Need help!

Re: Need help!

First, it is very difficult to build and "expandable" solar PV system... There are a few components that can change battery bank voltage (charge controllers are frequently defined for 12/24/48 volt @ XX amps operation--and the higher the bank voltage, the larger array you can support).

The problem is, usually you have to go with a higher bank voltage, so you need a new inverter. And as you add solar panels, you find that the >100 watt panels are cheaper $$/watt, but are also non-standard for Vmp (Vmp~17.5 volts for a 12 volt battery, and 2x or 4x for 24/48 volt systems). But these flexible/large controllers are ~$500-$600+ each. Not very cost effective for a small system.

You can probably double the size of a system--but beyond that, it is almost a complete tear down/rebuild with mostly new components.

And then you get into specific loads... Refrigerators, air conditioning (obviously), cooking, and computers/electronic entertainment are frequently the largest loads you will have to support. And pumping, while you do not use much "energy" (kWH per day), the pumps frequently have very high power demands for short periods of time--which drives battery/inverter sizing higher to support the short/peak loads.

To give you some ideas of power usage levels... My suggestion is to look at a 100 kWH per month (9 months of the year, use a backup genset for bad weather)... That is about 3.3 kWH or 3,300 Watt*Hours per day (maximum average). It is enough for many people to have a "pretty normal" home (lights, tv, computer, fans, washer, well pump) and using propane for cooking/heating (and/or solar heating).

You can build larger systems--but they are expensive not only to construct, but to maintain... Plan on battery replacement every 5-15 years and replacing major electronics (charge controllers, inverters, etc.) every ~10 years or so.

And look at ~$1-$2+ per kWH for your off-grid power costs (very rough estimate of 20 year system/maintenance lifetime). That 100 kWH per month system will "cost you" around $100-$200 per month to power your very small electrical loads (I am on grid in SF Bay Area, no A/C, no heat 6+ months of the year, family of four, natural gas, using around 200-300 kWH per month).

If you are planning on using 1,000 kWH per month (typical North American Home) or 2,000+ kWH per month (typical home in the south with A/C loads)--those are very large systems. And usually cannot compete with grid power (even if you think power prices will continue to increase--In California, our peak summer afternoon rates can be in the $0.52 per kwH for heavy power usage--still less than "going off grid" without major conservation).

In the end, for a "cost effective" system (whether on grid or off grid)--you really need to start with conservation.

For example, instead of putting a 1-2 HP pump 200' down your well and running it for 10-60 minutes a day into a pressure tank, you can get low power pumps (AC, DC, even AC/DC) that have low average power and low peak power (i.e., soft start). The pumps are not cheap, but they can save you a lot on your power costs (and system capital costs). Also, you can pump into a cistern, then use a simple DC (RV type) pressure pump plus small bladder tank to provide pressure for the home.

In the end, designing for conservation and knowing/measuring your energy usage before you design/build your solar PV system will usually save you lots of aggravation and money.

For many people, they really do not have a good idea of how much power they will need. Building a smaller PV system and using a fuel efficient genset (Honda eu2000i is great for smaller homes/systems) as a backup/assist until you have a better handle on your loads may be a good place to start.

If you are interested, here is a thread with lots of links/information to conservation (and solar) ideas, projects, and information.

Working Thread for Solar Beginner Post/FAQ

-Bill