A DIY real-life solution to your power issues.
By Brad Roberts
I was first introduced to solar power by a boater friend in our marina. This was many years ago, and solar has come a very long way since then, but he had a small rigid solar panel laid on his helm under the windshield and connected directly to his batteries. It worked, admittedly crudely, as a trickle-charger. So I put one on our express cruiser and noticed a measureable difference in how long our house batteries lasted when we were out cruising. So much so that my kids commented “how come you’re not telling us the batteries are down, Dad?”
I figured there had to be something to this that was worth exploring further. I’ve invested time over the past decade researching what can be a complicated and confusing industry, and now for the past two years, I’ve been using solar power on my boat and up at our cottage in Central Ontario. This article is a basic introduction to solar power meant to get you thinking about how this green energy solution might benefit you and your family’s boating or cottaging.
In the simplest terms – solar power refers to the process of capturing the sun’s energy and storing it in a battery that will later be used to power an electric tool or appliance. As opposed to getting the hydro that your home appliances need from “the grid” (and paying for it by the kilowatt), you get it from a renewable (and free) source – the sun. There are five essential components to any solar system, that all have to work in harmony with each other for the system to function properly: your power needs, the inverter, the storage capacity of the batteries, the charge controller, and the production capacity of the solar panels. To correctly size your solar system, you should work backwards from your actual power consumption.
Power Needs. To determine how much power you need from your solar system, you have to add up the watts that each appliance on your boat uses, per day. So a coffeemaker run for 30 minutes in the morning uses “X” number of watts, the stereo on for three hours in the afternoon uses “X” watts, the microwave at dinner, the TV and cabin lights at night, etc. Add it all together and you get a total number of kilowatts (1 kW = 1,000 watts). You may have done this already to size your house batteries correctly for your boat.
The Inverter. Basically a transformer that converts the power (DC) stored in the batteries into household power (AC) suitable for use in 120 volt appliances. There are pure-sine and modified-sine wave inverters. Make sure you buy one designed specifically to overcome the corrosion and fuel vapours ever-present in the marine environment. Inverters vary in size (200 watts versus 4000 watts) and need to be sized according to your maximum power needs.
Storage Batteries. The heart of any solar system is the batteries. For a simple solar system, plan to use true deep-cycle AGM batteries that are maintenance-free. (Flooded batteries require maintenance and equalization, but cost about 30% less.) Either way, batteries have a maximum amount of energy they can store per battery, and thus a maximum amount of power you can get out of them before they are discharged. You can add batteries to increase storage capacity, to a limit. Batteries should never be discharged lower than 50%, doing so shortens their life cycle considerably. Deep-cycle batteries are rated in amp hours.
Charge controller. This devise monitors the amount of charge being generated by the solar panels, and controls how much of that charge is put into the batteries based on what their level of discharge is at. It ensures the batteries are not damaged by overcharging.
Production Capacity. This refers to the amount of energy the solar panels in your system can produce. For example, a 260 watt solar panel exposed to full sun for 4 hours will generate about 1000 watts (1 kW). Allowing for cable loss and charge controller loss, this will add approximately 900 watts into your batteries.
Sizing Your Custom Solar System
So let’s say, for example, that you calculate that you’ll need 1500 kilowatts of power per day on your boat between the coffeemaker, lights, stereo and TV. (To learn an easy way to do this, use the spreadsheet at https://www.microgreen.ca/downloads/Load-Evaluation-Sheet.xlsx) That means that you’ll need to add 1500 watts of power back into your batteries each day. Except that the sun doesn’t shine each day, so perhaps you’ll want to size your batteries to have enough power to cover your power needs for two days (so you don’t have to run the generator if you have one), and you’ll want to size your solar panels to produce enough power on the days that the sun does shine to charge the batteries enough to store two days worth of energy. In this example, you’d need to generate 3,000 watts of power. The sun shines on average five hours per day in the summer. So 3 x 260watt panels = 750 watts per hour x 5 hours = 3,750 watts – more than the 3,000 watts needed. (Two panels would produce less power than you need.)
Plus, you’d need an inverter sized to the maximum power draw you’d be using at any one time – usually 2,000 watts on a boat (enough to operate a small microwave or coffee maker, but not at the same time), and deep-cycle battery storage for 3,000 watts.
To correctly size the battery bank multiply the battery system voltage by the amp/hr rating and see what the total storage watts will be. For example two 6volt batteries for a 12 volt system times the 428 amp/hr rating would be 5,136 watts. You can safely use 50% of this which would be 2,568 watts. If you need more power then add more groups of batteries.
Building Our System
Long ago I replaced my little 6-watt solar panel purchased at my local auto-parts store that sat on my helm and charged my starting battery, with a flexible solar panel. These come in various sizes and lie flat on your helm under the windshield, or outside on the deck or up on top of your canvas. They are lightweight and easy to remove when you store the canvas or winterize the boat. Well cared for, they should last 20 years.
At our cottage, we are over a kilometre away from the nearest hydro pole. It would cost us over $45,000 to bring power into our cottage, and that would mean being hooked up to an ever-increasing monthly hydro bill forever. We figured that we could purchase a lot of solar capability for that same $45,000, go off-grid, and never have a bill beyond our initial investment in the system.
We calculated that in our heaviest usage (winter time when it’s dark outside the longest), we would need 8,000 kilowatts total power consumption for a long weekend, including leaving the fridge running during the week when we were away. The next step was to work backwards. It’s too costly to make a mistake and over or undersize one of the five parts of the system, so make sure you consult an expert in solar power installations. After speaking with many self-proclaiming experts over the past decade, I found Peter Wetzel, a solar industry veteran of over 20 years, and VP Operations for Microgreen Solar (www.microgreen.ca). Peter designs customized DIY solar systems for cottagers, boaters and RV owners.
I consulted with Peter, to double check our power usage calculations, and along with his input we designed an off-grid solar system that is entirely DIY, and ULC rated for safety, that would work for our needs today, and be expandable in the future. We have eight 260W solar panels, powering two charge controllers (Four panels and 1000 watts/hour per controller), that charge four Surrette 6-volt deep cycle 428 amp-hour batteries wired in series to create a 24-volt battery bank, that is hooked to a 4kW inverter that powers our standard electrical fuse panel. The fuse panel is in the cottage, the batteries, inverter and charge controller are out in the battery shed at the base of the solar panels. We elected to run 240V wiring in from the inverter in the shed as it’s cheaper and offers less line loss that trying to run 12V wire in a long distance from the solar panels to the cottage. The 4kW inverter is actually Microgreen’s Power Pak, you hang it, connect the solar panel wires and the battery leads and you’re done. It is all pre-wired and pre-tested, so it makes a great DIY product. Our system has a backup 6kW propane generator (that we did use a gas fitter to install) that automatically kicks in if the Power Pak detects that the the battery voltage drops below a set level, because of a series of cloudy days.
There is no question that as the world looks for alternatives to its reliance on environmentally-damaging fossil fuels and an escape from high energy bills that solar power is a very viable solution. One look at what Greenline Yachts is doing by integrating solar power into their lineup, and what Toqeedo is doing as they expand the horsepower range of their electric outboards, or Volvo’s commitment to electrify their power offerings by mid-2020, and you’ll see that the solar solution is within our sights in the marine industry as well, and as prices continue to drop as technology improves, it’s also within the reach of our pocketbooks.