Solar savings calculator template

Free build guide: Solar savings calculator for WordPress

This guide rebuilds the Solar savings calculator from this site in Gravity Forms: 7 inputs, 7 live results and no submit button. Expect about 42 minutes by hand. The template above is the same form as an import file, and the bundle adds a PDF version of this guide with a screenshot of every setting, plus the stylesheet.

You will end up with:

• Net savings over the period
• System cost
• Your cost after the credit
• Electricity produced per year (kWh)
• First-year savings
• Simple payback (years)
• Total electricity savings

What you need

• Gravity Forms (any license) — Calculation fields are in core; the exponent in the savings series needs GP Advanced Calculations.
• GP Advanced Calculations (Gravity Wiz) — Exponents, functions and date math in calculation fields. The formulas in this template use its syntax. Part of Gravity Perks; needs the Spellbook plugin active as well.

The formulas below use GP Advanced Calculations syntax: exponents, functions or date math that core calculation fields cannot do. Install and activate it, with its Spellbook parent plugin, before you start; without it every result shows 0.

1. Create the form

1. Go to Forms → New Form and name it Solar savings.
2. In Form Settings → Form Layout, set the CSS Class Name to fo-live-only. Step 3 uses it to hide the submit button.
3. Leave the form open in the editor; the fields come next.

2. Add the fields, in this order

Field IDs are assigned as you add fields. If yours come out differently, change the {Label:ID} references in the formulas to match your IDs. Settings not mentioned stay at their defaults.

1. System size (kW) · Number · ID 1
Number Format 9,999.99; Default Value 8; Description “Home systems run 5–12 kW; about 400 W per panel.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

2. Installed cost per watt · Number · ID 2
Number Format Currency; Default Value 3.00; Description “$2.50–3.50 before incentives in most of the US.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

3. Tax credit (%) · Number · ID 3
Number Format 9,999.99; Default Value 30; Description “The federal credit is 30% through 2032 for systems you own; add any state rebate as a percentage.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

4. Peak sun hours per day · Number · ID 4
Number Format 9,999.99; Default Value 4.5; Description “3.5 in the Northeast and Pacific Northwest, 4.5 in the middle of the country, 5.5–6 in the Southwest.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

5. Electricity rate (¢ per kWh) · Number · ID 5
Number Format 9,999.99; Default Value 17; Description “From your bill. Assumes full net metering: every kWh produced is worth the retail rate.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

6. Rate increase (% per year) · Number · ID 6
Number Format 9,999.99; Default Value 3; Description “US retail rates have risen about 2–3% a year.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed).

7. Years to count · Number · ID 7
Number Format 9,999.99; Default Value 25; Description “The usual panel warranty. Panels lose about 0.5% of output a year; that is built in.”.

8. Net savings over the period · Number · ID 8
Number Format Currency; Description “Electricity savings less what the system cost you after the credit.”; Custom CSS Class (Appearance tab) fo-result; tick Enable Calculation, Rounding 0.

( ( ( {Size:1} * {Sun hours:4} * 365 * 0.8 ) * {Rate:5} / 100 ) * ( ( ( 1 + {Escalation:6} / 100 ) * 0.995 ) ^ {Years:7} - 1 ) / ( ( ( 1 + {Escalation:6} / 100 ) * 0.995 ) - 1 ) ) - ( ( {Size:1} * 1000 * {Cost per watt:2} ) * ( 1 - {Credit:3} / 100 ) )

9. System cost · Number · ID 9
Number Format Currency; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

( {Size:1} * 1000 * {Cost per watt:2} )

10. Your cost after the credit · Number · ID 10
Number Format Currency; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

( ( {Size:1} * 1000 * {Cost per watt:2} ) * ( 1 - {Credit:3} / 100 ) )

11. Electricity produced per year (kWh) · Number · ID 11
Number Format 9,999.99; Description “First year. The average US home uses about 10,500 kWh.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

( {Size:1} * {Sun hours:4} * 365 * 0.8 )

12. First-year savings · Number · ID 12
Number Format Currency; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

( ( {Size:1} * {Sun hours:4} * 365 * 0.8 ) * {Rate:5} / 100 )

13. Simple payback (years) · Number · ID 13
Number Format 9,999.99; Description “Net cost ÷ first-year savings. Rising rates shorten it a little.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 1.

( ( {Size:1} * 1000 * {Cost per watt:2} ) * ( 1 - {Credit:3} / 100 ) ) / ( ( {Size:1} * {Sun hours:4} * 365 * 0.8 ) * {Rate:5} / 100 )

14. Total electricity savings · Number · ID 14
Number Format Currency; Description “Over the period, before the system cost.”; Layout: half width, on the same row as its neighbor (drag the field beside it in the editor; no CSS class needed); Custom CSS Class (Appearance tab) fo-result fo-result--sub; tick Enable Calculation, Rounding 0.

( ( ( {Size:1} * {Sun hours:4} * 365 * 0.8 ) * {Rate:5} / 100 ) * ( ( ( 1 + {Escalation:6} / 100 ) * 0.995 ) ^ {Years:7} - 1 ) / ( ( ( 1 + {Escalation:6} / 100 ) * 0.995 ) - 1 ) )

3. Hide the submit button

The results are live, so nothing needs submitting. Add this filter to your theme’s functions.php or a code-snippets plugin; it hides the button on any form carrying the fo-live-only class:

add_filter( 'gform_submit_button', function ( $button, $form ) {
	return str_contains( (string) rgar( $form, 'cssClass' ), 'fo-live-only' ) ? '' : $button;
}, 10, 2 );

Or with CSS alone: .fo-live-only_wrapper .gform_footer { display: none; }

4. Put it on a page and make it look like this

Add the form to any page with the Gravity Forms block, or the shortcode [gravityform id="X" title="false" ajax="false"]. The form inherits your theme’s styles; the classes you set in step 2 are hooks for the look you see on this site:

• fo-result on a calculation field makes it the big teal result panel.
• fo-result fo-result--sub makes the smaller secondary figures.
• fo-segmented on a radio field turns it into a segmented switch.
• Two fields on one row is the editor’s own column layout: drag a field beside another and the row splits in half. No CSS class is needed, and the old gf_left_half Ready Classes are deprecated.

The bundle includes the two stylesheets that implement those classes, with notes on matching your brand colors. Without them the form still works; it just looks like your theme’s default Gravity Forms styling.

How the math works is explained under “How it’s calculated” on the live Solar savings calculator.