The purpose of this post is mostly to stimulate thought and open up some possibilities for you. Many folks would find these ideas impractical or even impossible if you live in an apartment or have a strict homeowners association. Wild stuff, but maybe there’s a mad scientist among you who could make it work.
If you know John Kimball, Sun Electronics’ fearless leader, he has been on a crusade for decades to bring affordable solar power to the people. As far as the PV modules go, he’s there. Solar panels are no longer the problem. I have noticed pricing on charge controllers dropping and pretty soon that will no longer be a huge part of the equation. With inverters, the problem is that there is such a flood of cheap Chinese inverters that you might be tempted to go with one of them, whereupon it is quite likely you’ll find you made a mistake and end up buying the more expensive model, too. What I am looking at as MY biggest issue in my personal solar power systems (yes, plural) is storage.
Where do you store your power? In a battery, right? Utility scale battery and electric automobiles would probably drive the price way down, but on the other hand there is a huge demand. LOTS of battery research is going on and someday someone will come up with the super cheap-but-good battery. In the meantime, there are OTHER possibilities to store energy, though not necessarily electrical energy.
Big utilities have used a couple of neat tricks over the years Hydro plants just let the water back up behind the dam, then run it through the turbines to make electricity, as needed. Some utilities not normally considered as hydro, take their excess electricity to pump water to a lake on a hill, then run it back down the hill through a turbine when they don’t have enough power from their regular supply. Some are now using pumped storage with solar, to keep the lights on at night. Now, I am thinking that this would be impractical for you and I, given the space required for a couple of lakes and a power station.
Another big utility trick is to pump air into underground caverns, using surplus power, and then letting the compressed air run a turbine to make extra power when needed. Again, that’s not going to be good for most of us. I don’t know about you, but I am pretty sure there aren’t any underground caverns where I live. This is not to say that compressed air could not be used, and in more ways than you might think. Let’s say your solar power system has your regular battery topped up for the morning and not much is running in the house, why not have it burn off the extra power from your panels by running an air compressor? For this kind of duty you’d need a pretty tough compressor, but they are out there.
You pump the air into a huge pressure tank (huge being a point of inconvenience to many), perhaps one like they use at those propane storage yards. Such a tank would be expensive, if bought new, but you can find amazing values in industrial surplus. You might find one for scrap value. When the sun goes down and the regular battery is getting low, you send the compressed air to an air motor. You may not be aware of these, but they are very common in industry and can be very durable. The air motor spins a DC generator to charge your batteries. This is dirt simple to do, but huge. Far fetched? Under the city of Paris, France, there is an abandoned network of pipes from an era where a central compressor station transmitted power to businesses all over the city, powering industry!
Google it and read THIS article. You can store a lot of power with compressed air. Even run a car!
There are side benefits to consider, too. When you compress any gas it gets hot. This is how heat pumps work. If you put your hand on the top of a running compressor then you will quickly notice it is quite hot as you pull your blistered fingers away. If you put that freshly compressed air through a heat exchanger you can heat your domestic water supply. On the reverse side of the process, when the air expands through a motor it comes out quite cool. The air can be run through a heat exchanger for storage, or exhausted directly into a room to keep it cool.
Ok, that’s pretty off the wall stuff. How about one that is so simple, even your cat understands it: thermal storage. The cat finds a spot where the sun shines through the window on a cool morning and is warm and cozy. John sells a thermal solar water heater that mounts in a sunny spot. It uses some super simple, but highly efficient technology that will do a dandy job of replacing the electricity or gas you use to heat your bath water or if you can use several of them and greater storage, you could probably do a good job of supplying water to a hydronic home heating system. You can run the hot water through pipes embedded in your slab, through baseboard heat exchangers, or through a radiator inline with your central air handler. Heating water directly from the sun bypasses the solar electric, charge controllers and batteries. Storage is just an insulated tank.
I have some other mad scientist ideas I will share with you as information is firmed up. A friend dropped off an extra pallet of solar modules and microinverters he had to use in the ongoing solar air-conditioning project. In conjunction with that, I’ll have some gear available to test some of the old wives’ tales about what you can and cannot do with certain pieces of equipment. I don’t think this will turn out quite as destructive as the time we used a 12 gauge shotgun to blow holes in a panel (it still worked), but there could be smoke.
–Neal