Thursday, February 28, 2013
Selling solar hot water or large scale pool heating into municipal facilities has always been a very difficult task. City people have to protect the interests of their taxpayers at all times. They are under tremendous scrutiny and every snake oil salesman out there is trying to dig his claws into municipal coffers. Cities tend to hire engineering companies in order to distance themselves from the sensitive decision making. Domestic solar hot water heating systems use evacuated tubes or boxed and glazed collectors. These small scale systems don't have good economics because they are small scale. The cost of tanks and controls and plumbing and roofing is high compared to the area of collector exposed to the sun and the collector choice is naturally an expensive one because if you're going to all this trouble you'll want something that delivers maximum bang, not maximum bang for the collector buck. When we start looking at larger scale systems like preheating showers for Aquatic Centers we start to see much lower fixed costs per collector area. Solar gets a lot more viable a lot quicker. What happened of course is that engineers specified the old school boxed and glazed or evacuated tube collectors. They didn't even consider unglazed collectors like Powerstrip. When we look at these performance curves we see that unglazed collectors are affected by wind and as we move right on the x axis (water getting warmer relative to air temperature) we see why engineers like the evacuated tubes and boxed and glazed collectors. They retain their efficiency into marginal weather conditions and into the higher end of the heating range. What engineers failed to recognize or perhaps never thought to even look at was the fact that most hot water heating is done at the low end of the temperature range when Powerstrips are even more efficient per area than the other types and on top of better efficiency they are far less expensive. Finally an engineer recognized this in Canada post rebate era. Yes the conservative government abandoned the Eco Energy program for Renewable Heat in 2010 and as a result Associated Engineering was tasked not with spending the City of Richmond's money as fast as possible in the safest way possible. Instead Charlie Smeenk PEng was tasked with spending the city's money with the best return on investment in mind. Charlie and I met early in the process and he was the one who pushed me toward the idea that we needed to plaster low cost unglazed collectors all over the Aquatic Center roof and move the cold water through them on their way to the boilers. The system has been installed for a year now and we've monitored it with our web based monitoring . The monitoring is not internet connected so the data is not always up to date and we've lost some data but we've still proven that we've displaced more energy here with this system than we would have with more expensive technology. We've also proven that cost effective solar hot water is possible. Its possible to deliver solar at $100/GJ That's $100 in capital cost up front in exchange for 1 GJ of annual energy production. If energy costs $10/GJ after boiler efficiency is included (which is close even with today's low natural gas prices) then its a simple ten year payback period. Others will brag that they are doing better than 10 years. They are incorrect. There's no way to do better than this kind of economics against cheap natural gas .......or is there? Some municipalities like Sechelt, Esquimalt, and Kimberley have installed our solar panels at their municipal facilities. They have gone one step further with all this. They are using the Powerstrips to heat a tank of water and that tank of water is the source for a heat pump. Heat pumps utilize low grade heat. Ground source heat pumps for example might take ground heat at 10C and use it so the ground cools down to 5 degrees. That 10C to 5C drop in ground temperature is converted through the heat pump to heating water at 60C or air at 20C or a pool at 29C. Heat pumps take low temperature energy and pump it up to a higher temperature for use. Solar needs to operate at low temperature in order to be able to take advantage of unglazed collector cost efficiency. Heat pumps are the means by which we can utilize that low grade heat. We've known this in the solar industry for decades but we've been distracted by grants for the tried and true conventional approaches. Since this is a blog posting about municipal pools I need to mention something. Solar heating municipal pools has been a failed experiment. Its usually a bad idea because the pool temperature can not fluctuate and it needs to in order to store solar energy, otherwise the only gains made are gains that can be made during a sunny day and at these times there is usually too much heat. The sun is heating the space (indoor pool) and the heat pumps are dumping that heat outside or if needed into the pool water. Municipal outdoor pools are only used in the heat of summer. Not much heat needed then and again thru half that season the sun on the pool is increasing the pool temperature and it started the day at setpoint so its a heat dissipation requirement and solar heaters never turn on. The only way solar works is when you are allowing the pool temp to fluctuate and its most beneficial in early and late season, before and after municipal pools operate. When we see solar on Aquatic Centers these systems are heating water for showers, not heating the pool.