Solar Hot Water - performance and lessons learned

[Nofossil]

Over the past two years, I've been refining, testing, and living with a solar hot water system during the non-woodburning seasons. I've put together a writeup for anyone who might be interested in a similar project.

This system sits on the ground, uses water, is not pressurized, and relies on thermosiphoning for water circulation. 80% reduction in oil for heating water this season!

Link is here - pictures, graphs, and writeup. Enjoy!

 

[Andre B.]

Most cool..........or make that HOT

Unfortunately it is not near high tech and complicated enough for government and big business types, they can't give/get grants to study the problem.
It is really too bad because simple stuff like this would go a long way to making this country or any country energy independent. And could be done very quickly and with very little investment. Mostly just takes education of the people in basic science.

Looks like a cloud went over just after 11:00 and judging by the temp dips 10 minutes later it takes about 20 minutes for water to make a trip from the tank thru the collector and back to the tank.

 

[Nofossil]

Don't know if you followed the link and visited the site - I have a lot more data. You're right about the clouds and the round trip, but the graph above is from an early test with a plastic rain barrel for heat storage.

I actually have a database with readings from the system every 30 seconds for the last two years. Disk space is cheap.

 

[eba1225]

Nofossil,

That looks pretty good and a wealth of information, paying attention to the "inexpensive" way of doing it, ie. minimal electric usage. If it really saved that much I just may look into adopting such a system.

Erik

 

[ozarkjeep]

read, and bookmarked.

in the last few days I have been researching and thinking of similar things.

Thank you for taking the time to keep good data!

 

[Sandor]

Excellent work!

 

[Nofossil]

Nofossil,

That looks pretty good and a wealth of information, paying attention to the "inexpensive" way of doing it, ie. minimal electric usage. If it really saved that much I just may look into adopting such a system.

Erik

It really does save that much - I am nothing if not anal about data ;-)

We have a great baseline for oil consumption. Exactly five months before we set up the first solar panel, our oil tank was filled. The day the panel was installed, the tank was filled again. We used 101 gallons of oil during those five months - all for heating hot water. I asked the oil guy what normal hot water usage was, and he said "oh, about 20 gallons a month".

My instrumentation captures oil boiler cycles as well as wood boiler and solar activity, so I know exactly how many times the boiler comes on and for exactly how long each time. (Well, within 30 seconds, if you want to be anal).

If you want to explore the data set, it's the one labeled Orlan Boiler on this page. The live graph feature is not entirely bug-free, but you can pick date, time, duration, and which signals you want to see. You can also download raw data in spreadsheet form. I've attached a screenshot showing solar panel, storage tank, and oil boiler cycles for August of this year.

 

[velvetfoot]

Nice work. Low cost. No roofs to climb, but only summer operation, I take it. I like all the instrumentation. I have not dabbled in this area. Do you talk about it (instrumentaion) elsewhere on your web site?

 

[cbrodsky]

We have a great baseline for oil consumption. Exactly five months before we set up the first solar panel, our oil tank was filled. The day the panel was installed, the tank was filled again. We used 101 gallons of oil during those five months - all for heating hot water. I asked the oil guy what normal hot water usage was, and he said "oh, about 20 gallons a month".

Nice site!

Your comment above is really interesting - I also came to nearly identical results on our house. What is shocking is that so much of that oil use is just standby loss keeping the boiler ready to go on standby. They are not have as well insulated as a good solar storage tank.

I realized this for myself when I tried to estimate how much hot water that 20 gallons per month would have made... if you assume that 70% of those BTUs go into making hot water by just accounting for operating boiler efficiency, it suggests you're using unbelievable volumes of hot water in your house. I know for a fact we weren't - it was going to standby losses.

I think for this reason, anyone who runs an oil boiler to make hot water year round can get a really good payback with solar HW. And I think it's also why in the shoulder season, it's far more efficient to use an electric element to close the gap to get the output up to temperature rather than fire up the boiler.

-Colin

 

[Nofossil]

I realized this for myself when I tried to estimate how much hot water that 20 gallons per month would have made... if you assume that 70% of those BTUs go into making hot water by just accounting for operating boiler efficiency, it suggests you're using unbelievable volumes of hot water in your house. I know for a fact we weren't - it was going to standby losses.

I think for this reason, anyone who runs an oil boiler to make hot water year round can get a really good payback with solar HW. And I think it's also why in the shoulder season, it's far more efficient to use an electric element to close the gap to get the output up to temperature rather than fire up the boiler.

-Colin

I have three teenagers, and we tend to have lots of long-term company in the summer. Even with low-flow showerheads, we use a fair amount of hot water - I estimate 80,000 BTU/day. That being said, the original system had two major sources of wasted heat: Standby loss from the hot water tank, and the leftover heat in the oil boiler when the hot water tank is back up to temperature. We were heating up the boiler more than three times per day, then letting the leftover heat warm the basement each time. One of the things I spent some time on was recovering that leftover heat from the oil boiler, which we still use for the shoulder seasons. Writeup is here.

 

[babalu87]

Links down nofossil?

Not opening here

 

[Nofossil]

Links down nofossil?

Not opening here

Server issues today - my ISP is giving me a headache. Should be resolved soon.

 

[jjbaer]

Very nice set-up.....clean, easy to implement. Good work!