One year with solar

Home solar install

In late June or early July of 2015, the grid-connected solar at our house was switched on by Xcel Energy (I’ve lost the precise date). By July 19th of 2016, I had twelve months worth of electrical bills during which the panels had been producing for the entire month. Here are some thoughts and data.

  • Our install included APsystems microinverters that malfunctioned on systems installed throughout the state. That meant the during the “sunny” months, the panels were limited to producing about half of their potential. The inverters were reprogrammed in May of 2016. In total, the system produced about 77% of what it was expected to over the course of the year.
  • Even with that hiccup, the system produced 3,367 kWh, or 17% more than our house used over the 12 month period.

usagesolar

  • We used 14% less electricity during the year than the previous year. I think some, but not all can be explained by the real-time metering that came with the system. I’ve spent far too many minutes (hours?) looking at the dynamic egauge chart, thinking about reducing peaks and total usage. (The winter of 2016 was warmer than 2015, but the summer was about equally hotter, so I’m calling weather factors a wash)
  • I need seasonal energy storage. July production was 6.5 times January production. I’m curious to see if next January is any better now that the inverters are fixed. We use electric heat in a small attic space, which means our electric usage in winter is probably above normal.
  • Our neighbors used more of our solar energy than our house did. Xcel has two meters on our home now, so over time they can track what is being provided to our plugs from our system, what is being provided by their grid, and how much energy is being exported. Over 12 months, our solar array delivered 25% of the kWhs our house used, and the grid delivered 75%. To put it another way, other grid users got 75% of the kWhs our solar array produced, while we only got 25%. This is primarily a function of when our house uses the most electricity (morning and nighttime) compared with when the array is producing (midday). The effect is most pronounced in the winter when it is dark both when we leave and when we return home.

sourceofelectricity

  • Our system produces when energy is most expensive for the grid operator.
  • Including the payments we made to finance the system, we paid about 13% less in total for electricity in this 12 month period than the period prior.
  • Putting solar on your roof is a great way to start conversations with your neighbors! People are curious, and love to ask how it is working, how much it cost, and who installed it.
  • After the sun comes out, snow slides off in a couple of days.

Measuring battery charging efficiency

I lied, it’s another solar post, sorry. I think I have another in the works too, but that one will be longer, and have maps!

Usually, I don’t get to see/use the full capacity of the two battery-connected panels on our roof. On perfect sunny days, the battery is usually out of bulk charging (it’s “full”, kind-of) before solar noon is reached, when the panels would be at full output. This is by design, as there needs to be extra capacity in the panels for cloudy days. Here’s what that usually looks like:

CurtailedAmps

By 9 am, the charge controller stops bulk charging, and reduces the amperage going in to the battery. Amps go back up periodically when the deep freeze compressor turns on, but most of the potential production is curtailed, so to speak.

A few days ago, the batteries had dropped to a pretty low state of charge after a few rainy days: slightly under the 50% mark. This is usually lower then I let it go, but won’t hurt unless it’s a regular occurrence. The next day was totally clear and cool – perfect for charging the batteries and trying to track the panels maximum output.

FullAmps

On this particular day, the battery stayed in bulk charging mode until about 1:30 pm. According to the specifications on my panels, under laboratory conditions, the maximum output for each panel should be just over 9 amps (so the output of two should be just over 18). At exactly 12:30 pm, the charge controller was pushing 17.49 amps into the batteries, which was the maximum that day. This is over 96% efficient! That seems like a pretty good result considering potential efficiency losses like the wiring run and the charge controller itself, which takes a percent or two.

So the panels, wiring and charge controller are all performing well (or can, when called upon). I thought this was the case, but hadn’t really tested it fully until now. Of course, getting the energy out the battery is a whole other story (a much more inefficient one). Exploring that will take some different measuring devices, and another post.

Should more solar panels should face west? (with local data)

Here are two charts I made using data from the output of our grid-tied solar array and data from the Midcontinent Independent System Operator (MISO), the people who keep the regional grid (including Minnesota’s) running.

LoadAndSolar

This shows the total load the grid is using in a given hour and the total production in that same hour from our solar array. Our array faces due south. The shape of MISO’s load curve is fairly consistent from day to day, and so is our production curve (on sunny days). The peaks are not coincident, and solar production drops off dramatically in the peak load time. Data from our home use is even uglier (on weekdays).

LMPAndSolar

The second chart compares the same solar production to price. For this one, I averaged all the locational marginal prices at the Minnesota Hub for all the days in July (average prices can vary somewhat by day and hour). The blue line basically shows how expensive wholesale electricity is in Minnesota at a given hour based on supply and demand (side note: check out this great real-time map of marginal electricity prices in MISO at different locations). Solar production seems to match this curve better in the morning, but still misses the opportunity to offset some of the more costly electricity in the afternoon. In July, west-facing panels could frequently be producing until 8 pm and beyond, when the price peak seems to start dropping off.

Rooftop solar usually doesn’t point west, probably because the incentives and utility rates (at least in Minnesota) are designed to maximize production rather than meeting peak load or reducing electricity prices. The New York Times has covered this dilemma. At current levels of solar generation in Minnesota, the issue of west- vs. south-facing panels doesn’t matter much. As generation grows however, this issue is something for utilities and regulators to consider.

The grid is good

We’ve had an Egauge monitor that tracks our home’s solar production on for about a month now. It’s fabulous. For the last week, it’s also been tracking our whole-home electricity usage. Here’s a graph of hourly average power (in kW) from production and consumption.

weekofsolarconsumptionThe solar installers are still adjusting breakers, so output is down, but here are a few things I’ve learned mostly based on our usage.

  • Our house is never using less than 100 watts. We do a pretty good job with power strips, turning off lights, etc. But even at night, even when the refrigerator is cycled off, we’re using around 100 – 200 watts. There are a few things constantly plugged in (battery chargers, sleeping computers, clocks, etc), and I’ll be tracking them down. I’m curious how close to zero watts we can get during the night.
  • Our weekday usage peaks do not match solar production peaks. In the morning, the coffee pot and the hair dryer are running before the sun rises above the trees. The microwave, dishwasher and washing machine often run in the evening on weekdays. On sunny weekdays, we’re sending a lot more energy to the grid than the house is using (since we’re at work). Weekend usage and production peaks match better (see the last to days on the chart). For many reasons, the grid is good.
  • I’m now more obsessed with finding out how much energy things use, and switching them off. The little red line moving in real time on the screen is a great motivator.
  • Our peak demand is probably about 4 kW. The above graph doesn’t show it, because it’s an hourly average, but we hit about 3.5 kW on a very hot weekend day when a number of window air conditioners were running. This is above our peak solar output, which is probably 2.8 kW under optimal conditions. This is also important for a future post I hope to write exploring what it might cost to actually take our house fully off-grid (at least on the electric side).

Home solar update – to the roof!

Home solar installMy small experiment with solar started with one 100 watt, battery-connected panel resting on the ground in the backyard. I soon added a second and eventually a third panel. I learned a lot about every component, as well as the seasonal and weather-related variability of production.

Over the last few weeks, the hobby was turned over to the professionals, panels went up on the roof, and most of the system is now “grid-tied” instead of going to a battery. We now have 3,840 watts on the roof! Thanks to a very attractive financing option from Innovative Power Systems, our total costs should be similar or slightly lower than normal pre-solar electricity bills. The system should produce very close to the amount of electricity we use in an average year. We’re still waiting for the Xcel Energy engineer to sign-off on the install and switch on the grid-tied portion, but are told that will happen in days/weeks.

Of course, copious data will flow, as solar production AND total home usage will be monitored in real time. I look forward to trying to match usage to production curves.

I kept a piece of the system battery-tied for my hobbyist tendencies. The two smaller panels on the right connect to the battery charge controller and small battery bank in the basement. Both the panels and the batteries have been upgraded in size from the backyard setup, and of course the panels will no longer be shaded by the neighbor’s walnut tree. The usability of the battery system should be way up, and this should allow an interesting comparison between battery- and grid-tied systems.

November solar doldrums

cloud gif

I made this gif of visible satellite imagery from the NOAA’s Geostationary Satellite Image Archives. It basically shows cloud cover over the last 12 days at about 1 pm (19:15 zulu) each afternoon. This is a high-tech way of saying we’ve barely seen the sun for the last two weeks.

The implications for my 300 watt off-grid solar project are that almost nothing is being produced, and I’m not running anything from the batteries. With no sun in the forecast, I’m concerned about them sitting at a low stage of charge for days (or weeks at this point), which can reduce the life of lead-acid batteries.

In Minnesota in the winter, solar needs a backup, or at least a supplement. It’s great to have a grid. If I were truly off-grid, I would need some other kind of backup unless I was willing to significantly overbuild batteries or panels.

100 days of solar

100dayssolar

Watt hours to the battery, first 100 days

Today I noticed that my solar charge controller has been running for 100 days (it logs this among many other data points).  Here are some highlights from the first 100 days:

  • The system has produced 32 kWhs from two 100-watt panels.  This is roughly 2% of the total electricity consumption we saw over the same period last year.
  • Converting from DC current to AC current at low wattages is wildly inefficient.  I usually run the wifi router and cable modem continuously off the battery and I lose about 40% of my produced energy to the inverter.  It is much happier running closer to its peak (1000 watts).  We should probably convert to DC.
  • Something happened to my charge controller settings when I converted to 24 volts.  Although the controller was still charging, I lost about 10 days worth of data (hence the gap in the chart) and wasn’t able to communicate with it over that time.  A firmware reboot fixed this.
  • Although very cold, clear days are when the panels perform their best, the sun just doesn’t shine for that long each day in January and February in Minnesota.  The panels being on the ground doesn’t help either.  Just from the middle of March to the middle of April I’ve about doubled my daily output.
  • All that said, this chart doesn’t really show total potential of the panels on a given day.  If I didn’t use much of the battery the day before, panel production the next day was curtailed by the controller to avoid overcharging the battery.  I’m trying to match the loads I put on the battery with the “capacity” of the season, but that’s sometimes tricky.
  • I recently learned we were accepted into the Minnesota solar rebate program for 2014!  So with the help of a friendly solar installer, we should have a 2.8 kW grid-tied system installed sometime this year. Along with the grid-tied panels, the installer will be adding two panels on the roof dedicated to battery charging.  Now I just have to wait…

Counting every watt hour

This little device is an ethernet to wi-fi adapter. It connects my solar charge controller to my home wi-fi network so I can make fancy graphs.  It uses 1.2 watts per hour.  I know this because I measured its usage using a watt meter.  I do this with everything I power from the solar batteries.

I have a hunch that this is what solar does to you, makes you compulsive about energy use.  Even if (when?) I have a large grid-tied system, I imagine myself checking the daily output, and constantly thinking about how to reduce my usage to match.

On very cloudy days, this little thing has used over 45% of the energy produced by the panels.  I unplugged it.  For now, graphs only on special occasions.

Home solar: adding MPPT and marvelous data

DSC02865

As part of my plan for the eventual expansion of my off-grid solar energy system, I recently added a new charge controller with Maximum Power Point Tracking (MPPT).  Besides being much more efficient, this controller is capable of producing reams and reams of wondrous data, and is network-connected, meaning I can geek out on battery voltage and array current from anywhere in the house!  The charge controller I had was great, but it wouldn’t handle anything beyond a few more small panels.  Now I should be able to go all the way up to 750 watts of panels (my goal).  So, thanks Santa!

While installing the controller, I also took the opportunity to install a breaker box, which should bring me closer to code, and upgrade to larger diameter battery cable, which should reduce efficiency losses.

The MPPT advantage

MPPT is a fancy way of saying the charge controller is able to send significantly more energy to the batteries from the same panels.  How much more? After only a few days of testing, I estimate 40 – 60% more than the Pulse-Width Modulation (PWM) controller on days when the battery is low.  (If you want to know the details of how MPPT works, I found this explanation helpful.)

Here’s some actual data from my system which I think illustrates the MPPT advantage well:

1-5 plain graph

The blue line is the amps, or current, coming from the panels.  The red line shows the amps the controller is putting in to the battery.  It’s higher!  The magical MPPT doohicky converts excess voltage into amperage (remember, amps X volts = watts) so less of your panel’s potential is wasted.  On this particular day, I estimate the charge controller may have been able to wring an extra 100 – 150 watt-hours from the panels.

There are other interesting things going on here, so here’s a little annotation:

1-5 annotated graph

Here’s the next day, when the battery starts out the day almost totally full.  It was very sunny.

1-6 amps graph

The controller limits the array current and current to the battery significantly because the battery is almost fulled charged.  The gentle downward slope in the amperage is a function of battery charging called absorption.  Less current is pushed into the battery as it reaches capacity.

I can track hundreds of days of watt-hour production, so I’ll do another update when I can show some seasonal changes.  How I yearn for the days when the panels get more than 4 hours of sun per day!

Power surge

solar farm

My back yard solar farm has doubled in size to a massive 200 watts!

If you remember from the last post, the wooden frame was half empty (who built it like that?), and was feeling really lopsided without another panel.  The frame is now full (Amazon is a marvel of the modern age), so any further expansion will have to happen on the roof or elsewhere.

Untitled

Parallel wiring.

Under optimal conditions I think this will produce 480 watt-hours per day.  For reference, that’s about 60 percent of the power needed to run our chest freezer.  These panels are connected in parallel, meaning the voltage (12) is the same, but the amperage is doubled (to about 10 amps).  I ordered a cheap ammeter, which I’m excited to hook up so I can see real time results.

The last few weeks have been very cloudy, so I think output has been down.  The next week doesn’t look that great either.  When you’re a solar farmer, you start caring about the weather a lot more.

After adding some additional wiring, I now have access to a solar-powered power strip in the living room, rather than just having access in the basement where I could run an extension cord from the inverter.  Now I’m regularly running some lights and the stereo from the battery.  The cable modem and router are small, consistent loads, so I may move those downstairs to become battery-powered.  I’ve become somewhat obsessed about matching load to the production, since I don’t want to “waste” any electricity produced (and also don’t want to run my battery below 50%).

Stay tuned for another update when the ammeter arrives.