Solar Dropping in Price (Finally)

[Jack C]

The MPPT I use will not handle that voltage. Also as someone else said, DC Volts > 48V is not a good idea especially outside on a boat. When the nice light wires carrying 90VDC that you carefully snaked through your arch chafe and your arch goes live, turning off the power means covering the panels. Your fuse will not help and finding a GFI for 90VDC? Of course you could mount the MPPT under the panel, but that brings other problems.

So while using low cost technology on a boat is attractive, the savings may mean you pay in other sometimes less obvious ways.

[unbusted67]

What exactly does MPPT stand for?

[schoonerdog]

A maximum power point tracker (or MPPT) is a high efficiency DC to DC converter which functions as an optimal electrical load for a photovoltaic. What that means is that if you have a panel meant to charge at your batteries, and you batteries charge at say 14 volts, but there is 17 volts being led in, 3 volts is wasted. The MPPT brings that to the optimum voltage for charging your batteries. The outback MPPT 60 brings anything up to 120 volts down to your battery voltage charging levels, regardless of whether you have a 12 volt or 24 or 48 volt system.

[unbusted67]

Is it the same thing as a charging regulator?

[cal40john]

You can short the output of a solar panel through an ammeter and see the maximum current it can put out I-sc, and you can put a voltmeter on the open leads of a solar panel and see the maximum voltage it can put out, V-oc. In both of these cases you transfer essentially no power. Power = volts times current. In the first case there is no voltage drop, in the second no current flow. Look at figure 4 on the link.

Part II – Photovoltaic Cell I-V Characterization Theory and LabVIEW Analysis Code - Developer Zone - National Instruments

The top graph shows what voltage you get for a certain current drawn. The bottom graph shows the power transfered in for each point in the I-V curve (top graph). Note that there is only one place where you maximize the power transfered. This is not at the voltage that the battery will hold the solar panel at. An MPPT controller presents the correct resistance (OK, this point is fudged a bit) to the solar panel so that it is operating at its max power transfer point, and it presents the correct voltage to the battery to maximize current into the battery.

So in other words, it is not exactly just a regulator.

Another explanation:
MPPT Solar Charge Controllers

[ctsbillc]

Here's my new solar installation

PlanetSolar boat aims for Earth circumnavigation with Sun's help, enters testing stage (video) -- Engadget

Bill

[Eleven]

From land bound experiments I'd just mention that most solar cells loose some power when above 40 deg C. For tropical mounting allow an air gap behind to aid natural cooling, and, if it's important to get max power, consider some sort of water cooling for the panels which will also provide hot water!
The MPPT adds cost and efficiency. Port and Starboard Arrays could be commoned into port and starboard MPPT's. Shaded cells will sap some power so arrange accordingly, but shaded still do a bit of good if diffuse light rather than direct sunlight is still available.

[Ram]

Originally Posted by Eleven

From land bound experiments I'd just mention that most solar cells loose some power when above 40 deg C. For tropical mounting allow an air gap behind to aid natural cooling, and, if it's important to get max power, consider some sort of water cooling for the panels which will also provide hot water!
The MPPT adds cost and efficiency. Port and Starboard Arrays could be commoned into port and starboard MPPT's. Shaded cells will sap some power so arrange accordingly, but shaded still do a bit of good if diffuse light rather than direct sunlight is still available.

Any ideas on water cooling ??

[sarafina]

Originally Posted by Ram

Any ideas on water cooling ??

Had a friend in Panama who had a rig that was a long water hose in a bag ,that could be inserted into his system between the tank and the pump, that was designed to float overboard in the water. Only worked at anchor or dock, but it chilled tepid tropical water down to a nice drinkable temp.

He was a live aboard on a tri 45, so he had it out most the time. Thru a dorade vent maybe?

[Eleven]

First a flexi panel needs to go on some 16swg ally with an air gap behind to survive crews feet. A 1/4inch air gap will certainly help and the ally panel won't take a permanent set if it's stepped on.
A floppy poly bag of water with a couple of hoses will provide a circuit to a hot water tank but it's a problem not to use more power than gets saved. Domesically (house) it's a bit easier to mount the hot water header tank above the panels and let the rising hot water circulate the system.
Boat wise maybe a small header tank and use an intermittent pump (thermostat trip?) to provide some circulation. Depends how you value hot or warm water. A hand pump for the watch keeper would do just as well, maybe even the swell could assist, it doesn't need much to keep the water moving slowly around.
There should be info with various makes on how much temperature affects performance.

[Pelagic]

So prices are coming down…. Is that because they are selling soon to be obsolete technology in the solar cells of the last 10 years?

Would like to know before I make a planned large investment

[Kordie]

I just spoke to a Chinese manufacturer and they quoted me US$1.80 per watt FOB.

I have negotiated a price.

Long way from $1 per watt but I am sure we will get there.

[ctsbillc]

Originally Posted by Pelagic

So prices are coming down…. Is that because they are selling soon to be obsolete technology in the solar cells of the last 10 years?

Would like to know before I make a planned large investment

There will always be better stuff coming out, and for solar this is mainly a matter of efficiency, which practically means smaller panels for a given power output. Reliability is great already.

Though there is technology in the labs which promises more efficient panels, I can see no breakthrough technology likely to hit which will obsolete current generation panels, and price drops are due to stuff like the poor economy.

Bill

[Ram]

IM still not clear on how to cool the solar panel with water in a way that will work onboard-
Im going to be setting up 2 or 3, large panels on my arch , how would I cool them with water and be able to recover the water and still use it to drink??

[ctsbillc]

Originally Posted by Ram

IM still not clear on how to cool the solar panel with water in a way that will work onboard-
Im going to be setting up 2 or 3, large panels on my arch , how would I cool them with water and be able to recover the water and still use it to drink??

Efficency of crystaline solar cells decreases by about 0.5% per degree C. (from the starting point of 10 - 15%) i.e, a 20 degree rise will knock you down from 10% to 8%. I'm not sure if this is worth the effort of all the plumbing. Has anyone measured how hot the panels get?

Bill