You need to look at average sunlight - lots of days aren’t sunny. If you haven’t read through my page on solar hot water, it might make sense to look at the data. I’ve attached a graph below that shows panel output temps over the course of a (rare) perfectly sunny day. Peak output doesn’t happen for very long, and the average over the best 4 hours is considerably less.

I have three glazed panels that are in the same general size range as what you describe, and another 80 square feet of pool heater. I think I could supply our needs with two of the pool heaters at $140 each. Max temp is only 135 degrees, but lots of surface area means lots of BTUs.

I know that you’re willing to burn wood, but that might not seem so attractive come August.

24,000 BTU/day seems a bit low, but reasonable if you’re really careful about hot water use. With a family of five using low-flow shower heads and front-loading washing machine, we’re somewhere around 65,000 BTU/day.

Here is a source for solar products that look very reasonable http://www.s101470521.onlinehome.us/6901.html
leaddog

take a quick look at my solar setup. I posted in the green rm. No scientific data, just free hot water. My bill went from 80 to 100 therms down to 15 to 25 per month. It is only a savings of about 60 to 70 bucks a month. Seems hardly worth doing until you add it up over 4 yrs of doing nothing but going to bank with that dough.  As I have said before my favorite saying “shut up and do it”. (Not really meant to offend anyone,, buttt).
Mike

nofossil - 23 January 2008 10:54 AM

My simplistic view of solar:

Spring / summer / early fall: Sun angles good, wood boiler not running, solar is good. Solar is for domestic hot water, but I store solar output in my big storage tank (DHW tank is way too small). I reach tank temps over 150 degrees in the big tank with my el cheapo solar panels.

Winter: Sun angles bad, temps below freezing, snow on panels, wood boiler running, solar is pointless. I heat everything with wood and drain the panels. No antifreeze, no fuss, no bother.

Very helpful thread. The consensus seems to be that some amount of solar is worth it for augmenting wood, especially when sized to handle the summer dhw load. But really going for it with solar - say 8 panels or more to try to make a dent in the winter space heating - is throwing lots of money down the hole of diminishing returns. At least in climates like VT and NY, it’s more efficient just to cut an extra half cord or so to feed the beast.

Let me add one wrinkle - our farmhouse came with two flat-plate collectors on a glycol loop to the dhw heater. (A pretty standard-type installation.) I was planning on moving this loop to the proposed wood-boiler storage tank. Would having an existing four-season solar rig change anyone’s approach? Would you try to extend your solar season beyond the frost-free months? NoFossil - I notice from your site that you’re still burning some oil in the shoulder seasons to bridge from solar to wood. Could this bridge the gap?

VeggieFarmer - 24 January 2008 09:51 AM

Let me add one wrinkle - our farmhouse came with two flat-plate collectors on a glycol loop to the dhw heater. (A pretty standard-type installation.) I was planning on moving this loop to the proposed wood-boiler storage tank. Would having an existing four-season solar rig change anyone’s approach? Would you try to extend your solar season beyond the frost-free months? NoFossil - I notice from your site that you’re still burning some oil in the shoulder seasons to bridge from solar to wood. Could this bridge the gap?

The bridge is because the sun angles are too low and / or there are too many days without sunshine. I shut down the panels last fall on the same day I started my first fire. Last season I was still dialing it in, and the glazed panels didn’t come online until sometime in May, if I remember right.  The fall shoulder is probably what this coming spring will look like. Perhaps there will be years where there’s a gap between frost-free and wood boiler seasons, but it’s pretty small if it exists at all. Four season panels would certainly reduce the oil demand during the frost portion of the shoulder seasons, though they probably wouldn’t eliminate it.

My freebie glazed panels had heavy corrosion from some antifreeze solution that had been used in them. Don’t know if it was glycol, but I’ve heard that it can be corrosive under some conditions. For that reason and because I’m still chasing little leaks in the pool heater portion, I’m staying away from glycol.