The need for Active Solar power generation

With the our commitment to Zero fossil fuel sailing we have been having to review and update our initial Solar plan. Designing our Solar Arch has been part of that.

The traditional “passive” approach to solar is not going to work for us. By that I mean the idea of putting up a few solar panels and forgetting about them. We need to generate far more electricity from solar than this approach achieves.

So what do I mean by “Active Solar power generation”. Unlike shore based like people living on boats are used to being proactive about energy use and supply. So the mindset includes managing consumption and keeping an eye on battery state. However, for a long time this has been done with the expectation that you can always charge the batteries by running the diesel engine or a generator or by going into a marina and using the shore supply.

We are making a determined effort to keep electric consumption down through a number of deliberate choices:

  • Wind vane self steering, keeping the electric autopilot only for redundancy
  • No freezer. Yup it does constrain the food you can take and keep but fridge and freezer are huge electrical power hogs.
  • Reduced Computer consumption. We are going to be minimising laptop use by having Raspberry Pi single board computers for navigation, entertainment and “office work”. They run on 12 volt.

However, by committing to Zero fossil fuels we are increasing our electric consumption significantly and reducing our energy sources.

Increased consumption:

  • Electric Motor. This uses a lot of energy and is the opposite to the norm. When we motor we will be drawing lots of energy from our batteries rather than putting it in. While we will have regen (charging the batteries when the propeller spins while you are sailing) the change is incredibly significant as the norm is to see the diesel engine as a provider of almost unlimited “free” electricity and hot water. Of course it isn’t free at all, but more a desirable side effect that has resulted in a significant increase in the number of hours the engine is used. So has become a norm to motor whenever the wind speed drops because at the same time you will charge the batteries and heat the water.
  • Electric cooking. All forms of electric cooking (Induction hobs, Microwave, Pressure Cooker) use a lot of power (although mostly for a relatively short time). The norm is to burn bottled gas (occasionally diesel or paraffin). By cutting out another fossil fuel we increase our electric consumption.
  • Dinghy Outboard. We have an electric dinghy outboard engine. So far the boats we have seen with electric motors (Sailing Uma, Beau and Brandy) have not switched to electric outboards (despite the hours they spend maintaining their petrol outboards). In part that is because they want to be able to go faster in the dinghy (see this video from Sailing Atticus for a good reason for this) but it is also about the need to charge the outboard engine battery.

Increased generation

So this is the heart of the challenge. By committing to no fossil fuels all our energy needs to come from renewable sources. We have three options:

  • Engine regen. We are hoping this is going to be significant for us. On longer passages it will do more than recharge the motor batteries from leaving harbour but will contribute something to the daily consumption. It also has the potential to provide power through the night. However, it is only available while sailing and only while you are sailing fast enough (probably won’t contribute much below 5 knots). As liveaboard cruisers typically spend the vast bulk of their time at anchor the contribution isn’t that great.
  • Wind generators. These have the significant advantage of potentially providing significant power at night and through the winter. However, there are problems. Many people complain about the noise and vibration. Fitting them without causing shading on solar panels is a challenge. They do require a lot of wind, probably more than you would normally be looking for in a sheltered anchorage. We’ve looked at the Rutland 1200 but at the moment feel the cost and installation challenges are too great.
  • Solar. The typical installation of solar has been changing quite significantly. For liveaboard cruisers the norm now seems to be to have a solar arch with between 300 and 600 watts of solar panels. That is enough for minimal electric motor use (see Sailing Uma, Beau and Brandy or Rigging Doctor) but not for electric cooking, electric outboard etc.

So Active Solar

This is where our plan differs. We are going to have to be far more active about our solar generation. That means a number of things.

Our solar arch needs to be tiltable to increase it’s efficiency (both Sailing Uma and Beau & Brandy do this but the vast majority of solar arches do not).

When sailing we will need to be active in adjusting our solar generation. Some panel positions will be pretty much setup and forget (such as covering the upturned dinghy on the foredeck with panels before leaving harbour). Others will only be possible in lighter conditions (some along the guardrails for example).

The goal will be to have enough permanent solar when sailing (solar arch and wheelhouse = 510 watts) so that with the regen and battery bank we will be able to get through a gale when we have to put all the other panels below. That shouldn’t be too hard as in those conditions you are not likely to be doing much cooking and you can put off charging the dinghy outboard.

When conditions improve we should be able to sail in light to moderate with an additional 1,050 watts (2 x 175 watts on the dinghy, 4 x 175 watts on the guardrails from the cockpit to the stern. Some of this is going to suffer from massive shading at times so we are assuming it will be about 1/2 as efficient as the solar arch.

Then at anchor we need to have lots of solar panels that come out and are positioned dynamically. We will need to have solar panels positioned above the mizzen boom, around most of the guardrails and possibly above the deck. How many of these we will need is still uncertain (it depends so much on where we sail – if Coronavirus and Brexit mean we have too stay around the UK then we are going to need a lot more solar in Scotland than the Caribbean).

So far we are planning on a total of around 2,400 watts (13 x 175W + 4 x 40W) which so far I have only heard of on large catamarans.

We will need to be active in working with these panels. We will need to adjust the tilt during the day so that as the sun and boat move their efficiency is kept as high as possible. We will need to move them if other boats come alongside or if we are in a marina. We will need to put a lot of them below when sailing.

So I’m going to be building a standardised wooden surround for each panel. This will provide attachment points so that any panel can be fitted to any section of guardrail (and be tilt adjustable) or to the supports above the boom and dinghy. The edging will provide bump protection when moving them around and allow panels to be stacked without scratching the glass. We have chosen the 175W Victron panels as our standard because they are about as large as we can lift, manoeuvrer around the boat and fit through the main hatch into the cabin.

Exactly, where we will store all the panels that need to be “reefed” (taken down) in a gale is currently not fully sorted. Some might go on the aft deck or aft cabin. Some in the corridor to the aft cabin where one of the diesel tanks was. Some in the forecabin (which is likely to be mostly storage when there are only 2 of us).

We are under no illusions that we can achieve zero fossil fuel without ongoing, daily labour to maximise solar generation. But while that might seem a lot of work remember that we won’t spend any time (or money) finding and visiting fuel docks or carrying jerrycans around in the dinghy.

In summary

We believe we can capture several orders of magnitude more solar power than is generally the norm for monohull cruising yachts. But it will require us to work at it every day.

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