$2K Solar Space + Water:  System Cost, Payback & Rebates

This section covers estimating the cost of the system, figuring out how long it takes to payback that cost, and discusses rebates the system may qualify for.


Back to Table of Contents...


On this page:

Cost breakdown for the system we built...

How to estimate the payback period for he system...

The situation on rebates -- federal and state...




The table below gives an estimate for the cost of the system as we built it.


The total damage is about $2,200.  


While the federal rebate cannot be applied unless you build with SRCC certified collectors (see below), you may qualify for state rebates depending on where you live -- in MT, there would be a $500 tax credit.


When you consider that a typical commercially installed system costs about $8,000 for solar water heating only, you begin to see what an exceptional deal DIY solar thermal systems are.  I don't know of any DIY projects that will save you the kind of money that DIY solar thermal projects do.


There may be an item or three that I missed in adding this up, but it should be pretty close for US builders.  Project builders in Canada have reported higher material prices.


Note that if you have space for more collector area, the cost picture comes out even better as the collector gets larger because you are only adding some collector cost and a little bit of tank cost -- bigger is better.


On this project, we concentrated on long life and good appearance, not on saving money -- we did not cut corners to save a few dollars.



Item Description size qty unit price Total  
Collector Frame   2X6 42 $0.50 $21.00  
Twinwall glazing 10 mm twinwall polycarbonate 4X10 3 $90.80 $272.40  
Fins  Tom's fins lineal ft 120 $0.65 $78.00  
Insulation  polyiso 1 inch thick Rboard 4X8 3 $16.00 $48.00  
steel glazing support 1 by 1.25 inch steel tube 20 ft 1 $33.59 $33.59  
PVC lumber trim White PVC trim for collector   1 $54.00 $54.00  
Horizontal glazing supports 1/2 inch EMT conduit 1 ft 24 $0.15 $3.60  
Absorber risers 1/2 inch copper  1 ft 180 $1.05 $189.00  
Absorber manifolds 3/4 inch copper 1 ft 24 $1.95 $46.80  
Reducing T's and fittings   25 box 2 $32.00 $64.00  
Unions   3/4 union 2 $5.00 $10.00  
Paint, glue, Great Stuff,   1 gal 1 $30.00 $30.00  
Collector Total         $850.39  
Collector Loop            
Circulation pump Grundfos 15.58 + flanges 1 1 $61.00 $61.00  
supply and return plumbing 3/4 inch copper 1 ft 18 $1.95 $35.10  
Fittings elbows, T's   12 $1.00 $12.00  
Valves Shutoff and fill 1 2 $5.00 $10.00  
Collector Loop Total         $118.10  
sides and bottom 3/4 inch plywood 1 sf 64 $0.75 $48.00  
Frame 2X4s 1 ft 24 $0.30 $7.20  
Edge boards plastic wood deck boards   1 $20.00 $20.00  
Insulation 2 inch polyiso (2 layers) 1 sf 120 $1.00 $120.00  
EPDM liner   1 sf 160 $0.80 $128.00  
Lid screws log screws to hold lid down   10 $1.00 $10.00  
Water  Water is still free!       $0.00  
Tank Total         $323.20  
DHW Preheat            
PEX coil heat exchanger 300 ft coil of 1 inch PEX   1 $167.00 $167.00  
Valves Bypass valves   3 $5.00 $15.00  
connecting plumbing 3/4 inch copper 1 ft 10 $1.95 $19.50  
Fittings copper elbows,   6 $1.00 $6.00  
DWH Preheat Total         $207.50  
Radiant Floor            
PEX floor loops half inch PEX tubing 1 ft 200 $0.35 $70.00  
PEX floor manifolds 3/4 PEX tubing 1 ft 100 $0.58 $58.00  
PEX fittings, vlaves T's, elbows, 1 20 $1.80 $36.00  
Circulating pump Grundfos 15-58 + flanges   1 $61.00 $61.00  
Supply and Return pipes 3/4 inch copper  1 ft 18 $1.95 $35.10  
Valves shutoff and fill 1 2 $5.00 $10.00  
Heat spreader plates Alum soffit to fins 1 ft 100 $0.60 $60.00  
Radiant Floor Total         $330.10  
differential controller SHEM differential controller   1 $100.00 $100.00  
Floor heat thermostat standard furnace Tstat   1 $60.00 $60.00  
transformer 24 VAC transformer   1 $9.00 $9.00  
Thermostat relay 24VAC to 120VAC relay   1 $13.00 $13.00  
Tank thermostat control Johnson Controls A419   1 $60.00 $60.00  
Controls Total         $242.00  
Grand Total          $,2071  



Some things that would take the cost down a bit without impacting life or performance by very much if any.

- Single glazing on collector -- save about $150 with small performance hit in cold climates.

- Eliminate back insulation on collector -- save about $50

- Cut tank insulation down to 1 layer of 2 inch poliso (R13) -- save about $60

- Use a baseboard unit or PEX radiator to distribute heat instead of radiant floor -- save $150?

- Scrounge around eBay for deals on pumps, controllers, ...  -- save $200?


This all adds up to a potential of $600 savings -- brings the total price down to about $1500, and state rebates could help from there.




I'll try to provide more data here later, but for a start on payback, have a look at these two areas:

The $1K solar water heating system cost/payback page...   This gives estimates for payback for the $1K solar water heating system.  This is the system that this new combined  space + water heating system was derived from.   It covers the payback from just the solar water heating portion.  Typically about 3 years depending on your fuel price -- this gets even shorter with rebates.


The Solar Shed solar space heating system cost/payback page...  This is our mostly homemade existing solar space heating system.  The payback material for it will give you an idea how the space heating part pays.




The system as described here would not qualify for the 30% federal tax credit.  To qualify for the federal tax credit, the collectors must be certified by the SRCC to the OG100 procedure.  That is the only requirement, so if you buy certified commercial  collectors, the whole system then qualifies for the federal rebate.   If you took this approach with the system shown here, this is how you might end up on cost if you go with commercial collectors, but make the rest of the system:


Item   Cost $'s
Fully homemade system cost       $2200
      Buy 3 commercial collectors for about $1000 each plus freight  +$3300
      Save cost of making a collector  -$800
Total system cost with commercial collectors  $4700
Collect 30% federal rebate on full system cost    -$1400
Total system cost with commercial collectors after rebate  $3300


So, it comes out about 50% more expensive, but you save the work of building the collectors and you have nice set of commercial collectors.  Even with the 50% increase in cost, the total cost of the system is still FAR less than a comparable commercially designed and installed system. 


Just as an added plug for the DIY approach, for our particular situation, with the space we have available on the south side of the house, its hard to fit commercial collectors in.  The space is a little to narrow to put collectors 3 wide, and its not quite tall enough to put ten foot tall collectors in -- so you end up with something like two 4 by 8 ft collectors and take a large hit in collector area compared to a collector built to fit the exact space.


State rebates vary a lot.  In our state (Montana) the system qualfies for a $500 tax credit -- there are no certification requirements.

The best place to start to find out what your state offers for solar system rebates is here...   -- (check the DSIRE site).




Gary February 13, 2011