Size Matters

Reassessing capacity.

I read online solar news journals every morning while the coffee soaks in. Most of it is grid stuff, but those guys are in it for the money and have the bucks to pay for the research, so I pay attention.

I also paid attention when I lived very closely with my solar power during my 44 days aboard Sun King. What I learned there was that we waste an awful lot of solar potential. I had 1620 watts of panels, which is not a lot when you consider that it provided motive power, lighting, cooking and, most importantly, coffee. However, sitting there all day, arm’s length from the meters, I could see that by 10 or 11 a.m., the batteries were usually topped up and less than half of the solar power was being used to run the motor. The rest went unused.

I mitigated this, somewhat, by changing my load/use strategy. After about the first week, I’d get underway about 5 a.m. to burn off some of the 350 a.h. battery storage I had. That got me further up the river each day, typically around 50 miles and up to 100 miles, and I got to use more of those kilowatts shining down.

At home, I see much the same thing. By the time I get up and out, around noon, the batteries are often topped up or at least in bulk charge. The air conditioning season is beginning to make a seasonal adjustment to the load pattern. The house a/c starts up around 0930 and the man cave a/c in the Solar Shed starts around 10. I encourage my wife to use heavy loads, like the dishwasher (1kw) and cooking (separate solar hybrid, there) during the sunny hours. She baked me a blackberry cobbler this morning! She’s ok.

I honestly don’t know how many kilowatts of solar I have available right now, but I do know that I am not using all of it on a sunny day. I also know that when it is cloudy, I don’t have enough.

So back to the grid guys, that’s where the big money is and they keep coming up with bigger batteries and cool new gear. One battery beginning construction is rated at 100mw for utility backup. That is not mwh, that is mw output. Furthermore, it is rated to run for 150 hours at full output. 6 days at 100 MILLION watts! If you know the math, try calculating the number of John’s Sun 230 batteries you’d need to match that. Furthermore, the new chemistry of that battery uses water and air! Tesla has provided some pretty sporty lithium grid batteries in Australia, too.

All of this work is leading up to solar providing more power this year than coal. They can do this because they’ve been building an awful lot of solar AND they have been figuring out how to not waste it and continue using it after the sun goes down.

A new study from Wartsila (I’m sorry, but that name just conjures up an image of the offspring of Godzilla and a warthog) suggests the ultimate setup for the grid is to install 4.3 times the peak load of solar in sunny areas, with 4 to 10 days of storage. That may sound a bit extreme, but a utility can’t compel you to do your heavy power use only during the day, or even to be conservative in your consumption.

In looking at my own system, I have always tried for 4 days backup, though my ever-increasing load makes it closer to a single day if I maintained all loads and the sun didn’t come up. I’ve nearly 800 a.h., now and plan to add another 440 a.h. soon. That’ll give me nearly 60kwh of battery, but, of course, that’s only 30kwh at the usual 50% drawdown limit. I’m sure that won’t satisfy me, either, nor will it meet the Wartsila guidelines.

As far as meeting their guidelines on solar input, my inverter was tripping above 5500, so let’s say my current peak is 6kw. By their formula I should have 26 kw of solar input! Yikes! You guys will have John’s crew really hopping if you all install 26kw of panels! Or more. My best guess is that I have around 13kw actually running. I know I have two strings of around 720 watts each that are not working and maybe that much more up, but not connected pending the construction of the final bay of the Solar Shed. Just sitting in piles I have another 5 or 6 kw of panels that I have not nailed up, yet, but it seems I can get pretty close to their goal when the project is finished. My shortfall can be mitigated by not running street lights and traffic signals all night.

So that leaves batteries. Someday we should see all of this utility battery development trickle down to the solar homeowners. It is already, really, with the drop in lithium prices. At the present time, what I see is the cheapest entry into storage is the Sun Electronics Sun 230. Best bang for the buck, if you have the upfront cash, seems to be the SimpliPhi lithium. They are pricey, but should outlast you. Ask Roberto about them.

How does your system stack up to these new guidelines?


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