Volt Amp Hour

Volt Amp Hour
How long would it take to charge a 212 amp hour 12 volt deep cycle battery using a 60 watt solar panel?

I’m trying to develop a DIY grid tie system & know only the basics about electrical work.
No worries guys I’m a master plumber & have a friend who is a master electrician who would be doing all the wiring. He wasn’t around for me to ask initially. Thanks for the answers!

A typical 60W panel has a 4A short circuit current from spec in first link below. This is most likely about 3.5A of peak sun charging current.
Depending where you live, you may get 2 to 5 hours of peak sun charging current a day. You should be able to find this figure on the internet for your area. It is the number of equivalent full sun hours (that the panel will provide 3.5A). It will take all the daylight hours to achieve this equivalent. Lets say you have 3 hours equivalent, so you will get 3.5A x 3h = 10.5Ah per day average.

The battery is 212Ah, so it takes (1.4 x 212 = 300Ah) to charge it. How many days is this? Divide 300Ah by 10.5Ah per day to get 29 days. This assumes no power lost from the battery over that time. Basically the battery (depending on type) could lose almost that much charge over a month from self discharge, so this panel would just keep a battery of this size more or less fully charged if there is no load.

With an MPPT (Maximum Power Point Tracking) controller this figure could be improved, as the charge is derived from the maximum power, not the maximum current, and could provide more current than the maximum from the panel (using internal electronics).

If you want a grid tie system you need a higher voltage to operate the grid tie inverter. You don’t need batteries, that is one of the reasons for using such a system. These inverters typically require 150-500V from the panels. This is for good reasons of efficiency and cost. Look up “Sunny Boy” (a German model popular in the US and Australia and Europe at least) to get an idea. This inverter adjusts the load automatically to use the input voltage that gets the maximum power from the panels (MPPT tracking). You need 10 x 12V panels in series to get this voltage. That means you can deliver about 600W to the inverter. Usually smaller systems target 1KW as the power from the panels, using bigger panels, or 24V modules etc. The design starts with the total wattage of the panels, as this is the high cost item. A 1KW system may not export much power at all.

I recommend you research this much further, or get some sort of consultancy with someone familiar with your region before you go ahead. There are plenty of references on the web. The wiring is at voltages similar to household voltages so you should get a suitably qualified electrician to do that work.

I know it seems disappointing, but the power from a solar panel is small compared with household use, especially as the full power only occurs a few hours a day. For example, the standby power from your appliances alone will exceed the 60W rating of the panel, so it makes economic and environmental sense to eliminate that by turning things off at the wall outlet. This panel could perhaps power such a small thing as a network router on a 24 x 7 hour basis.

Depending where you live, solar hot water may make more sense than an electrical system, as it represents more energy saving due to higher efficiency, and also is more practical for a DIY project.

You may get government grants, Renewable Energy Certificates (RECs) etc. to offset the cost of some systems in some regions. Hope this helps.

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