Power Management. Energy, Chaos and Drama

We are often asked “How much power do you need on a yacht”? The answer of course is “Which yacht?”. I’m sure the exceptionally lovely super yacht “Black Pearl” uses slightly more power than we do :-).

Further more, so many ‘yachties’ think you should live on the smallest possible amount of power and that making water is something that God does, washing is for your birthday and entertainment is watching the sunset.

I love the sunsets but I don’t want to watch them every night, or have that as my only form of entertainment. I have computers I like to be connected, cameras I want charged, and I want my life onboard to be a close approximation of life in my house, but without perhaps all the distractions. I like my morning coffee hot and my evening beer cold. I like to wash my body and the boat at reasonably frequent intervals and having to return to an overpriced marina to get a basic of life such as water, which often is not drinkable, is simply not my idea of freedom.

So how much power do you actually need? Well let’s start with how much power do you use at home? Without some of the power consumption you have onboard, like a water-maker or running navigation gear.

When I looked at how much power I used at home on average, looking back through old power bills, I came up with 6-8KWH as a reasonable place to start.

Ok, so what do I need in order to provide that a sort of power on a sailing yacht? Other than a generator running for a couple of hours (at least) a day as that’s not our idea of self sufficient.

With a little research I worked out that solar tends to deliver on average, around 50% of the promised power. Higher amounts are generated in high summer weather, lower in shoulder season, and next to nothing in winter. So in order to generate 8KWH in a day I would need at least 2KW of solar and 8 hours of solid sunshine – which is a little more than the 800W that you might find on some boats.

But what happens if we don’t get decent sunshine for a couple of days? We all know that even in the Mediterranean you might get 2-3 days of cloudy rainy skies. That means we have to be able to store some of that power in batteries. But how much do you need? What’s the comfort level?

We opted for three days worth of battery storage, which equates to approximately 16Kwh of usable battery.

But here’s the catch. The amount of useable power is variable!!! To get 16Kwh hours of useable power with lead acid, or gel etc. I would need at least 32Kwh’s of battery capacity, because lead acid can only reliably be drained to around 50%. But then to live a comfortable life we intend to cook, run microwaves, refrigeration, TV’s and computers. These are all voltage sensitive items and lead acid will drop its voltage dramatically as load goes onto the batteries. So, in order to ensure we have sufficient useable capacity and enough to ensure that there is not a voltage drop that will result in a burnt casserole or my computer having a ‘spaz’ I might need a bit more again. But what about lithium iron?

Well quick research showed that lithium iron was more likely to cause a fire onboard, unless perhaps I used LifePo4 lithium batteries, and then they’re probably just as safe as lead acid. So LifePo4 was the decision …. that was until I saw the cost. I nearly passed out!

So, cost aside, if I was going to live on solar and batteries I would need at least 2.4Kw of solar, 16Kwh’s of LifePo4 batteries and a decent inverter capable of at least 5KVA.

Everybody aims for “what they can afford” or “what they can fit onto the boat”. But I think you should try to work out what you NEED and then workout from there, how to get it done.

This is what I did.

We have a catamaran, and there are always some limitations, but finding (or creating) space for 2.4kw of solar was less of a challenge than perhaps finding the space on a mono-hull. Our solution was to build a stainless solar arch. The arch was expensive; I did all the design but had it welded up by a professional and I then helped to fit and install it.

All this reduced the cost but it was still quite significant. You could do it cheaper. But also it is an enriching boat life item, which means it is worth investing in.

The solar panels themselves were not greatly expensive and I stayed away from “marine” which from my research were poor performers, much much more expensive and no more reliable in the “marine” environment (after all the industrial panels are designed to work outdoors in all environments well, so they are just as salt and corrosion proof!!!!).

The inverter is an investment you can not dodge. You need to buy a reliable unit and this means costly, or perhaps quality. But the batteries themselves … now this is the area where you can make big savings.

I built my own battery, using a high quality battery management system (BMS) that would integrate into the Victron solutions (inverter and MPPT’s) perfectly and save me enough so that I could afford to install 1400Ah of LifePo4 batteries (Circa 17Kwh). The quote for this system from a Victron distributor was £28k. I decided to build the battery pack myself, complete with cooling fans, heating pad, advanced BMS that controlled charging and discharging, switching battery connection etc. etc. for…. circa £3k. Yes, that’s not a typo. I saved £25,000 by building the battery pack with my own two hands and a little research.

Our system has been working wonderfully for two seasons now and does not show any signs of strain. We rarely, during the winter, have gotten down below 50% SOC and only under extreme circumstances the 5KVA inverter is not enough. Next time I would use 2 X 3KVA inverters, both redundancy and slightly more top end delivery.

So how much power do you need? How much do we really use? With making water, heating water, showering and laundry, running three refrigerators, and powering technology etc, we consume about 6KWH per day. We generate that easily during summer and even in the shoulder seasons. During winter we manage to slow down the need to start the generator to about an hour a week.

What I believe is that you don’t want to change your lifestyle too dramatically when you move from a home to a yacht. You will use less power but not as much as you would think. Don’t under estimate your needs and be forever trying to “save” power or water.

With some constructive thinking it is very possible to lower the costs and live a normal life on board.

If you would like me to write in more detail, more technically about how and what I have done. Let me know in the comments and I happily will. There are no trade secrets here.

Happy sailing.