Category: Photovoltaics

Photovoltaics - Solar Power Part III - Installation

5/26/2020

Introduction

The previous report outlined the equipment selected for our hybrid solar power system. This report will describe installation and the next report will describe operation and performance.

Installation

We had the system installed by American Solar and Alternative Energies last June.
americansolarenergies.com/american_solar_energies/

They arrived bright and early with a large crew so they were able to complete the installation in one long day. There was one crew on the roof installing the rails and panels, two electricians installing and wiring the SkyBox and a crew on the ground hoisting the panels up to the roof and installing a grounding rod for the system.

Hoisting Panels Up to the Roof

20 x 320W panels for a total of 6.4 kW.

The SkyBox and the battery bank are located in the utility area where power enters the house.

From left to right: the main breaker panel, critical circuits panel, networking hub and SkyBox. The battery bank is under the counter below the SkyBox. The whole system is pretty compact.

The next report will discuss performance.

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Photovoltaics - Solar Power Part II - Equipment

5/25/2020

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Introduction

It's been almost three years since my original post on Photovoltaics and just about a year since we installed our system. With a year of experience it's a good time to post some results. This report will outline the equipment selected and future reports will describe installation and performance.

Batteries

As mentioned in the previous post, I wanted a hybrid system that would include sufficient battery backup to run our critical circuits (refrigerator, well, microwave, networking) for at least 24 hours. Based on several years of monitoring the critical circuits, the battery bank would have to provide a minimum of 10 kWh.

I investigated Tesla Power Wall and LG RESU Lithium-ion batteries. Although lithium-ion batteries have a much longer service life than old-tech lead-acid batteries the cost is far greater. Since we only use the batteries for backup, service life (i.e. the number of charge-discharge cycles) is not an issue. I intentionally discharge the batteries once every 3-4 months just to verify they are functioning properly. Aside from that we have only had a couple of outages which were an hour or less.

I selected the Outback 106NC battery which stores approximate 100 Amp-Hours at 12 Volts. Since the batteries cannot be fully discharged they provide a bit less than 1 kWh of backup power per battery. To achieve the required 10 kWh of reserve power I went with 12 batteries arranged as three banks of 4. At a cost of $245/battery (with free shipping) the total cost was just under $3,000.00, which was about 1/4 the cost of an equivalent RESU or Power Wall.

Unfortunately, it appears that this series has been discontinued.

One side benefit is that the individual batteries are "only" 69 lbs each so I was able to schlep them into the basement and wire them together to save on installation cost.

Wired and Ready to Go

Inverter

A hybrid system is more complex than a grid-tied system with micro-inverters. It must be able to function in both grid-tied and off-grid modes. It must include a battery charger/controller and a central inverter that operates at battery voltage (48 volts in our case).

It's also nice if the system has a provision for a 240v backup generator to recharge the batteries if there's insufficient sunlight.

At the time, there were only two integrated hybrid controllers available:

The Outback SkyBox outbackpower.com/products-mobile/category/skybox
The Sol-Ark 8K www.sol-ark.com/sol-ark-8k-hybrid-all-in-one/

The specs on the Sol-Ark are superior... the inverter supports 8kW versus 5kW for the SkyBox and the Sol-Ark is more efficient. However, Sol-Ark was/is a relatively young company so I decided to go with SkyBox.

Sol-Ark is a better value and has received outstanding reviews over the past year. I would probably select Sol-Ark if I were installing a system today.

Solar Panels

Our design calls for a 6kW array with somewhat limited roof space. This requires panels with a relatively high efficiency (at least 18%).

I really wanted to purchase Hanwha Q.Peak panels since Hanwha produces them at a new factory in Dalton Georgia. Unfortunately all of their production was being consumed to build a huge solar farm to power a new Facebook server facility being built in Georgia. Interesting story here - www.npr.org/2019/06/24/733795962/how-georgia-became-a-surprising-bright-spot-in-the-u-s-solar-industry

I selected REC N.Peak 320 Watt panels since they are based on the same half-cut cell technology as Q.Peak (the two companies are in patent litigation over the similarity). www.recgroup.com/en/products/rec-n-peak-en

Last year we paid $215.00 per panel or about $0.67 per Watt. This was a really great price for panels that offer an efficiency greater than 19%. The panels are at $211.00 today so not much has changed and they remain an excellent value.

Rec has now introduced the new Alpha series that deliver 21% efficiency. However the price is much greater. A 365 Watt panel costs $345.00 or about $0.95/Watt. You should expect to pay a substantial premium for a bit greater efficiency.

In the next report I'll describe the installation process.

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Photovoltaics - Solar Power I

7/16/2017

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Introduction

The basement is almost complete and the first phase of neoTerra is coming to an end. The first phase has focused on passive design (i.e. passive solar and tight construction) to reduce energy consumption and on the the use of durable, low-maintenance materials to reduce the long term cost and effort to maintain the structure.

The second phase will investigate active system to further reduce consumption or produce energy.

Last winter we added a high-efficiency wood stove which I hope will provide 1/3 to 1/2 of our winter heat. This year we will add a small array of solar panels and this post will discuss some of the initial considerations and analysis.

Solar Potential
NREL (the National Renewable Energy Lab) has a treasure trove of information on solar energy. As the following diagram illustrates, the best solar potential is in the Southwest which has an arid climate and uninterrupted sunshine. The Southeast has good solar potential (about 5 kWh/meter/day) and enjoys a lush climate. I love Appalachia !!

Georgia - An Anti Solar State

Georgia is a seriously anti-solar state which makes installation of solar panels much less cost effective. Nevertheless, I enjoy a challenge so I've been spending a good deal of time trying to design a solution with a reasonable payback period.

SolarPowerRocks.com produces an annual "Solar Report Card" ranking all of the states. For 2017 Georgia comes in at an appalling 37th out of the 50 states.

To make matters even worse, That report card is based on Georgia Power which at least pays full price for any excess energy that you produce.

Here in North Georgia we are part of Amicalola Electric, a rural cooperative that is only obligated to pay 3.8 cents per kWh for power sent back to the grid. As a matter of public policy, the Georgia Rural Cooperatives are on record stating "[they] have opposed unreasonable regulations such as the EPA's Clean Power Plan (CPP)".

To put this in concrete terms, Georgia Power charges about 12 cents per kWh and pays the consumer 12 cents per kWh for any over production. If you oversize your array you will at least be compensated and it will not effect the eventual payback period.

Amicalola, on the other hand, charges approximately 10.5 cents per kWh but only pays 3.8 cents for overproduction. If you oversize your array then you are essentially donating 6.7 cents per kW to the utility company. In other words, if you oversize your array by any significant amount then the payback period will be NEVER-EVER.

Right Sizing

In an environment where you are penalized for supplying energy back to the grid it becomes especially important to optimize the size of your solar installation. Just as the corporate euphemism of "right-sizing" really means "down sizing", optimization of the solar array always means reducing the array to just below your minimum demand.

Optimization

There are several aspects or constraints that need to be considered to achieve a cost-effective design in a solar hostile environment.

Available Space - what is the largest array that could be installed
Minimum Need - what is the minimum amount of solar production that you require (this could be zero if you are only trying to reduce your monthly bill)
Minimum Demand - What is the lowest monthly load.

On the surface this seems pretty straightforward. However, solar production changes from month-to-month with much more in the Summer when days are longer and substantially less in Winter. If you live in an arid, air-conditioning climate, then this might align with your needs. But, for the rest of us, it is generally the opposite of what we require.

Let's look at some of the different considerations and constraints. I will be using neoTerra as a concrete example. Your Millage May Vary (YMMV).

Available Space vs Production

I hope that it's obvious that the more space you have, the more energy you can produce. neoTerra was primarily designed as a passive solar structure so the major roof (over the great room) slopes to the North. A North slope is not suitable for solar production.

We have enough South facing roof over the bedroom wing to carry 20 standard size solar panels. This will allow a maximum of 5.8 - 6.2 kW, depending on the grade (efficiency) of the panels.

The actual solar production changes from month to month. As an example, let's consider a 6kW array and use the tool at NREL to calculate the approximate monthly production for North Georgia. Note that the tool takes the latitude, longitude and estimated cloud cover into consideration. The following diagram shows the estimated production of a 6kW array located at neoTerra on a 2:12 slope roof facing south.

Theoretically, this array would produce about 850 kWh in May (when we need it the least) and about 400 kWh in January (when we need the most).

Minimum Need

When we built neoTerra we installed two separate circuit panels. One supplies the critical circuits such as the well, refrigerator, microwave, some lighting and networking. The other panel supplies everything else.

We have been monitoring the use of both panels for over a year and have established that we use approximately 350 kWh/month for the critical circuits. We would like to have enough solar power to run the critical circuits during an extended (several day) power outage.

In the event of a real power outage we would probably use a bit less power than what we have recorded... For example, I doubt that we would be watering plants or taking long, cold showers during a power outage.

The following chart indicates that a 6kW array (the dashed yellow line) would be sufficient to power all of the critical circuits (the red line) during the lowest solar production months and would have have a substantial surplus during the higher production months.

The conclusion is that a 6kW array would be more than sufficient to meet our minimum need.

Minimum Demand

As mentioned earlier, this topic is not a concern if you live in a state / utility that pays you a fair price for the energy you produce. But, here in Georgia, I want to meet my Minimum Need while avoiding overproduction, if possible.

The following chart shows the theoretical output of a 6kW array versus our actual energy use over the past two years. The theoretical array would produce slightly more energy than our minimum months from 2016 and slightly less than our current use in 2017. A 6kW array appears to be optimal.

Conclusions

A 6 kW array would likely meet our minimum needs in the low production Winter months and would not significantly overproduce in the Summer months.

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Photovoltaics - Solar Power Part III - Installation

Photovoltaics - Solar Power Part II - Equipment

Photovoltaics - Solar Power I

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