The Solar Calculator provides two “measures of goodness” for the project: the Third-Party Best Offer and the Simple Payback. In addition, it gives you an estimate for the installed cost of a SHW pool heating system.

The Third Party Best Offer is our estimate of the price a 3rd party investor is likely to charge you, the owner of the pool(s), for the heat supplied by the solar system to the pool. The best offer price is computed by setting the third-party’s after-tax internal rate of return at 15% and then determining what the third party must charge you for energy to realize that rate of return. You can compare the Third-Party Best Offer ($/MBtu) to what you are currently paying for the heat delivered to your pool.

Simple Payback is the length of time in years it will take for the energy savings to pay for the solar investment. The Calculator computes three simple payback numbers: a) payback for a pool cover alone, b) payback for a solar collector alone, and c) payback for a pool cover and a solar system combined.

Inputs to the Calculator

Fuel Cost: The costs of the fuel can be taken directly from a recent utility bill. Find the total amount of fuel that was delivered for that period and divide that into the total amount that was paid for that fuel. For example, if 1,000 Therms was delivered at a cost of $900, then the unit cost is $0.90/Therm ($900 divided by 1,000 Therms). The calculator let’s you input your energy cost in one of three units: $s per MBtu, $s per Therm, or $s per cubic foot.

Union or non-union labor:
The use of union versus non-union labor can have a large impact on the cost of installing a solar hot water (SHW) system. Even if the solar system under consideration were to be installed by a private sector entity, if the SHW system is installed on government property, government rules may require that the project be implemented with contractors who pay union-scale wages. Hence the government agency that is issuing the RFP must assess whether contractors are going to be required to use union or non-union labor.

Cost of Pool Cover and SHW System:
In the Solar Calculator the assumed cost of labor to be $19 per square foot of collector area for union labor, and $11 per square foot, for non-union labor. Note that a manual pool cover will not generally require installation labor and as such its cost is not affected by this user-input value. The pool cover was assumed to be a simple vinyl cover. Based on a brief market survey, the cost for the cover, including its take-up reel, was estimated to be $2.00 per square foot of pool surface area. The cover would have a manual take-up reel (or reels depending on the pool size). If you equip the cover with a motorized take-up reel, the total system cost will be in the several times greater. The motorized option is still worth considering if it means that the cover is more likely to be used regularly by those responsible for the pool.


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Indoor and outdoor pools:
We made the following assumptions in our performance calculations for indoor and outdoor pools:

The Region:
This is self-explanatory; simply click on the map in the region corresponding to the location of the swimming pool. Note that if you change any of the input values (such as energy cost), you will need to click once more on the region in order to re-compute the pay-back values.

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Guidelines for Interpreting the Calculator Results

Located at the bottom of the Calculator are the Simple Payback numbers and a best offer energy price.

Third Party Offer (best price for pool owner)

This Under a third-party financed project,

Simple Payback

If the payback is short, then it is likely that third-party financers could make money on the project and would submit a bid . If the payback is long, then it may not be worth the trouble to issue an RFP and since the probability that anybody will respond is low.
Generally speaking, here is some guidance for interpreting the Simple Payback values computed by the Calculator:

--Short payback (less than 3 years): Excellent economic prospects. The project is so good that it is a candidate not only for 3rd party independent ownership but also for internal capital funding. This project is likely to attract numerous bidders who would be interested in engaging in a independent power production contractual arrangement or energy savings contract.

--Moderate payback (4-8 years): Good economic prospects. The project would probably attract third parties who would be interested in engaging in a independent power production contractual arrangement or energy savings contract.

--Long payback (8-12 years): Fair to poor economic prospects. The project would probably not attract a lot of bidders for an independent power production or energy savings contract. The third-party financing approach is questionable because the economic value of the project may not yield a sufficient profit to the installer/operator to warrant the preparation of a proposal.

-Very long payback (greater than 12 yrs): Poor economic prospects. It is unlikely that an RFP would attract any qualified bidders for independent power generation.