Need advice of what solar system to use

System

I'm totally brand new to solar power. I'm doing all the solar assembly myself to keep costs down. I just set up a 1978 2-bedroom manufactured home on my 40 acre lot in Arizona. There is no power in my property so this is all off-grid. I need assistance on what solar system to use. I will be using this house on weekends only. The solar system will be used to power the following per day:

6 lightbulbs, 2 computers & 2 monitors, 1 TV, 1 VCR, 1 water booster pump (DC).

How many 100 W panels do I need? How many and what type of batteries do I need? What type of inverter do I need and what wattage? Please advise on what other equipment do I need to make this system work.

The old manufactured home have 110 AC wiring. How do I connect an inverter to the main service panel?

I also have a 3500W generator for backup power. How do I tie this to the solar power system. Please help. I'm so confused. Thanks.

icarus

Re: Need advice of what solar system to use

First piece of advice,,, don't buy anything (yet)! The biggest mistake people make is "Ready, fire, aim". The result is folks spend too much money on systems that are over price and under perform.

The first thing you must do is get an accurate handle on your loads. Use a Kill-a-watt meter to log you loads. Log or guess as best you can at the loads and their duration. What you will be left with is a watt/hour/day number. (injecting here to take conservation efforts to reduce loads as much as possible as it is cheaper to save a watt than produce it. niel) Once you get that you can begin to work backwards to find out how much Pv you need, how many batteries of what type, how big an inverter etc.

As for wiring it in, in simple terms, the output of your inverter would wire to the the house wire through a transfer switch, such that when the generator is running it energizes the house, or when the inverter is running it will energize the house. Pretty simple in theory, a bit complicated to wire. (Also depends on what inverter you end up with).

A couple or rules of thumb. Most people over estimate the amount of power they can actually get from solar, and underestimate their loads. Second, loads will almost always grow with time, so you want to design a system that has some head room. Third, and probably most importantly, off grid solar comes at about twice the price of grid tie solar, ~ 1/2 the efficiency, resulting in net power cost of about 4 times that of grid tie. This is due to battery costs, plus the inherent inefficiency of charging/discharging batteries, as well as other system losses. In addition, off grid, once the batteries are fully charged (or even nearly so) you end up throwing potential power away because you have no way to use it. Load management is very important in keeping system costs down and efficiency up.

A quick napkin calc is, take the name plate rating of a PV panel, divide that number by 2 to represent all system loses (wiring/charge controller/inverter/battery charging efficiency etc) and then multiply that number by 4. 4 represents the average number of hours of good sun one can expect to harvest day in and day out, over the course of the year.

If you go to PV watts :http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/
plug in you location, it can give you a pretty good idea of what you can harvest daily and annually.

So for example, a 1000 watt system might look like this: 1000/2*4=2000 wh/day

That would be enough to run a 200 watt television for 10 hours,,, and nothing else for example. A 1kw system, off grid might cost ~$8 watt or $8000 +-. The way you make any system cheaper is to reduce the load to an absolute minimum. Every WH you don't have to generate makes the system requirement smaller.

All that said, if you have grid power available, but you just don't want to pay for it, you have to consider the cost/benefit of the grid. After pricing out off grid solar, you will realize what a bargain grid power really is.

Welcome to the forum, and shout when you have more questions,

Tony

PS Seeing that you are going to use this house weekends only, consider a propane fridge. Doing so makes the PV system smaller, and if you use it only on the weekends it might be cheaper. On the other hand, if you are going to keep the fridge running during the week while you are not there, then a good energy star fridge would probably be cheaper net/net.

System2

Re: Need advice of what solar system to use

Thanks, Icarus! This is very helpful advice. I really appreciate it.