Evacuated solar tubes VS Geo thermal

I'm not aware that we have traditional geothermal energy (hot water) available here in Massachusetts, but maybe he was referring to groundwater heat pump systems, which take advantage of our 50°F groundwater temperature (map, right). The heat pump needs an external energy source to make up the difference.

I'm wondering, if you have sufficient solar tubes on your roof, can't you store excess energy on sunny days to use on the cloudy ones?

YES , i CAN , i HAVE A STORAGE TANK OF 3500 GALLONS WAITING TO BE INSTALLED JUST FOR THAT

Not saying I'm smarter, but, here's what I did.

Put a geothermal heat pump in and my wife loves it.

Then I constructed a solar collector out of an old ten foot satellite dish with mirrors that reflect the sun to a tank with circulating water thermostat controlled. It tracks the sun all day.

The collector gets to about 200 degrees on a sunny day and the water is then pumped into the thermal system. when the heat pump calls for heat, it uses the solar heated water, otherwise the water is pumped to the underground system and it acts as a bank so to speak.

All this is controlled by two PLC's that talk to each other.

Yeh, I've got some money stuck into this, but it's money I didn't spend in the bar because of nothing else to do.

Something to keep in mind, I own my own backhoe, shop with tools, welder, torch,etc. And I wrote the programs for the PLC's which probably saved a bunch of $$$.

Stub

It's be great if you posted some photos of your solar-tracking collector, and some of the other apparatus you made.

This is where I got my ideas, and they're almost identical.

http://www.youtube.com/watch?v=pEIEhwqu3bE&NR=1

my geo system is horizontal with 3000 feet of 3/4" inch pipe seven feet underground, five runs of 300 feet out and back, and this is in Minnesota.

Another thing, in a dry run with outside temps in the low 50's, the interior of the tank hit 226 degrees while the outside hit 350 degrees with no water in the tank and five minutes exposure into the sun

Stub

Look up the solar insolation data for your area - your buddy is blowing smoke as it is a function of how much collector area you have - nothing more and nothing less.

http://rredc.nrel.gov/solar/pubs/redbook/

Except for 'when the sun don't shine' of course. If you buy the collectors it will be expensive. www.builditsolar.com has plans people have used that seem reasonable.

GSHP is expensive upfront - the coils (loops buried shallow as mentioned previously) or wells are costly and the heat pump itself is costly. Possibly the hardest part with geothermal is finding someone that understands how the earth in your area will transfer heat. Different soils and rock have different characteristics. Wet is very different from dry.

If the pipe field is too small or you have inadequate wells (total meters of well) you can end up with a real disaster. The whole system needs to be designed correctly - this is not like an air source heat pump in that regard.

Russ

Recent studies I have seen show the output of flat plate collectors to be not much different than vacuum tube collectors in total heat collected. The flat plate type work over more of the day it seems.

You need to determine how many kW you need to collect to last you over night and then for a second day. It is a lot of storage.

If you go with solar you will have to have some type of backup - if a storm lasts for several days no solar system is going to be adequate.

You haven't told us how many of the tubes you're planning on using, because that's a critical factor in energy capture regardless of where you're located. Size does count after all! ***LOL*** Also, know that your tubes should be able to capture the IR part of the spectrum for heating purposes, even on cloudy days. Check the manufacturer's test ratings.

What angle (to the horizontal) are you planning on installing the tube arrays? This is vitally important in the NE, especially during the Winter months when you need to capture as much energy as possible. Latitude (your location) + 15 degrees is normal to capture the Sun's energy during the Winter. I live in the mid-Hudson Valley and my Lat. is slightly more than 40 degrees North, so my tubes will be installed at 55 Degrees in regard to horizontal plane.

But FIRST, you need to do some energy calculations....start off determining your house energy losses and what it takes to heat your house. Then, make sure you have enough insulation installed to lessen the losses and hence reduce your need to heat the house. This will help lessen the size and complexity of your Solar Heating System Also, one of the greatest heat losses is through the windows, so looking at insulated curtains or quilted.insulated pull-downs is essential.

All-in-all, make sure you understand how to perform the energy calculations and the principals behind them, okay? If you need help there's a ton of info available online and in books........check out Amazon or even Ebay. I was able to find some very good DIY solar design books in Ebay for my system design.......I'm using 50 evacuated tubes in my closed loop system, with a oil-fired boiler/Hydronic system as backup. I'm till behind the 8-Ball getting things fabricated for my system, plus buying some more components.

Seems to me that your 3,500 gallon tank is way oversized. Is it insulated? Installed in the basement or buried outside? If it's poly, make sure that the manufacturer certifies it to withstand +200 Degrees F, otherwise it will melt! Most poly tanks are rated for maximum operating (melting point) of around 150 degrees F. In is crucial that you verify this rating!

I don't know your friend and what he does for a living, but is he a Mechanical Engineer? If not and he's not qualified to give you engineering answers, then don't entirely listen to him.

Also, where in MA are you located? We may be in driving distance of one another, and can discuss our respective systems over coffee.

Have a Sunny day!

He is talking about a hydronic house heating system.

If you are talking about contributing to the heating of your home with a 50 tube solar thermal installation you are hopelessly deluded.

Russ

I didn't mention in my posting that I'll be installing 12-inch wide x 46-inch long Linear Fresnel Lenses (curved poly lenses made in the UK) above each and every Evacuated Tube, thereby increasing my capture amount tremendously....each lense capture is approximately 12 to 15 Suns.

Already ran a test bench this past May with and w/o the Fresnel Lens above a single tube. The heat bulb w/o the lenses typically ran close to 200 Degrees F. W/ the Fresnel lenses the heat bulb temps approached 300 Degrees F. As you can see, it really makes a huge difference in energy capture using the lenses. Tubes will be spaced 12 inches o.c., thus providing room for 12 inch wide curved linear Fresnel lenses installed with 8-inch focal point

BTW, my tubes are NASA surplus w/ the inner tube coated with Gold surface coating to improve IR capture. I didn't buy these from any old solar equipment supply store..... their performance is far superior than that trash.

Oh Gee! I stand in awe!

BTW - You quite often read of the NASA type gold coated tubes being used.

1)

Vocational teacher, ss 3500 gal top 5ft deep/insulated top:

two standard tube drain down collectors and a peanut pump;

(clean, no deposits as a worry) Well-fed boosted 52f water to geothermal in1981/...

still on-line, still saving over 800 gal of oil with a 43k compressor water:water TETCO 050. then the Col OH design, before now TETCO at Enertec/Hydron/GeoComfort OEM

2) Simple air solar, with filtered-air-inlet : Insulated cabinet with 3 (OEM 500f baked) window screens

and about 55 cfm per collector of 8x3ft sizes;

use 1.1/2" back insulation of poly-iso, or better, isolated from air that is breathed;

to a simple fan-coil for HW (200sq inch x 2 row) and small circulator to HW tank:

With a vinyl flap 3 piece "air-check" at lowest outlet (between blower and sending air to collectors) of the air collectors (use better material for that for longevity) the solar-air night-time "air-cooler" effect is blocked///

all is 3-way air diverter- "valved' to rend space comforts and HW

Lasted over 20 years, then might have been longer if maintained.

6 collectors was too big for half area of a 2000 sq ft ranch, so a foor fan was used to send to near by return air of then running HVAC blower during the day for distribution. Two collector systems were minimal, in Dayton Ohio.