Lecture 26

October 25, 2013

Monthly Variations for Energy Production in Boulder with Angle

Normalized Energy Production in USSingle Axis Tracker and Fixed Plate

Design Considerations• 1. How much power per year do you need? • 2. How much area is available to work with?• 3. What type of solar cells , inverters and how many

modules do you want to use ? 4. How much budget is available?• 5. What are your current costs for electricity and what

fraction can you get from a solar energy system?• 5. Can you use the grid for backup or do you need

storage? • 6. Will the utility pay for excess power?

Costs $/watt

Sensitivity to Module Price and Efficiency

Theoretical Maximum Efficiency

Lecture 27

Capital Recovery Factor

• 1

2. Example Cost $4942 kWh/yr with i = 4.5% on 30 year loanWith costs $0.057/WDC then CRF=.06139 Annual payment $1177.8/yrCost = $0.238/kWh . This is high compared to utility rates most places.

1)1()1(),(

n

n

iiiniCRF

Capital Recovery Factor

Taxes Reductions Can Help

Tax Reduction Example

• Cost $19,186 for 4942 kWh/yr• 30% tax credit Price goes to $13,430• Annual Payment A=$824/yr, Interest $604 first

year. Tax saving 25% = $151.09• Cost $673.40 • Cost $0.136 /kwh

First Year Net System Costs After Rebates

Cash Flow Analysis

• Build Spread Sheet with initial cost, loan amount, interest, taxes, derating, rebates, CRF, discount rate, utility rate. See page 345

• Note present worth or present value calculations. P =dollars today is worth more than the same value in the future by what you can get by investing it. F = (1+d)n or P=

• d is the discount rate or interest rate.

Residential Rate Structures

• 1. Flat rate• 2. Decreasing with use. • 3. Increasing with use. • 4. Time of Use ,TOU , use for shifting load.• 5. Real time pricing, RTP. Bid into market. • 6. Critical Peak Pricing CPP, Get low rates for

letting one be cut of a limited number of unscheduled times.

California Residential Rate StructureSummer

Time of Use Example

Critical Peak Pricing Rates

Commercial Pricing

• 1. Basic rates plus demand charges. • 2. The basic rate may be time of use based. • 3. Demand charges are high and based on

peak 15 minute period in a given month. • Example base at peak $0.13/kWh• Demand Charge to $14.59/kWh and is charged

on top of the regular rate.

Commercial Rates Charges

Demand Charges

• Demand charges can add 50% or more to the total bill.

• This give an incentive to use PV if it can reduce the peak load particularly if it is near peak load on the system.

Modified Accelerated Cost Recovery System ( MACRS)

• 1. Businesses allowed to Depreciate Capital costs before taxes.

• 2. Can also get a tax credit• 3. Example 30% tax credit and the amount

that can be depreciated can be reduced by half of the 30%

• Net cost can be less than half the name plate cost.

MACRS Example

Power Purchase Agreements

• 1. Used when can not get tax advantage • 2. Third party buys and installs and operates

the PV system. • 3. Can start a little higher or lower than the

utility rate but is fixed so as to save money over time. The third party may make its money on taxes or selling power to the utility.

Power Purchase Agreement

Utility Scale PV• 1. Must compete at whole sale rates. Time of

Delivery rates (TOD)

Power Purchase

• Need to have a good estimate of how much power you are going to generate to be able to set the price.

• RPSs may drive the need by the utility to buy the power.

Stand Alone PV

Battery

Battery Equivalent Circuits

Battery Charge Discharge

Household Loads

Household Loads.

Electronic Loads

Battery Types Energy Density.

Temperature Dependence of Lead Acid Battery