Expensive Energy Solutions Aren’t Really Solutions At All
The energy industry is about cost-effectiveness; I think we all know that. That’s why we’re generating electricity from coal: it’s deadly, but it’s cheap. Where is this all going? I’m not sure, but I do know this: Replacements for fossil fuels, even if their costs to the environment are next to nothing, stand no chance if they are not affordable.
Two quick points on the subject:
• The American Council on Renewable Energy (ACORE) recently published its report on the activities in this sector in the northeast region of the U.S. and presented a shockingly significant reduction in costs across the board. Here’s an excerpt: “Three large utilities in Massachusetts, for example, recently signed long-term contracts to purchase renewable energy at less than $0.08 per kilowatt hour, below the cost of most conventional sources in the region.”
• My own work for my client Plexisun, a breakthrough in solar thermal hot water, is all about cost-reduction. The product boasts an efficiency in the mid-teens, approximately the same as PV. Anyone who needs hot water in any significant quantity (laundromats, dairy barns, apartment complexes, hotels, etc.) is going to love this stuff.
There you have it: two bits of good news for the adoption on renewable energy.
Craig,
First, good article.
Second… you must have the efficiency of the solar hot water system incorrect. There’s simply no way it could be that low. They would have had to paint the collectors white.
While it’s very difficult to get energy conversion to electricity or kinetic energy (governed by 2nd law limits then further restricted by inefficiencies within the system), converting energy to heat can always approach 100% efficiency. The only losses are the amount of energy that is conducted or radiated away. I’d be very surprised and very confused if your client doesn’t have an efficiency of >50%.
It’s possible that I did this incorrectly, but I don’t see how. A fence 132 feet long and 4 feet high heated a 20,000 gallon pool 8 degrees F in 4 days. I converted everything to metric, and calculated:
Total time (in seconds) * the capacity factor (I assumed 30%) * the area exposed (in square meters) * the power of incident sunlight / square meter (about 1000 Watts) * the efficiency = the volume of water (in milliliters) * the density of water (1) * the specific heat of water (also 1) * the delta T (in C). Isn’t that correct?
Craig,
I’d say you were aggressive in the capacity factor – there are very few places on Earth that can claim 30% without tracking in the early spring (the only place that I could think of in America would be in Hawaii at high elevation), and anywhere that would have something close to 30% cf wouldn’t need to heat a pool after ~ April… Then again, I guess if the elevation was high enough you could get high solar performance and still have colder temperatures…
But the big issue is I didn’t know that Plexisun’s focus was pool heating. Normally the focus of Solar Hot Water is to replace or augment a hot water heater, and the efficiency consideration revolves around the system’s heat loss from the reservoir and pipes… because again the upper limit on the actual conversion of sunlight to heat is 100%… so the “blackness” of the coating on the aluminum and – far more importantly – the resilience of that coating under thermal cycling are the most important considerations… otherwise you just use copper tubing pressed against an aluminum sheet… and you get very near 100% efficiency at the actual panel itself. Then it’s a question of how much heat bleeds out of the rest of the system before it is used in the water heater… For the pool, the “bleed” is going to be far higher – since your reservoir has a large open face losing a tremendous amount of energy to evaporation and conduction to air, and the rest of the reservoir has un-insulated conduction into the ground (though not nearly as significant as the evaporative cooling once the ground immediately surrounding the pool is heated and begins to serve as a thermal mass). So your efficiency numbers are still a little low (because I think you are aggressive on capacity factor), but quite believable for a pool heating system – while they would have been laughably absurd for a hot water system for the house.
(You may not have been aware, but my father tried to start a solar hot water company in the 80’s – Doty Solarway… The panels themselves were naturally near 100% efficient, while the system at large was ~50% efficient, but the price of natural gas was simply too low for solar hot water to be competitive, especially considering interest rates at the time… and as Reagan killed off subsides for alternative energy, Solarway was unsuccessful… SHW today has a much easier marketplace – natural gas is much more expensive now, while interest rates are MUCH lower, and prices for metal and labor have not increased nearly as fast as fossil energy prices… and there’s more government support for alternative energy purchasing).
Ah! You explained it; it’s the energy bleed at night; I had forgotten about that. And yes, I should use a lower capacity factor.
Btw, I was just out on a walk with my wife Becky (who follows the blog) and our two dogs, during which I told her about your comment: “There are very few places on Earth that can claim 30% without tracking in the early spring (the only place that I could think of in America would be in Hawaii at high elevation).” She asked, “Who (in blazes) knows more than you about this stuff?” and I replied, “Oh lots of people. That happened to be Glenn Doty.” She chuckled, “I should have known.” 🙂