Solar Costs in Germany and USA

I found this interesting article that analyses the differences in costs of solar PV systems in Germany versus USA. I don't have a similar analysis of Ontario costs, but I am looking - let me know if you have seen any research on Ontario solar PV costs.
http://cleantechnica.com/2013/02/17/why-german-solar-is-so-much-cheaper-than-u-s-solar-updated-study/

Charting out the Generation, Revenue, Expense of our PV System

I've cumulatively plotted out the revenue my PV system has generated over time as well as what I've paid on our load. I've also plotted out the microFIT payments I've received from Guelph Hydro. Note the following:

• revenue (blue) increases relatively over the spring and summer months and slows down over the winter
• our revenue was initaially greater than out payments, then over the first winter revenue was lower than the payments. The revenue overtook the loan payments in June 2011 and has been a net income ever since
• our net earnings to date have been approximately $8500-$7500=$1000
• the microFIT payments are lagging my loan payments - I've needed to keep a float in my account to cover the delay of payments
• the time period between microFIT payments from Guelph Hydro is rather variable. The last payment in particular was delayed quite a bit and I had to put extra money in my account to cover the automatic withdrawal of the loan payments. Guelph Hydro told me they are implementing a new billing and payment system that will automate their payments. They told me they had now over 100 microFIT contracts connected in Guelph. It also tells me that Guelph Hydro is much more consistent in sending bills to me than wanting to pay me.

Revenue generated, loan expenses, and microFIT payments

Generation Results up to June 2012

A quick post here to share my June power generation. It was a great month, and so far every month this year has been better than last year. Much more sun, not as much snow.

Sum - Revenue, daily	Years
Date	2010	2011	2012	Total Result
Jan		$136.10	$205.18	$341.29
Feb		$220.57	$258.66	$479.22
Mar		$449.77	$456.57	$906.34
Apr		$395.30	$501.84	$897.14
May		$428.51	$607.72	$1,036.24
Jun		$567.19	$573.10	$1,140.30
Jul		$616.75	$61.57	$678.32
Aug	$131.53	$528.09		$659.62
Sep	$351.28	$423.49		$774.77
Oct	$360.90	$313.65		$674.55
Nov	$285.03	$253.69		$538.72
Dec	$62.74	$176.31		$239.05
Total Result	$1,191.47	$4,509.43	$2,664.65	$8,365.55

Data Catch-up!

Several months have gone by without me posting my data - sorry about that. Actually the last posting was 1 September - shame on me. Sorry again!
Our system has now been running for almost 1.5 years and we can now compare data between two months of different years to begin to see how variable the solar energy received is. Since our system was commissioned August 2010, we can now compare September to December (and in a few days January). We know that weather and solar energy will be different between the years, but I didn't know by how much. Also, the effects of weather will affect the solar generation - I'm primarily referring of snow and its persistence. So, on to the data...

Daily Power Generation

The data is downloaded from my Fronius datalogger and creates two M$ excel files: a daily summary file and a instantaneous (15 min average) file. The files report the kWhr, AC and DC voltage, and error messages (never had any error messages. I'll have to do a posting on the AC power but I don't know enough about it to say anything intellegent about it (yet). I add the daily data to a spreadsheet file where I do calculations and the figures.
The annual trend in solar radiation is clearly visible now that we have more than a full year cycle in Figure 1. There is considerable daily variability - as much as 30 kWhr for the system or 6 kWhr per kW per day. The highest variability is during the spring months of March and April. In August and September the variability ranges about 20-25 kWhr or 5 kWhr per kW per day. One reason for the larger daily variability in the spring months is because the overall potential output is highest (35 kWhr) and there is still the good chance that snow covers the panels or there is a very dark overcast day. The days are also still a little short therefore the total accumulated solar radiation will be less than the longer summer days. This is why we see the lowest generation days in mid-summer still seldom being less than 10 kWhr. This means the variability per kW to be closer to 5 kWhr/kW/day and not 6 kWhr/kW/day.
December was an interesting month to compare between the two years. December 2010 received a quite a few snow days and this resulted in many days with very little power generation (see all the points clustered around the x-axis during the second week in Dec with virtually no days over 10-15 kWhr until mid-January. I've (begrudgingly) reported this in an early posting. Even though we love the snow and winter, the good news for December 2011 was that there was virtually no snow fall this year and there were many days where the system generated over 10 kWhr. Several good days over the month makes a big impact on monthly revenue.

Figure 1. Daily Power Generation, 4.9 kW DC PV System

PV Generation Output Levels Over Time

I will attempt to answer the question of "how much power is the system generating right now"? I'll expand on this to summarize how often the 4.9 kW system is generating at different levels. This is very interesting once you see the results. For example, during a day with sun and cloud the output may be less than 1 kW much of the time, but when the sun finally appears for an hour the output may be 4 kW. So, how much money do I make during cloudy periods and how critical are bright sunny days? Let's look!
The Questions :

• How often is the PV system generating at different levels [in watts]
• How much money is earned at each output level
• How often are the panels generating near maximum output or above

The Data :

• Fronius Datalogger Pro installed on PV system noon 2010-10-31
• Wattage output averaged and reported by data logger every 15 minutes
• Continuous monitoring when inverter putting power to the grid [greater than 15 W]
• 2011-06-07 17:15 is last measurement event
• Data points n = 9658

The Method :

• 15 minute interval data downloaded from datalogger and imported into spreadsheet
• Watts used to calculate kW, revenue at $0.802/kWhr, and watts generated per wattage of panels [20 SolarWorld SunModule poly panels at 245 kW each]
• Frequency distribution curves generated by pivot tables function

The Results :

Raw data

Figure 1 shows the raw data used for the analysis. You can see the output levels for each 15 minute period of the day when the system is operating [it shuts down automatically at dust when the panels generate less than 15 watts]. During November the maximum output is around 4000 watts. This drops to 100-200 watts during December other than a few days when it rises above 500 watts when there is no snow on the panels. A similar pattern is seen at the end of January 2011. From February to June there are many days when generation is over 4000 watts, even over the 4900 watts which is the maximum rated output of the panels. The maximum level seems to decrease back down to 4000 watts after March. This could be partially explained by the warmer temperatures during the Spring daytime compared to the colder February and March air temperatures. Power output decreases significantly when the panels are over 30 degrees Celsius.  Of course the panels only output their maximum daily limit for a short period. The morning and afternoon output is much lower and this is a larger duration of the day compared to the peak generation time period. Cloudy days also decrease the output level.

Figure 1.

Power Generation Levels

The shape of the power generation frequency distribution curve should come as no surprise when you consider the many points in Figure 1 that are less than 1000 watts. Sixty two per cent of the time the PV system is generating less than 1000 watts. Snow shading, mornings and afternoons, and clouds do not yield a lot of solar energy. Considering our house consumes about 300 to 400 watts continuously [1200 when the pool pump is running], the data show our house is a net power exporter much of the daytime over the year. The similar frequency of output from 1000 watts to 4500 watts is interesting. It suggests to me that once the sun rises there is quite a lot of time when the clouds are partially blocking the sun. Also, if we assume that the system can generate at least 3000 watts once the sun is up [i.e. 9 am to 6 pm] then we can see that Guelph has had a fairly cloudy period. There are 1327 15 minute intervals when the output is over 3000 watts, or 331 hours of "bright sunshine" out of 2415 hours of generation time! Let the Beatles some "Here Comes the Sun" come true this summer! Also:

• 45 minutes was 5000 watts to 5130 watts over this period - end of March. 5130 watts is 4.7% over the panel rated output, and that does not include the derating factors such as DC power line losses and inverter efficiency losses

Figure 2.

Revenue by Output Level

As frequent as <1000 watts may be, is it important for overall revenue, or what about the sunny periods. This really shocked me initially and now I know why I am so happy when it is sunny outside! Before I blab on any further, here is Figure 3. And this figure shows some very important information that relates to solar PV designs. I'll no doubt discuss this figure in future postings.

Figure 3.

Revenue resulting from 3000 watts and more represents the highest revenue levels! And our 4.9 kW rated system produced over its rated limit for 2 3/4 hours and earned $11.25 over this time.
Additional observations :

• total revenue to date generated is $2,229
• most revenue is earned at <3000 watts, but not by much
• about $100 was earned when revenue was greater than 4500 watts. If we use a common solar industry practice to oversize the panels relative to the inverter by approximately 10%, we would have lost approximately $100 in potential revenue. This undersized inverter is rationalized that a larger inverter may be considerably more expensive. In fact this may not be the best economically decision based on the data presented in Figure 3. [Of course, sizing the inverter and panels is more complicated than that]
• my initial solar configuration was going to be 4.9 kW of panels and a 4 kW inverter. Lost revenue would have been close to $400 [assuming that inverter efficiency across the power level range is equal for the inverter sizes]
• the generation frequency distribution in Figure 2 is opposite to the frequency distribution curve of Figure 3
• the frequent low sunlight levels is financially less important than sunny periods

Initial Conclusions

• your solar system should be designed to maximize the higher sunlight levels. Shade, ventilation, panel orientation, inverter sizing are all very important factors that must be explicitly accounted for when you have your PV system installed
• sizing your panels and your inverter is critical. Use the inverter manufacturers' software to properly design the number of panels, types of panels, the number of strings
• ensure that the inverter is sufficiently large to handle the high end of your panel output levels. Under-sizing the inverter by over 10% should be seriously rationalized unless there are upper limits to amount you are permitted to generate
• for example, the Ontario Power Authority's micro Feed-In Tariff Program has a 10 kW upper limit. You could maximize the amount of low sunlight level generation by increasing the number of panels, thereby shifting the mode of the Figure 3 revenue chart to the right. But this can only be done after using the inverter manufacturers' system configuration software. Failing to do this may result in lost power generation or damage to the inverter
• the 5100 watt inverter on our system is able to take advantage of the few periods of very intense sunshine yet this has earned me significant revenue. Over the period of 10-20 years of our microFIT program this will add up to a sizable income cohort
• choosing the location and orientation of the panels should try to maximize the bright sunlight periods of the day

Undoubtedly there are many more things I'll see in these data. My next posting will evaluate the power generation frequencies relative to panel size. This will partially answer a question I faced when I was choosing what type and brand of inverter to install [string inverter vs. micro-inverter - hint : I think i made the right decision].

Solar Model vs. Actual Solar Generation

When I wanted to know if our solar PV system would make any money for us under the Feed In Tariff program through the Ontario Power Authority, i could either listen to sales reps or calculate it. Some sales reps "guaranteed" that we'd make money, others said that it would pay for itself without over promising. I was skeptical of the former guys even though I knew our system would pay under the FIT program with $0.802/kWhr. I used RETScreen and PVWatts to do my modelling. I posted my results in an earlier post. Essentially what I found was that each month saw good generation, higher in the summer than December.
I've plotted my cumulative generation against the RETScreen model of our 4.9 kW system. What I found was the generation was greater than modelled during the autumn of 2010, much lower than the model during the winter, and it seems that March and April are fairly closely modelled.
The plotted data below shows several data sets :

• the blue curve is the results from the datalogger. The PV system was online on 24 August, but I didn't have the datalogger until 01 November so I simply read the meter at the end of each day until the datalogger was installed
• the open brown circles are the Guelph Hydro electricity meter readings
• the RETScreen model is the purple curve with triangles
• our household consumption [load meter] are the red closed circles

The chart is plotting cumulative kWhr. Broad observations of model accuracy should be made on multiple years of data, but we can still see how the model compares. So, what do we see???

• over the autumn our PV system was generating about 2/3rds of our consumption but after the dark and snowy days after 10 December our electricity consumption remained constant or slightly increased, however our panels virtually flat-lined. Our panels cover much of our south-facing roof but it is still not enough to supply our home's consumption. Technically we are not using any of the electricity we are producing - it is metered and sent directly onto the grid. But it would be nice to know that we are contributing what we are using albeit at different times of the day. 
• the panels generated more than the house consumed between 17 March and 27 April. The panels generated 745 kWhrs and the house load was 595 kWhrs [25.2% generation over consumption].
• the Guelph Hydro meter continues to be slightly below the datalogger. I wish they were the same! It could be that the datalogger is recording total generation which is occasionally greater than the inverter rating of 5 kW, whereas the Guelph Hydro meter is recording what is actually going out onto the grid. Or maybe not! Maybe they are measuring the same thing but one of them is wrong! Fortunately the difference is small.
• the RETScreen model seems to be approximating the generation starting around 15 February. Indeed the PV generation may be very slightly higher than the model.
• my financial calculations were based on RETScreen and PVWatts models, after mid-December we are less than my predicted generation [and therefore revenue]. I hope we have a nice bright summer to get close to the model again so we make our forecasted revenue!

Our loan costs from 24 August 2010 to 27 April 2011 was $2,646 and our revenue was $2,354. This is a deficit, however we also went from August to the darkest part of the year and we are just coming back into the sunnier season. I am confident that the low revenues of December and January will be more than offset by this summer's generation. We only need 30 days of over 20 kWhr to make up the $310 deficit, so I am not worried.