Maximizing Solar Self-Consumption


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Some modern appliances can be programmed or controlled remotely to operate when there is PV-made electricity, thus increasing self-consumption.
Whole-house monitoring and management systems, like this one from Geli, can track energy production, use, storage, and patterns to maximize self-consumption.
A simple electrical outlet timer can control when electrical appliances turn on or off, coinciding with PV production.
Proprietary control systems, such as Rheem’s EcoNet, are designed to work with the companies’ other equipment like water heaters, furnaces, and air conditioners.
Several new options for monitoring and controlling electrical outlets remotely with web-based apps have hit the market.
Due to the size of a water-heater load in an efficient home, even a simple timer can help shift substantial amounts of energy consumption to times of high PV production.
Example Equipment for SC Systems SolarEdge’s StorEdge inverter can be installed with lithium batteries from Tesla or LG Chem, along with its meter (for energy-management capability) and autotransformer to balance backed-up load panel circuits.
Example Equipment for SC Systems Offered in 4 to 16 kWh capacities, the sonnenBatterie eco combines lithium iron phosphate batteries with the power electronics for a full-sized, prepackaged energy-storage system suitable for both energy management (SC and TOU shifting) and backup power applications.
Example Equipment for SC Systems JLM Energy’s Phazr lithium iron phosphate microstorage units pair with microinverters and mount behind the PV module (shown with the Measurz monitoring software system).
Example Equipment for SC Systems JLM Energy’s Phazr Measurz monitoring software system.
Example Equipment for SC Systems Shipping in mid-2017, SMA’s Sunny Boy Storage inverter can be used with high-voltage lithium battery banks (such as those from LG and Tesla) for energy management, such as peak load shaving, self consumption, and zero-export. Higher backup capacity is expected to be available by the end of 2017.
Example Equipment for SC Systems Integrating lithium iron phosphate battery chemistry with its microinverter, the Enphase AC battery has a 1.2 kWh capacity and can be AC-coupled (with up to 14 units per 20 A branch circuit) for use in self-consumption and TOU-optimizing systems.
Smart thermostats like this Wiser Air from Schneider Electric are WiFi enabled, allowing settings to be adjusted via a smartphone.
“Smart” thermostats can be used to help manage energy consumption in new ways. Honeywell’s Lyric thermostat (below) can sync to a utility’s automated demand response system, shutting off air-conditioning for short periods when grid demand is peaking. Nest Labs thermostat (right) automatically programs itself for your utility’s TOU rate plan, adjusting its operation to save energy and money.
The Ice Bear air conditioner stores energy as ice, to continue cooling after solar production drops off.

A PV “self-consumption” (SC) system maximizes the use of solar array-produced electricity on-site and minimizes using electricity from the utility grid. Loads are managed so they run during prime solar-production hours and, optionally, the PV-generated electricity can be stored for later use.

An SC PV system, however, is different from a net-metered PV system. In a net-metered system, excess PV-generated electricity is sent back onto the grid and credited, kilowatt-hour by kilowatt-hour, to the user’s account at the utility’s retail rate on a 1-for-1 basis. In net-metered systems, loads do not need to be coordinated with the PV system’s production. In SC PV systems, as much as possible, loads are coordinated with the system’s production.

In reality, any PV system that has loads on during the day when the PV modules are producing energy has some “self-consumption.” In some areas, recent regional policy and regulation changes to net metering have made it more advantageous to maximize self-consumption. Some motivations include:

True solar energy use. To address climate change, home and business owners can make conscientious choices about the type of fuel powering their loads. Most utilities are producing electricity with fossil fuels that net-metered homes use when their loads exceed the PV production, and at night. If you’re striving to not use fossil fuels and be truly solar-powered, then you need to implement SC PV strategies in which the PV-generated electricity is consumed directly during the day or stored on-site for later use.

Non-net-metering utilities. Some utilities have not adopted net metering or are ending their net-metering policies. Although these utilities may allow export, the PV electricity sent to the utility is credited at a lower wholesale rate, while the utility energy used by the consumer is charged at a higher retail rate. Increasing the SC of PV systems reduces the amount of higher-priced utility energy that is consumed.

Zero export restrictions. Some utilities have restricted exporting electricity from PV systems to the grid. If you live in such an area and if the utility rates are high, having an SC PV system can reduce the amount of utility electricity you’ll need to purchase and can reduce your utility bills substantially.

SC Strategies

Here are three strategies that can be used to increase self-consumption of PV-produced energy in the order of lowest to highest cost:

Grid-direct PV with load management. For batteryless grid-tied systems located in areas where utilities allow systems to export energy, the simplest and least expensive method is to manually control when loads operate. Examples include designating sunny weekend days to do loads of laundry or using your slow cooker only on sunny winter days. Using timers and relays can also reduce nighttime consumption.

Inexpensive plug-in and hard-wired time controllers are available from hardware stores, and can be used to ensure that large, energy-consuming loads (such as water heaters) operate only during the daytime when the PV array is producing energy. “Smart” Internet-connected controllers are also available that allow adjustment of water-heater temperatures via a schedule or from your smartphone. This strategy is most appropriate in areas where the utility still allows PV systems to export energy, and would rely on the grid to power loads at night and during cloudy weather.


Comments (4)

Peter Gruendeman_2's picture

Whoa! I looked up the on-line price for the Phoenix solar hot water heater and saw a price of $9,539. That's getting to be real money. You'll no doubt add some additional cost because this is not a compete system by itself.

This is a complete system:
2kW of PV panels, at $0.80- $1.00/ watt or about $1,600- 2,000;
racking for your roof or a ground mount, made of aluminum and steel, $600;
#6 or #8 wiring to bring this electricity to the new electric water heater you just installed upstream from your natural gas unit. This would be a
80 or 119 commodity electric water heater that you buy from any home center for $800- 1,000;
and you assemble a simple on-off controller as described on:
except I might use a Omron solid state relay and a 12 volt wall wart as the DC supply. Otherwise, this guy's instructions are spot-on.
Or use a MPPT controller. I built my own and you can too.
This brings the total system cost to around $4,000 including a brand new 119 gallon electric water heater. I include no $$ for installation because this is totally a DIY proposition.

Alternatively, you could hire someone to install this for you but only after you teach them how it works. Some installers get it that PV--> DHW works; most deny that it's possible to do what I have been doing for the last year and a half. They either don't know or don't want to know.

To answer the question you posed, yes, you can build a system around the Phoenix solar water heater. My question to you is why would you want to?
Pete Gruendeman, La Crosse, WI

Peter Gruendeman_2's picture

The sidebar in this article includes these words from Utah based installer Kienan Maxfield:
> My customer wanted a system that would offset
> all of the home's electricity needs and provide
> backup power to the whole house during a
> long-term outage or in case of a "collapse of the grid."

Backup power for the whole house can be an expensive proposition, but for some needs such as medical devices, communications and possibly to power a well pump, backup power can be essential. At one time the cost of such a system had to be justified based on critical needs. Now PV is the same price as solar thermal, and it's cheaper than solar thermal for domestic hot water if installation is included. Installing PV is easier than installing solar thermal and is a DIY project for more people than solar thermal. Using PV for DHW requires no inverter, no batteries and no grid connection. You won't care if your utility doesn't play nice with net metering because your PV-->DHW system won't be connected to their grid. It does require a garden variety electric resistance water heater (available at any home center) and DC rated or solid state switches. AC rated switches are NOT ok for DC use!

Solar thermal is useless for backup power, and depending on the type of system, it can be a liability if the panels overheat and fry the glycol when the circulation pumps are not running. The same PV array can be used for DHW and backup power. Just add a step-down charge controller and a battery bank large enough for one's critical loads. 2kW of PV is a LOT for DHW and it can be much more than most people need for their critical loads. This is 2017. 2kW of PV now costs $1,600- 2,000. This is not real money when it comes to solar DHW or backup power.

I often ask "How much backup power would you want if it was free because using the PV for DHW paid for the PV panels?" The step-down charge controller + inverter + battery add-ons will not cover the needs of the entire house but provides a lot of benefit for little extra cost.
Pete Gruendeman, La Crosse, WI

Frank Achille's picture

Peter, can I jump in for your input of my intended use? I want to DVM to a Hot water tank to a heat exchanger inside a air heat pump air supply. Not sure of the design, DC or AC inputs to the HW tank, and capacities. Do I need all these trades (solar, electrician, plumber, HVAC) to make it happen? A Phoenix Solar Hot Water Heater at seems doable.

Mr. Bruce Arkwright, Jr.'s picture

It was great just unloading all my power on to grid, but First Energy, just changed my very workable, easy to turn backwards meter to a stupid 'smartmeter'. I refuse to netmeter, partially because I using a non UL certified inverter, it super cheap! And I don't like their terms, it should be one for one, not buy low sell high....
I am using a grid-tie limiter inverter now, only $300-500 for 1000-2000 watts, house-tied but doesn't feedback! I'm saving up for batteries, getting very soon....
Currently only 1300 w of solar panels (but sadly never seen more then 750 watts produced) , but once batteries here up goes a 400 watt wind turbine and then another round of 1000 watts of panels....
The inverter is only 1000 watts but that will help out not loading down and 'killing' battery system quickly, if I need more it simply comes from the grid....

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