such arrangements will give you hot floors in summer and won’t do much in winter. A simpler and much cheaper way to achieve a better result is to install some skylights of the same area as your panels and let the sun shine onto the floor directly.