Questions about Solar equipment

Re: Questions about Solar equipment

When all is said and done, you will get, very roughly, 400 Watt*Hours of useful energy out of your system per sunny day with the one 190 watt panel and MPPT solar charge controller...

Battery wise, it should be sized around 1/5%-1/10% of charging capacity (10-20x the available charging energy). So that would be 4 to 8 kW*Hour of storage battery for, roughly balanced/optimum storage capacity (if this were designed as a real off-grid application).

But, you don't really need 3 days of no sun (poor weather) performance for a demonstration system.

Another way to look at sizing of the battery is how much power do you wish to draw from it... Normally, if you can discharge the battery by 20% or less per day (80% State Of Charge)--it will last a good long time. You can discharge it as much as 50% maximum in a day, but it will not last that many cycles (but if you are only doing this a few times per year--it probably does not matter). And if you can recharge the battery quickly (like within 24 hours)--the sulfates will not harden (which kills the battery).

Also, you could look at AGM batteries--they will take deeper discharges without damage (but--deep cycling will kill them faster too).

So--if you want 800 watts for 30 minutes per day--the one panel will just about support it (or 100 watts for 8 hours per day, etc.)... Exact numbers really depend on where you are at (San Luis Obispo, CA?). And the time of year (winter, summer, etc.)...

There are still quite a few issues in your decision (flooded cell requires watering once per month, AGM's are 2x as expensive).

And, you may want to experiment with the Mod Sine Wave inverter (MSW). For some electronics (radios, TV's, digital clocks, some motors), you may have problems with noisy audio/video, clocks may not keep correct time, and some motors and electronic devices may overheat. Most items will probably work OK--but you should "pre-test" your setups before you go out for a demo (or get a true sine wave inverter which will pretty much support anything within its power rating).

Also, watch the maximum power you want to use--800 watts is going to be close to 100 amps from 12 volt batteries (even more if surge is above 800 watts--such as starting a motor). For a small battery bank, that is quite a large current--which will quickly flatten a battery (battery energy discharge curves are non-linear--the larger the current, the less energy the battery can deliver).

Keeping loads small (CFLs, fans, boom-box, laptop computer, etc.) will help--You don't want to give the idea that a few solar panels is equivalent of a 120 VAC 15 amp wall outlet.

And, if you plan on adding more panels later, it would be helpful if they are the same Current or Voltage rating (depending on if you will be adding these is series or parallel--which depends on the solar charge controller you have or will be replacing when adding on). And, if you add more batteries, you will have issues of the new batteries not lasting much longer than the original batteries (all will begin to fail around the same time).

In the end, what is it you want to do? Make a simple demo tool for sunny weather, a slightly more sophisticated power station for night time demos and some light emergency work. Or, a full blown design/installation project with automated charge/load control with full monitoring (Battery Monitor) and an automatic start electric generator for periods of no sun...

-Bill

PS: One other possibility would be to use the extra space for a solar thermal hot water heater--that would be different and cheaper too (plus more solar design/build experience)... Add a solar panel, pumps, insulated tank and watch the temperature rise--put a hot water faucet on the side (you may need to temper with cold water to prevent scalding).