There are solar thermal hot air boxes (STHABs) videos and write-ups all over youtube (videos) and BuildItSolar.com (pictures& text) that show how to make them yourselves for maybe a couple hundred dollars USD (or even a lot less if you have the right stuff laying around) but I have yet to find one that includes an airtight seal for the inlet/outlet ducts. An airtight duct seal makes the difference between getting free heat in the dead of winter and getting free heat AND unwanted free freezing air conditioning in the dead of winter. The laws of physics are pretty reliable, and they work the same way during a sunny day and a dark freezing night – air temperature is changed by what the exterior environment is doing to the inside of the the solar thermal hot air box. On a sunny day, the sun sends photons through the glazed front of the solar thermal hot air box, which hits something that changes the sunlight into heat, and thereby heats the air being moved through the STHAB (solar thermal hot air box). In the middle of a freezing cold winter night, the ambient temperature will chill the interior of the STHAB and thereby chill any air that passes through it. You would wipe out any benefits from the daytime heating if you don’t have an air-tight seal covering the exit duct during long winter nights. You might not care about that if the STHAB is just being used to provide heat during the day to a place that won’t be negatively impacted by severely cold weather – for instance, if this is attached to an unheated shed/garage with no plumbing or items that will be damaged by freezing temperatures. This also doesn’t apply to STHABs that are entirely inside a conditioned space – in that case, the cold doesn’t get to it, and it doesn’t become a cold generation machine.
The STHAB shown in my picture is a commercially made box, from Northern Comfort / Sunsiaray, but I think the guy who made them retired in 2018?
I also made one myself, which my brother sort of remade, but that is not as good looking, and probably not as productive, though I haven’t been able to test that carefully. I used two old window sashes that I got for free as the front glazing, which has the benefit of being able to easily withstand the heat generated inside the box on a sunny day, though putting a sheet of Lexan over those window sashes would trap more heat inside the box, and thereby make it more productive. If you do a really good job of building one of these boxes and then put an acrylic or polycarbonate sheet on the front of it, instead of a glass sheet (window sashes, screen door, etc), you run the risk of that potentially expensive sheet melting. I was able to measure temperatures of over 200 degrees Fahrenheit coming out of my homemade STHAB on a sunny day when no fan was running, and how long would polycarbonate or acrylic stand up to that?
This is really great and durable technology, and I encourage you to give it a try, but remember to make sure you have an airtight seal on the ducts when the sun is not shining on it!
60 Minutes did a report on how the Bahamas are upgrading their electrical grid to better handle the increasingly violent and increasingly frequent hurricanes hitting their low-lying islands, and I encourage you to watch their video if you can. If you can’t watch it, you can at least read the transcript at the link above.
It’s incredibly exciting to see progress being made in the search for hurricane-proof solar PV microgrids, and I really hope they succeed. The solar panels are much closer to the ground in this new type of installation and will supposedly withstand 180 mile-an-hour winds; I think it would be ground-breaking if this microgrid actually does withstand what are expected to being increasingly frequent category 5 hurricanes. This type of installation will become more in-demand in more places as our world continues to warm.
I do have one quibble about this otherwise well-done presentation and it’s this – Bahamian Prime Minister Hubert Minnis mentions that he said at the U.N. ‘First World nations make the greatest contribution to climate change, (t)hey are the ones responsible for the changes that we see. The increase in velocity and ferocity of the hurricanes and the different– and the changes, typhoons that we see today, but we’re the innocent victim. We’re the ones that are being impacted by what you have created.” Minnis seems to want the U.S. and European countries to contribute to an insurance fund to help rebuild from future storms. My quibble is this – the electricity generated on these islands is so expensive now that installing solar PV arrays/microgrids even with battery backup will surely cost what they’re already paying now, or, more likely, even cost less. I could see asking for loans to help with the initial installation of solar, which could be paid back with money paid by electricity customers on their monthly bills. And I could see asking for some financial help to rebuild after climate-change-influenced storms, but solar is such a good financial move that it would be a freebie /handout to ask for the U. S. and Europe to pay for that.
PLEASE NOTE – the date this was written was July 15th, 2019, so depending on when you read this, it might be very out-of-date.
I just spent a bunch of time on the phone trying to track down the answer to a simple question, so I’m going to put this out there in the unlikely event that anybody can find this post. My question was – can I get the $0.25 USD/watt rebate that Ameren, the local electric utility, is giving out to people who install solar PV panels on a residence **if I am just adding to an already existing array**? I was told the answer is maybe, depending on whether money become available, sort of. To clarify that answer, let me tell you that we installed an 8.17 kW solar PV array on our home’s garage in 2012 and it has worked almost without incident since then. We would like to add some solar PV panels to the array in order to further decrease our dependence on electricity mostly generated from coal, so we will be adding 1.71 kW with the addition of 6 new 285 watt SolarWorld panels. I wanted to know if we could get the advertised solar PV rebate from our local utility if we were adding to an already existing PV system and the person I talked to on the phone said that although all the money available has already been spoken for (which means no money for me, possibly) that if customers who have already been approved for systems fail to install them in a timely fashion that money might then become available for me. The woman I spoke to about this on the phone said that my application would get in line behind all the other applications hoping to get money, and if enough customers cancelled their orders. So, the answer is quite dependent on the actions of others, but almost certainly I would get no money from Ameren for extending our PV array.
This rebate is/was only available in Missouri, for customers who get their electricity from Ameren.
I recommend this device! I bought a Kaito brand device, KA340, for about $34 from my usual online retail overlord (smile.amazon.com) and it has a surprising number of features for the low cost. One issue is that, so far, low cost has meant low amount of power generated and stored. The paperwork included with this device claims it has about 8.5 watts of power storage built in, but I haven’t been able to verify how much energy this device will store IRL. The paperwork claims that it’s enough for 14 – 16 hours of light, presumably on a full charge. If you are able to put it in full sun on a clear sunny day and charge it using the built in .5 (yes, that’s one half) watt solar PV panel, with about 5.5 “peak sun hours” (not the same as daylight hours) in the summer (in Saint Louis, MO USA), you’d only be able to pick up about 2.75 watts of energy per day….so maybe you’d have to charge it for 3 days to fill the tiny batteries??? How in the world do they get away with such tiny PV panels and battery packs, you ask? If you charge it all day, in good sun, that’s still enough for several hours of light, which most people will accept. It probably takes about 5 watts to charge a cell phone, so if you want light AND cell phone charging you are going to spend a very long time using the hand crank as an energy input. Beware – there’s no indication that this is waterproof – keep it in a sealed ziploc bag if there’s any chance it could get wet – rained on, spilled on, etc. Please check out this review – this guy does a pretty good job of describing the features.