Which antifreeze safe and affordable
 

I finally got the time and weather to get the solar water panels on the roof. I have it hooked to the pool for now. Will switch it over to heat the house by this fall. Still need to run lines to the water tank. Also angle them for best winter sun.

I need to start thinking about antifreeze, to treat 500 gallon for 10F about -12C. Which antifreeze eco-safe and affordable? Wondered if anyone had a brand or type to recommend.

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My brother, talked me into re-soldering the panels serpentine instead of grid. Thinking being better heat gain.

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Nuisance the cat. Giving the final inspection.

It's hard to say what brands are sold around you, but you can buy propoline glycol antifreeze in 5 gallon buckets, mix it so it's about 60% water (should give solid numbers on the bucket) and you will be set.
this type of anti freeze costs a little more then what you put in your car but the advantage is, your car has stuff that a small amount will kill you, this stuff you can drink.

Just did a quick search and saw propylene glycol for $80-100 per 5 gallon bucket. Thats gonna get crazy pricey if you're gonna need 200 gallons of it.

Guess, I need to keep thinking. 20F would be good for 99% of winter.

Wonder if an aquarium air pump, blowing through the lines would keep them from busting during low temps.

You can water it down a fair amount and it will not freeze, it might get slushy, you need your pipes insulated anyway, it's been almost 5 years sense I've installed a solar hot water system so it would be well worth fact checking my info for your self.