Amal Kabalan, LEED A.P.
MDCSystems®
Consulting Engineer 
May 2009

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Engineering and Financial Analysis 

In the article “Pennsylvania Solar Energy Rebate on Hold: How Consumers Can Still Save Energy” published in the February 2009 edition of the MDCAdvisor®, the steps that homeowners can take in order to reduce their energy consumption were outlined. This article discusses a case study that shows the effect of implementing two of the mentioned suggestions namely: increased attic insulation and powered, thermostatically controlled roof ventilation. Moreover, since the Pennsylvania Solar Energy Rebate program has been funded, a detailed analysis of costs and benefits of installing a solar power system on a residential house will be outlined and whether such a project is a viable option in light of all the federal and state incentives will be discussed.

The residential unit considered in this study is a suburban residential property located in West Chester, Pennsylvania - 28 miles west of Philadelphia. The owner, in previous efforts to reduce the energy consumption of the house, improved the attic insulation and added thermostatically powered, controlled roof ventilators. The implementation of those strategies showed a significant decrease in the energy usage and thus in the monthly bills.

Figure 1 depicts a comparison between the 2007 and 2008 monthly bills for the residence. The bills tend to be high in the summer cooling and winter heating seasons, reaching a peak of $425 in August 2007. The 2008 January-May bills are higher than 2007 bills for the corresponding months. This trend reverses in the rest of the months. Figure 2 also shows that the consumption of electricity has decreased in July, August, September, October and December from 2007 to 2008. This shift is a result of adding attic insulation and ventilations.

Since the highest bills are in the summer this means that it may be favorable to install solar panels. A solar power system has the best performance in the summer when the sun is out and the days are long; this allows the system to operate as long as 14 hours per day. Moreover, the electricity rates are the highest during the summer peak hours. This corresponds to when the sun is available and the solar power system is operating close to peak performance. Thus a solar power system alternative to avoid those high rates will be the viable option to investigate in order to shave off those peaks and save on utility costs.

Utility Increases

As a result of Pennsylvania's 1997 electric utility restructuring law, PECO no longer produces electricity. Electric power generation is sold in a separate, competitive wholesale market. As part of the restructuring, PECO's customers have benefited from capped electricity generation rates since 1996. Since then, wholesale market power prices have risen, driven by increasing fuel costs and global competition. When the electricity generation rate caps expire for PECO customers on January 1, 2011, the company will be required to buy power on the wholesale market at prices that are expected to be higher than today's capped rates (1).

In an attempt to provide a smooth transition to the new rates PECO said it is filing a plan with the Pennsylvania Public Utility Commission that will help its customers deal with the expected increase in their electricity bills when its rate caps are lifted at the start of 2011. The plan would give electricity customers of the Philadelphia-based electric and gas utility company the option of preparing for the expected increase by making payments into a savings account that pays 6 percent interest. Customers who make the payments would have the payments and the interest they generate applied to their bills after the limit is lifted. Customers could also defer a portion of any initial rate increase by spreading out the amount of the first year’s increase over the following two or three years.

Under the plan, PECO would also spend more than $50 million on programs and products to help customers manage costs by using energy as efficiently as possible. Strategies such as offering a discounted residential rate to qualifying low-income customers to buying power through a series of competitive purchases at different times, rather than at one time, when market prices could be high and launching a multimillion-dollar consumer education campaign about the coming change in electric rates from now through 2012 are all included in PECO’s plan.

The market prices are highly unpredictable so PECO would be able to announce an average increase rate but not the exact rate. Given this situation the best practice a consumer can acquire to be ready for the increases is to be energy efficient and aware of consumption. This can be done by installing electric meters in the house instead of outside and observing the daily consumption of the house. There are multiple electronic gadgets that will tell you if your consumption is average or high given the size of your house. Another practice would be to generate one’s own power through a solar power system. Once the system is installed no extra fees need to be paid. Think of it as installing your own customized power generator on the roof of your house: a generator that is quiet, clean, and environmentally friendly.

Solar Power System Analysis
The example residence is located near West Chester, Pennsylvania - 28 miles west of Philadelphia. Due to its proximity to Philadelphia, it is reasonable to consider that it has the same latitude, longitude and weather conditions to that of Philly for the purpose of the analysis. Latitude is 39.88 and longitude 75.25. Elevation is 9 meters. Figure 3 shows the location of the house (B) in correspondence to Philadelphia (A).

Orientation
The house has south, north, and west exposures. It has one roof facing south with a 24x30 ft2 dimension. The orientation is shown in figure 4.

Incident Solar Radiation
The south facing roof gets the maximum exposure of sun during the day, so this is where the solar panels can be mounted. The incident solar radiation (KW/m2) that the roof will get changes with the time of the day and the month of the year and the inclination of the roof. Figure 5 provides the incident solar radiation data for Philadelphia which can be used in West Chester as well.

Shading
The roof might get shading from the trees on the east side of the house. It is recommended to use a solar pathfinder for a proper shading analysis. It is worth noting that shading one or two panels may decrease the performance of the system by 50%.

Calculation
The decision on the capacity of the solar power system depends upon the following factors:

• Available roof space
• Owner’s available budget

There is always room for optimization in terms of what is the best size to have that would result in the most savings. This is however beyond the scope of the article as it requires a deeper analysis. In this article we will confine our limiting factors to those mentioned above. The roof area is 720 ft2 which can handle up to a 26KW system. Our limiting factor remains the budget and based on that we will choose to design a nominal 5 KW system which is common in residential houses.

The house has an energy usage of 24,414 KWh/ year. Installing a 5 KW solar power system will generate 6000 KWh/ year (this number is arrived at by a series of calculations that involved converting from DC to AC power and taking into account the solar radiation of West Chester). Thus a 5KW system will provide 24.5 % of the house energy. The total cost of the system without any incentives is $36,500. Figure 6 shows the effect of the solar power system on the electric bills. In October 2008 the electric utilities mounted to $152. If a solar power system is installed the electric bill would have been $112. This is a decrease of 26% in electric bills.

Financial Analysis:
The question now becomes: is it financially sound to invest in a solar power system? The answer depends on the following factors:

• The federal tax incentives and subsidies available
• The state tax incentives and subsidies available
• The tax bracket that the owner’s property falls under
• The percentage of rate increase and rate structure changes of the local utility
• Financing options available

Figure 7 shows how factors 1, 2 and 3 are related and their effect on the final cost of the system. In the latest federal energy bill passed by the government, the consumer can make use of a 30 percent incentive of the cost of the solar power system. Based on the system mentioned above the homeowner can get $10,964 as incentives from the government. Moreover, The Pennsylvania Commonwealth Financing Authority board voted on April 14th unanimously to borrow $30 million to get the Pennsylvania Sunshine Program (Sunshine) started.
Enacted in July as part of Gov. Rendell's $650 million Alternative Energy Funding Act, Sunshine is expected to provide rebates of 35 percent of the system cost to help cover the cost of buying solar power systems. Accordingly, the owner can also receive $12,792 from the state. This state incentive will be taxed by the federal government according to the federal tax bracket that the owner falls under. In this case it is 33 percent. Thus the state incentive that the owner will get will be $8,570. Adding all these numbers together the final cost of the system to the homeowner will be $17,014.

As mentioned in the prior utilities section the electricity rates are going to increase by 2011. Based on the unpredictability of the market, PECO and other utilities in Pennsylvania are not able to provide an exact number of the increase. The projections are starting at a 20 percent increase and reaching 75 percent in regions such as Allegheny County. For the purpose of this discussion it is going to be assumed that the owner will experience a 37 percent increase in the rates which is the current estimated increase given by the utilities for the West Chester , Pennsylvania area.

Another uncertainty is the rate structure. Currently, the owner pays 6.84 cents/ KWh for the generation charge for the first 600 KWh used and 3.9 cents/KWh for the rest of the energy purchased. The same trend applies to the transmission and distribution charges. Adding the generation, transmission and transition charges the owner will pay 14.8 cents/KWh for the first 600 KWh and 7.29 cents/KWh for 815 KWh. This is illustrated in Figure 8, 9 and 10. Figure 8 depicts October 2008, where the house consumed 1,415 KWh. The first 600 KWh were billed at 14.8 cents/KWh and the 815 KWh were billed at 7.29 cents/KWh as shown in Figure 9. Figure 10 shows that the pricing is designed in a way that encourages the consumer to spend rather than save as he/she is paying less for more energy used.

When the property owners are considering installing a solar power system they should be cautioned to use the correct rate structure in their calculation. It is a common error to use the higher rate in sales proposals to make the solar power system more attractive; however, in practice the owner will not realize the savings that he/she was promised. For instance, in this case, when solar panels generate around 500 KWh per month, the bill profile will be as shown in Figure 11. The 500 KWh will be shaved off from category B and thus the 7.29 cents/KWh rate should be used in the analysis and not the 14.8 cents/KWh. This shows that a thorough technical analysis is necessary before installing a solar power system as consumption profiles vary, thus affecting the decision on whether solar is an economical option or not. In this analysis the correct charges were used and if the utility rate structure changes, the owner will be on the positive side and reap more benefits from the installation.

Financing
The financing option depends on the markets and the banks. For the purpose of this analysis we will assume that the owner is entitled to a loan with an interest rate of 6 % and period of 20 years. The capital recovery factor for this loan would be 0.08718/year. As stated above the loan needed is $17,013. Figure 12 shows how the loan payment is broken down and the different factors that affect it. For example, every year the owner will pay $1,483 toward the loan. This payment includes an interest portion and a financial payment. The owner will be also eligible for a deduction on the interest paid; in this case it is equal to $337. The resulting final yearly payment will be $1,146.

Figure 13 shows the electrical bills between January and October 2008. Shown in Red is what the estimated new electrical bill will be after installing the solar power system. In green is what the monthly payment will be. Evidently installing the system does not generate profit for the owner and does not break even. Figure 14 shows the estimated old and new bills over 30 years. The estimation takes into consideration the 37% increase in the utilities rates and also a 2% increase of the rate from one year to another. The solar power system will be paid for over 20 years. After that the owner will start generating some savings. The pay pack period is around 30 years. Considering all the above it can be concluded that it is not currently cost effective to install a solar power system.

It is also noted that installing a solar power system increases the value of the house as the house would be considered energy efficient. According to the study “Evidence of Rational Market Valuations for Home Energy Efficiency” published in the Appraisal Journal, residential real estate markets assign to energy efficient homes an incremental value that reflects the discounted value of annual fuel savings. The capitalization rate used by homeowners was expected to be 4%-10%, reflecting the range of after-tax mortgage interest rates during the 1990s and resulting in an incremental home value of $10 to around $25 for every $1 reduction in annual fuel bills(3).

Let’s consider that the value of the house under study will increase by $10 for every $1 of energy saved. By installing a solar power system the house will save around $500 on the annual electrical bill. That means the annual incremental increase of the home value will be approximately $5000. With this consideration the payback period of the system is proposed to be 24 years.

Conclusion
A comprehensive engineering and financial analysis of installing a solar power system on a residential house was discussed. The location and incident solar radiation of the unit under study is very favorable for installing the system. The house has minimal shading which makes it ideal for a solar power system. The house has ample roof area for installing such a system as well. Studying the energy consumption of the unit showed that consumption peaks in the summer, which adds to the advantages of installing a solar power system. Finally a financial analysis was conducted that took into account the increase in utility rates and financing option available for the owner. The analysis showed that it is not profitable to install the system if the owner is seeking immediate revenue from such a project. The payback period is around 24 years and only after this time the owner will be able to generate profit. Finally, this analysis is based on current market predictions. The electricity rates may increase rapidly, thus making a solar power system investment viable.

Renewable energy systems, especially solar power systems, are highly customized. What might work for one region or one house might not necessarily work for another. A thorough engineering and financial analysis is required before embarking on such projects. The house orientation and location, the roof structure and area, budget and consumption profile, to name few, are all factors that must be investigated. As realized from this analysis an initial overview of the house location and energy consumption profile made a solar power system an attractive option; however, further detailed analysis showed that the system is not currently cost effective.

Bibliography

1. Masters, Gilbert M. Renewable and Efficient Electric Power Systems. New Jeresey : John Wiley & Sons, 2004.
2. Reuters. www.reuters.com. [Online] September 10, 2008. http://www.reuters.com/article/pressRelease/idUS211109+10-Sep-2008+BW20080910.
3. Evidence of Rational Market Valuations for Home Energy Efficiency. Watson, Rick Nevin and Gregory. Chicago : The Appraisal Journal, 1998.