Tag: "powerwall"

08/17/18

  03:15:00 am, by Jim Jenal - Founder & CEO   , 1210 words  
Categories: All About Solar Power, Residential Solar, Energy Storage

What I Saw at Enphase - Mind Blown!

Enphase hqLast month during Intersolar, I (along with colleagues Sara and Victoria) was lucky enough to get invited to see a microgrid demonstration featuring the Enphase next-gen IQ8 at their headquarters in Petaluma, California.  As I had to sign an NDA as the price of admission, I was unable to write about what I had seen until today, when Enphase hosted their annual Analyst’s Day.  But I am no longer bound by that agreement, and can now tell you about what I saw. 

To say that I was impressed would be a gross understatement - quite simply, it was the most astonishing thing I have ever seen in the solar industry.  Settle in and let me tell you what I saw…

What Happens Today

Before I launch into describing the demo, let me remind you of what happens today.  All of the systems that we have installed are what is referred to as “grid-tied” which means that if the grid goes down, the PV system that is capable of back-feeding the grid also goes down, and remains down until the grid comes back.  (This is to prevent your house from being an island of energy, feeding the grid, and potentially injuring a worker trying to restore grid service.  As a result, this feature is known as “anti-islanding” and it is required of all inverter systems that are connected to the grid.)

Normally this is not a problem, but last month, when it got super hot out here (think 115° F hot!), both SCE and LADWP suffered dozens of outages, taking down PV systems across large swathes of LA County, and leaving frustrated PV owners without power, or A/C, just like their PV-less brethren.  Not good.

What I Saw in the Lab

Which brings us to what I saw at Enphase last month.

The lab looked like an ordinary industrial space, but with a series of household appliances and tools at one side.  There was a simulated array feeding a bank of IQ8 inverters, and a display that showed the output of the array (i.e., PV production), the total consumption from the loads, and any power being exported or imported to support those loads.  At the start of the demo the only load was a single red lamp, and the display indicated that it was drawing roughly 90 Watts.  The PV array was producing roughly 1.9 kWs, so the excess 1,800 Watts was being exported to the grid.  All super normal stuff.

But then things got interesting…

One of the engineers switched off the breaker that connected the PV array to the grid… and nothing happened!  Well, actually, a lot happened, but what didn’t happen was that the red light did not go off.  It didn’t even flicker to the extent that we could detect it.  But then when you looked at the display you noticed something amazing.  Not only had the microinverters created a grid on their own in fractions of a second, but they had throttled the output down so that now the production of the PV array exactly matched the load of the red light!  And here’s the kicker - there were no batteries attached to this system!!!

But what fun is just having a light on?  How about some toast?  So they switched on a toaster, and it lit up, and the total load jumped by about 1,000 Watts, making the total load now around 1.1 kW, and the PV array scaled up to meet it!  Still no batteries.  And how about this - there was no central controller, no master-slave relationship between the microinverters.  Rather, this was the “hive mind” at work, as the micros sensed the demand and scaled up or down as necessary to meet that load!

But wait, there’s more!

The next load to be added was a grinder like you might find on your workbench in the garage.  All by itself, that device drew roughly 1,200 Watts, bring our total load to roughly 2.3 kW - more than the maximum output of our simulated array.  What would happen when that was added to the mix?  Surprisingly little.  The grinder spun normally, but the red light dimmed slightly.  What was going on?  The system’s “hive mind” had lowered the voltage slightly (a microgrid equivalent of a brown out) to meet the amperage demand of the new load mix!  So slightly slower than normal, cooler than normal, dimmer than normal, but all operating.

Of course, all good things must come to an end.  Our already overloaded microgrid faced one more challenge - a vacuum cleaner with a significant in-rush current, far in excess of what the grid could sustain.  Indeed, as soon as they switched the vacuum cleaner to “on", everything shut off.  Nothing was damaged, the microinverters just shut off to protect themselves.

Turning on the vacuum cleaner served as the “ah-ha” moment for the potential homeowner - I guess I can’t run everything in grid outage mode.  So what do you do when something you just did produced an undesired result?  Well if you can, you undo it!  Turning the vacuum cleaner off, immediately restored the microgrid to its previous state of operation!  No delay.  No human intervention - just turn off that latest (over)load, and the system recovers on its own!

How cool is that?  Pretty damn cool, if you ask me!

Batteries Please?

So what about batteries, how do they play with this new system?  Just exactly as you would want.

The engineers added a bank of batteries to the mix, each with an IQ8 installed.  Now the display also indicated the battery’s overall state of charge, and whether they were charging or discharging.  Reset the demo to just the red light as a load and the batteries at 30% state of charge.  The PV array output jumped back to its maximum, with the surplus energy being used to charge the batteries.  As more loads were added, the PV array remained at maximum output, and as needed, drew power from the batteries.  Should the batteries reach full capacity and the PV output is greater than the loads, the microinverters will once again throttle down.

Sweet!

What’s Next?

I hope you agree that this was an amazing demo, and the IQ8 (or Ensemble, as Enphase refers to the overall system) has tremendous potential, both for Enphase as a company, and for so many nascent markets.  Think of how this product could have helped out in Puerto Rico, or in parts of Africa which have never, ever seen a grid!  Makes me want to book a trip to bring power to a village somewhere - hey Laurel, what do you say?

For our own clients, this has the potential to be the answer we have been seeking ever since Elon’s whoppers got people thinking about storage for the first time ever.

A point we raised with Enphase management is the need to have a reasonable upgrade path for existing clients.  Indeed, I have a call with Enphase tomorrow to discuss that very topic.  We know that current Enphase IQ products (the 6+ and 7+ we have been installing this year) will be compatible with Ensemble.  We expect to be able to work with older systems, though there may be a higher retrofit cost.  When we have that information, we will surely let you know!  The IQ8 is expected to be available in 1H2019… watch this space!

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05/10/15

  04:49:00 pm, by Jim Jenal - Founder & CEO   , 1451 words  
Categories: All About Solar Power, Solar Economics, Residential Solar, Ranting, Energy Storage

Elon Musk's 3-Biggest Powerwall Whoppers

Elon Musk is a visionary and a showman, but occasionally his enthusiasm for his vision gets way out ahead of reality.  Nowhere was that disconnect more on display than this past week when he made his much talked about announcement of the Tesla Powerwall battery storage system.  While we share the vision for the potential of battery systems (such as the one Enphase Energy is set to release later this year, albeit in a far more understated fashion), when 38,000 people go online to order a product that doesn’t yet exist, it is time to debunk some of the more exorbitant claims made by Musk. 

Here are the three biggest whoppers that Musk made during his Powerwall presentation (video below).

Whopper #3 - Power for an ice storm or other significant grid failure event

Musk touted the “peace of mind” that would come from having the Powerwall, and said, “if there’s a cut in the utilities you’re always gonna have power, particularly if you’re in a place that’s very cold, now you don’t have to worry about being out of power if there’s an ice storm.” (See video at 8:35.)

The Powerwall unit that Musk was talking about that was designed for “daily cycling” was a 7 kWh unit that is priced at $3,000.  The average home in the Run on Sun service area uses 25 kWh/day.  So a single Powerwall unit provides roughly one quarter of the energy demand of an average home.  If your desire for “peace of mind” means running your home for a full day in normal fashion, you will need to purchase 4 Powerwall units (assuming you have the wall space to mount them) and that will cost you $12,000.

Of course, many outages last longer than a day.  The longer you want to stay powered, the more units you will need.

Whopper #2 - Powerwall will work with existing solar systems

Musk insisted that Powerwall has been designed to work with solar systems, “right out of the box."  (See video at 8:25.)

Except… that the Powerwall is designed to fit between existing solar panels and the DC-AC inverter(s) in the system (i.e., on the DC side of the system).  But here’s the thing - the vast majority of inverters are what are known as “grid-tied,” which means if the grid goes down, the inverter shuts off, and stays off until the grid comes back.  If the Powerwall is on the DC side, there is no way for it to “mimic” the grid (which, of course, is on the AC side), and so the inverter will shut off.  While the inverter could certainly be replaced with a hybrid inverter (that can work both independently and tied to the grid) such a replacement is a pricey undertaking and certainly not a plug-and-play installation.

But Musk, like the true showman that he is, saved his biggest Whopper for the end…

Whopper #1 - You can go off grid… for $3,500!

Warming to his subject, Musk really brought down the house with his most outrageous claim of all:

You could actually go, if you want, completely off-grid.  You can take your solar panels, charge the battery packs and that’s all you use.  So it gives you safety, security, and it gives you a complete and affordable solution.  And the cost of this is $3,500."  [Gasps and applause from audience.] (Video at 8:55.)

No.  No you cannot.

Let’s unpack his statement.  There’s two major claims here, neither of which is true.  The first is that you could go completely off-grid, and the second is that it would cost you $3,500.  So let’s start with the easy one to disprove, indeed, we already did above: this won’t cost $3,500.  The Powerwall provides 7 kWh of storage.  The average house uses 25 kWh/day.  If the battery has to run your house for just one day, you would need 4 Powerwall units at a cost of $12,000.  (The 7 kWh unit is the one designed for daily cycling - what you need to go off-grid, and it costs $3,000 - if you could actually purchase one, which you can’t.)

So that’s easy to debunk.  But what about the second, more fundamental question.  Can I use this Powerwall system to go off-grid without changing my middle-class, suburban lifestyle?  For most folks the answer is simply, no.  Here’s why.  When you go off-grid you need to be able to meet all of your energy needs all the time without assistance from your local utility.  To do that, you need a battery system large enough to last you during the longest typical shortfall of available energy (i.e., how many stormy/cloudy days in a row will you see), plus a solar array large enough to charge that battery on sunny days while meeting the household needs.  Turns out, that is quite a lot of both.

Folks who design off-grid systems (very few of which are found in areas like Pasadena), typically design for three (or more) days of self-sufficiency (or autonomy, as they put it).  For our typical, 25 kWh/day home, that would require storage of a minimum of 75 kWh.  But according to Tesla, you can only stack a maximum of nine Powerwall units, which limits you to 63 kWh.  Sometime around noon on that third day without sun, your house will shut down.  Oh, and that much storage will cost you $27,000.

What about the solar array side of the equation?  Let’s start by asking how big an array can you fit on an average house?  House sizes have trended bigger in the past couple of decades, so more recently built houses are an overstatement of the average house out there.  Still, to have a starting point (and to give Musk the benefit of the doubt), let’s assume that our average house is 2,400 square feet (a fair estimate based on US Census data), and that it is optimally designed to maximize solar production: a near perfect square with a true south face, pitched at latitude (34° here in Pasadena), with no shading.  Of course, we still have to give the Fire Marshall the desired setoffs so that gets us to 1,115 square feet of roof space (math available upon request), enough for 62 LG 305 solar modules, but because we need to use a hybrid inverter with fixed string sizes, we will drop that down to 60 solar modules. That yields an 18.3 kW system which at $3.50/Watt would cost a cool $64,000 - and be bigger than our biggest ever residential installation. 

So the Sixty-four Thousand Dollar question becomes: How well will that do on meeting our needs?  Per the CSI calculator, this maximal system will produce roughly 29,000 kWh in Year 1, or an average daily output of 79.5 kWh.  (Less in the winter, of course, when you are most likely to see those cloudy days.)  After providing for my daily needs of 25 kWh, I have 54.5 kWh to spare, not quite enough to fully charge my batteries (which require 63 kWh).  A scenario where I have two cloudy days, followed by one partly sunny day, followed by two more cloudy days could easily leave you in the lurch.  And for this you paid a total of $91,000!  If you live somewhere with poorer weather than what we find in the Run on Sun service area (i.e., pretty much the entire rest of the country!) your performance will be even more dismal.

The true value of storage

The sad part of this whole thing is that battery storage combined with solar is going to be huge, but not for the reasons Musk alluded to in his speech.  The future of utility rates is the shift to time-of-use rate structures - a fact already well and painfully known by our clients in SCE territory, and soon to be seen by everyone.  Time-of-use rates, where utility customers pay more for energy during the peak part of the day, are the only way to match utility costs with customer charges.  (It is the head of the Duck in the famous Duck Curve below.)

The famous duck curve

That “overgeneration” that drives down demand at noon is presently fed back to the grid, where the grid operator has to modify the power mix to accommodate it - in essence, it is wasted.  (Although presently, net metering customers get full retail credit for it - something, that in all likelihood, will soon go away.)

But add storage to the mix, and you shift that overgeneration from the middle of the day, to the evening peak hours, benefiting the time-of-use customer as well as the utility.  It is the way to bring about a peaceful end to the utility-solar wars, and it is the true benefit of storage to solar customers - without oversizing either your solar array or your storage system.

So let’s all get excited over solar with storage, but for the right, and much more cost-effective reasons - and not the nonsensical hype being spewed by that super showman, Elon Musk.

Jim Jenal is the Founder & CEO of Run on Sun, Pasadena's premier installer and integrator of top-of-the-line solar power installations.
Run on Sun also offers solar consulting services, working with consumers, utilities, and municipalities to help them make solar power affordable and reliable.

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