Simon and Garfunkel performed the song the Sound of Silence many years ago. I wonder if they were contemplating that the noise of a generator would become a thing of the past leaving only cool air silence on a boat?
This post answers the question: Is the Integrel silent solution for you? The answer lies in the math.
BUT FIRST WHAT IS INTEGREL
Integrel is essentially (except it is not) a very high-power alternator that straps on your regular inboard diesel engine in much the same manner as an alternator and being driven by a belt – same as an alternator. It generates a huge amount of electricity – as much as a stand-alone heavy, loud, and expensive generator. The secret sauce to the Integrel is the solid-state controller which automatically makes safe management decisions about making the electricity. The electronics are constantly asking the engine questions about how much power is available to take from the engine given what the engine is doing such as the RPM, if the RPM is changing, and in gear or out of gear. From this, the solid-state controller makes a decision about how much magnetic field to apply to the device – the determination of this is based also on the specific engine HP rating. This then generates the precise amount of electricity desired based on the conditions. For example, if you were at full throttle in gear, it probably means you need all the power the engine is creating to feed to the propeller, so the decision from Integrel would be to take no energy away from the engine. If the engine is at 1500 rpm and not in gear, then the decision would be to take as much power off the engine as allowed to load the engine up into the efficient operating zone (and if you know anything about diesels – they love to be operated under load. Idling with not load reduces the life of your engine). With the engine in gear at 1500 rpm, Integrel knows already how much is needed for the prop from the prop-power curve of the engine and will, therefore, take most of the available power leaving some for the prop.
Given the above, you can see that there is a huge difference between an Alternator and an Integrel, albeit they are about the same size. But here is the mathematical difference, an alternator kicks in to start generating electricity at about 1200 rpm. At about 1500 rpm it generates at first about 1 kilowatt of power, then as it heats up is generates less at about 800 watts. Integrel however, will start generating at idle and at about 1000 rpm it is outputting 2 kilowatts, at 1200 rpm about 5 kilowatts, at 1500 rpm about 7 kilowatts, and at 1800 rpm about 9 kilowatts. On a standard charter boat, every charter company will tell you that you have to run the engine for 4 hours per day to keep the batteries topped up. They are right. Because with an alternator, you will get about 3.5 kilowatt-hours of energy in 4 hours of engine running. If you had an Integrel you’d run the engine for less than ½ hour.
So, should you put an Integrel on your boat or not? The decision lies in the math so let’s do that now.
ENERGY AND ENERGY FLOW RATE. A 101 LESSON
Thinking about energy can be likened to a bucket of water. In a bucket there is a specific amount of water – 10 liters say. Likewise, in a battery, there is a specific amount of energy – a kilowatt.hour, say.
Thinking about energy flow (or usage rate) can be likened to pouring out the water from the bucket. You might pour out water at a rate of 1 liter per second. A 10-liter bucket would then empty in 10 seconds. Likewise, if you turned on an electrical device and used energy, you might be flowing energy at a rate of say 100 watts. Thus in 10 hours, you would use 1 kilowatt.hour of energy (100 watts for 10 hours = 100 watts x 10 hours = 1000 watt.hours = 1 kilowatt.hour). Often times people make the mistake of thinking watts per hour but there is no such thing as a watt per hour. A light bulb is rated at 100 watts say, meaning that in 1 hour it uses 100 watt.hours of energy. And if you look at your electric bill it will be listed in kilowatt.hours of energy used each month. You are billed then for the amount of energy you used expressed in kilowatt.hours. The cost of energy from the grid to run your house is about 20 cents/kilowatt .hour.
For perspective, a typical marine lead-acid battery holds about 1200 watt.hours of energy. Usually in the USA, a battery is rated in amp.hours. But amp.hours is not a real measurement of energy. The amp.hours number must be multiplied by the voltage to get energy stored. Thus a 12 volt-100 amp.hour battery holds 12 x 100 = 1200 watt.hours.
A regular boat with the usual comforts such as a fridge/freezer, chart plotter, electric toilets, an electric winch, stereo player, etc will use about 4-kilowatt .hours of energy per day.
Air conditioning uses a huge amount of electrical energy. The amount largely depends on the size of the boat and the water and air temperature. The temperature determines the amount of heat flow into the boat through the boat’s walls and hull which must now be ejected by the air conditioner. The test we ran was on a 41-foot Beneteau with a water temperature of 80 degrees (27 deg C) and an average nighttime air temperature of 78 degrees (25.6 deg C). The thermostat was set to 75 degrees (24 deg C). The amount of energy consumed by the air conditioner over a 12 hour night was 12-kilowatt .hours or 1 kilowatt.hour every hour. This number will grow by each person on board because of their own body heat. The average person puts out about 100 watts or 100 watt.hours every hour. So if 4 people sleep onboard that 41 ft monohull, then you’d use 1.4-kilowatt.hours every hour or for say a 10 hour night, 14-kilowatt.hours.
Throughout the night, the air conditioner kicks on and kicks off according to the thermostat.
Generators are typically rated to output at an electrical energy flow rate of about 8 kilowatts for a medium-sized boat. They are rated to account for the maximum electrical draw from the air conditioner(s). Generators are designed to be run continuously through the night and are thus feeding energy to the air conditioners when they are on and generating no electricity with no load on the generator engine when the air conditioners are off.
On a good day, a solar panel will put out about 170 watts per square meter. On a monohull, about 2 sq meters would be the max mounted upon the top of a dinghy davit. Allowing for an average of about 5 hours per day the amount of energy you could expect from solar is about 170 watts/sqm x 2 sqm x 5 hours = 1.7-kilowatt .hours.
Integrel generates up to 9 kilowatts of energy flow from the main propulsion engine and stores the energy in Li-Ion batteries.
SO NOW FINALLY THE MATH
No Air conditioning:
- If you have no air conditioning, you’re going to use about 4-kilowatt .hours of energy every day. Where do you get that energy from?
- 4+ hours of running the engine to get the energy from the alternator
- ½ hour of running the main propulsion engine to get it from Integrel
- Can be supplemented with solar if you have it.
With all the solutions, you generate then store the energy into and draw from the house bank of batteries.
With Air Conditioning:
You’re going to use about 18-kilowatt.hours of energy (dependent on the boat size and water/air temperature). For a larger Catamaran in the Caribbean – consider more like 30-kilowatt.hours.
- There is no way you can generate this from the alternator or from solar although solar can again supplement.
- With a generator, even though the generator generates at 8 kilowatts, you’ll still need to run the generator all night long because the generator feeds the air conditioner directly.
- With Integrel you would generate this energy from running the main propulsion engine about 2-3 hours either while performing normal maneuvering operations or running at sat 1500 rpm in neutral. You store this energy in Li-Ion batteries and draw from it as needed. In a Catamaran, you’d consider putting an Integrel on each engine to generate at up to 18 kilowatts = > 1 hour of engine operations.
A generator costs around $30k to have installed properly plus maintenance and fuel costs afterward which equates to about $1/kilowatt.hour. Over a 10-year period operating 200 days per year gives a cost of $66,000.
An Integrel system costs $13k but fully installed with 20-kilowatt.hours of Li-ion batteries it costs closer to $43k plus fuel @ 30c per kilowatt.hour which adds about another $5k over the 10 year period (assuming that half of the time the Integrel is generating during maneuvering operations). This all equals about $48,000.
But let’s say the dollar differences were minimal for $ to $ comparison sake, what is the cost to get rid of that THRUMB-THRUMB-THRUMB all night long listening to a generator and replace it with the Sound of Silence? The answer is Nothing. We can also consider the benefit to the environment. In the BVI there are about 1000 charter boats. All of them either run their engines 4 hours per day to charge from their alternators or run their generators 12 hours every night. That’s a lot of diesel being churned every day.
We did an energy analysis of your boat’s energy and the cost of that energy.
- Integrel outperforms a generator in run time efficiency by about a factor of ten.
- Integrel outperforms a generator in noise factor by infinity
- Integrel runs about the same cost as a generator and even with a few dollars spare when you take into account the real cost of the runtime of a generator