Posted by Mike Holm on May 1, 2010
Well, I knew the day would come. History repeats itself. The progression of solar in Canada is a tough one. It has usually been a Liberal government that sets in place some progressive rebates or support for solar thermal and it is usually a Conservative one that removes it. This has been untrue only once Federally. After much lobbying the Conservatives re-named a Liberal program, actually made it better in some ways, and just when it was getting to the point of sustainability and general acceptance, they killed it again…claiming that it was too popular. When it was killed the first time, in 2006, they told us in a meeting that it was because they did not believe in global warming and as an industry we were too small to care about. Well, times have changed some. We are a much bigger industry than we were 4 years ago and regardless of their beliefs, global warming is an accepted fact (unless you listen to oil industry paid “scientists”).
While they still don’t believe in global warming, they gave $850 million to the nebulous and ineffective program called “Carbon Capture and Storage”, while the cheaper and much more effective EcoEnergy program, which helped pave the way for 1000s of jobs retrofitting houses and buildings, not to mention solar, was plowed under.
So, in Ontario, we are left with their part of the program: $1250 for a water heater. Not enough to get anyone’s pulse racing … but probably the best program ever made just wrapped up in Toronto. The Solar Neighbourhoods project gave the 0% interest loan to anyone who wanted it. Although it was only a pilot project, it had the effect of allowing those who could not normally afford the upfront cost of installing a solar system to do so, something no other program has done before, to my knowledge. And when it was combined with the $1250 from the feds and the renovation tax credit, a perfect storm was created. One that, I fear, is never to be repeated. Unfortunately, governments don’t tend to care much for the working poor, and solar in all its forms needs upfront money so they are left out of the loop. Solar Neighbourhoods was the exception.
So we are left with the FIT and MicroFIT program, may they never die. It is a progressive a program as we have in North America at this time. Enter the PVT (PVthermal). Piggyback the thermal onto the PV panels, get a bit more electrical production from it, save some racking and installation cost, and provide for a lot more of the annual energy bill by providing for hot water.
As the rebates come and go, we must find ways to be more efficient and keep the pulse racing.
Posted by Mike Holm on March 27, 2010
PVThermal panels are not new. There has been a lot of research done on them in Europe and the US since the 1970s, but they have been a niche market. Now is the time for the system to gain some prominence.
The basics of the panel are quite simple. A heat exchanger, similar to that in a regular flat solar water heating panel, made of copper tubing and aluminum sheeting is placed behind the PV cells.
Water or glycol is piped to the panels in the same way as any hot water solar system. The solar panels in this type of system can only get to around 70-80C (158-176F). Because of this limiting factor the glycol will never boil and will therefore last a very long time, maybe 15-20 years. In a drainback system the operation is the same as in a traditional system but the installer must remember to tilt the panels to allow for the liquid to drain back. Most of the reasons for using a drainback system over a glycol system disappear because the drainback’s main advantage is to prevent liquid boiling and degrading quickly.
The main reason why the temperature cannot get as high as a standard panel is that there isn’t the insulating effect of a glass cover. In this way it is similar to a pool panel. The limiting effect of the heat loss over the PV glass keeps the temperature down.
From an electrical point of view, a PV panel can have a 20-25% reduction in efficiency when the cell temperature is at 80C. This amount of heating happens quite regularly in the hot summer. If we can reduce the temperature of the panel to 25-30C, we can expect to see an annual improvement or 10-15% in electrical output. With a standard 2kw PV system, for example, the payment under the Ontario microFIT program will be approximately $2000. Therefore with the PVThermal system we should see an extra $200-300 annually.
The hot water production is equally impressive. The average solar water heater is 5-6m2. With a 2kw PVThermal system there is 15m2 of panel area. The panel is not as efficient (per m2) as a standard panel, but there should be no shortage of hot water during the prime solar months of March to October. During the colder months, performance per m2 will be less than a standard panel but the extra surface area allows for some heat for other purposes.
One other benefit of the the PVThermal comes when snow or frost has covered the panels. Some solar controls will allow the panels to be defrosted by warm water in the storage tank which could give you electrical production when otherwise you would have to rely on the grid. More coming soon including diagrams and sizing info.
Posted by Mike Holm on
Boss Solar will be at the 2010 Toronto Green Living Show in April from the 23rd to the 25th. We will we showing the Analog Energy combination PV and hot water collector. This system takes the excess heat from the PV panel and uses it for domestic hot water or space heating. An added benefit is an increase in PV efficiency due to the reduction of the panel temperature. Expect a 10-15% increase in PV output annually.
Posted by Mike Holm on October 30, 2009
We are having a resurgence in interest in solar water heating and PV systems in North America. There are a few reasons for this. Aside for the general acknowledgment that something needs to be done about climate change, for the first time since the 80′s we have some decent subsidies from most levels of government.
In Ontario the Provincial govt matches the Feds $1250 and for a limited time the renovation tax credit is with us. This allows for a nearly 50% subsidy for the system and along with the increased publicity more people feel the deal is a good one. 20% subsidies are not enough and talk alone is not enough. The subsidies have made manufacturers and new installers believe that they should enter the market at this time. Unfortunately this also includes the usual groups of cheap vacuum tube collectors which come with a world of promises, most of which will never be met, but that is another story.
In the 70′s and 80′s, when we had our last big explosion in solar installations, the subsidies were impressive. When both Canada and the US had changes in governments in 80 and 84, those subsidies died and so too did all but a couple of manufacturers in Canada. At the time nearly all the manufacturers were Canadian and the technology was home grown as well. When we abandoned solar most government support either died or was severely cut.
Europe was somewhat different. The Germans, who had little natural resources to burn, decided that it was time to try to build an industry which now has over 100,000 people employed. Canada might have 3-4000 at this time. The techniques used in Europe mesh very well with the boilers used for heating every home. The technology is similar and the installers of boilers understand solar much better than our heating installers do (many have never soldered a pipe and only install forced air). We, as a country make choices which are much more individualistic than community oriented. This is why we can only see a short time into the future when it comes to support for technologies which don’t have very fast paybacks for the purchaser. It is also why we demand lower taxes and then complain when there is not enough money going into the educational or health care systems. We do not see very far ahead.
Since 2000 the government of Canada has decided that it will support one company, far above all others, and do so blindly. The official line is that, if you have an EcoEnergy assessment after some undisclosed time in 2010 any solar water heater installations wanting to get EcoEnergy funding must be CSA tested and approved. The heads of some of the divisions in NRCan were assured that there was a lot of option for consumers but this is not true. As of July 2009, there was only one middle of the road system flat collector system available in Ontario (there is one in Alberta) and it is the one the NRCan supported so strongly. There is also 2-3 cheap vacuum tube systems, one of which just barely managed to get the certification and in my opinion, does not deserve it.
There will be some more systems getting certification in the coming months but if all the systems currently on the list for testing are approved, it will only number 14-15 and this is not enough. The difficulty in getting a CSA approval and the time needed to do it means that any manufacturer has to be willing to wait for 3-5 years just to get to a level playing field with the other companies. Other countries do not put as many restrictions on their own industry, but we do. With the exception of these few companies, this government would rather see offshore companies (good quality or bad) get a toe hold here than build our own industry.
Boss Solar has a perfectly good, well made product with above average performance and good reliability and we strive to make as much of the product in North America as possible. This is a lot better than our most well known competitor who keeps having to change pumps on a regular basis and the company still gets the government favouritism. Anyway, I vent and that is what a blog is for……more to come.
Posted by Mike Holm on June 26, 2009
I am constantly finding companies (contractors, not manufacturers) who advertise that the tankless water heater they install will give you 7-8 gpm of hot water when heating from 10C to 50C (122F). Sorry, but this should not be believed. The amount of gas needed to give this amount of hot water is twice the input rating of most tankless heaters and is more than the gas meter outside the house will allow.
It is a simple fact that a tankless water heater with a 200 mbtu input could give 3.5-4gpm of hot water. Most tankless heaters have a lower gas input than 200 mbtu.
People who come from countries where tankless heaters are common understand intuitively how they work. They do not expect the units to supply every tap in the house at the same time. For some reason, however, we in North America seem to feel that our water heater should be able to supply all our demands at once. It is a wasteful attitude some of us have, and I applaud those who rise above it.
The amount of flow you can get is determined in large part by the gas supply and the temperature rise you desire. If you would like water that is heated only to 40C you will get a higher flow. Alternatively, if you preheat the water with solar so that it is only being raised from 30 -50C, you also will get a higher flow.
Tankless heaters also have the reputation for taking longer to get the hot water to your tap. This can be true for a lot of units. One of the problems with a normal tank (and it is partly why they are so wasteful) is that the heat from the tank rises through the output piping towards your taps even if you do not use the water. It therefore takes less time until you feel warmth coming to the tap than with a tankless heater. We sacrifice a small amount of time for gas efficiency.
The other truth about most tankless heaters is that a minimum water flow is needed to trigger the gas valve. Therefore, when you turn on the tap for only a few seconds the unit tries to come on but does not complete the process as you have finished using the water. If you need a small amount of water for hand washing, use soap and cold water. The soap will still work fine. When shaving, fill the sink rather than turning the water on and off for a few seconds at a time. The heater will last a lot longer and you will have a more satisfying shave.
Another issue is the desired temperature of the heater. Just like the tank type water, we should keep the set temperature as low as possible. This means that when a tap is turned on, there will be a higher flow through the unit and it will operate as desired sooner. Having a high temperature from the water heater forces you to mix more cold water with it at the tap and the resulting flow from the heater can be too low, causing it to turn on and off rapidly.
A few simple rules will help us get the most out of our tankless heaters.
Posted by Mike Holm on June 13, 2009
No solar system can run without an expansion tank. But many water boiler installers and engineers have no idea how to size an expansion tank for solar.
It is often believed by many engineers and contractors new to solar that an expansion tank is sized (in btu or Kw) solely to the output of the solar system. This is only one component of the equation to look at.
In a boiler system we look at the difference in temperature that the boiler runs at, typically 20-70C (70-158F) and the volume of liquid in the system. As this is a very controlled system (we can easily turn of or on the boiler), the rules of thumb are well known. A 30kw (100mbtu) boiler in most houses with a liquid volume of 80L (20gal) using floor heating or old cast iron rads, will need a #30 tank (about 8 gal) and will likely never see much change in pressure.
If we took a solar system with the same output, 30kw which is about the same as about 15 flat collectors (depending on collector size and efficiency) and used the same #30 expansion, the system would go over pressure on the first fine day and probably blow the relief valve. But the pressure relief valve should be the last line of defense for the system. (BTW… I would put a #120 tank on that one)
The first line of defense in any solar system is the expansion tank. It is there to take up whatever pressure there is in the system and keep it at an equilibrium. As the storage tank heats up, the temperatures in all parts of the system increase and the expanding liquid must go somewhere and the only place it can go is the expansion tank. When the storage tank can hold no more heat and the pump shuts of, the collectors will continue to increase in temperature until it equals the heat loss of the enclosure. In a good flat collector this will be at 200C or higher (250C+ for vacuum collectors)
So, instead of a deltaT of perhaps 60C max (20 deg nominal) for a boiler, we can have a deltaT of 160C or more if you remember that some components of the solar system can be at -30C at 2AM on January 1st and 200C+ on a hot summers day.
On the hottest days of the year and when the storage tank is full of heat and pump is off, some of the water/glycol (propylene glycol should be used……never ethylene glycol or car antifreeze) will turn to steam. No matter at what pressure this happens, the water in the mixture will expand hundreds of times its volume and push the rest of the liquid out of the collector and down towards the pump station and expansion tank. Therefore, the rule of thumb is that the acceptance volume of the expansion tank must be greater than 10% of the system liquid volume (typical systems will expand this much on a regular basis) plus the entire volume of the collectors and the near collector piping.
Here is an example. A Viessmann system with 300L Viessmann tank and two flat collectors contains about 30L of liquid. Collector volume is 4L so the expansion tank must accept the 4L plus 3L of normal liquid expansion plus the volume of the liquid in the first 20 feet of piping (lets assume 3L for now). Expansion tanks for solar run at a higher static pressure than heating expansion tanks (typically 2-3 Bar or 30-45psi…1 bar is = to 1 atmosphere or 14.7psi) to be able to keep enough pressure to get the liquid to the top of some tall roofs. A tank will probably have 50% of its true volume filled (membrane will be flat across) when started up for the first time.
The total volume needed will be in the neighbourhood of 10L X 2 = 20L (5 gal) tank with a 10L acceptance volume. The equivalent tank in the heating style would be a #30 by Amtrol, for example. But….I am not through yet. These tanks are not designed either for the pressure or for the temperature they can be subjected to. In North America, where true solar expansion tanks are not sold in the average plumbing wholesaler, we have opted for the equivalent sized domestic water expansion tank which can take a higher pressure and larger changes in pressure and temperature.
I remember a number of years ago I was called in to look at a 10 collector system consisting of 30 Thermomax tubes each (30m2 system). Not only was there no pressure relief valve on the system, there was a #60 expansion tank. There was there no pressure in the system and when I went to the roof to see the piping I found 1″ copper elbows half blown apart. This system was a mess and the collectors were garbage. I found out after that the system was designed by a reputable mechanical engineering firm which refused any help from collector manufacturer (pride goeth before a fall).
Lesson………never undersize your expansion tank. A bit more glycol and a bit more expensive tank can create a system where the glycol does not have to be changed for 10 years.
Posted by Mike Holm on June 12, 2009
Vacuum tube collectors
There are a lot of vacuum tube collectors (i.e. solar panels) available on the market these days, and there is definitely a lot of misinformation out there. I shall try to rectify this to some extent.
“Vacuum collectors are more efficient than flat collectors.” TRUE or FALSE?
False most of the time and true some of the time. A good flat collector will start off with a higher efficiency than almost any tube collector (with a few exceptions from Europe). During the summer, or whenever the collector is operating at less then 60C above the outside temperature, the flat collector will be superior to the vacuum collector (different collectors have different characteristics and efficiency curves so 60C is a bit of a generalization)
The time spent below a delta T (temperature difference) of 60C is actually the majority of the time for domestic water heating systems. It is only when it is -10C outdoors for example that the vacuum collector will outshine a flat collector, and due to the range of collectors out there this is not true of all collectors.
Flat panel collectors on a private home
Here is an example: a Viessmann flat collector, at its most efficient (no heat loss through the enclosure of the collector) is about 79% efficient. When the outside temperature is 60 deg colder than the collector temperature, the efficiency drops to about 58%. This range is where the collector will spend 75% of the time. By contrast a good vacuum collector coming from China using the Sydney type double tube (the most used type of tube) has an initial efficiency of 60%. At 60C delta T the efficiency is 50%. The efficiencies of the collectors will meet when the temperature difference is closer to 80C. It is only in the dead of winter when this will happen and we don’t have a lot of energy in the sun at that time of year.
Another real issue is longevity. The Sydney tube is only about 20 years old and has only seen the light of day in North America and Europe for 6-8 years. As a matter of fact, of the hundreds of tube suppliers in China, only a small fraction will meet any certification. Most operate with no manufacturing standards controls. The market in China is much different than here. The tubes were designed to last 7-8 years and could be replaced one at a time if one broke. The economics of life in China dictated that the tubes needed to be cheap enough to grow the market. Few will last 20-25 years and not without a tube or two being replaced annually. The vacuum tube works under a lot more structural stress than a flat collector so it is natural to expect that it will not last as long.
Many flat collectors, by contrast, have been running for 25-30 years and show no sign of dying. More to come on this topic.
Here is an article from Germany printed a few years ago. There have been moderate improvements in both flat and tube collectors since then but nothing that would change the essence of the paper. Performance Test – Flat Plate and Vacuum Tube Collector
Posted by Mike Holm on June 10, 2009
Vacuum tube collectors
I have about 20 years in the solar business as well as installing high efficiency boilers and floor heating. In the 90s when there was cheap gas and oil, most people who were in the solar business were true believers, and maybe there were a few business people among them. Now though, everyone smells the money. Except that it is not there….at least not in the normal sense of buying and selling heating equipment. When you go to buy a furnace or boiler, it has gone from the manufacturer, possibly to a distributor, then to a wholesaler, a contractor and finally to you. Each level adds anything from 5 to 30% to the cost of the product. This is not the case with solar hot water.
Solar thermal systems are held to a higher standard of payback than any other heating product because they are not considered a necessity. Therefore we have to try to keep the price down. The simple fact is that a good solar water system costs $8000 (without any government rebates) or more, and will produce about 500-600 kw/h of heat per square metre of collector. Many collectors don’t produce that much. ( If my numbers don’t make sense to non metric folks, I include an explanation below.) Since most solar water heaters have two 4×8 foot collectors (3m2 each), the output for a good system could be 3000 kwh annually. This however is under ideal conditions. In practice you can expect about 25oo kwh per year.
Where I live in Ontario, if you have an electric water heater you are paying about $.12/kwh including all fees and taxes. The equivalent customer on natural gas is paying about $.08 /kwh. This means that if you’re on electricity, a solar thermal system will net you an annual savings of $300. If you’re on gas (in Toronto, we pay about $.50/m3 or $1.50 per therm) the savings would be about $200 per year.
I am always coming across companies who are new to the business and promise the world. I know of one company, for example, that sells a very cheap thermosyphon system (tank on the roof with collectors made of vacuum tubes from China) and advertises a savings of $350. This is impossible. The collectors are only 2.7m2 size and the sun puts out about 3000 watts (at peak times) onto the face of the collector. The entire system would have to be well over 100% efficient to deliver this kind of savings, which is mathematically impossible. The best systems (collectors, tank, pump, and taking into consideration all the heat losses from piping etc.) are really only about 50% efficient. The system this company is selling has been tested and actually produces about $60 in savings (based on electricity) per year. The package is very tempting as the vacuum tubes from China are at a really good price. But as in most things in life, you get what you pay for.
