more musical deer art?

Actually, 15 watts at 20 volts = 0.75 amps. Your voltage regulator can't add amps, so while it's rated for 2.25 amps, the actual output of 0.75 amps at 13 volts is 9.75 watts.

So, even less power than you said!

That said, my solar powered house has only around 100 watts capacity (128 watts of panels, degraded by being somewhere over 15 years old), and with all 4 of your panels you'd get 60 watts. I could live on that comfortably enough in the summer..

The bad lifespan is the killer. Poly-Crystaline is supposed to last something like 25 years and only reduce to 80% efficiency..

Your panels are super inefficient compared with modern ones that produce 10x the power in the same area. Even my 1 sq ft travel solar panel produces 17 watts.

What can you do with these panels? Well, 15 watts is sufficient to run a laptop for around 4 hours a day, or fully recharge a cell phone. So, find someplace out of the way where there's no power and that would be nice to have, and mount them. Perhaps on the Applalachian Trail..

Or, 15 watts is sufficient to run an embedded computer as long as the sun is shining. So, bolt a arm box on the back, and do this 4 times and you can have a chain of solar powered wifi repeaters going to some corner of the homestead. Etc.

Add a small battery with the arm box, and a USB infared camera, and you'd have a mobile wildlife photography setup.

Didn't see the picture before ... I think you have 6 of these 15 watt panels, and 90 watts is nearly what I have here, and should be enough to charge a couple of golf cart batteries over the course of a sunny summer day.

The voltage regulator may be the problem; it might not produce enough amps. A charge controller senses the state of the battery and plays tricks to charge it much more efficiently and completely than a constant 13v can.

My charge controller cost $90, but I think some MPTT charge controllers are significantly less expensive these days.

12 years ago I bought a 30-watt panel from Ebay to run the bilge pump that pulls water from my creek to irrigate my garden. Has been doing that for a decade now and I'm quite happy with it. Then I made the mistake of buying Harbor Freights' solar panels as well and then got educated by a guy who attends the marital arts school I go to. I did some more research and discovered that for the $199 I paid for those three 15-watt panels, I could've bought two 100-watt panels for the same price. Oy!

Moral of the story: do the research first!!! Don't be taken in by advertisements.

Regulated 13 volts will not charge a lead acid battery. Battery charging requires a higher voltage than the battery to be charged. Charging current is a function of the voltage difference. The reason these panels produce 20 volts "no load" is so they can charge a battery to 14 volts. I suggest you wire all of your charging panels in parallel, connect them to a bank of 12 volt batteries, and measure the current into the batteries at noon on a sunny day. You can also measure the battery charging voltage. Most likely, you will be charging at 14 volts, at somewhere between 1 and 10 amps, depending on how many panels you have. In the old days, we used either series or shunt regulators to prevent overcharging. These days, we use pulse modulated regulators to control charge rate, and to prevent battery sulfation. Either way, you can charge your batteries from these panels. You can contact me directly to discuss this further.

Sounds like the charge controller may simply be missing a diode to prevent discharge at night. http://www.instructables.com/id/Make-the-Harbor-Freight-45W-Solar-Panel-Charger-Co/

We built a MPPT for solar panels using MOSFETs for a solar powered vehicle that in the end became my bachelor's project. That was in 1993. I find it hard to understand why you would not want to use MPPT.

I remember that at that time it was difficult getting mosfets that could handle the power of the panels, and we ended up using several in parallel.

But now a mosfet that can handle 150 W doesn't seem to be a problem anymore. And doing a quick scan I found several MPPT/charge controllers online. Like e.g. from victron for around € 80 here in the Netherlands

Hi Mark and Anna,

The panels I see on the houses around here seem to be mostly 280Watt and seem to be selling for about $0.32/watt or about $100 per panel. Much cheaper than I originally thought.

I have been thinking of building a 'poor' man's solar system without all the fancy power switchover stuff. Using cheap lead-acid batteries.

For a simple rig to provide power without any external hook up. Much simpler.

warm regards, John

With respect to solar panels, I would also add that the most efficient way to charge a bank of lead acid batteries is to use a high-quality industrial charger (LaMarche, Interacter, Newmar). If you connect one of these chargers to your battery bank, it will cost you a few cents per day to maintain your batteries at optimal charge. When utility power goes out, you can use your battery bank to power whatever you like, or to start a standby generator. In commercial service, we replace standby generator starting batteries every 2 years. For homestead use, I have gone 15 years with starting batteries using a high-quality industrial charger. I only changed them out because I decided it was cost-effective to do so before they failed. Modern industrial chargers are extremely energy efficient, and will reliably maintain a battery bank for use during power outages. Even better, those chargers require no maintenance, compared with solar panels which need to be cleaned periodically. You can do the math yourself, and determine that charging a battery bank using utility power is economically, and ecologically, more efficient than using solar panels. In some U.S. states, tax incentives for solar panels may appear to be attractive, but even then, they are not necessarily the best choice. As always, you can contact me directly if you wish. Harry

Aquired 6 panels (2 boxes) in 2005. Hooked to trolling deep cycle marine batteries, next year ice storm left us without grid power for 3 days. We ran a small tv, 2 led lights, and small blower on airtight wood heater. Took freezer food to kids house, and tried to eat all in fridge, we kept warm and informed. Since 2014 have newer set of HF 4 panels,(100 WATTS) that keep power to small rv In storage lot, before would have to replace rv Battries every year, once dead, would not hold charge. BATTERIES now 6 years old, and still at least 90% of original charge! So $150 has saved me $500 or more.