Tuesday, October 7, 2014
Solar Thermal Isn’t Dead. It was Never Alive! The Sustainable Home Puzzle.
What will the sustainable home of the future look like? Will the solar space (the rooftops) be populated with evacuated tubes, PV, boxed and glazed, pool collectors, wind turbines, air conditioners or what exactly? Over recent years thanks to enormous efforts on the part of governments to further solar electricity (photovoltaics or PV) the cost is down and technology has advanced, so much so that we’re competing with PV for roof space almost every time we try to solar heat a pool in California! Consider these facts and try to connect the dots… Swimming pools represent a large thermal storage and pool owners don’t mind pool temperature fluctuation. Heat pumps can cool a home and dump that heat into a pool. Heat pumps can heat a home in winter and need a large thermal storage to draw energy from. Ground source heat pumps use energy stored in the ground but excavation and access is expensive and the ground isn’t all that warm. The warmer the heat pump’s source the higher the COP (the ratio of energy delivered to electricity used) Unglazed solar panels and storage tanks as the source for heat pumps have been tried and proven to be the lowest cost energy system at 5 municipal Aquatic Centers in Canada. If we can cool a PV panel we can improve its performance by as much as 20%. Solar thermal systems employing evacuated tubes require the use of glycols which cannot handle the high temperatures seen during overtemperature conditions. If a system is properly designed to handle the worst case mid summer heat wave no load condition it becomes ridiculously expensive and burdened with heat mitigation strategies that are difficult to failsafe. As a result most evacuated tube systems in North America are simply not functioning after 5 years. The jury is in and generally it’s a conclusive thumbs down to conventional high temperature solar thermal. Where do all these observations of reality lead us? First it’s important to understand that an unglazed solar panel like our Hot Sun Solar Collector is more efficient than an evacuated tube. At low temperatures where our technology is always applied, we can be over 100% efficient at collecting solar energy because our lack of insulation means we can be gaining heat from the air as well as the solar radiation. An evacuated tube on the other hand is only about 56% efficient due to the spaces between the tubes and the tubes themselves. Yes an evacuated tube retains that efficiency to high temperature differences but when heating cold water, much lower cost pool collectors are more efficient and when heating hot water we are always heating cold water up to hot. We don’t have to heat hot water. Its already hot. Taking all of these realities together combined with the fact that we want our sustainable home to be comfortable and we don’t want to live with compromise in comfort or convenience it becomes obvious that we need to use a swimming pool as the central thermal storage and heat dump. The pool is the source for the heat pump that cools and heats the house and hot water. Unglazed solar panels heat the pool keeping it from freezing. PV panels on the roof supply our electricity to charge our electric cars and provide our lighting and cooking. The pool heating collector space and the PV space must be combined because PV panels need cooling anyway. If you considered an evacuated tube or boxed and glazed collector solar hot water heater it would be applied to a smaller load because we’d already be heating up to pool temperature with heat exchange off the pool and directly off our pool solar. What’s left is such a small amount of energy why not just use the heat pump system? The electricity for it is coming from the PV system. Pool heating solar collectors from cold to warm and heat pump from warm to hot instead of high temperature solar collectors over the whole range. The economics of solar thermal all on its own just don’t fly. Already we have stopped seeing solar DHW pre-heaters installed along with PV on solar homes. The cost benefit wasn’t there and the existing systems weren’t even worth fixing. Solar thermal was never alive. If it was it was killed by outrageously optimistic numbers like 5 year payback when the truth was 80. In the solar business 15 year payback is really 45. 15 years is a 4 page calculation. 45 years is a simple ratio of annual energy saved vs system cost. That’s PV in BC but in California electricity is as much as 5 times more expensive at peak in summer and there’s twice as much sun and the government pays for at least half and as a result Elon Musk wants to lease the space on your roof from you in exchange for selling you that electricity cheaper than the power company. PV is here to stay. There are no moving parts. It lasts and it produces regardless of how much or when you use it. Excess is sold back to the grid to be used by others. The jury is in and the conclusion is unanimous. Humans love their PV systems. In a future world where we tackle climate change we won’t be burning fossil fuels locally. Centralized plants tied to the grid can be made cleaner through carbon scrubbing and sequestering and economies of scale in efficiency improvements. Low cost natural gas is a barrier toward moving closer to this Utopian vision. When we can burn fossil fuel at our homes for less than we can deliver energy from electricity via a heat pump that low cost fossil fuel is blocking progress. Policies that limit electricity production to clean sources also block progress. We need to move to an exclusive electricity based power distribution system. We need to take advantage of PV and PV cooling in turn heating our swimming pool which in turn heats and cools our homes. Applying this thinking in Northern climates and getting closer to zero energy means insulating the tops of our swimming pools and sealing that energy in. We need larger solar systems and we’re going to run short but luckily northern climates correspond to available hydroelectric generation capability and there seems to be ample natural gas available at low cost. The natural gas that is a so called bridge to an alternate energy future is the natural gas burned at a centralized electricity generating station. Canada has mothballed gas fired electricity plants that need to be added back into the mix as needed. A greater focus on energy efficiency is required and all things taken together mean it can be possible to reach zero energy living all over North America. Policy makers need to realize that burning fossil fuels at home is a roadblock to progress and policies must be crafted that don’t incentivize it. Policy makers in the sunbelt need to understand that their grand incentives for PV focus attention on one element of what should be a broader vision. People with swimming pools are not the rich and entitled. Swimming pools are just the storage tanks for the solar thermal component of their futuristic zero energy homes and finally solar thermal with unglazed collectors is not the poor cousin of the solar thermal industry to be dismissed as ineffective as it has been by the Canadian Solar Industries Association. It is the future of the solar thermal industry.