Beyond CE Code 64-112’s 120 and 125 percent rules

Moustafa YoussefBlog

load_side_connection_CE_code_64_112

Most solar PV systems are connected to a propery’s distribution centre. Solar electricity feeds appliances connected to it, and any extra power is back-fed to the grid. However, the Canadian Electrical Code limits the connecting capacity of multiple power sources feeding a distribution centre. In this article I will explain why such limitations exist and ways to increase a solar PV system’s capacity beyond CE Code 64-112’s 120 and 125 percent rules.

Why load side connections?

Load side connections are the simplest way to connect a solar PV system. The only upgrade required to a panelboard is an installation of a bi-directional breaker as far away as possible on the bus from the other source breaker(s).  However 64-112 limits the sum rating of the supply breakers at 125% of bus rating for homes, and 120% for non-dwellings, and I’ll give an example to show why.

What’s the point of CE Code 64-112’s 120 and 125 percent rules?

Consider a bus that has a rating of 225A and connected to its only supply source through a 200A breaker. No problem here. The bus is always protected because if more than 200A of current tried to reach it, the supply breaker will trip and interrupt the current. Is this still true when the bus is connected to other power sources? Below is a picture of a panelboard being fed from two sources, namely a solar inverter and another power source, which could for example be a generator, a transformer or another panelboard. Each power source is connected through a breaker that limits the current or power flow reaching the bus.

solar inverter interconnection

This is how most small grid-tried solar PV systems (<500kW) are interconnected to the grid. They are installed behind a breaker like any other appliance connected to the bus.

Suppose that a solar inverter is connected through a 100A breaker. Now if both sources were feeding the bus at their maximal capacity, they could be pushing a total of 300A into the bus, which exceeds the bus rating of 225A :

The purpose of CE Code 64-112’s 120 and 125 percent rules are to protect distribution nodes from multiple sources of power.

For a 225A bus in a home,CE Code 64-112 requires that the sum of the breakers feeding a bus can’t exceed (225+25%) 281A as per CE Code 64-112 (4). So if the main breaker that’s connecting the home to the grid has a rating of 200A, the solar breaker(s) can’t exceed a rating of 81A or 80A. So we can install one 80A breaker to tie-in one inverter or for example, 4x20A breakers to tie-in four separate inverters or panelboards connecting several inverters.

CE Code 64-112’s 120 and 125 percent rules

64-112 (4) limits the sum of the sources feeding a bus to 125% of the bus’ rating for homes, and 120% for non-dwellings. If we want to install a greater output capacity, we can

  1. buy a bigger panelboard/distribution centre with a greater bus ampacity. This is the most expensive option, and its impact is limited. For example, panelboards are limited in their capacities – it’s not easy to find single phase panelboards with rating greater than 225A. We can also
  2. reduce the rating of the main 200A breaker. This depends on whether or not the client can afford to reduce their loading capacity.  Again this option is limited.

History of line vs load side connections in Canada

When Ontario spread-headed the adoption of distributed solar in 2009 with their microFIT program, they required output of solar inverters to be connected to a separate meter. A home would still have one run from a transformer, but it would split to two meters, one for consumption, the other for generation. Most jurisdictions today including Ontario are providing either net-metering or net-billing settlement systems that don’t require a separate meter. This load meter just has to be replaced with a bi-directional one to be able to measure exported energy.

Advantage of line side connections

Many installers and inspectors outside of Ontario are only familiar with load side connections because it is the most popular way of interconnecting relatively small systems. But CE Code 64-112 actually allows for line side connections (rule #1) before it allows for load side connections (rule #4). A line side connection will bypass any load-side connection limitation, including CE Code 64-112’s 120 and 125 percent rules.

CE_Code_64_112_Line_Side_Splitter_Solar_Grid_Tied

As we can see with a line side connection the panelboard is now fully protected and risks no overload. With a line side connection the panelboard no longer limits the interconnecting capacity of a grid-tied solar PV system. Furthermore, the line side equipment such as the meter socket doesn’t have to be upgraded at all, unless of course the capacity of the solar inverters exceeds the ampacity of the meter socket.

Line side connection on meter socket

If the bus bar on meter socket already has enough extra space for the new cables you want to install I would just install them there. It’s important to note to the inspector you are not actually increasing the capacity of power flow through the meter socket since solar is a negative load. So unlike a load side connection that increases the current through the bus, any current from the solar on line side will decrease the current from the grid and so the ampacity of the meter socket need not be greater than what it already is. Of course that’s assuming the size of the solar pv breaker is less than or equal to the rating of the main breaker on the home panel.

Is solar PV a reliable energy source?

Moustafa YoussefBlog

solar-pv-reliable

solar-pv-reliable

Solar PV is often criticized for not being a consistent or reliable source of energy. The sun doesn’t always shine when we need it, and it can be difficult or impossible to accurately predict short-term performance because it is strongly influenced by the weather. However if one were to take a step back and evaluate over the long-term they may find that there is a high degree of consistency in the performance of solar PV systems. In this article I am going to do some statistical analysis on production data one of the first systems we installed.

About the solar array

The system is located in Calgary. The array is flush mounted and made up of two sub-arrays of four modules, one facing SW with a true direction of 225 degrees; the other is facing SE with a direction of 135 degrees. Both sub arrays have a pitch of 4/12 or a tilt of 18 degrees. The system was commissioned in August 2014 so there are three full sets of annual data to analyze. The array experiences a little bit of shading and hasn’t experienced any serious power outages.

Annual energy production is highly consistent

Below are charts depicting the annual energy production of each module in 2015, 2016 and 2017. We can see that some modules consistently produce more or less energy than adjacent modules. This can be attributed to shading and surface temperature variation. Having said that the system’s total annual production is incredibly consistent. The system produced a total of:

  • 2,287 kilowatt-hours in 2015,
  • 2,218 kWh in 2016, and
  • 2,141 kWh in 2017.

These numbers yield a mean of 2,216kWh and a coefficient of variation of only 3%. Assuming performance is normal we can be:

  • 95% confident that next year’s energy production will be between 2,070kWh and 2,360kWh, or we can be
  • 99.5% confident that it will be between 2,000kWh and 2,450kWh.
2015 solar production kwh

2015 solar production

2016 solar production

2016 solar production

solar pv reliable energy source

2017 solar production

Methodology

  • I collected four data points for each month for all months except for June, July and August which have only three data points each.
  • Data was not corrected for cell degradation. You may have noticed that the total and modular annual energy production has been decreasing year by year, but it’s too early to relate this to cell degradation.
  • Monthly averages are a mean of the monthly production data.
  • Monthly coefficients of variation are calculated in order to compare variation in production. A dataset with a higher COV means that it’s less predictable.

Results

In red below is the ratio of a month’s mean production to annual mean production, whilst the blue represents the month’s COV.
COV solar production

Observations

  • The summer months May, June and July each produced about one-seventh of the average annual production, which will  be called ‘annual’.
  • May to September have an incredibly high consistency. For example the month of May has produced a total of 318kWh in 2015, 308kWh in 2016, 316kWh in 2017, and 319kWh in 2018, yielding a COV of only 2%.
  • Production from December up to and including February accounts for about 5% of annual.
  • The COV and monthly mean curve seem to be opposite one another. The higher the mean, the lower the COV and vice versa. Production is a lot more consistent between May and September than it is in the winter. But is this high winter variance really a problem?
  • Winter has a higher variance, but because there is very little production its influence is limited. For example, a COV of 32% for the month of January means that we are 95% confident that production to be between 0.5% and 2.3%. The bottom line is the amount of energy is negligible and will be absorbed by a design margin.
  • On the other hand, June makes up for about 15% of the energy and it has a COV of 3%. This translates to a 95% confidence that production is going to be between 14% and 15% of annual. That is a higher quality prediction, and an important one as well because of the amount of energy it accounts for.

Conclusion

We only analyzed four years of a system that is expected to stay in operation for 25 years. Therefore this analysis is still in its infancy. However I think it puts the question of reliability of solar PV in a good light. When looked at from a monthly or annual basis, solar PV seems to be a consistent energy source. Or at least one can say that this approach enables stand-alone system designers to efficiently communicate and justify generation and storage capacities. With probabilistic data a system’s size can be based on a client’s appetite for risk. Of course grid operators will still require short term forecasting as more solar is adopted across their jurisdictions, and a model based on observed data alone has its limitations.

I wrote an article about averages in the context of off-grid systems showing how it is favourable to use longer measuring intervals because they evolve to normal distributions with low variance i.e. higher quality.

May the power of averages be with you.

Click here for a .pdf of this article.

Saskatchewan’s Small Power Program

Moustafa YoussefBlog

Saskpower Small Power Program

In our last blog post we discussed Saskatchewan’s solar net metering program offered by Saskpower. The Small Power Program is another type of settlement that Saskpower offers which may be suitable for large power consumers.

The Small Power Producers Program is a Feed-in-Tariff agreement where Saskpower will pay for all the energy generated on-site for a guaranteed rate for 20 years. Depending on your energy consumption, applied rates, Small Power may be a better option for you.

Lets first look at how Small Power Systems are configured

Saskpower Small Power Program

As we can see, compared to net metering which has a single bidirectional meter, the Small Power program doesn’t affect the existing service. Instead a new meter is installed to measure all the electrical energy that is produced and exported to the grid. In reality, this energy turns around and goes into the service to feed the loads when needed but the systems are treated independently and they have different settlement rates.

Is the Small Power Program Right For Me?

To determine which of Saskpower’s Net-metering Program or Small Power Program is right for your situation we have to determine which settlement method will generate more revenue. In our last blog post we looked at a small commercial service that was consuming about 3,000kWh per month. The service is consuming less than 14,500kWh and so the customer is charged 13.2 c/kWh. Any greater energy consumption beyond 14,500kWh will be charged at a rate of 6.971c/kWh.

Let us suppose the commercial service is consuming an average 20,000kWh per month. Now the monthly energy charges would be 14,500 kWh at 13.2 c/kWh and 4,500kWh at 6.971 c/kWh, for a total cost of $2,228. Now let’s say it has a net-metered system that produces an average 1,000 kWh per month. Let’s re-calculate the savings.

Now the average month will have its energy charges reduced from 20,000kWh to 19,000kWh. The 1,000kWh that was exported reduced the charges at a rate of only 6.971c/kWh not 13.2c/kWh. This is much lower than in the previous example because the shop was consuming a total less than 14,500kWh per month. Although larger consumers are charged less for consuming more, they are also credited at a lesser rate for their solar exports under the Net-Metering Program.

Small Power Program

The customer is reducing their consumption at the balance rate of 6.971c/kWh not 13.2c/kWh. Small Power program would be more cost-effective than Net Metering.

 

This is where the Small Power Program can be cost-effective, for large commercial and agricultural services that have consumptions beyond the first block. To know whether Small Power is right for you please fill out our site assessment below or give us a call.