I was going to email a few of my readers and go over this topic, but have decided to just throw it out there and you never know what may come…..
I bought 3 broken solar panels a few weeks back and am in the middle of repairing them and will put them up at my house.
Ok, thats pretty straight forward, so whats so confusing about that?
Whats the best way (ie, the cheapest) to use the power they generate?
If you are interested in the panels and the repair process, have a quick read of the blog I did on them over on the Opto website… I will wait here while you go do that……
http://blog.opto22.com/optoblog/repairing-broken-solar-panels
Ok, so thats the panels and I plan to epoxy / repair the next two this weekend. They should be on the roof a few weeks after that.
Thats all well and good, but then what?
They are 30 volt panels. I sorta planned to wire all three in series and get 90 volts, this way if one or more is a little shaded, I will still get some power from them.
I also planned to run a 12 volt battery and inverter, this way I could use the power from the panels during a blackout.
I chose 12 volt as I can easily get stuff to run off 12v and any parts I buy could be used in a car or RV down the track if (when) we move out of the house.
So whats the problem?
90 volt to 12 volt chargers are expensive.
Here is the ‘best’ one that I might be able to afford…..
http://www.amazon.com/Solar-Charge-Controller-150VDC-Display/dp/B00K71C7PI
The thing is, when you do the numbers, I will have 60 amps, and this thing is limited to 50, so I am throwing away 10 amps, but only if the sun is shining and the batteries are flat, so I am not sure how often that is going to happen.
Should (can?) I run a 24 volt system and forget this charger all together and just run the solar panels into the battery with a simple on/off switch?
If I do this, then I save 250 bucks but at the loss of the usefulness of having a 12 volt system…. What is that going to cost me in the long run?
Should I forget the idea of putting the panels in series, and just get a 30v to 12 volt solar charger for each panel? (I have not looked, but suspect that I could buy 3 of these for less than the cost of the one big charger).
The other issue I have is working out the size of the 12 volt battery…. I have a 400 watt load I want to run as long as I can after the sun goes down.
So how many amp hour battery do I need to run 400 watts for 10 to 12 hours and only have around a 20 to 30 percent depth of discharge of the battery?
I was thinking of going for a 12 volt deep cycle battery, either gell or lead acid. Lithium batteries are around, but they are still really expensive. (I was quoted 1000 bucks for 200 amp hour for a used pack).
My house runs around 800 watts all the time, of that 400 watts is my computer gear. As it happens ALL the computer gear is plugged into my UPS, so the plan is to have the solar system run an inverter that will be switched in and out of the UPS, thus running all my hobbie stuff off solar / battery when it can. When I can’t, the UPS just gets switched back to mains and the batteries can recharge off the solar.
So, thats where I am at. I have 750 watts of solar. I have 400 watts of load that is wired back to one outlet via a UPS. Seems prime to switch the UPS between mains and solar and try and run the UPS for as long as I can after the sun goes down.
How do I do that as cheap as possible?
