In my experience the estimates from EP conversion companies are rather often
overly optimistic and very often use "fuzzy math" or incomplete math..
The vast majority of the owners who contact us for an EP
consult want no ICE engines what so ever, including generators of any kind. The hatred for the Honda/Yamaha etc. generators is usually beyond that of diesel, for most owners, that we talk to about an EP conversion. This means your system will need to be designed, built and exxcuted in a manner that gives you reliability and the range you need for your use. Regen, solar or wind, won't cut it for propulsion needs unless you have lots of time to wait for the bank to recharge.
A few years ago we shared a booth with an EP company at a trade show. I was horrified at the utter disregard for Ohm's law, Peukert and the sheer reality disconnect that spewed forth to potential customers about range and the abilities of solar, wind etc... To say I was
horrified at the
marketing messages was an understatement. Bad marketing and less than honest math is what gives EP the bad rap...
Most owners we talk to and consult for (using real math not marketing math) are really dreamers who have some rather unrealistic expectations of EP. Weight savings being one of these often unrealistic expectations. Speed gains from the "weight savings" are another. Unless those expectations become more realistic, and they are willing to consider things such as ICE, as a supplement, the realities are
constrained if you expect range. In other words EP needs to fit in your "box" of how you will use the boat.
The first question we ask most of these customers is:
"How long does your current house bank of batteries last you?"
They are usually surprised by this question, and confused. Most are answering "Three to four years"... If an owner can't manage a house bank to last more than 3-4 years, they are typically going to have trouble managing an EP bank.
One consult we did was a guy with a 32 footer who wanted to be able to continue his annual 3 week cruise in Maine. He uses 80-100Ah each day, on the 12V house bank side alone. He was is already chronically undercharging it getting just 2-3 years from a bank.. He was expecting a range of 30nm on the EP side day one then 15nm each day there after all supplied by wind and solar on a flooded lead acid bank.
He was 100% resistant to any form of ICE and had the room for two wind gens and about 400W of solar to share between both banks. Wind generation in Maine simply does not perform, in our protected anchorages, except in the tail seasons or for the occasional windy day.. His desires for EP were simply
unrealistic, without ICE, in order to continue how he had already been using the boat and how he expected to continue using it. When we did the real math his desires vs. reality were not even close to a reality. He just wanted the silence and to be "greener". When I suggested a small DC or AC gen set or aa Honda the guy literally went bonkers.
Expectations vs.
reality need to work in
concert...
Don't get me wrong I am definitely a
contrarian. I took the leap to LiFePO4, our LiFePO4 bank is now 10.5 years old. Just because LiFePo4 it works for
me does not mean it will work for everyone and we went into this with multiple years of research before even considering the switch..
Sadly, in my experience, the EP market needs to:
-Stop misleading customers
-Learn to do real math
-Follow by Ohm's law
-Adopt better battery technologies
-Understand batteries & battery technology
-Be honest about range
-Be honest about solar, wind and hydro in their daily abilities
-Learn to say "This is not the right fit for you right now"
EP does work if the owners expectations and the EP systems capabilities mesh and fit into a well defined box.
The image below is a prime example of where salesmanship, lack of real math, owner desires and reality failed to be in agreement.
This owner built a gorgeous brand new small wood day sailor (huge $$$ BTW). They wanted EP and EP should meet the desires of the day sailor, right?
In this case the actual use of the system, wind died on an outgoing tide, failed to meet the owners expectations based upon what they had been "sold"...
This photo is of the actual boat tied to an active "working dock" after being towed in in order to recharge the EP bank. It was there, utilizing dock space not intended for this, for 24 hours while recharging (see extension cords). Here in Maine we don't have many marinas and our docks are not intended for tying along side for longer than filling with water or getting fuel or ice. To spend 24 hours at a "working dock" is simply not being courteous to the dock owner or fellow boaters.. Sadly this owner had been sold an EP system that failed to perform to the marketing they were sold on. When I asked the owner about the possibility of using a larger charger and carrying a small Honda I got the evil death stare, as if I had just suggested the world was flat...
Please use real math, don't try to reinvent Ohm's law or Peukert and be realistic in your expectations..
Batteries for EP:
When comparing LiFePO4 vs. lead we need to remember that an LFP battery cell is usually rated at a 1C discharge for its Ah capacity. This means:
A 100Ah LFP battery can be discharged at 1C or 100A (1X Ah rating) and still deliver 100Ah this is a major leap for high current EP use.
A 100Ah high performance AGM battery, when discharged at 1C or 100A will only deliver about 62Ah's this is a 38Ah deficit to an LFP bank
A 100Ah deep cycle flooded battery discharged at 1C or 100A will only deliver about 47Ah's this is a -53Ah deficit to LFP.
This is called Peukert.
In other words;
The only way to get 100Ah out of a 100Ah rated lead acid battery is at a 5A discharge rate, this is called the 20 hour rating.. EP systems draw multiples the 20 hour rating thus you can't get 100Ah's out of a 100Ah lead acid battery when running an EP system.....
On the flip side, you can get 100Ah out of a 100Ah LFP battery at a 100A discharge rate.
Comparing lead acid to LFP based on Ah's or kWh's alone is like racing a Westsail 32 against and Open 60 with no handicap rating system, in other words unfair.
This was a direct quote of an EP user who was grossly mislead:
"I did do a short trip today. At 69.8 amps straight in to a 7 mph wind turning 1580 rpm she did 3.8 mph for about 1 hour."
His bank was 6V GC2 batteries for a 48V bank at 225 Ah's.. If we do the real math on this:
A 225Ah (at the 20 hour rate) 48V bank with a Peukert of about 1.30 yields a battery that is only capable of 130Ah's from 100% SOC to 0% SOC.... We only want to discharge to 50% SOC for useful cycle life so a 1 hour run at 69.8A had already consumed
more than half the capacity of the battery. he was led to believe that he had 225 Ah's of capacity and he did not.
My point is that usable kWh or Ah is not the same when trying to A/B LiFePO4 & lead. A lead acid battery of the same kWh/Ah capacity will not deliver the same usable capacity as an LFP battery because the 225Ah battery is rated at an 11.25A load and not at a 69.8A load.
As we increase the load on lead acid the battery gets smaller. It only meets that rating at the 20 hour rate. High discharge rates on LiFePO4 do not impact the energy it can deliver like it does with lead acid.
I could write a lot more but best to just say BE SURE you are getting real math information when discussing EP systems!!