SAM Solar Model Recommends a Very Small System

Hello,

I have a SAM Solar System Model that inputs the PNM rate tariff 4B (please see attached) that recommends a very small system that has a yearly production of around 3,000,000 kWh for a facility that consumes 25,000,000 kWh per year. This is especially strange since an earlier model with similar monthly loading patterns but under the PNM rate tariff 3B recommends a system that produces around half of the facility's consumption. Is there a reason for the recommended system being so small? Thanks!

Hi Sara,

Can you explain what you mean by SAM "recommending" a system size? The system capacity is an input to the model that you provide when you specify the system's configuration.

Best regards,
Paul.

Hi Paul,

When I say that SAM "recommended" a system size, I mean that I ran the Parametrics analysis from the Simulate tab and input the system size in the System Design tab based on the maximum net present value. Then, I ran the simulation again and analyzed the sized system's energy outputs versus the energy demand.

I hope that clears it up.

Thank you,
Sara

Hi Sara,

Thank you for the clarification.

Please see this post on running a parametric analysis on system size with the Detailed Photovoltaic model:

sam.nrel.gov/forum/forum-general/2808-parametric-analysis-on-pv-system-size-or-dc-ac-ratio.html#7633

Best regards,
Paul.

Hi Paul,

The Parametric Analysis had worked as expected (please see attached image), but what I want to know is why it recommended such a small array size (1500 kWdc). The annual energy expenditure from the Electric Load and our data is around 25 million kWh, but from the Simulate analysis the 1500 kW array would only produce 3 million kWh per year. I tried changing the rate tariff in the Electricity Rates but it gave a similar answer. Why is the percentage of energy produced vs. consumed so low?

Thank you,
Sara

Hi Sara,

In your analysis, the cash flow is determined by the value of electricity savings and project costs. Project costs consist of debt payments, operation and maintenance expenses, and annual insurance payments. Project costs increase with the system size. There are no taxes or incentives. The monthly load is much higher than the system's total monthly electricity production for the range of system sizes you are considering, so there are no net metering credits. The monthly electricity bill savings come from a reduction in energy charge and demand charges, which both vary with system size. There is a fixed $585.29 charge that does not vary with system size, but is much smaller than the total bill.

The following graph shows the annual-after tax cash flow for three system sizes from your .sam file. The net present value is calculated from the after-tax cash flow, so the graph gives a visual representation of the NPV. The 900 kW system has lower costs than the larger systems in the first 10 years, but then has lower savings in the later years. The 1800 kW system has higher savings in the later years, but higher costs in the earlier years. The balance of these costs and savings for the 1500 kW system results in the lowest NPV given the inflation and discount rates you assumed for your analysis.



Best regards,
Paul.