What angle and what size tank

[organic farmer]

I have calculated the requirements for solar HW space heating for the northeast numerous ways in the past with flat plates & evacuated tubes. December, january, and 1/2 of Feb. just cannot supply a system with sufficient BTU'S . Even a small house requires 50k BTU per hr at 10 degrees. 50 k btu per day during those month's requires a large array. I try to stay under 160 sq. ft of panels because of cost vs payback. Even 160 sq ft if not heating a pool in summer is a stretch.
It seems like a waste to have panels idle in the summer month's. A good design balances a usable size array with seasonal effectiveness, and installation cost.

I do not have a very small house. Though it is fairly new and well insulated.

We go through 3 1/2 cords of firewood each winter for heat.

There are homes here that use only Solar-Thermal for heat. It is their only heat source.

For our home, we hope to simply reduce our firewood use by half.



I do understand that up in the North things may be different. But down here in Northern Maine, we do not require that much heat to heat our homes.

50kBTU/hr is a lot of heat. A bit more than most homes have. Even older uninsulated homes do not have that much heat available to them.

I have seen many homes here use a water-heater looped with radiant flooring for their heat system. Those things use a 40kBTU/hr burner in them.

In fact, that is exactly my back-up system now. A 40kBTU water-heater is the back-up heat source for my radiant floor system. The primary heat source is our woodstove.



It gets cold up North. But down here we rarely see anything below -20F. Just last week, and for a couple weeks there we had temps between -5F and -20F. That is all, nothing terribly cold.

Certainly nothing that requires so much as 50kBTU/hr.

My house is 2400 sq ft and is insulated at R-60. We go through 3 1/2 cords of firewood each winter. We intend to reduce that to around 1 to 1/2 cords.

We do have homes here that are 100% solar heated.

[Gutts]

Thanks everyone for the input !
I am only trying to preheat (in winter) my domestic HW .
I will have 2-4x8 panels to do this .
From what I have heard here it does not sound to promising .....

[inetdog]

From what I have heard here it does not sound to promising .....

It depends on what preheat temperature you are trying to achieve.
If you are trying to get 32F stream water up to 60F, then you have a good chance.
If you are trying to get 60F well water up to 100F, it will be more difficult.
If you are trying to get all the way up to 120F for minimum need for post-heat, good luck.
The higher the difference between the ambient air temperature and the desired water temperature, the better insulated your panels (and pipes) will need to be.

[LucMan]

Thanks everyone for the input !
I am only trying to preheat (in winter) my domestic HW .
I will have 2-4x8 panels to do this .
From what I have heard here it does not sound to promising .....

With 50 degree incoming water 2 panels should be fine for 100- 110 degree domestic hw water in dec, & jan. When the sun shines. Space heating is a whole other issue. If possible just add another panel. The main issue in the northeast is the number of overcast days in winter , too many.

[LucMan]

I do not have a very small house. Though it is fairly new and well insulated.

We go through 3 1/2 cords of firewood each winter for heat.

There are homes here that use only Solar-Thermal for heat. It is their only heat source.

For our home, we hope to simply reduce our firewood use by half.



I do understand that up in the North things may be different. But down here in Northern Maine, we do not require that much heat to heat our homes.

50kBTU/hr is a lot of heat. A bit more than most homes have. Even older uninsulated homes do not have that much heat available to them.

I have seen many homes here use a water-heater looped with radiant flooring for their heat system. Those things use a 40kBTU/hr burner in them.

In fact, that is exactly my back-up system now. A 40kBTU water-heater is the back-up heat source for my radiant floor system. The primary heat source is our woodstove.



It gets cold up North. But down here we rarely see anything below -20F. Just last week, and for a couple weeks there we had temps between -5F and -20F. That is all, nothing terribly cold.

Certainly nothing that requires so much as 50kBTU/hr.

My house is 2400 sq ft and is insulated at R-60. We go through 3 1/2 cords of firewood each winter. We intend to reduce that to around 1 to 1/2 cords.

We do have homes here that are 100% solar heated.

Here is a T sol annual simulation with 8 Buderus SKS 4.0 panels for Monticello NY . These panels are more efficient than standard flat plates in cold weather, much closer to evacuated tubes.
This should give you a much better idea of what to expect from a space heating solar application. Building heat loss at -2F = 53K BTU.

Domestic HW use was 60 gallons per day at 120 degrees.