Tag Archives: solar power

Tesla Powerwalls Installed

My two Tesla Powerwall 2‘s were installed last week and now I’m running on my own solar-generated power after dark!

You see, Powerwalls not only keep the lights on when the power goes out but they also let you automatically time shift energy daily to avoid using power from the grid at peak demand times – not something you get from a traditional backup generator.  Plus they don’t need any maintenance or fuel.

And yes, this does mean that now I will still have power for the whole house and, most importantly, running water the next time PG&E needs to shut down the power grid for fire safety.  Yay!

Avoiding Peak Demand Usage

It used to be that daily peak energy demand occurred through the mid to late afternoons but with the widespread adoption and installation of solar photovoltaic panels, that afternoon demand has evaporated and the peak demand now comes in the evenings.  As a result, power companies have been adjusting their rate schedules to reflect that, with the highest cost of energy running well after dark to 8 and 9 pm.

With battery storage, you not only get backup power for the whole house in the case of outages, but you can also automatically store energy generated during low demand periods of the day (including from your own solar panels) and automatically use that stored energy during the later peak hours, even after the sun goes down.  This means that your existing solar PV system ends up being even more effective and cost-efficient.

Time-shifting energy usage with battery storage works so well that Tesla and other companies have been actively deploying massive, utility level battery storage systems around the world, in place of traditional, expensive peaker plants. (Peaker plants are power plants whose primary purpose is to cover periods of high demand.)

Powerwall Configuration Options

I really like the Tesla app for configuring and monitoring your Powerwall and, if present, your solar PV system.  It continually displays the flow of power between your home, Powerwalls, solar panels and the power grid – in real time.

You can specify to keep the system in a “backup only” mode (keeping the batteries fully charged at all times), in a “self-powered” mode (where it stores any excess solar generated and uses it to power the home as much as possible each day), or in one of two time-based control modes where it forecasts your future energy usage and time-shifts your energy use and solar production to fit the peak, off-peak and shoulder periods of your particular electricity rate schedule.  And all of these modes operate under a “storm watch” feature that will automatically override the normal behavior of the Powerwall to prepare for forecasted storms or other events that may result in an outage.  All very cool!

Balanced vs Self-Powered on two cold, partly cloudy days with the heat pump cycling over much of each day.

I tried running in the “balanced” time-based mode for most of March but then switched to “self-powered” mode because, during the non-summer months (October – April), there is no peak rate and the difference between partial-peak and non-peak is only a couple of cents.  In “balanced” mode, the system would make a point of exporting any excess solar generation during the partial-peak period for credit rather than continuing to charge the Powerwalls.  This would mean it would be more likely to need grid power overnight.  Now in “self-powered” mode, the Powerwalls are charged more and usually able to handle the entire house load overnight – depending on the weather (solar production and house heating need).

Update (June 2020): Well, it’s not even summer yet and the Powerwalls are already letting the house run completely self-powered most days.  And by “house” I mean everything (central heating, water heater, cooktop/oven, washer/dryer, well & pressure pumps, septic system pumps) plus the cars (we’re both driving electric).  There were a couple of days that were a bit stormy and cold enough to want to heat the house and a couple days of heavier charging of one of the cars, but every other day required no power from the grid (day or night) – and yet the system still exported plenty of excess solar generation by the end of the day.  Having a couple of Powerwalls really does sort of double how much you get out of your existing solar panels.  (I’ve got a 9 kW solar system.)

During the summer months, when there’s a daily period of much higher peak pricing, I expected to make use of the time-based “balanced” mode to optimize how much credit I get for excess solar generation.  As it turns out, in the “balanced” mode the Powerwalls will switch to exporting solar power during the peak period even if the batteries aren’t yet full.  So I switched back to “self-powered” mode to let the batteries fully charge each day to be sure to have plenty for overnight usage.  They tend to fill up by early afternoon on sunny days and plenty of excess solar power gets exported at the peak rates anyway.  This excess solar generation during the spring to autumn months will still make up for the power I need from the grid over the winter when the house uses much more energy for heating.  (My panels were installed to optimize for summer peak rates – 75% of them are oriented to the west for summer afternoons.  Now that I have the Powerwalls, I almost wish I had optimized them more for the winter sun.)

If you’re interested in buying a Powerwall, using someone’s referral link will gain you (and the person who referred you) a small rebate.  Here’s my Tesla referral link.

Installation Issues

My installation by Tesla wasn’t without issues. Continue reading »

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My Newest Solar Milestone: $1000

I just got my latest net metering statement from PG&E and I’m happy to see that I’ve just crossed the $1000 mark as of July 6th — as in PG&E now owes me over $1000 for the excess electricity my system has generated over the six months so far (January through June).  Woot!

That’s after all my household consumption, including charging my electric car (Nissan LEAF), running my well pump and water treatment system, etc.  What it doesn’t yet include though is heating the house since my heat pump was installed after the cold months had past.  So I don’t yet know how much heating my home will dig into my solar production surplus come fall and winter.  (I also don’t have a regular daily commute right now so I don’t have as much of a need to recharge my car right now.)

Update (8/15): Looks like my excess production for July added another $400 to that total.  More woot!

However, the fine print here is that this number is just used to compute the net “true-up” amount for the whole year at retail energy prices.  If I end up with excess production for the year, PG&E will only be paying me at the much lower wholesale rate… yeah, not quite so much woot. ;-)

Another cool thing to see though is how well these SunPower panels perform in overcast conditions.  It’s still overcast just before noon today in Santa Cruz and yet they’re pumping out 2760W right now.  (Compared to 7000W on a sunny day at noon, or a peak of 7900W about 2 pm, even with dirty panels.)  Sweet!

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It’s the power of the sun, baby!

Saturday was my first day of making over 60 kWh of sunny power in a single day!  Yay!

With my average daily consumption down in the 20’s of kWhs (at least before the heat pump went in), PG&E is clearly going to be paying me!  And that’s using all this free electricity to heat the house (heat pump = no propane!) and to charge my Nissan LEAF (electric car = no gas!)  Sweet.

It’s tough to know what my consumption is any more because a) PG&E doesn’t provide daily usage data once you switch to a time-of-use meter (lame) and b) it would only read net usage (after solar production) so I still wouldn’t know.  Yeah, SunPower does offer a consumption monitoring hookup but I’m still trying to find out through my installer how much they would charge and I guess there’s some question about whether it can handle both my main and sub-panel.

All I do know is that I’m making more than I use.  Double-sweet.

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They did say "free energy"

Yay!  PG&E finally came out and installed my new meter last week so I’ve now got net metering going — I’m finally getting credit for all these thousands of watts I’m generating!  Until now, all I could do was to charge my car during daylight hours to at least use some of it.

I also like how SunPower has yet to ask for any payment.  Haven’t paid a dime.  Talk about free energy! ;-)

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More power, Scotty!


The sun is starting to get higher in the sky these days – now getting over 6000 watts at a time and 32 kWh for the day!  Woot!!

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9200 GigaWatts, Baby!

Okay, well… more like 9200 basic watts, but still….

So one of the first things I wanted to do when I finally bought a house was put in a solar PV system.

My system consists of forty SunPower E18 230 watt panels. For the fastest return on investment, you want to size a system based on your yearly consumption to just keep you out of the more expensive rate tiers. However, at 9.2 kW DC, my system is much larger than necessary because I just love the idea of offsetting * all * of my electricity consumption with solar generation. (And even get a little compensation from PG&E for any net excess for the year.)

I already drive an electric car (a Nissan LEAF) for nearby destinations but I fully expect that in a couple more years I’ll be able to trade in for something that will let me do all my driving via electricity. I’m also looking to get a heat pump installed soon to avoid needing to use propane as much. So I expect to be able to use much more of what I’m now generating.

DSC_1751.jpg DSC_1765.jpg DSC_1767.jpg

It’s December now — winter in the northern hemisphere and so the sun is low in the sky and the days are short but the system is already generating around 5500 watts AC at peak in full sunshine and even 2100 watts when cloudy/overcast. Sweet! All told, it’s generating over 30 kWH on a sunny day — and it’s winter! That’s much more than my current average daily consumption. Of course that’s with me not commuting right now (so not charging the car as much) and no electric heat pump yet.

In summer, the peak production should be closer to 8000 watts AC and the days will be longer but the mornings can often be foggy in the summer here. And of course there will be days with little sun. It’ll be fun to see how my little power plant does over the course of the year though!

By the way, Solar Technologies was a great installer and I highly recommend them! And remember, you can even have solar installed with no money down with a lease: you replace your monthly electric bill with a smaller lease payment!

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What a pretty sight!

Gotta love that negative sign:

(That’s my PG&E electric meter running backwards to the tune of almost 5000 watts!  Yeah, baby!)
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Forty SunPower panels sitting in my driveway… woot!  Installation starts today!

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