I'm heating my 1900sf house, a 24x24 detached garage, and my domestic hot water with a Central Boiler Classic 5036. No complaints at all on operation or wood use aside form the quality of the digital temp readout on the stove, but that's another story. I have a standard 30 gallon electric water heater with a sidearm heat exchanger that works quite well when the furnace is lit. I have a cutout system of valves to switch back and fourth between the electric and wood but I've been thinking it would be nice to go a step further and add solar for at least hot water. Easy enough to plumb in solar panels to the water heater itself, but was also wondering if it's worth trying to supplement my wood usage by tapping solar heated water into the furnace itself? At the easiest, its a shorter run from the ideal location for the panels to the furnace than it is to the water heater. Any thoughts/opinions greatly appreciated.
Water heating
- Thread starter bsarider
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Nofossil
Moderator Emeritus
I think you'll find that solar hot water panels contribute a fairly insignificant amount of heat in winter. Ours do around 100KBTU on a good summer day, but would only provide 30K or less in the winter, and that's if the sun actually managed to shine.
For me, not worth it. I fill mine with water rather than glycol, and drain them before the first frost. In the winter, I throw an extra log in the boiler and save myself the aggravation.
For me, not worth it. I fill mine with water rather than glycol, and drain them before the first frost. In the winter, I throw an extra log in the boiler and save myself the aggravation.
maple1
Minister of Fire
Also feeling here that it is not worth it.
Might even extend that to saying solar thermal might not be worth it, period.
Might even extend that to saying solar thermal might not be worth it, period.
woodsmaster
Minister of Fire
woodsmaster
Minister of Fire
30 gallon is not big enough for a sidearm to recovery rate in my opinion. only way it's going to recover quickly is if your always running very hot water threw it.
I was really only looking to use solar during the summer, but since the water heater is already hooked up to the boiler my thoughts were to use the existing pump and piping of the boiler. My boiler holds 200 gallons, and I was really wondering about the fesibility of heating the water in the boiler with solar and continuing to pump it through the sidearm on the electric water heater rather than switch it back to electric
maple1
Minister of Fire
That won't work well, if at all. Sidearms don't transfer heat as good as say a flat plate, so require fairly hot water on the boiler side. Hotter than solar panels will maintain in an OWB.
Petty much what I figured but thought I might put it out there. My second option is a 50 gallon hybrid water heater. Leave the existing water heater with sidearm in line and unhooked from the electric and feed it into the new hybrid. Still on the grid during summer, but not as much I guess.
Mike Fromme
Burning Hunk
Not sure it's possible or cost efficient.... But how about a small stand alone PV system to power the heat pump water heater during the day.
Could it be done with no batteries and NOT grid tied???
Solar Panels--->inverter--->heat pump
Nofossil
Moderator Emeritus
I've wondered about that. Does the efficiency of the heat pump make up for the inefficiency of the solar panels? Solar hot water panels capture a lot more usable energy (both per square foot and per dollar) than PV panels, but heat pumps can deliver more BTUs than the power they consume.
I'd suspect that a solar hot water panel could heat water even if there's partial sun or poor sun angles, where the PV panel might only provide enough power to run a heat pump under ideal conditions.
We have solar hot water panels on the ground below our storage tank so that they thermosiphon - no pumps, no electricity required. Of course many sites don't have that option. Would be perfect for off-grid, though.
Mike Fromme
Burning Hunk
Thinking about it more...
How about solar PV panels directly to DC resistance elements in the OWB? Or into the 30 gallon water tank.
I've wanted to do solar thermal DHW since I got my indoor wood boiler. But every time I've penciled it out it ends up looking like it's more $$$ and potential trouble then it's worth.
Nofossil
Moderator Emeritus
Here's the problem: Solar PV panels convert about 15% of the solar energy that hits the panel into electricity. This compares poorly with solar hot water panels, which convert more than half the incident solar energy into heat.
Back of the envelope, you'd need about 4 times the solar panel area to heat water using PV panels and DC resistance elements compared to using solar hot water panels. I haven't looked recently, but I think PV panels are also more expensive per square foot than solar hot water panels.
Heat pumps can provide significantly more useful heat output than the energy that it takes to run them. If that performance were good enough, you might end up ahead of the game. If the panels put out more energy than you need to heat your water, extra electricity could be more useful than extra heat.
Mike Fromme
Burning Hunk
I like the idea of the simplicity of PV directly to resistance elements. Not much to ever go wrong. Though a solar thermal panel set up for convective flow into an OWB is also pretty simple... But it won't work in the winter in freezing temps.
I'm about to show my naïveté when it comes to PV solar but here goes.
From what I found it takes .171 KWh to raise 1 gallon from 50 to 120 degrees. (Using resistance elements)
Assume 50 gallons of hot water per day
So 8.5 kWh daily
So about 10 270w panels here in the NE???
From what I've read you can connect DC power directly to the elements of a typical water heater but can't use the existing AC thermostats and switches. So the big cost is the panels and some misc installation supplies.
With a HPWH you could cut the number of panels by half or more but you add the cost of an inverter and the HPWH
Solar thermal seems the most expensive. You would need 3 or more 4x8 flat plate collectors. Along with pumps, a drain back tank and a heat exchanger. The flat panels themselves would probably be more then 10 PV panels.
Obviously if you can DIY the solar thermal collectors and have an OWB you can use as a drain back tank and heat exchanger you can cut some costs. But you still have to have pumps and a controller of some sort of you want to use it year round... With either PV system you will get much better winter production then with solar thermal.
http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-dead?page=2
http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-really-really-dead
I'm about to show my naïveté when it comes to PV solar but here goes.
From what I found it takes .171 KWh to raise 1 gallon from 50 to 120 degrees. (Using resistance elements)
Assume 50 gallons of hot water per day
So 8.5 kWh daily
So about 10 270w panels here in the NE???
From what I've read you can connect DC power directly to the elements of a typical water heater but can't use the existing AC thermostats and switches. So the big cost is the panels and some misc installation supplies.
With a HPWH you could cut the number of panels by half or more but you add the cost of an inverter and the HPWH
Solar thermal seems the most expensive. You would need 3 or more 4x8 flat plate collectors. Along with pumps, a drain back tank and a heat exchanger. The flat panels themselves would probably be more then 10 PV panels.
Obviously if you can DIY the solar thermal collectors and have an OWB you can use as a drain back tank and heat exchanger you can cut some costs. But you still have to have pumps and a controller of some sort of you want to use it year round... With either PV system you will get much better winter production then with solar thermal.
http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-dead?page=2
http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-really-really-dead
Nofossil
Moderator Emeritus
... and solar hot water doesn't get the same subsidies. I built my own hot water panels - total outlay around $200. I don't even bother with them in the winter. During the summer they heat my 880 gallon storage tank. Covers 100% of my hot water needs April through September, a bit less thhan 100% in the shoulder seasons.
Using PVwatts, I get about 9kwh average per day in the winter in New England from a 25 square meter PV array. That's 25 270 watt panels rather than 10 - about $5000 for the panels alone, unless I'm missing something.
Let's face it - the sun doesn't really shine in New England in the winter anyway. Throw another log on the fire.
Using PVwatts, I get about 9kwh average per day in the winter in New England from a 25 square meter PV array. That's 25 270 watt panels rather than 10 - about $5000 for the panels alone, unless I'm missing something.
Let's face it - the sun doesn't really shine in New England in the winter anyway. Throw another log on the fire.
Mike Fromme
Burning Hunk
Had never heard of pvwatts calculator
<--- newb
I had based the 10 panels on 80% efficiency and 4.0 solar radiation. Which works out to the ~3100kwh needed annually.
<--- newb
I had based the 10 panels on 80% efficiency and 4.0 solar radiation. Which works out to the ~3100kwh needed annually.
Nofossil
Moderator Emeritus
Yeah, the fine print gets more complicated. Even the pvwatt calculator is too optimistic in a lot of cases, and the numbers from that are a bit shocking when you compare them to the promises.
Sun angles and daylight hours are not so favorable in the winter. Right now, utilities are usually required to buy any excess that you produce, acting as a free infinite battery. It's not clear that that approach will continue as it doesn't scale well. If they don't have to buy your surplus, PV economics get even worse.
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