Air Cooled or Water Cooled?
- Category: Refrigeration
Which marine refrigeration system is better when cruising in warm waters: air cooled, pumped-water cooled, or Keel Cooled?
A well designed and fabricated air cooled refrigeration system, like the Frigoboat Capri 50, should be able to maintain refrigerator and freezer temperatures in the tropics if the application, installation, and operation are all within the manufacturers' guidelines.
But in tropical/Caribbean conditions, air cooling will be 25% to 35% less efficient than water cooling. As a result, the overall power consumption of an air cooled system will be considerably higher than for a pumped-water cooled system, and very much higher than for a Keel Cooled system.
Many serious cruisers these days install hybrid Air-plus-Keel Cooled systems, where the air cooling is only used when the boat is hauled for any reason. For a new installation, this could be a Frigoboat Capri 50 installed together with a Keel Cooler, with a switch installed in the fan circuit of the Capri 50. Existing Frigoboat Keel Cooled systems can be easily converted to an Air-plus-Keel Cooled system by installing an Air Add-On condenser. This is accomplished with the use of just basic tools, and without any adjustment to the refrigerant charge.
If your boat is aluminum, then due to corrosion considerations that prohibit the installation of a Keel Cooler, you would be best served by installing a pump-water cooled system like the Frigoboat W50. That, together with the Air Add-On air-only condenser for use when hauled out, will provide the same efficiency as a Keel Cooled system, although the added current draw from the water pump will negate some of the power savings normally experienced over an air cooled system.
Solar Panel Efficiencies: Aurinco vs Solara
- Category: Solar
Aurinco is insinuating that some solar panel manufacturers are trying to mislead the public by publishing cell efficiency figures rather than panel efficiencies. They are also suggesting that some manufacturers are embellishing results using tactics learned from the automaker VW.
Normally this sort of rhetoric would be quickly dismissed as being disingenuous and unprofessional, but it does merit some analysis.
There are several ways to measure solar panel efficiency. Some are shown below, all at Standard Test Conditions (STC)
Single Cell Efficiency - Solara has always stated cell efficiencies, not panel efficiencies, which can be very misleading (see below).
Overall Panel Efficiency - This takes into account the overall panel dimensions, and so can vary wildly between one panel manufacturer and another dependent on how they construct their panels. If a manufacturer is willing to risk edge damage and water intrusion by fabricating a panel with very small edge margins, then it will inevitably look to be more efficient than a similar panel that has wider, and subsequently much safer, edge margins and overlaps.
True Panel Efficiency - This is calculated from the actual total cell surface area, ignoring space between cells and margins/borders, and is by far the more reliable gauge of panel efficiency.
|Solara Power M
Cells - Aurinco use standard monocrystalline cells with bus lines and collector fingers on the surface that reduce effective surface area and actually create their own shadows at low light angles.
Solara Power M panels use genuine high-grade back-contact SunPower® cells that give superior performance in low irradiance, low light angle, and high cell temperature conditions.
Solar State of Play
- Category: Solar
We often get asked about the latest developments in solar technology, and when will they be available, if suitable, for boat applications. I am by no means a solar expert, geek would be more appropriate, but I do keep my ear to the ground and try to keep up with the latest developments.
The people at the National Renewable Energy Laboratory (NREL) make this a lot easier by publishing their chart (below) of research cell efficiencies for various solar technologies. This shows the state of play of the very best of the best cells available of each type of solar, measured by their efficiency, i.e. how much of the available solar irradiance is converted into electrical power. Here's a quick synopsis of the chart.
Potty Talk and Marine Refrigeration
- Category: Refrigeration
In my kitchen at home we use cooking pots and pans made from a variety of metals, and I thought it would be an interesting project to delve into the pros and cons of each material and then go on to see how that works with refrigerator evaporators.
After all, cooking pots and fridge evaporators both utilize metal surfaces to transfer heat, so many similarities exist.
When cooking on the stove, we're conducting heat from an external source (the burners), through the material of the pot or pan to the contents in the interior.
Simple enough you'd think, but different metals have different characteristics, and work in different ways. The ability of a material to transfer heat is known as its Thermal Conductivity. This is quoted in various units, but here we'll use good old fashioned BTU's per hour per foot per degree Fahrenheit (Btu/hr-ft-F).
Listed below are some of the common metals used for cooking pots and pans together with their Thermal Conductivity rating, starting with the most conductive and ending with the least. Basically, the higher the number, the more heat the material will conduct through it